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 $?
1