Thursday 31 December 2015

Performance tests

Code can always be optimized in terms of resources used. It makes sense adding performance tests when resources matter and their acceptable usage is a part of the requirements.

Resources can be time, memory, number of threads, sockets etc...but probably most measured are time and memory.

These tests are integration tests because:
- they rely on external factors (they are system- and hardware-dependent)
- asserted results can vary in time
- they can take much time to execute

An example of performance test is verifying that some algorithm performs some task within the acceptable time range.

There is a question on their consistency: e.g. the same algorithm takes more time to execute on slower machines so how to determine pass/fail criteria?

Further reading:

Thursday 24 December 2015

DRY in action - Use lambda to fixate method's argument

In the following example we have a situation where Foo() calls Bar() multiple times. Within each Foo() call, it passes to Bar() different value for string argument but always the same value for int argument:


i = 123, s = test1
i = 123, s = test2
i = 123, s = test3
i = 456, s = test1
i = 456, s = test2
i = 456, s = test3

To avoid unnecessary repetition we can introduce one level of indirection - a lambda which calls Bar() and provides it string value via its own argument and int value via capturing argument passed to Foo(). After refactoring:


i = 123, s = test1
i = 123, s = test2
i = 123, s = test3
i = 456, s = test1
i = 456, s = test2
i = 456, s = test3

Monday 21 December 2015

OperationCanceledException vs TaskCanceledException when task is canceled

In my previous post, "How to cancel a Task", I mentioned that MSDN recommends throwing OperationCanceledException from a cancelled task. But the following example shows that canceling .NET methods makes them throw a different exception type - TaskCanceledException:


System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Program.d__1.MoveNext()
Task.IsCanceled: True
Task.IsFaulted: False
Task.Exception: null

So why .NET does not follow its own rules? Why exception thrown in the example above was not OperationCanceledException?

I asked this question on SO and this is how I interpret the answer I got:

(1) System.OperationCanceledException class has been around longer than TPL. MSDN describes it as: "The exception that is thrown in a thread upon cancellation of an operation that the thread was executing." It is intended to be thrown from a thread in which operation is executed. .NET async API are actually synchronous operations (return Task, not marked as async). They don't have additional thread involved which makes OperationCanceledException not appropriate exception to be thrown.

(2) It is different to cancel a Task (setup of the engine which will execute "real work", user's operation) than to cancel operation itself. For example, we can pass already cancelled token to a task or can simply create already cancelled task. Operation and its thread are not started at all in these cases but if we await such task and catch OperationCanceledException we might think they were actually started. So it makes sense to use different type of the exception in these two different scenarios.

Example 1: Already canceled token is passed to task factory method:


System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Program.d__1.MoveNext()
Task.IsCanceled: True
Task.IsFaulted: False
Task.Exception: null

Example 2: Awaiting task which is created as already canceled:


System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNot
ification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at Program.d__1.MoveNext()
Task.IsCanceled: True
Task.IsFaulted: False
Task.Exception: null

From the points made above we can conclude that caller of the cancelable task can expect two types of exceptions:OperationCanceledException and TaskCanceledException. As the latter derives from the former, it is enough to handle OperationCanceledException if we want to handle the case of canceled task:

Further reading:
SO Q&A: OperationCanceledException VS TaskCanceledException when task is canceled
SO Q&A: Difference between OperationCanceledException and TaskCanceledException?
Andrew L Arnott: Recommended patterns for CancellationToken

Sunday 20 December 2015

How to cancel a Task

It is a good practice to offer users a chance to cancel some long-running operation. Such operation usually has to run asynchronously and in a TPL-based design is modeled as a method returning a Task.

Cancellation model requires some flag which is accessible by the caller and from inside the operation. Caller sets the flag when wants operation to be cancelled. Operation regularly checks the flag or is subscribed to the event "flag has been set" and if flag has been set, operation will stop doing the work. This model is in .NET abstracted with two types: CancellationTokenSource class and CancellationToken structure. Caller uses CancellationTokenSource to initiate cancellation and operation uses CancellationToken to check whether it has been cancelled.

When designing an API, if provision for operation cancellation is required, we have to add a CancellationToken to a list of method's arguments. API caller invokes CancellationTokenSource.Cancel method which sets CancellationToken.IsCancellationRequested to true. Target method checks this property and can either silently return or throw OperationCanceledException. The latter approach is better as only in this case returning task will come to Canceled state.

The following code depicts the whole process of task cancellation:

CancellationToken.ThrowIfCancellationRequested() method simply checks CancellationToken.IsCancellationRequested and if it's true, it throws OperationCanceledException. The output of the code above is:

.........System.OperationCanceledException: The operation was canceled.
   at System.Threading.CancellationToken.ThrowIfCancellationRequested()
   at MyService.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Program.d__1.MoveNext()
Task.IsCanceled: True
Task.IsFaulted: False
Task.Exception: null

The following code shows that the await-ed task does not get aware that the task it holds got canceled if method silently returns on cancellation:


..........Task.IsCanceled: False
Task.IsFaulted: False
Task.Exception: null

Further reading:
Andrew Arnott - Recommended patterns for CancellationToken
MSDN: Task Cancellation

Saturday 19 December 2015

await VS Wait() when Task throws exception

await and Wait() are two versions of the operation "wait for the task to complete": one is asynchronous (non-blocking) and the other one is synchronous (blocking). They are both capable of capturing the exception thrown from the task but they behave in a different way when propagating exception information up the stack: they themselves throw different type of exception.

await (case 1) propagates the original exception so the output is:

System.ArgumentNullException: Value cannot be null.
   at Program.<>c.b__1_0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Program.d__1.MoveNext()
Task.Status: Faulted
Task.IsFaulted: True
Task.Exception: System.AggregateException: One or more errors occurred. ---> System.ArgumentNullException: Value cannot be null.
   at Program.<>c.b__1_0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Program.d__1.MoveNext()
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.ArgumentNullException: Value cannot be null.
   at Program.<>c.b__1_0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Program.d__1.MoveNext()<---

Wait() (case 2) wraps original exception in System.AggregateException:

System.AggregateException: One or more errors occurred. ---> System.ArgumentNullException: Value cannot be null.
   at Program.<>c.b__1_0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
   at System.Threading.Tasks.Task.Wait()
   at Program.d__1.MoveNext()
---> (Inner Exception #0) System.ArgumentNullException: Value cannot be null.
   at Program.<>c.b__1_0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()<---

Task.Status: Faulted
Task.IsFaulted: True
Task.Exception: System.AggregateException: One or more errors occurred. ---> System.ArgumentNullException: Value cannot be null.
   at Program.<>c.b__1_0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.ArgumentNullException: Value cannot be null.
   at Program.<>c.b__1_0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()<---

Note that Task.Exception in both cases holds System.AggregateException. This difference comes from the desire of async-await implementers to keep use of await as simple as possible and to make its use to look like synchronous code as much as possible. System.AggregateException is not used in synchronous code (in non-TPL code) and we there always catch the first exception that is thrown from a try-block. That is why await is designed in such way so it throws only the first exception from a task (or aggregate of tasks) as usually we are interested only in that first exception (we usually handle the first error that occurs).

Null-Conditional Operator in C# 6

C# 6 introduced a Null-Conditional operator which makes null checks more concise. If object on which it is applied is null, it will immediately return null, if not, it will return result of the operation applied on that object (invoking method, property...onto which other operations might be chained). Instead of writing:

var personName = person == null ? null : person.Name;

...we can write:

var personName = person?.Name;

?. is a first form of this operator. The other one is ?[] and is used when accessing array elements. Instead of performing null check of the array and then accessing its elements, we can now put those two operations in a single expression:

var arr = new string[]{"abc" , "def"};
var arr0 = arr?[0]; // "abc"
arr = null;
arr0 = arr?[0]; // null

This operator comes very handy when raising events. Before, we would write:

public event Action SomeEvent;
private void OnSomeEvent()
   if (SomeEvent != null)

...but now we can write:

public event Action SomeEvent;
private void OnSomeEvent()

Friday 18 December 2015

String interpolation in C# 6

With C# 6 we can finally wave goodbye to the cumbersome, C-style way of injecting values into a string. Before, target string and arguments were separated and indexes were used to place the right argument at the right place inside the string. That was an error prone process.

var id = 123;
var name = "abc";
var s = string.Format("id = {0}, name = {1}", id, name);

New interpolation syntax allows direct injection of variables into the string:

var id = 123;
var name = "abc";
var s = $"id = {id}, name = {name}";

It is possible to inject string result of some more complex expressions:

var task = new Task();
var taskExceptionReport = 
   $"Task.Exception: {((task.Exception == null) ? "null" : task.Exception.ToString())}";

Further reading:
Interpolated Strings (MSDN)
Bill Wagner: "A Pleasant New C# Syntax for String Interpolation"

Sunday 13 December 2015

DO NOT use the same name for class and its namespace

In the following code namespace Foo contains class with the same name - Foo:

This causes compiler to issue an error:

Error CS0118: 'Foo' is a namespace but is used like a type

The problem is in that compiler does not know if we are trying to use new on the namespace or on the actual class. To rectify this, we have to use the fully qualified class name (which includes namespace):

In some cases this might not be enough so it is better to avoid using same name for class and for its namespace.

Eric Lippert has a series of blog articles on this topic:

Do not name a class the same as its namespace

Also, here are some SO Q&A:

'namespace used like a type' error
'CompanyName.Foo' is a 'namespace' but is used like a 'type'

Saturday 12 December 2015

How to set return values for methods returning Task<T>

Non-async method which returns Task<T>

If method is not marked as async and its return type is Task<T>, it has to return object of type Task<T> otherwise compiler issues an error. This is the example of the typical type mismatch error where code:

...causes a compiler error:

Error CS0029: Cannot implicitly convert type 'int' to 'System.Threading.Tasks.Task'

This can be rectified by simply returning expected type:

async method which returns Task<T>

If method is marked as async and its return type is Task<T>, it has to return object of type T, which is int in our case:

...but because async method lacks await in its body, this code generates compiler warning:

Warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.

We can await only methods which return Task or Task<T> so this can be fixed by returning value from awaited completed task:

We have to be careful when calling methods returning Task<T>. If not await-ed, they return Task<T>. If awaited, they return object of Task's generic argument type, T. The following code is not awaiting method returning Task<int>:

...which causes compiler error:

Error CS4016: Since this is an async method, the return expression must be of type 'int' rather than 'Task'

Both methods are awaitable because they return object of type Task:

Asynchronous lambda

If you try to await some task in lambda expression like here: will a compiler error:

Error CS4034: The 'await' operator can only be used within an async lambda expression. Consider marking this lambda expression with the 'async' modifier.

The fix is obvious: apply async to lambda - put it just before lambda's parameter list:

Monday 21 September 2015

A brief guide to cryptosystems

Cryptosystem Functions

  • Privacy/confidentiality: Ensuring that no one can read the message except the intended receiver.
  • Authentication: The process of proving one's identity.
  • Integrity: Assuring the receiver that the received message has not been altered in any way from the original.
  • Non-repudiation: A mechanism to prove that the sender really sent this message.
  • Key exchange: The method by which crypto keys are shared between sender and receiver.

Cryptosystem Algorithms

Each cryptosystem defines three algorithms:
  • key(s) generation
    • key size (length)
    • expiration date
  • encryption
  • decryption

Deterministic algorithm 
  • given a particular input it will always produce the same output
  • the underlying machine will always be passing through the same sequence of states
Block cipher
  • deterministic algorithm operating on fixed-length groups of bits, called blocks
  • consists of two paired algorithms, one for encryption, E, and the other for decryption, D.
    • Both algorithms accept two inputs: an input block of size n bits and a key of size k bits; and both yield an n-bit output block.
    • The decryption algorithm D is defined to be the inverse function of encryption

Cryptosystem types

  • Symmetric Encryption (Secret Key Cryptography)
    • Uses a single key for both encryption and decryption
    • Sender uses the key to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext.
    • Key must be known to both the sender and the receiver; key is the secret
    • Applications which use this type of encryption to securely store data can use user-supplied password as a key (or key gets generated from a password)
    • Same key/password is used to encrypt and decrypt content, which is helpful from a usability standpoint.
    • The biggest difficulty with this approach is the distribution of the key
    • Used for:
      • privacy/confidentiality
    • Types:
      • stream ciphers
      • block ciphers
    • Algorithms:
      • Advanced Encryption Standard (AES, Rijndael; NIST 2001)
        • variant of the Rijndael block cipher 
        • Rijndael is a family of ciphers with different key and block sizes.
        • For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192 and 256 (AES256) bits. 
        • Examples: Ansible Vault uses AES256
    • ...
  • Asymmetric Encryption (Public Key Cryptography)
    • Uses one key for encryption and another for decryption
    • Used for:
      • authentication
      • non-repudiation
      • key exchange
    • Algorithms:
      • RSA (Rivest, Shamir and Adleman) (PKCS#1) 
      • Diffie–Hellman key exchange protocol
      • PGP
      • GPG (GnuPG)
      • SSL/TLS
      • SSH
    • ...
  • Hash Functions (Message Digests, One-way Encryption)
    • Use a mathematical transformation to irreversibly "encrypt" information, providing a digital fingerprint
    • Use no key 
    • Fixed-length hash value is computed based upon the plaintext that makes it impossible for either the contents or length of the plaintext to be recovered
    • Used for:
      • message integrity. Examples:
        • ensure the integrity of a file; provide a digital fingerprint of a file's contents, often used to ensure that the file has not been altered by an intruder or virus
        • encrypt passwords
    • Algorithms:
      • Message Digest (MD) algorithms
        • byte-oriented algorithms that produce a 128-bit hash value from an arbitrary-length message
        • Algorithms:
          • MD2
          • MD4
          • MD5
            • weaknesses in the algorithm were demonstrated
      • Secure Hash Algorithm (SHA)
        • SHA-1
          • produces a 160-bit hash value
          • deprecated by NIST
        • SHA-2
          • SHA-1 plus
          • SHA-224
          • SHA-256
            • produces a 256-bit (32-byte) hash value, typically rendered as a hexadecimal number, 64 digits long
          • SHA-384
          • SHA-512
        • SHA-3
          •  Keccak 


Friday 7 August 2015

Wireshark Wi-Fi traffic sniffing support across Operating Systems


Promiscuous mode

  • WinPcap supports promiscuous mode but drivers for Wi-Fi NICs usually don't =>  Wireshark using WinPcap can't capture packets from Wi-Fi NIC in promiscuous mode on Windows

Monitor mode

  • WinPcap does not support monitor mode => Wireshark using WinPcap can't capture packets from Wi-Fi NIC in monitor mode on Windows 
  • Acrylic NDIS driver supports monitor mode => Wireshark + AirPcap/WiFi USB card +Acrylic NDIS driver is able to capture packets in monitor mode


Promiscuous mode

  • libpcap supports promiscuous mode => Wireshark can capture packets from Wi-Fi NIC in promiscuous mode on Unix

Monitor mode

  • libpcap supports monitor mode (on some flavors on Unix) => Wireshark can capture packets from Wi-Fi NIC in monitor mode on Unix

How to capture WiFi traffic using Wireshark on Windows

Thursday 6 August 2015

Promiscuous vs monitor mode of a wireless network interface

Wireless adapter in promiscuous mode:
  • connected to the Access Point (AP)
  • SSID filtering is switched on => it can receive packets only from AP it is associated with (it receives radio packets from all APs but forwards to the upper layers only those from that particular AP)
  • MAC filtering is switched off => it can receive packets destined for any MAC address
  • it can't decrypt packets to/from other nodes in secured (WEP, WPA...) networks 
  • it translates Wi-Fi data frames into wired Ethernet-style frames (IEEE 802.3) so they look like Ethernet frames captured on the LAN interface working in promiscuous mode

Wireless adapter in monitor mode:
  • usually NOT connected to the Access Point (depends on the adapter and its driver) => it does not transmit any packets
  • SSID filtering is switched off => it can receive packets from any AP within its range
  • MAC filtering is switched off => it can receive packets destined for any MAC address
  • it can decrypt packets to/from other nodes in secured networks

It is worth adding the following:
  • monitor mode does not make sense (and so does not exist) for LAN cards 
  • all LAN cards support promiscuous mode
  • not all Wi-Fi cards support promiscuous and monitor mode

Further reading:Promiscuous mode (Wikipedia)
Monitor mode (Wikipedia)
Wireshark - WLAN (IEEE 802.11) capture setup

Image editor for Linux: Pinta

As a happy user of Paint.NET on Windows I decided to install and use its fork for Linux, a Mono-based Pinta.


apt-get install pinta

And this is how it looks:

Wednesday 5 August 2015

How to sniff HTTP traffic on the local Wi-Fi network in 10 steps

We need:

(1) Attacker: Linux machine with two Wi-Fi cards; I am using Kali with internal Atheros and external Alfa (AWUS036NH) WiFi card.
(2) Victim: mobile device; I am using smartphone
(3) Wi-Fi router with set up Wi-Fi network


(1) Verify that both Wi-Fi network cards are connected to the same Wi-Fi network:

root@kali:/# iwconfig
wlan1 IEEE 802.11bgn ESSID:"MYWIFINET"
Mode:Managed Frequency:2.457 GHz Access Point: 10:AD:AF:CD:A7:A4
Bit Rate=1 Mb/s Tx-Power=20 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
Link Quality=70/70 Signal level=-37 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:4 Missed beacon:0

eth0 no wireless extensions.

lo no wireless extensions.

wlan0 IEEE 802.11bgn ESSID:"MYWIFINET"
Mode:Managed Frequency:2.457 GHz Access Point: 10:AD:AF:CD:A7:A4
Bit Rate=65 Mb/s Tx-Power=16 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
Link Quality=64/70 Signal level=-46 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:2 Invalid misc:332 Missed beacon:0

Atheros is wlan0 and Alpha is wlan1:

root@kali:/# ifconfig
eth0 Link encap:Ethernet

lo Link encap:Local Loopback

wlan0 Link encap:Ethernet HWaddr ac:ba:ad:aa:aa:aa
inet addr: Bcast: Mask:
inet6 addr: fe80::9eb7:dff:fe04:d2f5/64 Scope:Link
RX packets:993402 errors:0 dropped:16671 overruns:0 frame:0
TX packets:1037777 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1231583696 (1.1 GiB) TX bytes:293024209 (279.4 MiB)

wlan1 Link encap:Ethernet HWaddr 00:c0:ca:bb:bb:bb
inet addr: Bcast: Mask:
inet6 addr: fe80::2c0:caff:fe59:23d0/64 Scope:Link
RX packets:14 errors:0 dropped:0 overruns:0 frame:0
TX packets:13 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1164 (1.1 KiB) TX bytes:1882 (1.8 KiB)

(2) Put one of Wi-Fi interfaces into monitor mode:

root@kali:/# airmon-ng start wlan1

Found 5 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after
a short period of time, you may want to kill (some of) them!
PID Name
2539 NetworkManager
2644 wpa_supplicant
3037 dhclient
19213 dhclient
20374 dhclient
Process with PID 20374 (dhclient) is running on interface wlan1
Process with PID 19213 (dhclient) is running on interface wlan0

Interface Chipset Driver

wlan1 Ralink RT2870/3070 rt2800usb - [phy4]
(monitor mode enabled on mon0)
wlan0 Atheros AR9485 ath9k - [phy0]

(3) Go to Wireshark's WPA PSK (Raw Key) Generator page:
Type in your Wi-Fi network's name and password and click on Generate PSK button.

(4) Start Wireshark. If it is not installed, install it with apt-get install wireshark command.

(5) In Wireshark: go to Capture --> Options and check "Use promiscuous mode on all interfaces"

(6) In Wireshark: go to Edit --> Preferences --> Protocols --> IEEE802.11, check "Enable decryption" option and add generated PSK key as new wpa-psk key in Decryption Keys.

(7) In Wireshark's main dashboard select monitor interface created by airmon-ng; that is mon0 in my case.
Press "Start" button in order to start live capture.

(8) Connect mobile device to Wi-Fi network. Wireshark has to capture handshake packets exchanged between the victim and the router when victim joins Wi-Fi network.

(9) In the browser of the victim's device type in any http address and allow it to load. I typed in order to get weather forecast for London from BBC Weather mobile webiste.

(10) Stop Wireshark and search for the HTTP traffic which goes between any IP address which is not the IP address of local Wi-Fi interfaces. In my case that was I could see DNS requests to all services my smartphone uses (Google, Facebook, Whatsapp...) and also DNS query for, and HTTP GET request that was sent!

Tuesday 4 August 2015

How to get Linux distribution name and version in the command line

(1) Using lsb_release

root@kali:/# lsb_release -a

No LSB modules are available.
Distributor ID: Kali
Description: Kali GNU/Linux 1.1.0
Release: 1.1.0
Codename: moto

(2) Print the content of the *release files in /etc:

root@kali:/# cat /etc/*-release

PRETTY_NAME="Kali GNU/Linux 1.1.0 (moto)"
NAME="Kali GNU/Linux"
VERSION="1.1.0 (moto)"

This is the same as printing each *release file on its own:

root@kali:/etc# pwd


root@kali:/etc# ls *release

lsb-release os-release

root@kali:/etc# cat lsb-release


root@kali:/etc# cat os-release

PRETTY_NAME="Kali GNU/Linux 1.1.0 (moto)"
NAME="Kali GNU/Linux"
VERSION="1.1.0 (moto)"

(3) Use uname command:

root@kali:/etc# uname -a

Linux kali 3.14-kali1-amd64 #1 SMP Debian 3.14.5-1kali1 (2014-06-07) x86_64 GNU/Linux

(4) Print content of the /proc/version file:

root@kali:/# cat /proc/version

Linux version 3.14-kali1-amd64 ( (gcc version 4.7.2 (Debian 4.7.2-5) ) #1 SMP Debian 3.14.5-1kali1

Network mapper (Nmap) manual page

Network Mapper (Nmap) man page:

NMAP(1)                      Nmap Reference Guide                      NMAP(1)

       nmap - Network exploration tool and security / port scanner

       nmap [Scan Type...] [Options] {target specification}

       Nmap (“Network Mapper”) is an open source tool for network exploration
       and security auditing. It was designed to rapidly scan large networks,
       although it works fine against single hosts. Nmap uses raw IP packets
       in novel ways to determine what hosts are available on the network,
       what services (application name and version) those hosts are offering,
       what operating systems (and OS versions) they are running, what type of
       packet filters/firewalls are in use, and dozens of other
       characteristics. While Nmap is commonly used for security audits, many
       systems and network administrators find it useful for routine tasks
       such as network inventory, managing service upgrade schedules, and
       monitoring host or service uptime.

       The output from Nmap is a list of scanned targets, with supplemental
       information on each depending on the options used. Key among that
       information is the “interesting ports table”..  That table lists the
       port number and protocol, service name, and state. The state is either
       open, filtered, closed, or unfiltered.  Open.  means that an
       application on the target machine is listening for connections/packets
       on that port.  Filtered.  means that a firewall, filter, or other
       network obstacle is blocking the port so that Nmap cannot tell whether
       it is open or closed.  Closed.  ports have no application listening on
       them, though they could open up at any time. Ports are classified as
       unfiltered.  when they are responsive to Nmap's probes, but Nmap cannot
       determine whether they are open or closed. Nmap reports the state
       combinations open|filtered.  and closed|filtered.  when it cannot
       determine which of the two states describe a port. The port table may
       also include software version details when version detection has been
       requested. When an IP protocol scan is requested (-sO), Nmap provides
       information on supported IP protocols rather than listening ports.

       In addition to the interesting ports table, Nmap can provide further
       information on targets, including reverse DNS names, operating system
       guesses, device types, and MAC addresses.

       A typical Nmap scan is shown in Example 1. The only Nmap arguments used
       in this example are -A, to enable OS and version detection, script
       scanning, and traceroute; -T4 for faster execution; and then the two
       target hostnames.

       Example 1. A representative Nmap scan

           # nmap -A -T4

           Nmap scan report for (
           Host is up (0.029s latency).
           rDNS record for
           Not shown: 995 closed ports
           PORT     STATE    SERVICE     VERSION
           22/tcp   open     ssh         OpenSSH 5.3p1 Debian 3ubuntu7 (protocol 2.0)
           | ssh-hostkey: 1024 8d:60:f1:7c:ca:b7:3d:0a:d6:67:54:9d:69:d9:b9:dd (DSA)
           |_2048 79:f8:09:ac:d4:e2:32:42:10:49:d3:bd:20:82:85:ec (RSA)
           80/tcp   open     http        Apache httpd 2.2.14 ((Ubuntu))
           |_http-title: Go ahead and ScanMe!
           646/tcp  filtered ldp
           1720/tcp filtered H.323/Q.931
           9929/tcp open     nping-echo  Nping echo
           Device type: general purpose
           Running: Linux 2.6.X
           OS CPE: cpe:/o:linux:linux_kernel:2.6.39
           OS details: Linux 2.6.39
           Network Distance: 11 hops
           Service Info: OS: Linux; CPE: cpe:/o:linux:kernel

           TRACEROUTE (using port 53/tcp)
           HOP RTT      ADDRESS
           [Cut first 10 hops for brevity]
           11  17.65 ms (

           Nmap done: 1 IP address (1 host up) scanned in 14.40 seconds

       The newest version of Nmap can be obtained from The
       newest version of this man page is available at  It is also included as a chapter of
       Nmap Network Scanning: The Official Nmap Project Guide to Network
       Discovery and Security Scanning (see

       This options summary is printed when Nmap is run with no arguments, and
       the latest version is always available at It helps people remember
       the most common options, but is no substitute for the in-depth
       documentation in the rest of this manual. Some obscure options aren't
       even included here.

           Nmap 6.47 ( )
           Usage: nmap [Scan Type(s)] [Options] {target specification}

             Can pass hostnames, IP addresses, networks, etc.
             Ex:,,; 10.0.0-255.1-254
             -iL : Input from list of hosts/networks
             -iR : Choose random targets
             --exclude : Exclude hosts/networks
             --excludefile : Exclude list from file

           HOST DISCOVERY:
             -sL: List Scan - simply list targets to scan
             -sn: Ping Scan - disable port scan
             -Pn: Treat all hosts as online -- skip host discovery
             -PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports
             -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
             -PO[protocol list]: IP Protocol Ping
             -n/-R: Never do DNS resolution/Always resolve [default: sometimes]
             --dns-servers : Specify custom DNS servers
             --system-dns: Use OS's DNS resolver
             --traceroute: Trace hop path to each host

             -sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
             -sU: UDP Scan
             -sN/sF/sX: TCP Null, FIN, and Xmas scans
             --scanflags : Customize TCP scan flags
             -sI : Idle scan
             -sY/sZ: SCTP INIT/COOKIE-ECHO scans
             -sO: IP protocol scan
             -b : FTP bounce scan

             -p : Only scan specified ports
               Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9
             -F: Fast mode - Scan fewer ports than the default scan
             -r: Scan ports consecutively - don't randomize
             --top-ports : Scan most common ports
             --port-ratio : Scan ports more common than 

             -sV: Probe open ports to determine service/version info
             --version-intensity : Set from 0 (light) to 9 (try all probes)
             --version-light: Limit to most likely probes (intensity 2)
             --version-all: Try every single probe (intensity 9)
             --version-trace: Show detailed version scan activity (for debugging)

           SCRIPT SCAN:
             -sC: equivalent to --script=default
             --script=: is a comma separated list of
                      directories, script-files or script-categories
             --script-args=: provide arguments to scripts
             --script-args-file=filename: provide NSE script args in a file
             --script-trace: Show all data sent and received
             --script-updatedb: Update the script database.
             --script-help=: Show help about scripts.
                      is a comma-separated list of script-files or

           OS DETECTION:
             -O: Enable OS detection
             --osscan-limit: Limit OS detection to promising targets
             --osscan-guess: Guess OS more aggressively

             Options which take

             -oN/-oX/-oS/-oG : Output scan in normal, XML, s|                and Grepable format, respectively, to the given filename.
             -oA : Output in the three major formats at once
             -v: Increase verbosity level (use -vv or more for greater effect)
             -d: Increase debugging level (use -dd or more for greater effect)
             --reason: Display the reason a port is in a particular state
             --open: Only show open (or possibly open) ports
             --packet-trace: Show all packets sent and received
             --iflist: Print host interfaces and routes (for debugging)
             --log-errors: Log errors/warnings to the normal-format output file
             --append-output: Append to rather than clobber specified output files
             --resume : Resume an aborted scan
             --stylesheet : XSL stylesheet to transform XML output to HTML
             --webxml: Reference stylesheet from Nmap.Org for more portable XML
             --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
             -6: Enable IPv6 scanning
             -A: Enable OS detection, version detection, script scanning, and traceroute
             --datadir : Specify custom Nmap data file location
             --send-eth/--send-ip: Send using raw ethernet frames or IP packets
             --privileged: Assume that the user is fully privileged
             --unprivileged: Assume the user lacks raw socket privileges
             -V: Print version number
             -h: Print this help summary page.

             nmap -v -A
             nmap -v -sn
             nmap -v -iR 10000 -Pn -p 80


       Everything on the Nmap command-line that isn't an option (or option
       argument) is treated as a target host specification. The simplest case
       is to specify a target IP address or hostname for scanning.

       Sometimes you wish to scan a whole network of adjacent hosts. For this,
       Nmap supports CIDR-style.  addressing. You can append /numbits to an
       IPv4 address or hostname and Nmap will scan every IP address for which
       the first numbits are the same as for the reference IP or hostname
       given. For example, would scan the 256 hosts between (binary: 11000000 10101000 00001010 00000000) and (binary: 11000000 10101000 00001010 11111111),
       inclusive. would scan exactly the same targets. Given
       that the host  is at the IP address, the
       specification would scan the 65,536 IP addresses
       between and The smallest allowed value is /0,
       which targets the whole Internet. The largest value is /32, which scans
       just the named host or IP address because all address bits are fixed.

       CIDR notation is short but not always flexible enough. For example, you
       might want to scan but skip any IPs ending with .0 or
       .255 because they may be used as subnet network and broadcast
       addresses. Nmap supports this through octet range addressing. Rather
       than specify a normal IP address, you can specify a comma-separated
       list of numbers or ranges for each octet. For example,
       192.168.0-255.1-254 will skip all addresses in the range that end in .0
       or .255, and 192.168.3-5,7.1 will scan the four addresses,,, and Either side of a range may
       be omitted; the default values are 0 on the left and 255 on the right.
       Using - by itself is the same as 0-255, but remember to use 0- in the
       first octet so the target specification doesn't look like a
       command-line option. Ranges need not be limited to the final octets:
       the specifier 0-255.0-255.13.37 will perform an Internet-wide scan for
       all IP addresses ending in 13.37. This sort of broad sampling can be
       useful for Internet surveys and research.

       IPv6 addresses can only be specified by their fully qualified IPv6
       address or hostname. CIDR and octet ranges aren't yet supported for

       IPv6 addresses with non-global scope need to have a zone ID suffix. On
       Unix systems, this is a percent sign followed by an interface name; a
       complete address might be fe80::a8bb:ccff:fedd:eeff%eth0. On Windows,
       use an interface index number in place of an interface name:
       fe80::a8bb:ccff:fedd:eeff%1. You can see a list of interface indexes by
       running the command netsh.exe interface ipv6 show interface.

       Nmap accepts multiple host specifications on the command line, and they
       don't need to be the same type. The command nmap 10.0.0,1,3-7.- does what you would expect.

       While targets are usually specified on the command lines, the following
       options are also available to control target selection:

       -iL inputfilename (Input from list) .
           Reads target specifications from inputfilename. Passing a huge list
           of hosts is often awkward on the command line, yet it is a common
           desire. For example, your DHCP server might export a list of 10,000
           current leases that you wish to scan. Or maybe you want to scan all
           IP addresses except for those to locate hosts using unauthorized
           static IP addresses. Simply generate the list of hosts to scan and
           pass that filename to Nmap as an argument to the -iL option.
           Entries can be in any of the formats accepted by Nmap on the
           command line (IP address, hostname, CIDR, IPv6, or octet ranges).
           Each entry must be separated by one or more spaces, tabs, or
           newlines. You can specify a hyphen (-) as the filename if you want
           Nmap to read hosts from standard input rather than an actual file.

           The input file may contain comments that start with # and extend to
           the end of the line.

       -iR num hosts (Choose random targets) .
           For Internet-wide surveys and other research, you may want to
           choose targets at random. The num hosts argument tells Nmap how
           many IPs to generate. Undesirable IPs such as those in certain
           private, multicast, or unallocated address ranges are automatically
           skipped. The argument 0 can be specified for a never-ending scan.
           Keep in mind that some network administrators bristle at
           unauthorized scans of their networks and may complain. Use this
           option at your own risk! If you find yourself really bored one
           rainy afternoon, try the command nmap -Pn -sS -p 80 -iR 0 --open.
           to locate random web servers for browsing.

       --exclude host1[,host2[,...]] (Exclude hosts/networks) .
           Specifies a comma-separated list of targets to be excluded from the
           scan even if they are part of the overall network range you
           specify. The list you pass in uses normal Nmap syntax, so it can
           include hostnames, CIDR netblocks, octet ranges, etc. This can be
           useful when the network you wish to scan includes untouchable
           mission-critical servers, systems that are known to react adversely
           to port scans, or subnets administered by other people.

       --excludefile exclude_file (Exclude list from file) .
           This offers the same functionality as the --exclude option, except
           that the excluded targets are provided in a newline-, space-, or
           tab-delimited exclude_file rather than on the command line.

           The exclude file may contain comments that start with # and extend
           to the end of the line.

       One of the very first steps in any network reconnaissance mission is to
       reduce a (sometimes huge) set of IP ranges into a list of active or
       interesting hosts. Scanning every port of every single IP address is
       slow and usually unnecessary. Of course what makes a host interesting
       depends greatly on the scan purposes. Network administrators may only
       be interested in hosts running a certain service, while security
       auditors may care about every single device with an IP address. An
       administrator may be comfortable using just an ICMP ping to locate
       hosts on his internal network, while an external penetration tester may
       use a diverse set of dozens of probes in an attempt to evade firewall

       Because host discovery needs are so diverse, Nmap offers a wide variety
       of options for customizing the techniques used. Host discovery is
       sometimes called ping scan, but it goes well beyond the simple ICMP
       echo request packets associated with the ubiquitous ping tool. Users
       can skip the ping step entirely with a list scan (-sL) or by disabling
       ping (-Pn), or engage the network with arbitrary combinations of
       multi-port TCP SYN/ACK, UDP, SCTP INIT and ICMP probes. The goal of
       these probes is to solicit responses which demonstrate that an IP
       address is actually active (is being used by a host or network device).
       On many networks, only a small percentage of IP addresses are active at
       any given time. This is particularly common with private address space
       such as That network has 16 million IPs, but I have seen it
       used by companies with less than a thousand machines. Host discovery
       can find those machines in a sparsely allocated sea of IP addresses.

       If no host discovery options are given, Nmap sends an ICMP echo
       request, a TCP SYN packet to port 443, a TCP ACK packet to port 80, and
       an ICMP timestamp request. (For IPv6, the ICMP timestamp request is
       omitted because it is not part of ICMPv6.) These defaults are
       equivalent to the -PE -PS443 -PA80 -PP options. The exceptions to this
       are the ARP (for IPv4) and Neighbor Discovery.  (for IPv6) scans which
       are used for any targets on a local ethernet network. For unprivileged
       Unix shell users, the default probes are a SYN packet to ports 80 and
       443 using the connect system call..  This host discovery is often
       sufficient when scanning local networks, but a more comprehensive set
       of discovery probes is recommended for security auditing.

       The -P* options (which select ping types) can be combined. You can
       increase your odds of penetrating strict firewalls by sending many
       probe types using different TCP ports/flags and ICMP codes. Also note
       that ARP/Neighbor Discovery (-PR).  is done by default against targets
       on a local ethernet network even if you specify other -P* options,
       because it is almost always faster and more effective.

       By default, Nmap does host discovery and then performs a port scan
       against each host it determines is online. This is true even if you
       specify non-default host discovery types such as UDP probes (-PU). Read
       about the -sn option to learn how to perform only host discovery, or
       use -Pn to skip host discovery and port scan all target hosts. The
       following options control host discovery:

       -sL (List Scan) .
           The list scan is a degenerate form of host discovery that simply
           lists each host of the network(s) specified, without sending any
           packets to the target hosts. By default, Nmap still does
           reverse-DNS resolution on the hosts to learn their names. It is
           often surprising how much useful information simple hostnames give
           out. For example, fw.chi is the name of one company's Chicago
           firewall.  Nmap also reports the total number of IP addresses at
           the end. The list scan is a good sanity check to ensure that you
           have proper IP addresses for your targets. If the hosts sport
           domain names you do not recognize, it is worth investigating
           further to prevent scanning the wrong company's network.

           Since the idea is to simply print a list of target hosts, options
           for higher level functionality such as port scanning, OS detection,
           or ping scanning cannot be combined with this. If you wish to
           disable ping scanning while still performing such higher level
           functionality, read up on the -Pn (skip ping) option.

       -sn (No port scan) .
           This option tells Nmap not to do a port scan after host discovery,
           and only print out the available hosts that responded to the scan.
           This is often known as a “ping scan”, but you can also request that
           traceroute and NSE host scripts be run. This is by default one step
           more intrusive than the list scan, and can often be used for the
           same purposes. It allows light reconnaissance of a target network
           without attracting much attention. Knowing how many hosts are up is
           more valuable to attackers than the list provided by list scan of
           every single IP and host name.

           Systems administrators often find this option valuable as well. It
           can easily be used to count available machines on a network or
           monitor server availability. This is often called a ping sweep, and
           is more reliable than pinging the broadcast address because many
           hosts do not reply to broadcast queries.

           The default host discovery done with -sn consists of an ICMP echo
           request, TCP SYN to port 443, TCP ACK to port 80, and an ICMP
           timestamp request by default. When executed by an unprivileged
           user, only SYN packets are sent (using a connect call) to ports 80
           and 443 on the target. When a privileged user tries to scan targets
           on a local ethernet network, ARP requests are used unless --send-ip
           was specified. The -sn option can be combined with any of the
           discovery probe types (the -P* options, excluding -Pn) for greater
           flexibility. If any of those probe type and port number options are
           used, the default probes are overridden. When strict firewalls are
           in place between the source host running Nmap and the target
           network, using those advanced techniques is recommended. Otherwise
           hosts could be missed when the firewall drops probes or their

           In previous releases of Nmap, -sn was known as -sP..

       -Pn (No ping) .
           This option skips the Nmap discovery stage altogether. Normally,
           Nmap uses this stage to determine active machines for heavier
           scanning. By default, Nmap only performs heavy probing such as port
           scans, version detection, or OS detection against hosts that are
           found to be up. Disabling host discovery with -Pn causes Nmap to
           attempt the requested scanning functions against every target IP
           address specified. So if a class B target address space (/16) is
           specified on the command line, all 65,536 IP addresses are scanned.
           Proper host discovery is skipped as with the list scan, but instead
           of stopping and printing the target list, Nmap continues to perform
           requested functions as if each target IP is active. To skip ping
           scan and port scan, while still allowing NSE to run, use the two
           options -Pn -sn together.

           For machines on a local ethernet network, ARP scanning will still
           be performed (unless --disable-arp-ping or --send-ip is specified)
           because Nmap needs MAC addresses to further scan target hosts. In
           previous versions of Nmap, -Pn was -P0.  and -PN..

       -PS port list (TCP SYN Ping) .
           This option sends an empty TCP packet with the SYN flag set. The
           default destination port is 80 (configurable at compile time by
           changing DEFAULT_TCP_PROBE_PORT_SPEC.  in nmap.h)..  Alternate
           ports can be specified as a parameter. The syntax is the same as
           for the -p except that port type specifiers like T: are not
           allowed. Examples are -PS22 and -PS22-25,80,113,1050,35000. Note
           that there can be no space between -PS and the port list. If
           multiple probes are specified they will be sent in parallel.

           The SYN flag suggests to the remote system that you are attempting
           to establish a connection. Normally the destination port will be
           closed, and a RST (reset) packet sent back. If the port happens to
           be open, the target will take the second step of a TCP
           three-way-handshake.  by responding with a SYN/ACK TCP packet. The
           machine running Nmap then tears down the nascent connection by
           responding with a RST rather than sending an ACK packet which would
           complete the three-way-handshake and establish a full connection.
           The RST packet is sent by the kernel of the machine running Nmap in
           response to the unexpected SYN/ACK, not by Nmap itself.

           Nmap does not care whether the port is open or closed. Either the
           RST or SYN/ACK response discussed previously tell Nmap that the
           host is available and responsive.

           On Unix boxes, only the privileged user root.  is generally able to
           send and receive raw TCP packets..  For unprivileged users, a
           workaround is automatically employed.  whereby the connect system
           call is initiated against each target port. This has the effect of
           sending a SYN packet to the target host, in an attempt to establish
           a connection. If connect returns with a quick success or an
           ECONNREFUSED failure, the underlying TCP stack must have received a
           SYN/ACK or RST and the host is marked available. If the connection
           attempt is left hanging until a timeout is reached, the host is
           marked as down.

       -PA port list (TCP ACK Ping) .
           The TCP ACK ping is quite similar to the just-discussed SYN ping.
           The difference, as you could likely guess, is that the TCP ACK flag
           is set instead of the SYN flag. Such an ACK packet purports to be
           acknowledging data over an established TCP connection, but no such
           connection exists. So remote hosts should always respond with a RST
           packet, disclosing their existence in the process.

           The -PA option uses the same default port as the SYN probe (80) and
           can also take a list of destination ports in the same format. If an
           unprivileged user tries this, the connect workaround discussed
           previously is used. This workaround is imperfect because connect is
           actually sending a SYN packet rather than an ACK.

           The reason for offering both SYN and ACK ping probes is to maximize
           the chances of bypassing firewalls. Many administrators configure
           routers and other simple firewalls to block incoming SYN packets
           except for those destined for public services like the company web
           site or mail server. This prevents other incoming connections to
           the organization, while allowing users to make unobstructed
           outgoing connections to the Internet. This non-stateful approach
           takes up few resources on the firewall/router and is widely
           supported by hardware and software filters. The Linux
           Netfilter/iptables.  firewall software offers the --syn convenience
           option to implement this stateless approach. When stateless
           firewall rules such as this are in place, SYN ping probes (-PS) are
           likely to be blocked when sent to closed target ports. In such
           cases, the ACK probe shines as it cuts right through these rules.

           Another common type of firewall uses stateful rules that drop
           unexpected packets. This feature was initially found mostly on
           high-end firewalls, though it has become much more common over the
           years. The Linux Netfilter/iptables system supports this through
           the --state option, which categorizes packets based on connection
           state. A SYN probe is more likely to work against such a system, as
           unexpected ACK packets are generally recognized as bogus and
           dropped. A solution to this quandary is to send both SYN and ACK
           probes by specifying -PS and -PA.

       -PU port list (UDP Ping) .
           Another host discovery option is the UDP ping, which sends a UDP
           packet to the given ports. For most ports, the packet will be
           empty, though for a few a protocol-specific payload will be sent
           that is more likely to get a response..  The payload database is
           described at

           The --data-length.  option can be used to send a fixed-length
           random payload to every port or (if you specify a value of 0) to
           disable payloads. You can also disable payloads by specifying
           --data-length 0.

           The port list takes the same format as with the previously
           discussed -PS and -PA options. If no ports are specified, the
           default is 40125..  This default can be configured at compile-time
           by changing DEFAULT_UDP_PROBE_PORT_SPEC.  in nmap.h..  A highly
           uncommon port is used by default because sending to open ports is
           often undesirable for this particular scan type.

           Upon hitting a closed port on the target machine, the UDP probe
           should elicit an ICMP port unreachable packet in return. This
           signifies to Nmap that the machine is up and available. Many other
           types of ICMP errors, such as host/network unreachables or TTL
           exceeded are indicative of a down or unreachable host. A lack of
           response is also interpreted this way. If an open port is reached,
           most services simply ignore the empty packet and fail to return any
           response. This is why the default probe port is 40125, which is
           highly unlikely to be in use. A few services, such as the Character
           Generator (chargen) protocol, will respond to an empty UDP packet,
           and thus disclose to Nmap that the machine is available.

           The primary advantage of this scan type is that it bypasses
           firewalls and filters that only screen TCP. For example, I once
           owned a Linksys BEFW11S4 wireless broadband router. The external
           interface of this device filtered all TCP ports by default, but UDP
           probes would still elicit port unreachable messages and thus give
           away the device.

       -PY port list (SCTP INIT Ping) .
           This option sends an SCTP packet containing a minimal INIT chunk.
           The default destination port is 80 (configurable at compile time by
           changing DEFAULT_SCTP_PROBE_PORT_SPEC.  in nmap.h). Alternate ports
           can be specified as a parameter. The syntax is the same as for the
           -p except that port type specifiers like S: are not allowed.
           Examples are -PY22 and -PY22,80,179,5060. Note that there can be no
           space between -PY and the port list. If multiple probes are
           specified they will be sent in parallel.

           The INIT chunk suggests to the remote system that you are
           attempting to establish an association. Normally the destination
           port will be closed, and an ABORT chunk will be sent back. If the
           port happens to be open, the target will take the second step of an
           SCTP four-way-handshake.  by responding with an INIT-ACK chunk. If
           the machine running Nmap has a functional SCTP stack, then it tears
           down the nascent association by responding with an ABORT chunk
           rather than sending a COOKIE-ECHO chunk which would be the next
           step in the four-way-handshake. The ABORT packet is sent by the
           kernel of the machine running Nmap in response to the unexpected
           INIT-ACK, not by Nmap itself.

           Nmap does not care whether the port is open or closed. Either the
           ABORT or INIT-ACK response discussed previously tell Nmap that the
           host is available and responsive.

           On Unix boxes, only the privileged user root.  is generally able to
           send and receive raw SCTP packets..  Using SCTP INIT Pings is
           currently not possible for unprivileged users..

       -PE; -PP; -PM (ICMP Ping Types) .
           In addition to the unusual TCP, UDP and SCTP host discovery types
           discussed previously, Nmap can send the standard packets sent by
           the ubiquitous ping program. Nmap sends an ICMP type 8 (echo
           request) packet to the target IP addresses, expecting a type 0
           (echo reply) in return from available hosts..  Unfortunately for
           network explorers, many hosts and firewalls now block these
           packets, rather than responding as required by RFC 1122[2]..  For
           this reason, ICMP-only scans are rarely reliable enough against
           unknown targets over the Internet. But for system administrators
           monitoring an internal network, they can be a practical and
           efficient approach. Use the -PE option to enable this echo request

           While echo request is the standard ICMP ping query, Nmap does not
           stop there. The ICMP standards (RFC 792[3].  and RFC 950[4].  “a
           host SHOULD NOT implement these messages”. Timestamp and address
           mask queries can be sent with the -PP and -PM options,
           respectively. A timestamp reply (ICMP code 14) or address mask
           reply (code 18) discloses that the host is available. These two
           queries can be valuable when administrators specifically block echo
           request packets while forgetting that other ICMP queries can be
           used for the same purpose.

       -PO protocol list (IP Protocol Ping) .
           One of the newer host discovery options is the IP protocol ping,
           which sends IP packets with the specified protocol number set in
           their IP header. The protocol list takes the same format as do port
           lists in the previously discussed TCP, UDP and SCTP host discovery
           options. If no protocols are specified, the default is to send
           multiple IP packets for ICMP (protocol 1), IGMP (protocol 2), and
           IP-in-IP (protocol 4). The default protocols can be configured at
           compile-time by changing DEFAULT_PROTO_PROBE_PORT_SPEC.  in nmap.h.
           Note that for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17)
           and SCTP (protocol 132), the packets are sent with the proper
           protocol headers.  while other protocols are sent with no
           additional data beyond the IP header (unless the --data-length.
           option is specified).

           This host discovery method looks for either responses using the
           same protocol as a probe, or ICMP protocol unreachable messages
           which signify that the given protocol isn't supported on the
           destination host. Either type of response signifies that the target
           host is alive.

       -PR (ARP Ping) .
           One of the most common Nmap usage scenarios is to scan an ethernet
           LAN. On most LANs, especially those using private address ranges
           specified by RFC 1918[5], the vast majority of IP addresses are
           unused at any given time. When Nmap tries to send a raw IP packet
           such as an ICMP echo request, the operating system must determine
           the destination hardware (ARP) address corresponding to the target
           IP so that it can properly address the ethernet frame. This is
           often slow and problematic, since operating systems weren't written
           with the expectation that they would need to do millions of ARP
           requests against unavailable hosts in a short time period.

           ARP scan puts Nmap and its optimized algorithms in charge of ARP
           requests. And if it gets a response back, Nmap doesn't even need to
           worry about the IP-based ping packets since it already knows the
           host is up. This makes ARP scan much faster and more reliable than
           IP-based scans. So it is done by default when scanning ethernet
           hosts that Nmap detects are on a local ethernet network. Even if
           different ping types (such as -PE or -PS) are specified, Nmap uses
           ARP instead for any of the targets which are on the same LAN. If
           you absolutely don't want to do an ARP scan, specify

           For IPv6 (-6 option), -PR uses ICMPv6 Neighbor Discovery instead of
           ARP. Neighbor Discovery, defined in RFC 4861, can be seen as the
           IPv6 equivalent of ARP.

       --disable-arp-ping (No ARP or ND Ping) .
           Nmap normally does ARP or IPv6 Neighbor Discovery (ND) discovery of
           locally connected ethernet hosts, even if other host discovery
           options such as -Pn or -PE are used. To disable this implicit
           behavior, use the --disable-arp-ping option.

           The default behavior is normally faster, but this option is useful
           on networks using proxy ARP, in which a router speculatively
           replies to all ARP requests, making every target appear to be up
           according to ARP scan.

       --traceroute (Trace path to host) .
           Traceroutes are performed post-scan using information from the scan
           results to determine the port and protocol most likely to reach the
           target. It works with all scan types except connect scans (-sT) and
           idle scans (-sI). All traces use Nmap's dynamic timing model and
           are performed in parallel.

           Traceroute works by sending packets with a low TTL (time-to-live)
           in an attempt to elicit ICMP Time Exceeded messages from
           intermediate hops between the scanner and the target host. Standard
           traceroute implementations start with a TTL of 1 and increment the
           TTL until the destination host is reached. Nmap's traceroute starts
           with a high TTL and then decrements the TTL until it reaches zero.
           Doing it backwards lets Nmap employ clever caching algorithms to
           speed up traces over multiple hosts. On average Nmap sends 5–10
           fewer packets per host, depending on network conditions. If a
           single subnet is being scanned (i.e. Nmap may only
           have to send two packets to most hosts.

       -n (No DNS resolution) .
           Tells Nmap to never do reverse DNS resolution on the active IP
           addresses it finds. Since DNS can be slow even with Nmap's built-in
           parallel stub resolver, this option can slash scanning times.

       -R (DNS resolution for all targets) .
           Tells Nmap to always do reverse DNS resolution on the target IP
           addresses. Normally reverse DNS is only performed against
           responsive (online) hosts.

       --system-dns (Use system DNS resolver) .
           By default, Nmap resolves IP addresses by sending queries directly
           to the name servers configured on your host and then listening for
           responses. Many requests (often dozens) are performed in parallel
           to improve performance. Specify this option to use your system
           resolver instead (one IP at a time via the getnameinfo call). This
           is slower and rarely useful unless you find a bug in the Nmap
           parallel resolver (please let us know if you do). The system
           resolver is always used for IPv6 scans.

       --dns-servers server1[,server2[,...]]  (Servers to use for reverse DNS
       queries) .
           By default, Nmap determines your DNS servers (for rDNS resolution)
           from your resolv.conf file (Unix) or the Registry (Win32).
           Alternatively, you may use this option to specify alternate
           servers. This option is not honored if you are using --system-dns
           or an IPv6 scan. Using multiple DNS servers is often faster,
           especially if you choose authoritative servers for your target IP
           space. This option can also improve stealth, as your requests can
           be bounced off just about any recursive DNS server on the Internet.

           This option also comes in handy when scanning private networks.
           Sometimes only a few name servers provide proper rDNS information,
           and you may not even know where they are. You can scan the network
           for port 53 (perhaps with version detection), then try Nmap list
           scans (-sL) specifying each name server one at a time with
           --dns-servers until you find one which works.

       While Nmap has grown in functionality over the years, it began as an
       efficient port scanner, and that remains its core function. The simple
       command nmap target scans 1,000 TCP ports on the host target. While
       many port scanners have traditionally lumped all ports into the open or
       closed states, Nmap is much more granular. It divides ports into six
       states: open, closed, filtered, unfiltered, open|filtered, or

       These states are not intrinsic properties of the port itself, but
       describe how Nmap sees them. For example, an Nmap scan from the same
       network as the target may show port 135/tcp as open, while a scan at
       the same time with the same options from across the Internet might show
       that port as filtered.

       The six port states recognized by Nmap

           An application is actively accepting TCP connections, UDP datagrams
           or SCTP associations on this port. Finding these is often the
           primary goal of port scanning. Security-minded people know that
           each open port is an avenue for attack. Attackers and pen-testers
           want to exploit the open ports, while administrators try to close
           or protect them with firewalls without thwarting legitimate users.
           Open ports are also interesting for non-security scans because they
           show services available for use on the network.

           A closed port is accessible (it receives and responds to Nmap probe
           packets), but there is no application listening on it. They can be
           helpful in showing that a host is up on an IP address (host
           discovery, or ping scanning), and as part of OS detection. Because
           closed ports are reachable, it may be worth scanning later in case
           some open up. Administrators may want to consider blocking such
           ports with a firewall. Then they would appear in the filtered
           state, discussed next.

           Nmap cannot determine whether the port is open because packet
           filtering prevents its probes from reaching the port. The filtering
           could be from a dedicated firewall device, router rules, or
           host-based firewall software. These ports frustrate attackers
           because they provide so little information. Sometimes they respond
           with ICMP error messages such as type 3 code 13 (destination
           unreachable: communication administratively prohibited), but
           filters that simply drop probes without responding are far more
           common. This forces Nmap to retry several times just in case the
           probe was dropped due to network congestion rather than filtering.
           This slows down the scan dramatically.

           The unfiltered state means that a port is accessible, but Nmap is
           unable to determine whether it is open or closed. Only the ACK
           scan, which is used to map firewall rulesets, classifies ports into
           this state. Scanning unfiltered ports with other scan types such as
           Window scan, SYN scan, or FIN scan, may help resolve whether the
           port is open.

           Nmap places ports in this state when it is unable to determine
           whether a port is open or filtered. This occurs for scan types in
           which open ports give no response. The lack of response could also
           mean that a packet filter dropped the probe or any response it
           elicited. So Nmap does not know for sure whether the port is open
           or being filtered. The UDP, IP protocol, FIN, NULL, and Xmas scans
           classify ports this way.

           This state is used when Nmap is unable to determine whether a port
           is closed or filtered. It is only used for the IP ID idle scan.

       As a novice performing automotive repair, I can struggle for hours
       trying to fit my rudimentary tools (hammer, duct tape, wrench, etc.) to
       the task at hand. When I fail miserably and tow my jalopy to a real
       mechanic, he invariably fishes around in a huge tool chest until
       pulling out the perfect gizmo which makes the job seem effortless. The
       art of port scanning is similar. Experts understand the dozens of scan
       techniques and choose the appropriate one (or combination) for a given
       task. Inexperienced users and script kiddies,.  on the other hand, try
       to solve every problem with the default SYN scan. Since Nmap is free,
       the only barrier to port scanning mastery is knowledge. That certainly
       beats the automotive world, where it may take great skill to determine
       that you need a strut spring compressor, then you still have to pay
       thousands of dollars for it.

       Most of the scan types are only available to privileged users..  This
       is because they send and receive raw packets,.  which requires root
       access on Unix systems. Using an administrator account on Windows is
       recommended, though Nmap sometimes works for unprivileged users on that
       platform when WinPcap has already been loaded into the OS. Requiring
       root privileges was a serious limitation when Nmap was released in
       1997, as many users only had access to shared shell accounts. Now, the
       world is different. Computers are cheaper, far more people have
       always-on direct Internet access, and desktop Unix systems (including
       Linux and Mac OS X) are prevalent. A Windows version of Nmap is now
       available, allowing it to run on even more desktops. For all these
       reasons, users have less need to run Nmap from limited shared shell
       accounts. This is fortunate, as the privileged options make Nmap far
       more powerful and flexible.

       While Nmap attempts to produce accurate results, keep in mind that all
       of its insights are based on packets returned by the target machines
       (or firewalls in front of them). Such hosts may be untrustworthy and
       send responses intended to confuse or mislead Nmap. Much more common
       are non-RFC-compliant hosts that do not respond as they should to Nmap
       probes. FIN, NULL, and Xmas scans are particularly susceptible to this
       problem. Such issues are specific to certain scan types and so are
       discussed in the individual scan type entries.

       This section documents the dozen or so port scan techniques supported
       by Nmap. Only one method may be used at a time, except that UDP scan
       (-sU) and any one of the SCTP scan types (-sY, -sZ) may be combined
       with any one of the TCP scan types. As a memory aid, port scan type
       options are of the form -sC, where C is a prominent character in the
       scan name, usually the first. The one exception to this is the
       deprecated FTP bounce scan (-b). By default, Nmap performs a SYN Scan,
       though it substitutes a connect scan if the user does not have proper
       privileges to send raw packets (requires root access on Unix). Of the
       scans listed in this section, unprivileged users can only execute
       connect and FTP bounce scans.

       -sS (TCP SYN scan) .
           SYN scan is the default and most popular scan option for good
           reasons. It can be performed quickly, scanning thousands of ports
           per second on a fast network not hampered by restrictive firewalls.
           It is also relatively unobtrusive and stealthy since it never
           completes TCP connections. SYN scan works against any compliant TCP
           stack rather than depending on idiosyncrasies of specific platforms
           as Nmap's FIN/NULL/Xmas, Maimon and idle scans do. It also allows
           clear, reliable differentiation between the open, closed, and
           filtered states.

           This technique is often referred to as half-open scanning, because
           you don't open a full TCP connection. You send a SYN packet, as if
           you are going to open a real connection and then wait for a
           response. A SYN/ACK indicates the port is listening (open), while a
           RST (reset) is indicative of a non-listener. If no response is
           received after several retransmissions, the port is marked as
           filtered. The port is also marked filtered if an ICMP unreachable
           error (type 3, code 1, 2, 3, 9, 10, or 13) is received. The port is
           also considered open if a SYN packet (without the ACK flag) is
           received in response. This can be due to an extremely rare TCP
           feature known as a simultaneous open or split handshake connection

       -sT (TCP connect scan) .
           TCP connect scan is the default TCP scan type when SYN scan is not
           an option. This is the case when a user does not have raw packet
           privileges. Instead of writing raw packets as most other scan types
           do, Nmap asks the underlying operating system to establish a
           connection with the target machine and port by issuing the connect
           system call. This is the same high-level system call that web
           browsers, P2P clients, and most other network-enabled applications
           use to establish a connection. It is part of a programming
           interface known as the Berkeley Sockets API. Rather than read raw
           packet responses off the wire, Nmap uses this API to obtain status
           information on each connection attempt.

           When SYN scan is available, it is usually a better choice. Nmap has
           less control over the high level connect call than with raw
           packets, making it less efficient. The system call completes
           connections to open target ports rather than performing the
           half-open reset that SYN scan does. Not only does this take longer
           and require more packets to obtain the same information, but target
           machines are more likely to log the connection. A decent IDS will
           catch either, but most machines have no such alarm system. Many
           services on your average Unix system will add a note to syslog, and
           sometimes a cryptic error message, when Nmap connects and then
           closes the connection without sending data. Truly pathetic services
           crash when this happens, though that is uncommon. An administrator
           who sees a bunch of connection attempts in her logs from a single
           system should know that she has been connect scanned.

       -sU (UDP scans) .
           While most popular services on the Internet run over the TCP
           protocol, UDP[6] services are widely deployed. DNS, SNMP, and DHCP
           (registered ports 53, 161/162, and 67/68) are three of the most
           common. Because UDP scanning is generally slower and more difficult
           than TCP, some security auditors ignore these ports. This is a
           mistake, as exploitable UDP services are quite common and attackers
           certainly don't ignore the whole protocol. Fortunately, Nmap can
           help inventory UDP ports.

           UDP scan is activated with the -sU option. It can be combined with
           a TCP scan type such as SYN scan (-sS) to check both protocols
           during the same run.

           UDP scan works by sending a UDP packet to every targeted port. For
           some common ports such as 53 and 161, a protocol-specific payload
           is sent, but for most ports the packet is empty..  The
           --data-length option can be used to send a fixed-length random
           payload to every port or (if you specify a value of 0) to disable
           payloads. If an ICMP port unreachable error (type 3, code 3) is
           returned, the port is closed. Other ICMP unreachable errors (type
           3, codes 1, 2, 9, 10, or 13) mark the port as filtered.
           Occasionally, a service will respond with a UDP packet, proving
           that it is open. If no response is received after retransmissions,
           the port is classified as open|filtered. This means that the port
           could be open, or perhaps packet filters are blocking the
           communication. Version detection (-sV) can be used to help
           differentiate the truly open ports from the filtered ones.

           A big challenge with UDP scanning is doing it quickly. Open and
           filtered ports rarely send any response, leaving Nmap to time out
           and then conduct retransmissions just in case the probe or response
           were lost. Closed ports are often an even bigger problem. They
           usually send back an ICMP port unreachable error. But unlike the
           RST packets sent by closed TCP ports in response to a SYN or
           connect scan, many hosts rate limit.  ICMP port unreachable
           messages by default. Linux and Solaris are particularly strict
           about this. For example, the Linux 2.4.20 kernel limits destination
           unreachable messages to one per second (in net/ipv4/icmp.c).

           Nmap detects rate limiting and slows down accordingly to avoid
           flooding the network with useless packets that the target machine
           will drop. Unfortunately, a Linux-style limit of one packet per
           second makes a 65,536-port scan take more than 18 hours. Ideas for
           speeding your UDP scans up include scanning more hosts in parallel,
           doing a quick scan of just the popular ports first, scanning from
           behind the firewall, and using --host-timeout to skip slow hosts.

       -sY (SCTP INIT scan) .

           SCTP[7] is a relatively new alternative to the TCP and UDP
           protocols, combining most characteristics of TCP and UDP, and also
           adding new features like multi-homing and multi-streaming. It is
           mostly being used for SS7/SIGTRAN related services but has the
           potential to be used for other applications as well. SCTP INIT scan
           is the SCTP equivalent of a TCP SYN scan. It can be performed
           quickly, scanning thousands of ports per second on a fast network
           not hampered by restrictive firewalls. Like SYN scan, INIT scan is
           relatively unobtrusive and stealthy, since it never completes SCTP
           associations. It also allows clear, reliable differentiation
           between the open, closed, and filtered states.

           This technique is often referred to as half-open scanning, because
           you don't open a full SCTP association. You send an INIT chunk, as
           if you are going to open a real association and then wait for a
           response. An INIT-ACK chunk indicates the port is listening (open),
           while an ABORT chunk is indicative of a non-listener. If no
           response is received after several retransmissions, the port is
           marked as filtered. The port is also marked filtered if an ICMP
           unreachable error (type 3, code 1, 2, 3, 9, 10, or 13) is received.

       -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans) .
           These three scan types (even more are possible with the --scanflags
           option described in the next section) exploit a subtle loophole in
           the TCP RFC[8] to differentiate between open and closed ports. Page
           65 of RFC 793 says that “if the [destination] port state is CLOSED
           .... an incoming segment not containing a RST causes a RST to be
           sent in response.”  Then the next page discusses packets sent to
           open ports without the SYN, RST, or ACK bits set, stating that:
           “you are unlikely to get here, but if you do, drop the segment, and

           When scanning systems compliant with this RFC text, any packet not
           containing SYN, RST, or ACK bits will result in a returned RST if
           the port is closed and no response at all if the port is open. As
           long as none of those three bits are included, any combination of
           the other three (FIN, PSH, and URG) are OK. Nmap exploits this with
           three scan types:

           Null scan (-sN)
               Does not set any bits (TCP flag header is 0)

           FIN scan (-sF)
               Sets just the TCP FIN bit.

           Xmas scan (-sX)
               Sets the FIN, PSH, and URG flags, lighting the packet up like a
               Christmas tree.

           These three scan types are exactly the same in behavior except for
           the TCP flags set in probe packets. If a RST packet is received,
           the port is considered closed, while no response means it is
           open|filtered. The port is marked filtered if an ICMP unreachable
           error (type 3, code 1, 2, 3, 9, 10, or 13) is received.

           The key advantage to these scan types is that they can sneak
           through certain non-stateful firewalls and packet filtering
           routers. Another advantage is that these scan types are a little
           more stealthy than even a SYN scan. Don't count on this though—most
           modern IDS products can be configured to detect them. The big
           downside is that not all systems follow RFC 793 to the letter. A
           number of systems send RST responses to the probes regardless of
           whether the port is open or not. This causes all of the ports to be
           labeled closed. Major operating systems that do this are Microsoft
           Windows, many Cisco devices, BSDI, and IBM OS/400. This scan does
           work against most Unix-based systems though. Another downside of
           these scans is that they can't distinguish open ports from certain
           filtered ones, leaving you with the response open|filtered.

       -sA (TCP ACK scan) .
           This scan is different than the others discussed so far in that it
           never determines open (or even open|filtered) ports. It is used to
           map out firewall rulesets, determining whether they are stateful or
           not and which ports are filtered.

           The ACK scan probe packet has only the ACK flag set (unless you use
           --scanflags). When scanning unfiltered systems, open and closed
           ports will both return a RST packet. Nmap then labels them as
           unfiltered, meaning that they are reachable by the ACK packet, but
           whether they are open or closed is undetermined. Ports that don't
           respond, or send certain ICMP error messages back (type 3, code 1,
           2, 3, 9, 10, or 13), are labeled filtered.

       -sW (TCP Window scan) .
           Window scan is exactly the same as ACK scan except that it exploits
           an implementation detail of certain systems to differentiate open
           ports from closed ones, rather than always printing unfiltered when
           a RST is returned. It does this by examining the TCP Window field
           of the RST packets returned. On some systems, open ports use a
           positive window size (even for RST packets) while closed ones have
           a zero window. So instead of always listing a port as unfiltered
           when it receives a RST back, Window scan lists the port as open or
           closed if the TCP Window value in that reset is positive or zero,

           This scan relies on an implementation detail of a minority of
           systems out on the Internet, so you can't always trust it. Systems
           that don't support it will usually return all ports closed. Of
           course, it is possible that the machine really has no open ports.
           If most scanned ports are closed but a few common port numbers
           (such as 22, 25, 53) are filtered, the system is most likely
           susceptible. Occasionally, systems will even show the exact
           opposite behavior. If your scan shows 1,000 open ports and three
           closed or filtered ports, then those three may very well be the
           truly open ones.

       -sM (TCP Maimon scan) .
           The Maimon scan is named after its discoverer, Uriel Maimon..  He
           described the technique in Phrack Magazine issue #49 (November
           1996)..  Nmap, which included this technique, was released two
           issues later. This technique is exactly the same as NULL, FIN, and
           Xmas scans, except that the probe is FIN/ACK. According to RFC
           793[8] (TCP), a RST packet should be generated in response to such
           a probe whether the port is open or closed. However, Uriel noticed
           that many BSD-derived systems simply drop the packet if the port is

       --scanflags (Custom TCP scan) .
           Truly advanced Nmap users need not limit themselves to the canned
           scan types offered. The --scanflags option allows you to design
           your own scan by specifying arbitrary TCP flags..  Let your
           creative juices flow, while evading intrusion detection systems.
           whose vendors simply paged through the Nmap man page adding
           specific rules!

           The --scanflags argument can be a numerical flag value such as 9
           (PSH and FIN), but using symbolic names is easier. Just mash
           together any combination of URG, ACK, PSH, RST, SYN, and FIN. For
           example, --scanflags URGACKPSHRSTSYNFIN sets everything, though
           it's not very useful for scanning. The order these are specified in
           is irrelevant.

           In addition to specifying the desired flags, you can specify a TCP
           scan type (such as -sA or -sF). That base type tells Nmap how to
           interpret responses. For example, a SYN scan considers no-response
           to indicate a filtered port, while a FIN scan treats the same as
           open|filtered. Nmap will behave the same way it does for the base
           scan type, except that it will use the TCP flags you specify
           instead. If you don't specify a base type, SYN scan is used.

       -sZ (SCTP COOKIE ECHO scan) .
           SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes
           advantage of the fact that SCTP implementations should silently
           drop packets containing COOKIE ECHO chunks on open ports, but send
           an ABORT if the port is closed. The advantage of this scan type is
           that it is not as obvious a port scan than an INIT scan. Also,
           there may be non-stateful firewall rulesets blocking INIT chunks,
           but not COOKIE ECHO chunks. Don't be fooled into thinking that this
           will make a port scan invisible; a good IDS will be able to detect
           SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO
           scans cannot differentiate between open and filtered ports, leaving
           you with the state open|filtered in both cases.

       -sI zombie host[:probeport] (idle scan) .
           This advanced scan method allows for a truly blind TCP port scan of
           the target (meaning no packets are sent to the target from your
           real IP address). Instead, a unique side-channel attack exploits
           predictable IP fragmentation ID sequence generation on the zombie
           host to glean information about the open ports on the target. IDS
           systems will display the scan as coming from the zombie machine you
           specify (which must be up and meet certain criteria).  This
           fascinating scan type is too complex to fully describe in this
           reference guide, so I wrote and posted an informal paper with full
           details at

           Besides being extraordinarily stealthy (due to its blind nature),
           this scan type permits mapping out IP-based trust relationships
           between machines. The port listing shows open ports from the
           perspective of the zombie host.  So you can try scanning a target
           using various zombies that you think might be trusted.  (via
           router/packet filter rules).

           You can add a colon followed by a port number to the zombie host if
           you wish to probe a particular port on the zombie for IP ID
           changes. Otherwise Nmap will use the port it uses by default for
           TCP pings (80).

       -sO (IP protocol scan) .
           IP protocol scan allows you to determine which IP protocols (TCP,
           ICMP, IGMP, etc.) are supported by target machines. This isn't
           technically a port scan, since it cycles through IP protocol
           numbers rather than TCP or UDP port numbers. Yet it still uses the
           -p option to select scanned protocol numbers, reports its results
           within the normal port table format, and even uses the same
           underlying scan engine as the true port scanning methods. So it is
           close enough to a port scan that it belongs here.

           Besides being useful in its own right, protocol scan demonstrates
           the power of open-source software. While the fundamental idea is
           pretty simple, I had not thought to add it nor received any
           requests for such functionality. Then in the summer of 2000,
           Gerhard Rieger.  conceived the idea, wrote an excellent patch
           implementing it, and sent it to the announce mailing list.  (then
           called nmap-hackers)..  I incorporated that patch into the Nmap
           tree and released a new version the next day. Few pieces of
           commercial software have users enthusiastic enough to design and
           contribute their own improvements!

           Protocol scan works in a similar fashion to UDP scan. Instead of
           iterating through the port number field of a UDP packet, it sends
           IP packet headers and iterates through the eight-bit IP protocol
           field. The headers are usually empty, containing no data and not
           even the proper header for the claimed protocol. The exceptions are
           TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for those
           is included since some systems won't send them otherwise and
           because Nmap already has functions to create them. Instead of
           watching for ICMP port unreachable messages, protocol scan is on
           the lookout for ICMP protocol unreachable messages. If Nmap
           receives any response in any protocol from the target host, Nmap
           marks that protocol as open. An ICMP protocol unreachable error
           (type 3, code 2) causes the protocol to be marked as closed Other
           ICMP unreachable errors (type 3, code 1, 3, 9, 10, or 13) cause the
           protocol to be marked filtered (though they prove that ICMP is open
           at the same time). If no response is received after
           retransmissions, the protocol is marked open|filtered

       -b FTP relay host (FTP bounce scan) .
           An interesting feature of the FTP protocol (RFC 959[9]) is support
           for so-called proxy FTP connections. This allows a user to connect
           to one FTP server, then ask that files be sent to a third-party
           server. Such a feature is ripe for abuse on many levels, so most
           servers have ceased supporting it. One of the abuses this feature
           allows is causing the FTP server to port scan other hosts. Simply
           ask the FTP server to send a file to each interesting port of a
           target host in turn. The error message will describe whether the
           port is open or not. This is a good way to bypass firewalls because
           organizational FTP servers are often placed where they have more
           access to other internal hosts than any old Internet host would.
           Nmap supports FTP bounce scan with the -b option. It takes an
           argument of the form username:password@server:port.  Server is the
           name or IP address of a vulnerable FTP server. As with a normal
           URL, you may omit username:password, in which case anonymous login
           credentials (user: anonymous password:-wwwuser@) are used. The port
           number (and preceding colon) may be omitted as well, in which case
           the default FTP port (21) on server is used.

           This vulnerability was widespread in 1997 when Nmap was released,
           but has largely been fixed. Vulnerable servers are still around, so
           it is worth trying when all else fails. If bypassing a firewall is
           your goal, scan the target network for port 21 (or even for any FTP
           services if you scan all ports with version detection) and use the
           ftp-bounce.  NSE script. Nmap will tell you whether the host is
           vulnerable or not. If you are just trying to cover your tracks, you
           don't need to (and, in fact, shouldn't) limit yourself to hosts on
           the target network. Before you go scanning random Internet
           addresses for vulnerable FTP servers, consider that sysadmins may
           not appreciate you abusing their servers in this way.

       In addition to all of the scan methods discussed previously, Nmap
       offers options for specifying which ports are scanned and whether the
       scan order is randomized or sequential. By default, Nmap scans the most
       common 1,000 ports for each protocol.

       -p port ranges (Only scan specified ports) .
           This option specifies which ports you want to scan and overrides
           the default. Individual port numbers are OK, as are ranges
           separated by a hyphen (e.g.  1-1023). The beginning and/or end
           values of a range may be omitted, causing Nmap to use 1 and 65535,
           respectively. So you can specify -p- to scan ports from 1 through
           65535. Scanning port zero.  is allowed if you specify it
           explicitly. For IP protocol scanning (-sO), this option specifies
           the protocol numbers you wish to scan for (0–255).

           When scanning a combination of protocols (e.g. TCP and UDP), you
           can specify a particular protocol by preceding the port numbers by
           T: for TCP, U: for UDP, S: for SCTP, or P: for IP Protocol. The
           qualifier lasts until you specify another qualifier. For example,
           the argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP
           ports 53, 111,and 137, as well as the listed TCP ports. Note that
           to scan both UDP and TCP, you have to specify -sU and at least one
           TCP scan type (such as -sS, -sF, or -sT). If no protocol qualifier
           is given, the port numbers are added to all protocol lists.  Ports
           can also be specified by name according to what the port is
           referred to in the nmap-services. You can even use the wildcards *
           and ?  with the names. For example, to scan FTP and all ports whose
           names begin with “http”, use -p ftp,http*. Be careful about shell
           expansions and quote the argument to -p if unsure.

           Ranges of ports can be surrounded by square brackets to indicate
           ports inside that range that appear in nmap-services. For example,
           the following will scan all ports in nmap-services equal to or
           below 1024: -p [-1024]. Be careful with shell expansions and quote
           the argument to -p if unsure.

       -F (Fast (limited port) scan) .
           Specifies that you wish to scan fewer ports than the default.
           Normally Nmap scans the most common 1,000 ports for each scanned
           protocol. With -F, this is reduced to 100.

           Nmap needs an nmap-services file with frequency information in
           order to know which ports are the most common. If port frequency
           information isn't available, perhaps because of the use of a custom
           nmap-services file, Nmap scans all named ports plus ports 1-1024.
           In that case, -F means to scan only ports that are named in the
           services file.

       -r (Don't randomize ports) .
           By default, Nmap randomizes the scanned port order (except that
           certain commonly accessible ports are moved near the beginning for
           efficiency reasons). This randomization is normally desirable, but
           you can specify -r for sequential (sorted from lowest to highest)
           port scanning instead.

       --port-ratio ratio
           Scans all ports in nmap-services file with a ratio greater than the
           one given.  ratio must be between 0.0 and 1.1.

       --top-ports n
           Scans the n highest-ratio ports found in nmap-services file.  n
           must be 1 or greater.

       Point Nmap at a remote machine and it might tell you that ports 25/tcp,
       80/tcp, and 53/udp are open. Using its nmap-services.  database of
       about 2,200 well-known services,.  Nmap would report that those ports
       probably correspond to a mail server (SMTP), web server (HTTP), and
       name server (DNS) respectively. This lookup is usually accurate—the
       vast majority of daemons listening on TCP port 25 are, in fact, mail
       servers. However, you should not bet your security on this! People can
       and do run services on strange ports..

       Even if Nmap is right, and the hypothetical server above is running
       SMTP, HTTP, and DNS servers, that is not a lot of information. When
       doing vulnerability assessments (or even simple network inventories) of
       your companies or clients, you really want to know which mail and DNS
       servers and versions are running. Having an accurate version number
       helps dramatically in determining which exploits a server is vulnerable
       to. Version detection helps you obtain this information.

       After TCP and/or UDP ports are discovered using one of the other scan
       methods, version detection interrogates those ports to determine more
       about what is actually running. The nmap-service-probes.  database
       contains probes for querying various services and match expressions to
       recognize and parse responses. Nmap tries to determine the service
       protocol (e.g. FTP, SSH, Telnet, HTTP), the application name (e.g. ISC
       BIND, Apache httpd, Solaris telnetd), the version number, hostname,
       device type (e.g. printer, router), the OS family (e.g. Windows,
       Linux). When possible, Nmap also gets the Common Platform Enumeration
       (CPE).  representation of this information. Sometimes miscellaneous
       details like whether an X server is open to connections, the SSH
       protocol version, or the KaZaA user name, are available. Of course,
       most services don't provide all of this information. If Nmap was
       compiled with OpenSSL support, it will connect to SSL servers to deduce
       the service listening behind that encryption layer..  Some UDP ports
       are left in the open|filtered state after a UDP port scan is unable to
       determine whether the port is open or filtered. Version detection will
       try to elicit a response from these ports (just as it does with open
       ports), and change the state to open if it succeeds.  open|filtered TCP
       ports are treated the same way. Note that the Nmap -A option enables
       version detection among other things.  A paper documenting the
       workings, usage, and customization of version detection is available at

       When RPC services are discovered, the Nmap RPC grinder.  is
       automatically used to determine the RPC program and version numbers. It
       takes all the TCP/UDP ports detected as RPC and floods them with SunRPC
       program NULL commands in an attempt to determine whether they are RPC
       ports, and if so, what program and version number they serve up. Thus
       you can effectively obtain the same info as rpcinfo -p even if the
       target's portmapper is behind a firewall (or protected by TCP
       wrappers). Decoys do not currently work with RPC scan..

       When Nmap receives responses from a service but cannot match them to
       its database, it prints out a special fingerprint and a URL for you to
       submit if to if you know for sure what is running on the port. Please
       take a couple minutes to make the submission so that your find can
       benefit everyone. Thanks to these submissions, Nmap has about 6,500
       pattern matches for more than 650 protocols such as SMTP, FTP, HTTP,

       Version detection is enabled and controlled with the following options:

       -sV (Version detection) .
           Enables version detection, as discussed above. Alternatively, you
           can use -A, which enables version detection among other things.

           -sR.  is an alias for -sV. Prior to March 2011, it was used to
           active the RPC grinder separately from version detection, but now
           these options are always combined.

       --allports (Don't exclude any ports from version detection) .
           By default, Nmap version detection skips TCP port 9100 because some
           printers simply print anything sent to that port, leading to dozens
           of pages of HTTP GET requests, binary SSL session requests, etc.
           This behavior can be changed by modifying or removing the Exclude
           directive in nmap-service-probes, or you can specify --allports to
           scan all ports regardless of any Exclude directive.

       --version-intensity intensity (Set version scan intensity) .
           When performing a version scan (-sV), Nmap sends a series of
           probes, each of which is assigned a rarity value between one and
           nine. The lower-numbered probes are effective against a wide
           variety of common services, while the higher-numbered ones are
           rarely useful. The intensity level specifies which probes should be
           applied. The higher the number, the more likely it is the service
           will be correctly identified. However, high intensity scans take
           longer. The intensity must be between 0 and 9..  The default is 7..
           When a probe is registered to the target port via the
           nmap-service-probes ports directive, that probe is tried regardless
           of intensity level. This ensures that the DNS probes will always be
           attempted against any open port 53, the SSL probe will be done
           against 443, etc.

       --version-light (Enable light mode) .
           This is a convenience alias for --version-intensity 2. This light
           mode makes version scanning much faster, but it is slightly less
           likely to identify services.

       --version-all (Try every single probe) .
           An alias for --version-intensity 9, ensuring that every single
           probe is attempted against each port.

       --version-trace (Trace version scan activity) .
           This causes Nmap to print out extensive debugging info about what
           version scanning is doing. It is a subset of what you get with

       One of Nmap's best-known features is remote OS detection using TCP/IP
       stack fingerprinting. Nmap sends a series of TCP and UDP packets to the
       remote host and examines practically every bit in the responses. After
       performing dozens of tests such as TCP ISN sampling, TCP options
       support and ordering, IP ID sampling, and the initial window size
       check, Nmap compares the results to its nmap-os-db.  database of more
       than 2,600 known OS fingerprints and prints out the OS details if there
       is a match. Each fingerprint includes a freeform textual description of
       the OS, and a classification which provides the vendor name (e.g. Sun),
       underlying OS (e.g. Solaris), OS generation (e.g. 10), and device type
       (general purpose, router, switch, game console, etc). Most fingerprints
       also have a Common Platform Enumeration (CPE).  representation, like

       If Nmap is unable to guess the OS of a machine, and conditions are good
       (e.g. at least one open port and one closed port were found), Nmap will
       provide a URL you can use to submit the fingerprint if you know (for
       sure) the OS running on the machine. By doing this you contribute to
       the pool of operating systems known to Nmap and thus it will be more
       accurate for everyone.

       OS detection enables some other tests which make use of information
       that is gathered during the process anyway. One of these is TCP
       Sequence Predictability Classification. This measures approximately how
       hard it is to establish a forged TCP connection against the remote
       host. It is useful for exploiting source-IP based trust relationships
       (rlogin, firewall filters, etc) or for hiding the source of an attack.
       This sort of spoofing is rarely performed any more, but many machines
       are still vulnerable to it. The actual difficulty number is based on
       statistical sampling and may fluctuate. It is generally better to use
       the English classification such as “worthy challenge” or “trivial
       joke”. This is only reported in normal output in verbose (-v) mode.
       When verbose mode is enabled along with -O, IP ID sequence generation
       is also reported. Most machines are in the “incremental” class, which
       means that they increment the ID field in the IP header for each packet
       they send. This makes them vulnerable to several advanced information
       gathering and spoofing attacks.

       Another bit of extra information enabled by OS detection is a guess at
       a target's uptime. This uses the TCP timestamp option (RFC 1323[10]) to
       guess when a machine was last rebooted. The guess can be inaccurate due
       to the timestamp counter not being initialized to zero or the counter
       overflowing and wrapping around, so it is printed only in verbose mode.

       A paper documenting the workings, usage, and customization of OS
       detection is available at

       OS detection is enabled and controlled with the following options:

       -O (Enable OS detection) .
           Enables OS detection, as discussed above. Alternatively, you can
           use -A to enable OS detection along with other things.

       --osscan-limit (Limit OS detection to promising targets) .
           OS detection is far more effective if at least one open and one
           closed TCP port are found. Set this option and Nmap will not even
           try OS detection against hosts that do not meet this criteria. This
           can save substantial time, particularly on -Pn scans against many
           hosts. It only matters when OS detection is requested with -O or

       --osscan-guess; --fuzzy (Guess OS detection results) .
           When Nmap is unable to detect a perfect OS match, it sometimes
           offers up near-matches as possibilities. The match has to be very
           close for Nmap to do this by default. Either of these (equivalent)
           options make Nmap guess more aggressively. Nmap will still tell you
           when an imperfect match is printed and display its confidence level
           (percentage) for each guess.

       --max-os-tries (Set the maximum number of OS detection tries against a
       target) .
           When Nmap performs OS detection against a target and fails to find
           a perfect match, it usually repeats the attempt. By default, Nmap
           tries five times if conditions are favorable for OS fingerprint
           submission, and twice when conditions aren't so good. Specifying a
           lower --max-os-tries value (such as 1) speeds Nmap up, though you
           miss out on retries which could potentially identify the OS.
           Alternatively, a high value may be set to allow even more retries
           when conditions are favorable. This is rarely done, except to
           generate better fingerprints for submission and integration into
           the Nmap OS database.

       The Nmap Scripting Engine (NSE) is one of Nmap's most powerful and
       flexible features. It allows users to write (and share) simple scripts
       (using the Lua programming language[11],

       Tasks we had in mind when creating the system include network
       discovery, more sophisticated version detection, vulnerability
       detection. NSE can even be used for vulnerability exploitation.

       To reflect those different uses and to simplify the choice of which
       scripts to run, each script contains a field associating it with one or
       more categories. Currently defined categories are auth, broadcast,
       default.  discovery, dos, exploit, external, fuzzer, intrusive,
       malware, safe, version, and vuln. These are all described at

       Scripts are not run in a sandbox and thus could accidentally or
       maliciously damage your system or invade your privacy. Never run
       scripts from third parties unless you trust the authors or have
       carefully audited the scripts yourself.

       The Nmap Scripting Engine is described in detail at

       and is controlled by the following options:

       -sC .
           Performs a script scan using the default set of scripts. It is
           equivalent to --script=default. Some of the scripts in this
           category are considered intrusive and should not be run against a
           target network without permission.

       --script filename|category|directory|expression[,...] .
           Runs a script scan using the comma-separated list of filenames,
           script categories, and directories. Each element in the list may
           also be a Boolean expression describing a more complex set of
           scripts. Each element is interpreted first as an expression, then
           as a category, and finally as a file or directory name.

           There are two special features for advanced users only. One is to
           prefix script names and expressions with + to force them to run
           even if they normally wouldn't (e.g. the relevant service wasn't
           detected on the target port). The other is that the argument all
           may be used to specify every script in Nmap's database. Be cautious
           with this because NSE contains dangerous scripts such as exploits,
           brute force authentication crackers, and denial of service attacks.

           File and directory names may be relative or absolute. Absolute
           names are used directly. Relative paths are looked for in the
           scripts of each of the following places until found:
               ~/.nmap (not searched on Windows).
               HOME\AppData\Roaming\nmap (only on Windows).
               the directory containing the nmap executable
               the directory containing the nmap executable, followed by
               the current directory.

           When a directory name is given, Nmap loads every file in the
           directory whose name ends with .nse. All other files are ignored
           and directories are not searched recursively. When a filename is
           given, it does not have to have the .nse extension; it will be
           added automatically if necessary.  Nmap scripts are stored in a
           scripts subdirectory of the Nmap data directory by default (see

           For efficiency, scripts are indexed in a database stored in
           scripts/script.db,.  which lists the category or categories in
           which each script belongs.  When referring to scripts from
           script.db by name, you can use a shell-style ‘*’ wildcard.

           nmap --script "http-*"
               Loads all scripts whose name starts with http-, such as
               http-auth and http-open-proxy. The argument to --script had to
               be in quotes to protect the wildcard from the shell.

           More complicated script selection can be done using the and, or,
           and not operators to build Boolean expressions. The operators have
           the same precedence[12] as in Lua: not is the highest, followed by
           and and then or. You can alter precedence by using parentheses.
           Because expressions contain space characters it is necessary to
           quote them.

           nmap --script "not intrusive"
               Loads every script except for those in the intrusive category.

           nmap --script "default or safe"
               This is functionally equivalent to nmap --script
               "default,safe". It loads all scripts that are in the default
               category or the safe category or both.

           nmap --script "default and safe"
               Loads those scripts that are in both the default and safe

           nmap --script "(default or safe or intrusive) and not http-*"
               Loads scripts in the default, safe, or intrusive categories,
               except for those whose names start with http-.

       --script-args n1=v1,n2={n3=v3},n4={v4,v5} .
           Lets you provide arguments to NSE scripts. Arguments are a
           comma-separated list of name=value pairs. Names and values may be
           strings not containing whitespace or the characters ‘{’, ‘}’, ‘=’,
           or ‘,’. To include one of these characters in a string, enclose the
           string in single or double quotes. Within a quoted string, ‘\’
           escapes a quote. A backslash is only used to escape quotation marks
           in this special case; in all other cases a backslash is interpreted
           literally. Values may also be tables enclosed in {}, just as in
           Lua. A table may contain simple string values or more name-value
           pairs, including nested tables. Many scripts qualify their
           arguments with the script name, as in xmpp-info.server_name. You
           may use that full qualified version to affect just the specified
           script, or you may pass the unqualified version (server_name in
           this case) to affect all scripts using that argument name. A script
           will first check for its fully qualified argument name (the name
           specified in its documentation) before it accepts an unqualified
           argument name. A complex example of script arguments is
           The online NSE Documentation Portal at
           lists the arguments that each script accepts.

       --script-args-file filename .
           Lets you load arguments to NSE scripts from a file. Any arguments
           on the command line supersede ones in the file. The file can be an
           absolute path, or a path relative to Nmap's usual search path
           (NMAPDIR, etc.) Arguments can be comma-separated or
           newline-separated, but otherwise follow the same rules as for
           --script-args, without requiring special quoting and escaping,
           since they are not parsed by the shell.

       --script-help filename|category|directory|expression|all[,...] .
           Shows help about scripts. For each script matching the given
           specification, Nmap prints the script name, its categories, and its
           description. The specifications are the same as those accepted by
           --script; so for example if you want help about the ftp-anon
           script, you would run nmap --script-help ftp-anon. In addition to
           getting help for individual scripts, you can use this as a preview
           of what scripts will be run for a specification, for example with
           nmap --script-help default.

       --script-trace .
           This option does what --packet-trace does, just one ISO layer
           higher. If this option is specified all incoming and outgoing
           communication performed by a script is printed. The displayed
           information includes the communication protocol, the source, the
           target and the transmitted data. If more than 5% of all transmitted
           data is not printable, then the trace output is in a hex dump
           format. Specifying --packet-trace enables script tracing too.

       --script-updatedb .
           This option updates the script database found in scripts/script.db
           which is used by Nmap to determine the available default scripts
           and categories. It is only necessary to update the database if you
           have added or removed NSE scripts from the default scripts
           directory or if you have changed the categories of any script. This
           option is generally used by itself: nmap --script-updatedb.

       One of my highest Nmap development priorities has always been
       performance. A default scan (nmap hostname) of a host on my local
       network takes a fifth of a second. That is barely enough time to blink,
       but adds up when you are scanning hundreds or thousands of hosts.
       Moreover, certain scan options such as UDP scanning and version
       detection can increase scan times substantially. So can certain
       firewall configurations, particularly response rate limiting. While
       Nmap utilizes parallelism and many advanced algorithms to accelerate
       these scans, the user has ultimate control over how Nmap runs. Expert
       users carefully craft Nmap commands to obtain only the information they
       care about while meeting their time constraints.

       Techniques for improving scan times include omitting non-critical
       tests, and upgrading to the latest version of Nmap (performance
       enhancements are made frequently). Optimizing timing parameters can
       also make a substantial difference. Those options are listed below.

       Some options accept a time parameter. This is specified in seconds by
       default, though you can append ‘ms’, ‘s’, ‘m’, or ‘h’ to the value to
       specify milliseconds, seconds, minutes, or hours. So the --host-timeout
       arguments 900000ms, 900, 900s, and 15m all do the same thing.

       --min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel
       scan group sizes) .
           Nmap has the ability to port scan or version scan multiple hosts in
           parallel. Nmap does this by dividing the target IP space into
           groups and then scanning one group at a time. In general, larger
           groups are more efficient. The downside is that host results can't
           be provided until the whole group is finished. So if Nmap started
           out with a group size of 50, the user would not receive any reports
           (except for the updates offered in verbose mode) until the first 50
           hosts are completed.

           By default, Nmap takes a compromise approach to this conflict. It
           starts out with a group size as low as five so the first results
           come quickly and then increases the groupsize to as high as 1024.
           The exact default numbers depend on the options given. For
           efficiency reasons, Nmap uses larger group sizes for UDP or
           few-port TCP scans.

           When a maximum group size is specified with --max-hostgroup, Nmap
           will never exceed that size. Specify a minimum size with
           --min-hostgroup and Nmap will try to keep group sizes above that
           level. Nmap may have to use smaller groups than you specify if
           there are not enough target hosts left on a given interface to
           fulfill the specified minimum. Both may be set to keep the group
           size within a specific range, though this is rarely desired.

           These options do not have an effect during the host discovery phase
           of a scan. This includes plain ping scans (-sn). Host discovery
           always works in large groups of hosts to improve speed and

           The primary use of these options is to specify a large minimum
           group size so that the full scan runs more quickly. A common choice
           is 256 to scan a network in Class C sized chunks. For a scan with
           many ports, exceeding that number is unlikely to help much. For
           scans of just a few port numbers, host group sizes of 2048 or more
           may be helpful.

       --min-parallelism numprobes; --max-parallelism numprobes (Adjust probe
       parallelization) .
           These options control the total number of probes that may be
           outstanding for a host group. They are used for port scanning and
           host discovery. By default, Nmap calculates an ever-changing ideal
           parallelism based on network performance. If packets are being
           dropped, Nmap slows down and allows fewer outstanding probes. The
           ideal probe number slowly rises as the network proves itself
           worthy. These options place minimum or maximum bounds on that
           variable. By default, the ideal parallelism can drop to one if the
           network proves unreliable and rise to several hundred in perfect

           The most common usage is to set --min-parallelism to a number
           higher than one to speed up scans of poorly performing hosts or
           networks. This is a risky option to play with, as setting it too
           high may affect accuracy. Setting this also reduces Nmap's ability
           to control parallelism dynamically based on network conditions. A
           value of 10 might be reasonable, though I only adjust this value as
           a last resort.

           The --max-parallelism option is sometimes set to one to prevent
           Nmap from sending more than one probe at a time to hosts. The
           --scan-delay option, discussed later, is another way to do this.

       --min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout
       time (Adjust probe timeouts) .
           Nmap maintains a running timeout value for determining how long it
           will wait for a probe response before giving up or retransmitting
           the probe. This is calculated based on the response times of
           previous probes.

           If the network latency shows itself to be significant and variable,
           this timeout can grow to several seconds. It also starts at a
           conservative (high) level and may stay that way for a while when
           Nmap scans unresponsive hosts.

           Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than
           the defaults can cut scan times significantly. This is particularly
           true for pingless (-Pn) scans, and those against heavily filtered
           networks. Don't get too aggressive though. The scan can end up
           taking longer if you specify such a low value that many probes are
           timing out and retransmitting while the response is in transit.

           If all the hosts are on a local network, 100 milliseconds
           (--max-rtt-timeout 100ms) is a reasonable aggressive value. If
           routing is involved, ping a host on the network first with the ICMP
           ping utility, or with a custom packet crafter such as Nping.  that
           is more likely to get through a firewall. Look at the maximum round
           trip time out of ten packets or so. You might want to double that
           for the --initial-rtt-timeout and triple or quadruple it for the
           --max-rtt-timeout. I generally do not set the maximum RTT below
           100 ms, no matter what the ping times are. Nor do I exceed 1000 ms.

           --min-rtt-timeout is a rarely used option that could be useful when
           a network is so unreliable that even Nmap's default is too
           aggressive. Since Nmap only reduces the timeout down to the minimum
           when the network seems to be reliable, this need is unusual and
           should be reported as a bug to the nmap-dev mailing list..

       --max-retries numtries (Specify the maximum number of port scan probe
       retransmissions) .
           When Nmap receives no response to a port scan probe, it could mean
           the port is filtered. Or maybe the probe or response was simply
           lost on the network. It is also possible that the target host has
           rate limiting enabled that temporarily blocked the response. So
           Nmap tries again by retransmitting the initial probe. If Nmap
           detects poor network reliability, it may try many more times before
           giving up on a port. While this benefits accuracy, it also lengthen
           scan times. When performance is critical, scans may be sped up by
           limiting the number of retransmissions allowed. You can even
           specify --max-retries 0 to prevent any retransmissions, though that
           is only recommended for situations such as informal surveys where
           occasional missed ports and hosts are acceptable.

           The default (with no -T template) is to allow ten retransmissions.
           If a network seems reliable and the target hosts aren't rate
           limiting, Nmap usually only does one retransmission. So most target
           scans aren't even affected by dropping --max-retries to a low value
           such as three. Such values can substantially speed scans of slow
           (rate limited) hosts. You usually lose some information when Nmap
           gives up on ports early, though that may be preferable to letting
           the --host-timeout expire and losing all information about the

       --host-timeout time (Give up on slow target hosts) .
           Some hosts simply take a long time to scan. This may be due to
           poorly performing or unreliable networking hardware or software,
           packet rate limiting, or a restrictive firewall. The slowest few
           percent of the scanned hosts can eat up a majority of the scan
           time. Sometimes it is best to cut your losses and skip those hosts
           initially. Specify --host-timeout with the maximum amount of time
           you are willing to wait. For example, specify 30m to ensure that
           Nmap doesn't waste more than half an hour on a single host. Note
           that Nmap may be scanning other hosts at the same time during that
           half an hour, so it isn't a complete loss. A host that times out is
           skipped. No port table, OS detection, or version detection results
           are printed for that host.

       --scan-delay time; --max-scan-delay time (Adjust delay between probes)
           This option causes Nmap to wait at least the given amount of time
           between each probe it sends to a given host. This is particularly
           useful in the case of rate limiting..  Solaris machines (among many
           others) will usually respond to UDP scan probe packets with only
           one ICMP message per second. Any more than that sent by Nmap will
           be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate.
           Nmap tries to detect rate limiting and adjust the scan delay
           accordingly, but it doesn't hurt to specify it explicitly if you
           already know what rate works best.

           When Nmap adjusts the scan delay upward to cope with rate limiting,
           the scan slows down dramatically. The --max-scan-delay option
           specifies the largest delay that Nmap will allow. A low
           --max-scan-delay can speed up Nmap, but it is risky. Setting this
           value too low can lead to wasteful packet retransmissions and
           possible missed ports when the target implements strict rate

           Another use of --scan-delay is to evade threshold based intrusion
           detection and prevention systems (IDS/IPS)..

       --min-rate number; --max-rate number (Directly control the scanning
       rate) .
           Nmap's dynamic timing does a good job of finding an appropriate
           speed at which to scan. Sometimes, however, you may happen to know
           an appropriate scanning rate for a network, or you may have to
           guarantee that a scan will be finished by a certain time. Or
           perhaps you must keep Nmap from scanning too quickly. The
           --min-rate and --max-rate options are designed for these

           When the --min-rate option is given Nmap will do its best to send
           packets as fast as or faster than the given rate. The argument is a
           positive real number representing a packet rate in packets per
           second. For example, specifying --min-rate 300 means that Nmap will
           try to keep the sending rate at or above 300 packets per second.
           Specifying a minimum rate does not keep Nmap from going faster if
           conditions warrant.

           Likewise, --max-rate limits a scan's sending rate to a given
           maximum. Use --max-rate 100, for example, to limit sending to 100
           packets per second on a fast network. Use --max-rate 0.1 for a slow
           scan of one packet every ten seconds. Use --min-rate and --max-rate
           together to keep the rate inside a certain range.

           These two options are global, affecting an entire scan, not
           individual hosts. They only affect port scans and host discovery
           scans. Other features like OS detection implement their own timing.

           There are two conditions when the actual scanning rate may fall
           below the requested minimum. The first is if the minimum is faster
           than the fastest rate at which Nmap can send, which is dependent on
           hardware. In this case Nmap will simply send packets as fast as
           possible, but be aware that such high rates are likely to cause a
           loss of accuracy. The second case is when Nmap has nothing to send,
           for example at the end of a scan when the last probes have been
           sent and Nmap is waiting for them to time out or be responded to.
           It's normal to see the scanning rate drop at the end of a scan or
           in between hostgroups. The sending rate may temporarily exceed the
           maximum to make up for unpredictable delays, but on average the
           rate will stay at or below the maximum.

           Specifying a minimum rate should be done with care. Scanning faster
           than a network can support may lead to a loss of accuracy. In some
           cases, using a faster rate can make a scan take longer than it
           would with a slower rate. This is because Nmap's

           adaptive retransmission algorithms will detect the network
           congestion caused by an excessive scanning rate and increase the
           number of retransmissions in order to improve accuracy. So even
           though packets are sent at a higher rate, more packets are sent
           overall. Cap the number of retransmissions with the --max-retries
           option if you need to set an upper limit on total scan time.

       --defeat-rst-ratelimit .
           Many hosts have long used rate limiting.  to reduce the number of
           ICMP error messages (such as port-unreachable errors) they send.
           Some systems now apply similar rate limits to the RST (reset)
           packets they generate. This can slow Nmap down dramatically as it
           adjusts its timing to reflect those rate limits. You can tell Nmap
           to ignore those rate limits (for port scans such as SYN scan which
           don't treat non-responsive ports as open) by specifying

           Using this option can reduce accuracy, as some ports will appear
           non-responsive because Nmap didn't wait long enough for a
           rate-limited RST response. With a SYN scan, the non-response
           results in the port being labeled filtered rather than the closed
           state we see when RST packets are received. This option is useful
           when you only care about open ports, and distinguishing between
           closed and filtered ports isn't worth the extra time.

       --nsock-engine epoll|kqueue|poll|select .
           Enforce use of a given nsock IO multiplexing engine. Only the
           select(2)-based fallback engine is guaranteed to be available on
           your system. Engines are named after the name of the IO management
           facility they leverage. Engines currently implemented are epoll,
           kqueue, poll, and select, but not all will be present on any
           platform. Use nmap -V to see which engines are supported.

       -T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing
       template) .
           While the fine-grained timing controls discussed in the previous
           section are powerful and effective, some people find them
           confusing. Moreover, choosing the appropriate values can sometimes
           take more time than the scan you are trying to optimize. So Nmap
           offers a simpler approach, with six timing templates. You can
           specify them with the -T option and their number (0–5) or their
           name. The template names are paranoid (0), sneaky (1), polite (2),
           normal (3), aggressive (4), and insane (5). The first two are for
           IDS evasion. Polite mode slows down the scan to use less bandwidth
           and target machine resources. Normal mode is the default and so -T3
           does nothing. Aggressive mode speeds scans up by making the
           assumption that you are on a reasonably fast and reliable network.
           Finally insane mode.  assumes that you are on an extraordinarily
           fast network or are willing to sacrifice some accuracy for speed.

           These templates allow the user to specify how aggressive they wish
           to be, while leaving Nmap to pick the exact timing values. The
           templates also make some minor speed adjustments for which
           fine-grained control options do not currently exist. For example,
           -T4.  prohibits the dynamic scan delay from exceeding 10 ms for TCP
           ports and -T5 caps that value at 5 ms. Templates can be used in
           combination with fine-grained controls, and the fine-grained
           controls will you specify will take precedence over the timing
           template default for that parameter. I recommend using -T4 when
           scanning reasonably modern and reliable networks. Keep that option
           even when you add fine-grained controls so that you benefit from
           those extra minor optimizations that it enables.

           If you are on a decent broadband or ethernet connection, I would
           recommend always using -T4. Some people love -T5 though it is too
           aggressive for my taste. People sometimes specify -T2 because they
           think it is less likely to crash hosts or because they consider
           themselves to be polite in general. They often don't realize just
           how slow -T polite.  really is. Their scan may take ten times
           longer than a default scan. Machine crashes and bandwidth problems
           are rare with the default timing options (-T3) and so I normally
           recommend that for cautious scanners. Omitting version detection is
           far more effective than playing with timing values at reducing
           these problems.

           While -T0.  and -T1.  may be useful for avoiding IDS alerts, they
           will take an extraordinarily long time to scan thousands of
           machines or ports. For such a long scan, you may prefer to set the
           exact timing values you need rather than rely on the canned -T0 and
           -T1 values.

           The main effects of T0 are serializing the scan so only one port is
           scanned at a time, and waiting five minutes between sending each
           probe.  T1 and T2 are similar but they only wait 15 seconds and 0.4
           seconds, respectively, between probes.  T3 is Nmap's default
           behavior, which includes parallelization..  -T4 does the equivalent
           of --max-rtt-timeout 1250ms --initial-rtt-timeout 500ms
           --max-retries 6 and sets the maximum TCP scan delay to 10
           milliseconds.  T5 does the equivalent of --max-rtt-timeout 300ms
           --min-rtt-timeout 50ms --initial-rtt-timeout 250ms --max-retries 2
           --host-timeout 15m as well as setting the maximum TCP scan delay to
           5 ms.

       Many Internet pioneers envisioned a global open network with a
       universal IP address space allowing virtual connections between any two
       nodes. This allows hosts to act as true peers, serving and retrieving
       information from each other. People could access all of their home
       systems from work, changing the climate control settings or unlocking
       the doors for early guests. This vision of universal connectivity has
       been stifled by address space shortages and security concerns. In the
       early 1990s, organizations began deploying firewalls for the express
       purpose of reducing connectivity. Huge networks were cordoned off from
       the unfiltered Internet by application proxies, network address
       translation, and packet filters. The unrestricted flow of information
       gave way to tight regulation of approved communication channels and the
       content that passes over them.

       Network obstructions such as firewalls can make mapping a network
       exceedingly difficult. It will not get any easier, as stifling casual
       reconnaissance is often a key goal of implementing the devices.
       Nevertheless, Nmap offers many features to help understand these
       complex networks, and to verify that filters are working as intended.
       It even supports mechanisms for bypassing poorly implemented defenses.
       One of the best methods of understanding your network security posture
       is to try to defeat it. Place yourself in the mind-set of an attacker,
       and deploy techniques from this section against your networks. Launch
       an FTP bounce scan, idle scan, fragmentation attack, or try to tunnel
       through one of your own proxies.

       In addition to restricting network activity, companies are increasingly
       monitoring traffic with intrusion detection systems (IDS). All of the
       major IDSs ship with rules designed to detect Nmap scans because scans
       are sometimes a precursor to attacks. Many of these products have
       recently morphed into intrusion prevention systems (IPS).  that
       actively block traffic deemed malicious. Unfortunately for network
       administrators and IDS vendors, reliably detecting bad intentions by
       analyzing packet data is a tough problem. Attackers with patience,
       skill, and the help of certain Nmap options can usually pass by IDSs
       undetected. Meanwhile, administrators must cope with large numbers of
       false positive results where innocent activity is misdiagnosed and
       alerted on or blocked.

       Occasionally people suggest that Nmap should not offer features for
       evading firewall rules or sneaking past IDSs. They argue that these
       features are just as likely to be misused by attackers as used by
       administrators to enhance security. The problem with this logic is that
       these methods would still be used by attackers, who would just find
       other tools or patch the functionality into Nmap. Meanwhile,
       administrators would find it that much harder to do their jobs.
       Deploying only modern, patched FTP servers is a far more powerful
       defense than trying to prevent the distribution of tools implementing
       the FTP bounce attack.

       There is no magic bullet (or Nmap option) for detecting and subverting
       firewalls and IDS systems. It takes skill and experience. A tutorial is
       beyond the scope of this reference guide, which only lists the relevant
       options and describes what they do.

       -f (fragment packets); --mtu (using the specified MTU) .
           The -f option causes the requested scan (including ping scans) to
           use tiny fragmented IP packets. The idea is to split up the TCP
           header over several packets to make it harder for packet filters,
           intrusion detection systems, and other annoyances to detect what
           you are doing. Be careful with this! Some programs have trouble
           handling these tiny packets. The old-school sniffer named Sniffit
           segmentation faulted immediately upon receiving the first fragment.
           Specify this option once, and Nmap splits the packets into eight
           bytes or less after the IP header. So a 20-byte TCP header would be
           split into three packets. Two with eight bytes of the TCP header,
           and one with the final four. Of course each fragment also has an IP
           header. Specify -f again to use 16 bytes per fragment (reducing the
           number of fragments)..  Or you can specify your own offset size
           with the --mtu option. Don't also specify -f if you use --mtu. The
           offset must be a multiple of eight. While fragmented packets won't
           get by packet filters and firewalls that queue all IP fragments,
           such as the CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel,
           some networks can't afford the performance hit this causes and thus
           leave it disabled. Others can't enable this because fragments may
           take different routes into their networks. Some source systems
           defragment outgoing packets in the kernel. Linux with the iptables.
           connection tracking module is one such example. Do a scan while a
           sniffer such as Wireshark.  is running to ensure that sent packets
           are fragmented. If your host OS is causing problems, try the
           --send-eth.  option to bypass the IP layer and send raw ethernet

           Fragmentation is only supported for Nmap's raw packet features,
           which includes TCP and UDP port scans (except connect scan and FTP
           bounce scan) and OS detection. Features such as version detection
           and the Nmap Scripting Engine generally don't support fragmentation
           because they rely on your host's TCP stack to communicate with
           target services.

       -D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys) .
           Causes a decoy scan to be performed, which makes it appear to the
           remote host that the host(s) you specify as decoys are scanning the
           target network too. Thus their IDS might report 5–10 port scans
           from unique IP addresses, but they won't know which IP was scanning
           them and which were innocent decoys. While this can be defeated
           through router path tracing, response-dropping, and other active
           mechanisms, it is generally an effective technique for hiding your
           IP address.

           Separate each decoy host with commas, and you can optionally use
           ME.  as one of the decoys to represent the position for your real
           IP address. If you put ME in the sixth position or later, some
           common port scan detectors (such as Solar Designer's.  excellent
           Scanlogd).  are unlikely to show your IP address at all. If you
           don't use ME, Nmap will put you in a random position. You can also
           use RND.  to generate a random, non-reserved IP address, or
           RND:number to generate number addresses.

           Note that the hosts you use as decoys should be up or you might
           accidentally SYN flood your targets. Also it will be pretty easy to
           determine which host is scanning if only one is actually up on the
           network. You might want to use IP addresses instead of names (so
           the decoy networks don't see you in their nameserver logs).

           Decoys are used both in the initial ping scan (using ICMP, SYN,
           ACK, or whatever) and during the actual port scanning phase. Decoys
           are also used during remote OS detection (-O). Decoys do not work
           with version detection or TCP connect scan. When a scan delay is in
           effect, the delay is enforced between each batch of spoofed probes,
           not between each individual probe. Because decoys are sent as a
           batch all at once, they may temporarily violate congestion control

           It is worth noting that using too many decoys may slow your scan
           and potentially even make it less accurate. Also, some ISPs will
           filter out your spoofed packets, but many do not restrict spoofed
           IP packets at all.

       -S IP_Address (Spoof source address) .
           In some circumstances, Nmap may not be able to determine your
           source address (Nmap will tell you if this is the case). In this
           situation, use -S with the IP address of the interface you wish to
           send packets through.

           Another possible use of this flag is to spoof the scan to make the
           targets think that someone else is scanning them. Imagine a company
           being repeatedly port scanned by a competitor! The -e option and
           -Pn are generally required for this sort of usage. Note that you
           usually won't receive reply packets back (they will be addressed to
           the IP you are spoofing), so Nmap won't produce useful reports.

       -e interface (Use specified interface) .
           Tells Nmap what interface to send and receive packets on. Nmap
           should be able to detect this automatically, but it will tell you
           if it cannot.

       --source-port portnumber; -g portnumber (Spoof source port number) .
           One surprisingly common misconfiguration is to trust traffic based
           only on the source port number. It is easy to understand how this
           comes about. An administrator will set up a shiny new firewall,
           only to be flooded with complaints from ungrateful users whose
           applications stopped working. In particular, DNS may be broken
           because the UDP DNS replies from external servers can no longer
           enter the network. FTP is another common example. In active FTP
           transfers, the remote server tries to establish a connection back
           to the client to transfer the requested file.

           Secure solutions to these problems exist, often in the form of
           application-level proxies or protocol-parsing firewall modules.
           Unfortunately there are also easier, insecure solutions. Noting
           that DNS replies come from port 53 and active FTP from port 20,
           many administrators have fallen into the trap of simply allowing
           incoming traffic from those ports. They often assume that no
           attacker would notice and exploit such firewall holes. In other
           cases, administrators consider this a short-term stop-gap measure
           until they can implement a more secure solution. Then they forget
           the security upgrade.

           Overworked network administrators are not the only ones to fall
           into this trap. Numerous products have shipped with these insecure
           rules. Even Microsoft has been guilty. The IPsec filters that
           shipped with Windows 2000 and Windows XP contain an implicit rule
           that allows all TCP or UDP traffic from port 88 (Kerberos). In
           another well-known case, versions of the Zone Alarm personal
           firewall up to 2.1.25 allowed any incoming UDP packets with the
           source port 53 (DNS) or 67 (DHCP).

           Nmap offers the -g and --source-port options (they are equivalent)
           to exploit these weaknesses. Simply provide a port number and Nmap
           will send packets from that port where possible. Most scanning
           operations that use raw sockets, including SYN and UDP scans,
           support the option completely. The option notably doesn't have an
           effect for any operations that use normal operating system sockets,
           including DNS requests, TCP connect scan,.  version detection, and
           script scanning. Setting the source port also doesn't work for OS
           detection, because Nmap must use different port numbers for certain
           OS detection tests to work properly.

       --data-length number (Append random data to sent packets) .
           Normally Nmap sends minimalist packets containing only a header. So
           its TCP packets are generally 40 bytes and ICMP echo requests are
           just 28. Some UDP ports.  and IP protocols.  get a custom payload
           by default. This option tells Nmap to append the given number of
           random bytes to most of the packets it sends, and not to use any
           protocol-specific payloads. (Use --data-length 0 for no random or
           protocol-specific payloads..  OS detection (-O) packets are not
           affected.  because accuracy there requires probe consistency, but
           most pinging and portscan packets support this. It slows things
           down a little, but can make a scan slightly less conspicuous.

       --ip-options S|R [route]|L [route]|T|U ... ; --ip-options hex string
       (Send packets with specified ip options) .
           The IP protocol[13] offers several options which may be placed in
           packet headers. Unlike the ubiquitous TCP options, IP options are
           rarely seen due to practicality and security concerns. In fact,
           many Internet routers block the most dangerous options such as
           source routing. Yet options can still be useful in some cases for
           determining and manipulating the network route to target machines.
           For example, you may be able to use the record route option to
           determine a path to a target even when more traditional
           traceroute-style approaches fail. Or if your packets are being
           dropped by a certain firewall, you may be able to specify a
           different route with the strict or loose source routing options.

           The most powerful way to specify IP options is to simply pass in
           values as the argument to --ip-options. Precede each hex number
           with \x then the two digits. You may repeat certain characters by
           following them with an asterisk and then the number of times you
           wish them to repeat. For example, \x01\x07\x04\x00*36\x01 is a hex
           string containing 36 NUL bytes.

           Nmap also offers a shortcut mechanism for specifying options.
           Simply pass the letter R, T, or U to request record-route,.
           record-timestamp,.  or both options together, respectively. Loose
           or strict source routing.  may be specified with an L or S followed
           by a space and then a space-separated list of IP addresses.

           If you wish to see the options in packets sent and received,
           specify --packet-trace. For more information and examples of using
           IP options with Nmap, see

       --ttl value (Set IP time-to-live field) .
           Sets the IPv4 time-to-live field in sent packets to the given

       --randomize-hosts (Randomize target host order) .
           Tells Nmap to shuffle each group of up to 16384 hosts before it
           scans them. This can make the scans less obvious to various network
           monitoring systems, especially when you combine it with slow timing
           options. If you want to randomize over larger group sizes, increase
           PING_GROUP_SZ.  in nmap.h.  and recompile. An alternative solution
           is to generate the target IP list with a list scan (-sL -n -oN
           filename), randomize it with a Perl script, then provide the whole
           list to Nmap with -iL..

       --spoof-mac MAC address, prefix, or vendor name (Spoof MAC address) .
           Asks Nmap to use the given MAC address for all of the raw ethernet
           frames it sends. This option implies --send-eth.  to ensure that
           Nmap actually sends ethernet-level packets. The MAC given can take
           several formats. If it is simply the number 0, Nmap chooses a
           completely random MAC address for the session. If the given string
           is an even number of hex digits (with the pairs optionally
           separated by a colon), Nmap will use those as the MAC. If fewer
           than 12 hex digits are provided, Nmap fills in the remainder of the
           six bytes with random values. If the argument isn't a zero or hex
           string, Nmap looks through nmap-mac-prefixes to find a vendor name
           containing the given string (it is case insensitive). If a match is
           found, Nmap uses the vendor's OUI (three-byte prefix).  and fills
           out the remaining three bytes randomly. Valid --spoof-mac argument
           examples are Apple, 0, 01:02:03:04:05:06, deadbeefcafe, 0020F2, and
           Cisco. This option only affects raw packet scans such as SYN scan
           or OS detection, not connection-oriented features such as version
           detection or the Nmap Scripting Engine.

       --proxies Comma-separated list of proxy URLs (Relay TCP connections
       through a chain of proxies) .
           Asks Nmap to establish TCP connections with a final target through
           supplied chain of one or more HTTP or SOCKS4 --max-parallelism may
           help because some proxies refuse to handle as many concurrent
           connections as Nmap opens by default.

           This option takes a list of proxies as argument, expressed as URLs
           in the format proto://host:port. Use commas to separate node URLs
           in a chain. No authentication is supported yet. Valid protocols are
           HTTP and SOCKS4.

           Warning: this feature is still under development and has
           limitations. It is implemented within the nsock library and thus
           has no effect on the ping, port scanning and OS discovery phases of
           a scan. Only NSE and version scan benefit from this option so far—
           other features may disclose your true address. SSL connections are
           not yet supported, nor is proxy-side DNS resolution (hostnames are
           always resolved by Nmap).

       --badsum (Send packets with bogus TCP/UDP checksums) .
           Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets
           sent to target hosts. Since virtually all host IP stacks properly
           drop these packets, any responses received are likely coming from a
           firewall or IDS that didn't bother to verify the checksum. For more
           details on this technique, see

       --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums)
           Asks Nmap to use the deprecated Adler32 algorithm for calculating
           the SCTP checksum. If --adler32 is not given, CRC-32C (Castagnoli)
           is used.  RFC 2960[14] originally defined Adler32 as checksum
           algorithm for SCTP; RFC 4960[7] later redefined the SCTP checksums
           to use CRC-32C. Current SCTP implementations should be using
           CRC-32C, but in order to elicit responses from old, legacy SCTP
           implementations, it may be preferable to use Adler32.

       Any security tool is only as useful as the output it generates. Complex
       tests and algorithms are of little value if they aren't presented in an
       organized and comprehensible fashion. Given the number of ways Nmap is
       used by people and other software, no single format can please
       everyone. So Nmap offers several formats, including the interactive
       mode for humans to read directly and XML for easy parsing by software.

       In addition to offering different output formats, Nmap provides options
       for controlling the verbosity of output as well as debugging messages.
       Output types may be sent to standard output or to named files, which
       Nmap can append to or clobber. Output files may also be used to resume
       aborted scans.

       Nmap makes output available in five different formats. The default is
       called interactive output,.  and it is sent to standard output
       (stdout)..  There is also normal output,.  which is similar to
       interactive except that it displays less runtime information and
       warnings since it is expected to be analyzed after the scan completes
       rather than interactively.

       XML output.  is one of the most important output types, as it can be
       converted to HTML, easily parsed by programs such as Nmap graphical
       user interfaces, or imported into databases.

       The two remaining output types are the simple grepable output.  which
       includes most information for a target host on a single line, and
       sCRiPt KiDDi3 0utPUt.  for users who consider themselves |<-r4d .="" br="">
       While interactive output is the default and has no associated
       command-line options, the other four format options use the same
       syntax. They take one argument, which is the filename that results
       should be stored in. Multiple formats may be specified, but each format
       may only be specified once. For example, you may wish to save normal
       output for your own review while saving XML of the same scan for
       programmatic analysis. You might do this with the options -oX
       myscan.xml -oN myscan.nmap. While this chapter uses the simple names
       like myscan.xml for brevity, more descriptive names are generally
       recommended. The names chosen are a matter of personal preference,
       though I use long ones that incorporate the scan date and a word or two
       describing the scan, placed in a directory named after the company I'm

       While these options save results to files, Nmap still prints
       interactive output to stdout as usual. For example, the command nmap
       -oX myscan.xml target prints XML to myscan.xml and fills standard
       output with the same interactive results it would have printed if -oX
       wasn't specified at all. You can change this by passing a hyphen
       character as the argument to one of the format types. This causes Nmap
       to deactivate interactive output, and instead print results in the
       format you specified to the standard output stream. So the command nmap
       -oX - target will send only XML output to stdout..  Serious errors may
       still be printed to the normal error stream, stderr..

       Unlike some Nmap arguments, the space between the logfile option flag
       (such as -oX) and the filename or hyphen is mandatory. If you omit the
       flags and give arguments such as -oG- or -oXscan.xml, a backwards
       compatibility feature of Nmap will cause the creation of normal format
       output files named G- and Xscan.xml respectively.

       All of these arguments support strftime-like.  conversions in the
       filename.  %H, %M, %S, %m, %d, %y, and %Y are all exactly the same as
       in strftime.  %T is the same as %H%M%S, %R is the same as %H%M, and %D
       is the same as %m%d%y. A % followed by any other character just yields
       that character (%% gives you a percent symbol). So -oX 'scan-%T-%D.xml'
       will use an XML file with a name in the form of scan-144840-121307.xml.

       Nmap also offers options to control scan verbosity and to append to
       output files rather than clobbering them. All of these options are
       described below.

       Nmap Output Formats

       -oN filespec (normal output) .
           Requests that normal output be directed to the given filename. As
           discussed above, this differs slightly from interactive output.

       -oX filespec (XML output) .
           Requests that XML output be directed to the given filename. Nmap
           includes a document type definition (DTD) which allows XML parsers
           to validate Nmap XML output. While it is primarily intended for
           programmatic use, it can also help humans interpret Nmap XML
           output. The DTD defines the legal elements of the format, and often
           enumerates the attributes and values they can take on. The latest
           version is always available from

           XML offers a stable format that is easily parsed by software. Free
           XML parsers are available for all major computer languages,
           including C/C++, Perl, Python, and Java. People have even written
           bindings for most of these languages to handle Nmap output and
           execution specifically. Examples are Nmap::Scanner[15].  and
           Nmap::Parser[16].  in Perl CPAN. In almost all cases that a
           non-trivial application interfaces with Nmap, XML is the preferred

           The XML output references an XSL stylesheet which can be used to
           format the results as HTML. The easiest way to use this is simply
           to load the XML output in a web browser such as Firefox or IE. By
           default, this will only work on the machine you ran Nmap on (or a
           similarly configured one) due to the hard-coded nmap.xsl filesystem
           path. Use the --webxml or --stylesheet options to create portable
           XML files that render as HTML on any web-connected machine.

       -oS filespec (ScRipT KIdd|3 oUTpuT) .
           Script kiddie output is like interactive output, except that it is
           post-processed to better suit the l33t HaXXorZ who previously
           looked down on Nmap due to its consistent capitalization and
           spelling. Humor impaired people should note that this option is
           making fun of the script kiddies before flaming me for supposedly
           “helping them”.

       -oG filespec (grepable output) .
           This output format is covered last because it is deprecated. The
           XML output format is far more powerful, and is nearly as convenient
           for experienced users. XML is a standard for which dozens of
           excellent parsers are available, while grepable output is my own
           simple hack. XML is extensible to support new Nmap features as they
           are released, while I often must omit those features from grepable
           output for lack of a place to put them.

           Nevertheless, grepable output is still quite popular. It is a
           simple format that lists each host on one line and can be trivially
           searched and parsed with standard Unix tools such as grep, awk,
           cut, sed, diff, and Perl. Even I usually use it for one-off tests
           done at the command line. Finding all the hosts with the SSH port
           open or that are running Solaris takes only a simple grep to
           identify the hosts, piped to an awk or cut command to print the
           desired fields.

           Grepable output consists of comments (lines starting with a pound
           (#)).  and target lines. A target line includes a combination of
           six labeled fields, separated by tabs and followed with a colon.
           The fields are Host, Ports, Protocols, Ignored State, OS, Seq
           Index, IP ID, and Status.

           The most important of these fields is generally Ports, which gives
           details on each interesting port. It is a comma separated list of
           port entries. Each port entry represents one interesting port, and
           takes the form of seven slash (/) separated subfields. Those
           subfields are: Port number, State, Protocol, Owner, Service, SunRPC
           info, and Version info.

           As with XML output, this man page does not allow for documenting
           the entire format. A more detailed look at the Nmap grepable output
           format is available from

       -oA basename (Output to all formats) .
           As a convenience, you may specify -oA basename to store scan
           results in normal, XML, and grepable formats at once. They are
           stored in basename.nmap, basename.xml, and basename.gnmap,
           respectively. As with most programs, you can prefix the filenames
           with a directory path, such as ~/nmaplogs/foocorp/ on Unix or
           c:\hacking\sco on Windows.

       Verbosity and debugging options

       -v (Increase verbosity level) .
           Increases the verbosity level, causing Nmap to print more
           information about the scan in progress. Open ports are shown as
           they are found and completion time estimates are provided when Nmap
           thinks a scan will take more than a few minutes. Use it twice or
           more for even greater verbosity: -vv, or give a verbosity level
           directly, for example -v3..

           Most changes only affect interactive output, and some also affect
           normal and script kiddie output. The other output types are meant
           to be processed by machines, so Nmap can give substantial detail by
           default in those formats without fatiguing a human user. However,
           there are a few changes in other modes where output size can be
           reduced substantially by omitting some detail. For example, a
           comment line in the grepable output that provides a list of all
           ports scanned is only printed in verbose mode because it can be
           quite long.

       -d (Increase debugging level) .
           When even verbose mode doesn't provide sufficient data for you,
           debugging is available to flood you with much more! As with the
           verbosity option (-v), debugging is enabled with a command-line
           flag (-d) and the debug level can be increased by specifying it
           multiple times,.  as in -dd, or by setting a level directly. For
           example, -d9 sets level nine. That is the highest effective level
           and will produce thousands of lines unless you run a very simple
           scan with very few ports and targets.

           Debugging output is useful when a bug is suspected in Nmap, or if
           you are simply confused as to what Nmap is doing and why. As this
           feature is mostly intended for developers, debug lines aren't
           always self-explanatory. You may get something like: Timeout vals:
           srtt: -1 rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987 rttvar:
           14987 to: 100000. If you don't understand a line, your only
           recourses are to ignore it, look it up in the source code, or
           request help from the development list (nmap-dev)..  Some lines are
           self explanatory, but the messages become more obscure as the debug
           level is increased.

       --reason (Host and port state reasons) .
           Shows the reason each port is set to a specific state and the
           reason each host is up or down. This option displays the type of
           the packet that determined a port or hosts state. For example, A
           RST packet from a closed port or an echo reply from an alive host.
           The information Nmap can provide is determined by the type of scan
           or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed,
           but the TCP connect scan (-sT) is limited by the implementation of
           the connect system call. This feature is automatically enabled by
           the debug option (-d).  and the results are stored in XML log files
           even if this option is not specified.

       --stats-every time (Print periodic timing stats) .
           Periodically prints a timing status message after each interval of
           time. The time is a specification of the kind described in the
           section called “TIMING AND PERFORMANCE”; so for example, use
           --stats-every 10s to get a status update every 10 seconds. Updates
           are printed to interactive output (the screen) and XML output.

       --packet-trace (Trace packets and data sent and received) .
           Causes Nmap to print a summary of every packet sent or received.
           This is often used for debugging, but is also a valuable way for
           new users to understand exactly what Nmap is doing under the
           covers. To avoid printing thousands of lines, you may want to
           specify a limited number of ports to scan, such as -p20-30. If you
           only care about the goings on of the version detection subsystem,
           use --version-trace instead. If you only care about script tracing,
           specify --script-trace. With --packet-trace, you get all of the

       --open (Show only open (or possibly open) ports) .
           Sometimes you only care about ports you can actually connect to
           (open ones), and don't want results cluttered with closed,
           filtered, and closed|filtered ports. Output customization is
           normally done after the scan using tools such as grep, awk, and
           Perl, but this feature was added due to overwhelming requests.
           Specify --open to only see hosts with at least one open,
           open|filtered, or unfiltered port, and only see ports in those
           states. These three states are treated just as they normally are,
           which means that open|filtered and unfiltered may be condensed into
           counts if there are an overwhelming number of them.

       --iflist (List interfaces and routes) .
           Prints the interface list and system routes as detected by Nmap.
           This is useful for debugging routing problems or device
           mischaracterization (such as Nmap treating a PPP connection as

       Miscellaneous output options

       --append-output (Append to rather than clobber output files) .
           When you specify a filename to an output format flag such as -oX or
           -oN, that file is overwritten by default. If you prefer to keep the
           existing content of the file and append the new results, specify
           the --append-output option. All output filenames specified in that
           Nmap execution will then be appended to rather than clobbered. This
           doesn't work well for XML (-oX) scan data as the resultant file
           generally won't parse properly until you fix it up by hand.

       --resume filename (Resume aborted scan) .
           Some extensive Nmap runs take a very long time—on the order of
           days. Such scans don't always run to completion. Restrictions may
           prevent Nmap from being run during working hours, the network could
           go down, the machine Nmap is running on might suffer a planned or
           unplanned reboot, or Nmap itself could crash. The administrator
           running Nmap could cancel it for any other reason as well, by
           pressing ctrl-C. Restarting the whole scan from the beginning may
           be undesirable. Fortunately, if normal (-oN) or grepable (-oG) logs
           were kept, the user can ask Nmap to resume scanning with the target
           it was working on when execution ceased. Simply specify the
           --resume option and pass the normal/grepable output file as its
           argument. No other arguments are permitted, as Nmap parses the
           output file to use the same ones specified previously. Simply call
           Nmap as nmap --resume logfilename. Nmap will append new results to
           the data files specified in the previous execution. Resumption does
           not support the XML output format because combining the two runs
           into one valid XML file would be difficult.

       --stylesheet path or URL (Set XSL stylesheet to transform XML output) .
           Nmap ships with an XSL.  stylesheet.  named nmap.xsl.  for viewing
           or translating XML output to HTML..  The XML output includes an
           xml-stylesheet directive which points to nmap.xml where it was
           initially installed by Nmap. Run the XML file through an XSLT
           processor such as xsltproc[17].  to produce an HTML file. Directly
           opening the XML file in a browser no longer works well because
           modern browsers limit the locations a stylesheet may be loaded
           from. If you wish to use a different stylesheet, specify it as the
           argument to --stylesheet. You must pass the full pathname or URL.
           One common invocation is --stylesheet
  This tells an XSLT processor to
           load the latest version of the stylesheet from Nmap.Org. The
           --webxml option does the same thing with less typing and
           memorization. Loading the XSL from Nmap.Org makes it easier to view
           results on a machine that doesn't have Nmap (and thus nmap.xsl)
           installed. So the URL is often more useful, but the local
           filesystem location of nmap.xsl is used by default for privacy

       --webxml (Load stylesheet from Nmap.Org) .
           This is a convenience option, nothing more than an alias for

       --no-stylesheet (Omit XSL stylesheet declaration from XML) .
           Specify this option to prevent Nmap from associating any XSL
           stylesheet with its XML output. The xml-stylesheet directive is

       This section describes some important (and not-so-important) options
       that don't really fit anywhere else.

       -6 (Enable IPv6 scanning) .
           Nmap has IPv6 support for its most popular features. Ping scanning,
           port scanning, version detection, and the Nmap Scripting Engine all
           support IPv6. The command syntax is the same as usual except that
           you also add the -6 option. Of course, you must use IPv6 syntax if
           you specify an address rather than a hostname. An address might
           look like 3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are
           recommended. The output looks the same as usual, with the IPv6
           address on the “interesting ports” line being the only IPv6

           While IPv6 hasn't exactly taken the world by storm, it gets
           significant use in some (usually Asian) countries and most modern
           operating systems support it. To use Nmap with IPv6, both the
           source and target of your scan must be configured for IPv6. If your
           ISP (like most of them) does not allocate IPv6 addresses to you,
           free tunnel brokers are widely available and work fine with Nmap. I
           use the free IPv6 tunnel broker.  service at
  Other tunnel brokers are listed at
           Wikipedia[18]. 6to4 tunnels are another popular, free approach.

           On Windows, raw-socket IPv6 scans are supported only on ethernet
           devices (not tunnels), and only on Windows Vista.  and later. Use
           the --unprivileged.  option in other situations.

       -A (Aggressive scan options) .
           This option enables additional advanced and aggressive options. I
           haven't decided exactly which it stands for yet. Presently this
           enables OS detection (-O), version scanning (-sV), script scanning
           (-sC) and traceroute (--traceroute)..  More features may be added
           in the future. The point is to enable a comprehensive set of scan
           options without people having to remember a large set of flags.
           However, because script scanning with the default set is considered
           intrusive, you should not use -A against target networks without
           permission. This option only enables features, and not timing
           options (such as -T4) or verbosity options (-v) that you might want
           as well.

       --datadir directoryname (Specify custom Nmap data file location) .
           Nmap obtains some special data at runtime in files named
           nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc,
           nmap-mac-prefixes, and nmap-os-db. If the location of any of these
           files has been specified (using the --servicedb or --versiondb
           options), that location is used for that file. After that, Nmap
           searches these files in the directory specified with the --datadir
           option (if any). Any files not found there, are searched for in the
           directory specified by the NMAPDIR.  environment variable. Next
           comes ~/.nmap.  for real and effective UIDs; or on Windows,
           HOME\AppData\Roaming\nmap (where HOME is the user's home directory,
           like C:\Users\user). This is followed by the location of the nmap
           executable and the same location with ../share/nmap appended. Then
           a compiled-in location such as /usr/local/share/nmap or

       --servicedb services file (Specify custom services file) .
           Asks Nmap to use the specified services file rather than the
           nmap-services data file that comes with Nmap. Using this option
           also causes a fast scan (-F) to be used. See the description for
           --datadir for more information on Nmap's data files.

       --versiondb service probes file (Specify custom service probes file) .
           Asks Nmap to use the specified service probes file rather than the
           nmap-service-probes data file that comes with Nmap. See the
           description for --datadir for more information on Nmap's data

       --send-eth (Use raw ethernet sending) .
           Asks Nmap to send packets at the raw ethernet (data link) layer
           rather than the higher IP (network) layer. By default, Nmap chooses
           the one which is generally best for the platform it is running on.
           Raw sockets (IP layer).  are generally most efficient for Unix
           machines, while ethernet frames are required for Windows operation
           since Microsoft disabled raw socket support. Nmap still uses raw IP
           packets on Unix despite this option when there is no other choice
           (such as non-ethernet connections).

       --send-ip (Send at raw IP level) .
           Asks Nmap to send packets via raw IP sockets rather than sending
           lower level ethernet frames. It is the complement to the --send-eth
           option discussed previously.

       --privileged (Assume that the user is fully privileged) .
           Tells Nmap to simply assume that it is privileged enough to perform
           raw socket sends, packet sniffing, and similar operations that
           usually require root privileges.  on Unix systems. By default Nmap
           quits if such operations are requested but geteuid is not zero.
           --privileged is useful with Linux kernel capabilities and similar
           systems that may be configured to allow unprivileged users to
           perform raw-packet scans. Be sure to provide this option flag
           before any flags for options that require privileges (SYN scan, OS
           detection, etc.). The NMAP_PRIVILEGED.  environment variable may be
           set as an equivalent alternative to --privileged.

       --unprivileged (Assume that the user lacks raw socket privileges) .
           This option is the opposite of --privileged. It tells Nmap to treat
           the user as lacking network raw socket and sniffing privileges.
           This is useful for testing, debugging, or when the raw network
           functionality of your operating system is somehow broken. The
           NMAP_UNPRIVILEGED.  environment variable may be set as an
           equivalent alternative to --unprivileged.

       --release-memory (Release memory before quitting) .
           This option is only useful for memory-leak debugging. It causes
           Nmap to release allocated memory just before it quits so that
           actual memory leaks are easier to spot. Normally Nmap skips this as
           the OS does this anyway upon process termination.

       -V; --version (Print version number) .
           Prints the Nmap version number and exits.

       -h; --help (Print help summary page) .
           Prints a short help screen with the most common command flags.
           Running Nmap without any arguments does the same thing.

       During the execution of Nmap, all key presses are captured. This allows
       you to interact with the program without aborting and restarting it.
       Certain special keys will change options, while any other keys will
       print out a status message telling you about the scan. The convention
       is that lowercase letters increase the amount of printing, and
       uppercase letters decrease the printing. You may also press ‘?’ for

       v / V
           Increase / decrease the verbosity level

       d / D
           Increase / decrease the debugging Level

       p / P
           Turn on / off packet tracing

           Print a runtime interaction help screen

       Anything else
           Print out a status message like this:

               Stats: 0:00:07 elapsed; 20 hosts completed (1 up), 1 undergoing Service Scan
               Service scan Timing: About 33.33% done; ETC: 20:57 (0:00:12 remaining)

       Here are some Nmap usage examples, from the simple and routine to a
       little more complex and esoteric. Some actual IP addresses and domain
       names are used to make things more concrete. In their place you should
       substitute addresses/names from your own network. While I don't think
       port scanning other networks is or should be illegal, some network
       administrators don't appreciate unsolicited scanning of their networks
       and may complain. Getting permission first is the best approach.

       For testing purposes, you have permission to scan the host  This permission only includes scanning via Nmap and
       not testing exploits or denial of service attacks. To conserve
       bandwidth, please do not initiate more than a dozen scans against that
       host per day. If this free scanning target service is abused, it will
       be taken down and Nmap will report Failed to resolve given hostname/IP: These permissions also apply to the hosts,, and so on, though those hosts do
       not currently exist.

       nmap -v

       This option scans all reserved TCP ports on the machine
       . The -v option enables verbose mode.

       nmap -sS -O

       Launches a stealth SYN scan against each machine that is up out of the
       256 IPs on the class C sized network where Scanme resides. It also
       tries to determine what operating system is running on each host that
       is up and running. This requires root privileges because of the SYN
       scan and OS detection.

       nmap -sV -p 22,53,110,143,4564 198.116.0-255.1-127

       Launches host enumeration and a TCP scan at the first half of each of
       the 255 possible eight-bit subnets in the 198.116 class B address
       space. This tests whether the systems run SSH, DNS, POP3, or IMAP on
       their standard ports, or anything on port 4564. For any of these ports
       found open, version detection is used to determine what application is

       nmap -v -iR 100000 -Pn -p 80

       Asks Nmap to choose 100,000 hosts at random and scan them for web
       servers (port 80). Host enumeration is disabled with -Pn since first
       sending a couple probes to determine whether a host is up is wasteful
       when you are only probing one port on each target host anyway.

       nmap -Pn -p80 -oX logs/pb-port80scan.xml -oG logs/pb-port80scan.gnmap

       This scans 4096 IPs for any web servers (without pinging them) and
       saves the output in grepable and XML formats.

       While this reference guide details all material Nmap options, it can't
       fully demonstrate how to apply those features to quickly solve
       real-world tasks. For that, we released Nmap Network Scanning: The
       Official Nmap Project Guide to Network Discovery and Security Scanning.
       Topics include subverting firewalls and intrusion detection systems,
       optimizing Nmap performance, and automating common networking tasks
       with the Nmap Scripting Engine. Hints and instructions are provided for
       common Nmap tasks such as taking network inventory, penetration
       testing, detecting rogue wireless access points, and quashing network
       worm outbreaks. Examples and diagrams show actual communication on the
       wire. More than half of the book is available free online. See for more information.

       Like its author, Nmap isn't perfect. But you can help make it better by
       sending bug reports or even writing patches. If Nmap doesn't behave the
       way you expect, first upgrade to the latest version available from If the problem persists, do some research to determine
       whether it has already been discovered and addressed. Try searching for
       the error message on our search page at
       or at Google. Also try browsing the nmap-dev archives at  Read this full manual page as well. If nothing
       comes of this, mail a bug report to Please include
       everything you have learned about the problem, as well as what version
       of Nmap you are running and what operating system version it is running
       on. Problem reports and Nmap usage questions sent to are
       far more likely to be answered than those sent to Fyodor directly. If
       you subscribe to the nmap-dev list before posting, your message will
       bypass moderation and get through more quickly. Subscribe at

       Code patches to fix bugs are even better than bug reports. Basic
       instructions for creating patch files with your changes are available
       at Patches may be sent to nmap-dev
       (recommended) or to Fyodor directly.

       Gordon “Fyodor” Lyon (

       Hundreds of people have made valuable contributions to Nmap over the
       years. These are detailed in the CHANGELOG.  file which is distributed
       with Nmap and also available from

   Nmap Copyright and Licensing
       The Nmap Security Scanner is (C) 1996–2013 Insecure.Com LLC. Nmap is
       also a registered trademark of Insecure.Com LLC. This program is free
       software; you may redistribute and/or modify it under the terms of the
       GNU General Public License as published by the Free Software
       Foundation; Version 2 (“GPL”), BUT ONLY WITH ALL OF THE CLARIFICATIONS
       AND EXCEPTIONS DESCRIBED HEREIN. This guarantees your right to use,
       modify, and redistribute this software under certain conditions. If you
       wish to embed Nmap technology into proprietary software, we sell
       alternative licenses (contact Dozens of software
       vendors already license Nmap technology such as host discovery, port
       scanning, OS detection, version detection, and the Nmap Scripting

       Note that the GPL places important restrictions on “derivative works”,
       yet it does not provide a detailed definition of that term. To avoid
       misunderstandings, we interpret that term as broadly as copyright law
       allows. For example, we consider an application to constitute a
       derivative work for the purpose of this license if it does any of the
       following with any software or content covered by this license
       (“Covered Software”):

       ·   Integrates source code from Covered Software.

       ·   Reads or includes copyrighted data files, such as Nmap's nmap-os-db
           or nmap-service-probes.

       ·   Is designed specifically to execute Covered Software and parse the
           results (as opposed to typical shell or execution-menu apps, which
           will execute anything you tell them to).

       ·   Includes Covered Software in a proprietary executable installer.
           The installers produced by InstallShield are an example of this.
           Including Nmap with other software in compressed or archival form
           does not trigger this provision, provided appropriate open source
           decompression or de-archiving software is widely available for no
           charge. For the purposes of this license, an installer is
           considered to include Covered Software even if it actually
           retrieves a copy of Covered Software from another source during
           runtime (such as by downloading it from the Internet).

       ·   Links (statically or dynamically) to a library which does any of
           the above.

       ·   Executes a helper program, module, or script to do any of the

       This list is not exclusive, but is meant to clarify our interpretation
       of derived works with some common examples. Other people may interpret
       the plain GPL differently, so we consider this a special exception to
       the GPL that we apply to Covered Software. Works which meet any of
       these conditions must conform to all of the terms of this license,
       particularly including the GPL Section 3 requirements of providing
       source code and allowing free redistribution of the work as a whole.

       As another special exception to the GPL terms, Insecure.Com LLC grants
       permission to link the code of this program with any version of the
       OpenSSL library which is distributed under a license identical to that
       listed in the included docs/licenses/OpenSSL.txt file, and distribute
       linked combinations including the two..

       Any redistribution of Covered Software, including any derived works,
       must obey and carry forward all of the terms of this license, including
       obeying all GPL rules and restrictions. For example, source code of the
       whole work must be provided and free redistribution must be allowed.
       All GPL references to "this License", are to be treated as including
       the terms and conditions of this license text as well.

       Because this license imposes special exceptions to the GPL, Covered
       Work may not be combined (even as part of a larger work) with plain GPL
       software. The terms, conditions, and exceptions of this license must be
       included as well. This license is incompatible with some other open
       source licenses as well. In some cases we can relicense portions of
       Nmap or grant special permissions to use it in other open source
       software. Please contact with any such requests.
       Similarly, we don't incorporate incompatible open source software into
       Covered Software without special permission from the copyright holders.

       If you have any questions about the licensing restrictions on using
       Nmap in other works, are happy to help. As mentioned above, we also
       offer alternative license to integrate Nmap into proprietary
       applications and appliances. These contracts have been sold to dozens
       of software vendors, and generally include a perpetual license as well
       as providing for priority support and updates. They also fund the
       continued development of Nmap. Please email for further

       If you have received a written license agreement or contract for
       Covered Software stating terms other than these, you may choose to use
       and redistribute Covered Software under those terms instead of these.

   Creative Commons License for this Nmap Guide
       This Nmap Reference Guide is (C) 2005–2012 Insecure.Com LLC. It is
       hereby placed under version 3.0 of the Creative Commons Attribution
       License[19]. This allows you redistribute and modify the work as you
       desire, as long as you credit the original source. Alternatively, you
       may choose to treat this document as falling under the same license as
       Nmap itself (discussed previously).

   Source Code Availability and Community Contributions
       Source is provided to this software because we believe users have a
       right to know exactly what a program is going to do before they run it.
       This also allows you to audit the software for security holes (none
       have been found so far).

       Source code also allows you to port Nmap to new platforms, fix bugs,
       and add new features. You are highly encouraged to send your changes to for possible incorporation into the main distribution. By
       sending these changes to Fyodor or one of the Insecure.Org development
       mailing lists, it is assumed that you are offering the Nmap Project
       (Insecure.Com LLC) the unlimited, non-exclusive right to reuse, modify,
       and relicense the code. Nmap will always be available open source,.
       but this is important because the inability to relicense code has
       caused devastating problems for other Free Software projects (such as
       KDE and NASM). We also occasionally relicense the code to third parties
       as discussed above. If you wish to specify special license conditions
       of your contributions, just say so when you send them.

   No Warranty.
       This program is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of
       General Public License v2.0 for more details at, or in the COPYING file
       included with Nmap.

       It should also be noted that Nmap has occasionally been known to crash
       poorly written applications, TCP/IP stacks, and even operating
       systems..  While this is extremely rare, it is important to keep in
       mind.  Nmap should never be run against mission critical systems unless
       you are prepared to suffer downtime. We acknowledge here that Nmap may
       crash your systems or networks and we disclaim all liability for any
       damage or problems Nmap could cause.

   Inappropriate Usage
       Because of the slight risk of crashes and because a few black hats like
       to use Nmap for reconnaissance prior to attacking systems, there are
       administrators who become upset and may complain when their system is
       scanned. Thus, it is often advisable to request permission before doing
       even a light scan of a network.

       Nmap should never be installed with special privileges (e.g. suid
       root)..  That would open up a major security vulnerability as other
       users on the system (or attackers) could use it for privilege

   Third-Party Software and Funding Notices
       This product includes software developed by the Apache Software
       Foundation[20]. A modified version of the Libpcap portable packet
       capture library[21].  is distributed along with Nmap. The Windows
       version of Nmap utilized the Libpcap-derived WinPcap library[22].
       instead. Regular expression support is provided by the PCRE
       library[23],.  which is open-source software, written by Philip Hazel..
       Certain raw networking functions use the Libdnet[24].  networking
       library, which was written by Dug Song..  A modified version is
       distributed with Nmap. Nmap can optionally link with the OpenSSL
       cryptography toolkit[25].  for SSL version detection support. The Nmap
       Scripting Engine uses an embedded version of the Lua programming
       language[26]..  The Liblinear linear classification library[27] is used
       for our IPv6 OS detection machine learning techniques[28].

       All of the third-party software described in this paragraph is freely
       redistributable under BSD-style software licenses.

       Binary packages for Windows and Mac OS X include support libraries
       necessary to run Zenmap and Ndiff with Python and PyGTK. (Unix
       platforms commonly make these libraries easy to install, so they are
       not part of the packages.) A listing of these support libraries and
       their licenses is included in the LICENSES files.

       This software was supported in part through the Google Summer of
       Code[29] and the DARPA CINDER program[30] (DARPA-BAA-10-84).

   United States Export Control.
       Nmap only uses encryption when compiled with the optional OpenSSL
       support and linked with OpenSSL. When compiled without OpenSSL support,
       Insecure.Com LLC believes that Nmap is not subject to U.S.  Export
       Administration Regulations (EAR)[31] export control. As such, there is
       no applicable ECCN (export control classification number) and
       exportation does not require any special license, permit, or other
       governmental authorization.

       When compiled with OpenSSL support or distributed as source code,
       Insecure.Com LLC believes that Nmap falls under U.S. ECCN 5D002[32]
       (“Information Security Software”). We distribute Nmap under the TSU
       exception for publicly available encryption software defined in EAR

        1. Nmap Network Scanning: The Official Nmap Project Guide to Network
           Discovery and Security Scanning

        2. RFC 1122

        3. RFC 792

        4. RFC 950

        5. RFC 1918

        6. UDP

        7. SCTP

        8. TCP RFC

        9. RFC 959

       10. RFC 1323

       11. Lua programming language

       12. precedence

       13. IP protocol

       14. RFC 2960

       15. Nmap::Scanner

       16. Nmap::Parser

       17. xsltproc

       18. listed at Wikipedia

       19. Creative Commons Attribution License

       20. Apache Software Foundation

       21. Libpcap portable packet capture library

       22. WinPcap library

       23. PCRE library

       24. Libdnet

       25. OpenSSL cryptography toolkit

       26. Lua programming language

       27. Liblinear linear classification library

       28. IPv6 OS detection machine learning techniques

       29. Google Summer of Code

       30. DARPA CINDER program

       31. Export Administration Regulations (EAR)

       32. 5D002

       33. EAR 740.13(e)

Nmap                              08/13/2014                           NMAP(1)