Execute commands in running containers¶

We can execute an additional command in a container using the

docker exec -it <container id> <command>

The -it flags allows us to provide input to the container, it connects the STDIN, STDOUT and STDERR channels between your terminal and the running process. The -i flag connects the channels, the -t basically formats the output so it is prettier.

 davis@davis-arch  ~  docker create redis
5e993caa8ff4debe7e0bf6879546c76a8e21b372b560b8f348158c0b1c98ca86
 davis@davis-arch  ~  docker start 5e993caa8ff4debe7e0bf6879546c76a8e21b372b560b8f348158c0b1c98ca86
5e993caa8ff4debe7e0bf6879546c76a8e21b372b560b8f348158c0b1c98ca86
 davis@davis-arch  ~  docker ps
CONTAINER ID        IMAGE                          COMMAND                  CREATED             STATUS                          PORTS                     NAMES
5e993caa8ff4        redis                          "docker-entrypoint.s…"   8 seconds ago       Up 1 second                     6379/tcp                  relaxed_williamson
 davis@davis-arch  ~  docker exec -it 5e993caa8ff4debe7e0bf6879546c76a8e21b372b560b8f348158c0b1c98ca86 redis-cli
127.0.0.1:6379> set myvalue 5
OK
127.0.0.1:6379> get myvalue
"5"

When using the exec without the -it it will just execute the redis-cli command and we will not be able to interact with it.

You can also use the exec command to get full terminal access of the container for debugging:

davis@davis-arch  ~  docker exec -it 5e993caa8ff4debe7e0bf6879546c76a8e21b372b560b8f348158c0b1c98ca86 bash
root@5e993caa8ff4:/data# ls /
bin  boot  data  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@5e993caa8ff4:/data# hostname
5e993caa8ff4

You can also create the image at the start to use the terminal:

davis@davis-arch  ~  docker run -it busybox sh  
/ # ls /
bin   dev   etc   home  proc  root  sys   tmp   usr   var
/ # hostname
946745b94a5e