Usage:  docker exec [OPTIONS] CONTAINER COMMAND [ARG...]

Run a command in a running container

Options:
  -d, --detach         Detached mode: run command in the background
      --detach-keys    Override the key sequence for detaching a container
  -e, --env=[]         Set environment variables
      --help           Print usage
  -i, --interactive    Keep STDIN open even if not attached
      --privileged     Give extended privileges to the command
  -t, --tty            Allocate a pseudo-TTY
  -u, --user           Username or UID (format: <name|uid>[:<group|gid>])

The docker exec command runs a new command in a running container.

The command started using docker exec only runs while the container's primary process (PID 1) is running, and it is not restarted if the container is restarted.

First, start a container.

$ docker run --name ubuntu_bash --rm -i -t ubuntu bash

This will create a container named ubuntu_bash and start a Bash session.

Next, execute a command on the container.

$ docker exec -d ubuntu_bash touch /tmp/execWorks

This will create a new file /tmp/execWorks inside the running container ubuntu_bash, in the background.

Next, execute an interactive bash shell on the container.

$ docker exec -it ubuntu_bash bash

This will create a new Bash session in the container ubuntu_bash.

If the container is paused, then the docker exec command will fail with an error:

$ docker pause test

test

$ docker ps

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                   PORTS               NAMES
1ae3b36715d2        ubuntu:latest       "bash"              17 seconds ago      Up 16 seconds (Paused)                       test

$ docker exec test ls

FATA[0000] Error response from daemon: Container test is paused, unpause the container before exec

$ echo $?
1