Exploring Docker commands: docker container

 Let's learn what commands can be used when object is container in the following Docker CLI syntax:

 docker <object> <command> <options> 

docker container

$ docker container 

Usage:  docker container COMMAND

Manage containers

Commands:
  attach      Attach local standard input, output, and error streams to a running container
  commit      Create a new image from a container's changes
  cp          Copy files/folders between a container and the local filesystem
  create      Create a new container
  diff        Inspect changes to files or directories on a container's filesystem
  exec        Run a command in a running container
  export      Export a container's filesystem as a tar archive
  inspect     Display detailed information on one or more containers
  kill        Kill one or more running containers
  logs        Fetch the logs of a container
  ls          List containers
  pause       Pause all processes within one or more containers
  port        List port mappings or a specific mapping for the container
  prune       Remove all stopped containers
  rename      Rename a container
  restart     Restart one or more containers
  rm          Remove one or more containers
  run         Run a command in a new container
  start       Start one or more stopped containers
  stats       Display a live stream of container(s) resource usage statistics
  stop        Stop one or more running containers
  top         Display the running processes of a container
  unpause     Unpause all processes within one or more containers
  update      Update configuration of one or more containers
  wait        Block until one or more containers stop, then print their exit codes

Run 'docker container COMMAND --help' for more information on a command.

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If we try to start some container which requires opening some port on the localhost while another running container has already opened it, we might get the following error:

$ docker-compose up --build

Starting my_app_1 ... 

ERROR: for my-app_db_1  Cannot start service db: driver failed programming external connectivity on endpoint my-app_db_1 (a456b10867b734493c831aa99f227147110f61233652c4984415c12ecdf9a9b3): Bind for 0.0.0.0:5432 failed: port is Starting my-app_my-service_1 ... done

ERROR: for db  Cannot start service db: driver failed programming external connectivity on endpoint my-app_db_1 (a456b10867b734493c831aa99f227147110f61233652c4984415c12ecdf9a9b3): Bind for 0.0.0.0:5432 failed: port is already allocated
ERROR: Encountered errors while bringing up the project.

To resolve this, we first need to check which containers are running and then to stop them:

$ docker container ls 
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
499c43a9c28b        postgres:latest     "docker-entrypoint.s…"   3 days ago          Up 3 days           0.0.0.0:5432->5432/tcp   my-app-2_db_1

$ docker container stop my-app-2_db_1
my-app-2_db_1

Let's verify that no containers are running:

$ docker container ls
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES

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docker container inspect

Useful command for debugging issues. It shows info about various container's properties e.g. network.

% docker container inspect --help

Usage:  docker container inspect [OPTIONS] CONTAINER [CONTAINER...]

Display detailed information on one or more containers

Options:

  -f, --format string   Format the output using the given Go template

  -s, --size            Display total file sizes

docker container kill

Stops container (non-gracefully). Killing the container does not give a chance to applications running inside it to shut down / terminate gracefully. This command sends a SIGKILL signal to the main process running inside container. This signal immediately terminates this process and this process cannot ignore it. SIGKILL also automatically terminates all child processes. 

% docker container kill --help

Usage:  docker container kill [OPTIONS] CONTAINER [CONTAINER...]

Kill one or more running containers

Options:

  -s, --signal string   Signal to send to the container (default "KILL")

docker container ls 

$ docker container ls --help

Usage:  docker container ls [OPTIONS]

List containers

Aliases:
  ls, ps, list

Options:
  -a, --all             Show all containers (default shows just running)
  -f, --filter filter   Filter output based on conditions provided
      --format string   Pretty-print containers using a Go template
  -n, --last int        Show n last created containers (includes all states) (default -1)
  -l, --latest          Show the latest created container (includes all states)
      --no-trunc        Don't truncate output
  -q, --quiet           Only display numeric IDs
  -s, --size            Display total file sizes



To list all containers:

$ docker container ls -a

To list only numeric IDs of all containers:

$ docker container ls -a -q

or

$ docker container ls -aq

docker container pause

This command transits specific container(s) into a Paused state. This feature is used to lower container's utilization of host's resources (CPU etc...so its battery) when running applications in container is not currently needed.

$ docker container pause --help

Usage:  docker container pause CONTAINER [CONTAINER...]

Pause all processes within one or more containers

CONTAINER is a full container id or just first several characters that can uniquely identify it.

Example:

$ docker container pause 5a7

To resume the processes and transit the container back to Up state:

$ docker container unpause 5a7

docker container rm

$ docker container rm --help

Usage:  docker container rm [OPTIONS] CONTAINER [CONTAINER...]

Remove one or more containers

Options:
  -f, --force     Force the removal of a running container (uses SIGKILL)
  -l, --link      Remove the specified link
  -v, --volumes   Remove the volumes associated with the container


To remove all containers:

$ docker container rm $(docker container ls -aq)

To display detailed information on one or more containers:

$ docker container inspect <container id or name>

If container is running (its state is UP), it needs to be stopped before we can remove it.

docker container run

Exploring Docker commands: docker [container] run | My Public Notepad

docker container stop 

Stops the container (gracefully). Stopping the container in this way gives applications running inside it to stop/terminate gracefully. This can be verified by observing docker logs for a given container during the process of stopping it. Unix signal that gets sent to the main process running inside the container is SIGTERM. Process can handle this signal or can even ignore it. SIGTERM does not kill child processes so main process can choose to stop them gracefully.

% docker container stop --help

Usage:  docker container stop [OPTIONS] CONTAINER [CONTAINER...]

Stop one or more running containers

Options:

  -t, --time int   Seconds to wait for stop before killing it (default 10)

When the terminal is attached to a container output we can press CTRL+C in order to to shut down the container.