What are they?
- files that contain a reference to another file or directory on the same system
- like shortcuts on Windows OS
What is their purpose?
- to avoid copying the same binary (usually a library) at multiple locations but simply creating a symlink where file is required to be
- various clients might require the same file but with name in different format so instead of having multiple copies of the same file but with different names we'd have multiple symlink, each with the name that satisfies requirements of each service
How do they work?
- opening/running the symlink would open/run the target file
- editing the content of the symlink edits the content of the target file
- if target file is deleted symlink becomes a dangling symlink
- if symlink is deleted, target file remains unaffected
- it is possible to create symlink that refers to another symlink [How can I create a symlink which points to another symlink?]
How to create them?
How to: Linux / UNIX create soft link with ln command
Use ln command:
NAME
ln - make links between files
SYNOPSIS
ln [OPTION]... [-T] TARGET LINK_NAME (1st form)
ln [OPTION]... TARGET (2nd form)
ln [OPTION]... TARGET... DIRECTORY (3rd form)
ln [OPTION]... -t DIRECTORY TARGET... (4th form)
DESCRIPTION
In the 1st form, create a link to TARGET with the name LINK_NAME. In the 2nd form, create a link to TARGET in the current directory. In the 3rd and 4th forms, create links to each TARGET in DIRECTORY. Create hard links by default, symbolic links with --symbolic. By default, each destination (name of new link) should not already exist. When creating hard links, each TARGET must exist.
Symbolic links can hold arbitrary text; if later resolved, a relative link is interpreted in relation to its parent directory.
Mandatory arguments to long options are mandatory for short options too.
--backup[=CONTROL]
make a backup of each existing destination file
-b like --backup but does not accept an argument
-d, -F, --directory
allow the superuser to attempt to hard link directories (note: will probably fail due to system restrictions, even for the superuser)
-f, --force
remove existing destination files
-i, --interactive
prompt whether to remove destinations
-L, --logical
dereference TARGETs that are symbolic links
-n, --no-dereference
treat LINK_NAME as a normal file if it is a symbolic link to a directory
-P, --physical
make hard links directly to symbolic links
-r, --relative
create symbolic links relative to link location
-s, --symbolic
make symbolic links instead of hard links
-S, --suffix=SUFFIX
override the usual backup suffix
-t, --target-directory=DIRECTORY
specify the DIRECTORY in which to create the links
-T, --no-target-directory
treat LINK_NAME as a normal file always
-v, --verbose
print name of each linked file
--help display this help and exit
--version
output version information and exit
The backup suffix is '~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX. The version control method may be selected via the --backup option or through the VERSION_CONTROL environment variable.
Here are the values:
none, off
never make backups (even if --backup is given)
numbered, t
make numbered backups
existing, nil
numbered if numbered backups exist, simple otherwise
simple, never
always make simple backups
Using -s ignores -L and -P. Otherwise, the last option specified controls behavior when a TARGET is a symbolic link, defaulting to -P.
Example:
$ sudo ln -s /usr/local/go/bin/go /usr/local/bin/go
Creating a symlink from one folder to another with different names?
Types of symlinks:
- absolute
- relative; If you create a symbolic link to a relative path, it will store it as a relative symbolic link [Make a symbolic link to a relative pathname]
$ pwd
/home/beau
$ ln -s foo/bar.txt bar.txt
$ readlink -f /home/beau/bar.txt
/home/beau/foo/bar.txt
Or:
$ cd foo
$ ln -s foo/bar.txt ../bar.txt
How to list all symbolic links in the current directory?
$ find -type l[man find]: If no paths are given, the current directory is used.
[How to list all symbolic links in a directory]
# save symlinks and their targets (relative to ./path/to/dir/) in csv file which will also be pushed to S3
cd ./path/to/dir/
find . -type l -ls | awk '{print $11,",",$13}' > symlinks.csv
How do I tell if a folder is actually a symlink and how do I fix it if it's broken?
Here are some ways that can be used to verify symlink:
$ stat ./data-vol/content/app/74.0.1365.76
File: ./data-vol/content/app/74.0.1365.76 -> data-vol/content/app/win/x86/74.0.1365.76
Size: 45 Blocks: 0 IO Block: 4096 symbolic link
Device: fd01h/64769d Inode: 26479224 Links: 1
Access: (0777/lrwxrwxrwx) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2019-07-12 17:17:09.278071996 +0100
Modify: 2019-07-12 17:17:08.666073171 +0100
Change: 2019-07-12 17:17:08.666073171 +0100
Birth: -
$ stat -L ./data-vol/content/app/74.0.1365.76
stat: cannot stat './data-vol/content/app/74.0.1365.76': No such file or directory
$ file -L ./data-vol/content/app/74.0.1365.76
./data-vol/content/app/74.0.1365.76: cannot open `./data-vol/content/app/74.0.1365.76' (No such file or directory)
$ ls ./data-vol/content/app/74.0.1365.76
./data-vol/content/app/74.0.1365.76
$ ll ./data-vol/content/app/74.0.1365.76
lrwxrwxrwx 1 root root 45 Jul 12 17:17 ./data-vol/content/app/74.0.1365.76 -> data-vol/content/app/win/x86/74.0.1365.76
How to see full symlink path
$ readlink -f symlinkName
Hard links
How to create hardlink of one file in different directories in linux
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