docker container exec

Introducing Docker Debug

To easily get a debug shell into any container, use docker debug . Docker Debug is a replacement for debugging with docker exec . With it, you can get a shell into any container or image, even slim ones, without modifications. Plus, you can bring along your favorite debugging tools in its customizable toolbox.

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Description

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

The command you specify with docker exec only runs while the container's primary process ( PID 1 ) is running, and it isn't restarted if the container is restarted.

The command runs in the default working directory of the container.

The command must be an executable. A chained or a quoted command doesn't work.

• This works: docker exec -it my_container sh -c "echo a && echo b"
• This doesn't work: docker exec -it my_container "echo a && echo b"

Options

Examples

Run docker exec on a running container

First, start a container.

$ docker run --name mycontainer -d -i -t alpine /bin/sh

This creates and starts a container named mycontainer from an alpine image with an sh shell as its main process. The -d option (shorthand for --detach ) sets the container to run in the background, in detached mode, with a pseudo-TTY attached ( -t ). The -i option is set to keep STDIN attached ( -i ), which prevents the sh process from exiting immediately.

Next, execute a command on the container.

$ docker exec -d mycontainer touch /tmp/execWorks

This creates a new file /tmp/execWorks inside the running container mycontainer , in the background.

Next, execute an interactive sh shell on the container.

$ docker exec -it mycontainer sh

This starts a new shell session in the container mycontainer .

Set environment variables for the exec process (--env, -e)

Next, set environment variables in the current bash session.

The docker exec command inherits the environment variables that are set at the time the container is created. Use the --env (or the -e shorthand) to override global environment variables, or to set additional environment variables for the process started by docker exec .

The following example creates a new shell session in the container mycontainer , with environment variables $VAR_A set to 1 , and $VAR_B set to 2 . These environment variables are only valid for the sh process started by that docker exec command, and aren't available to other processes running inside the container.

$ docker exec -e VAR_A=1 -e VAR_B=2 mycontainer env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=f64a4851eb71
VAR_A=1
VAR_B=2
HOME=/root

Escalate container privileges (--privileged)

See docker run --privileged .

Set the working directory for the exec process (--workdir, -w)

By default docker exec command runs in the same working directory set when the container was created.

$ docker exec -it mycontainer pwd

You can specify an alternative working directory for the command to execute using the --workdir option (or the -w shorthand):

$ docker exec -it -w /root mycontainer pwd
/root

Try to run docker exec on a paused container

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

$ docker pause mycontainer
mycontainer
$ docker ps
CONTAINER ID   IMAGE     COMMAND     CREATED          STATUS                   PORTS     NAMES
482efdf39fac   alpine    "/bin/sh"   17 seconds ago   Up 16 seconds (Paused)             mycontainer
$ docker exec mycontainer sh
Error response from daemon: Container mycontainer is paused, unpause the container before exec
$ echo $?