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I am able to run arbitrary shell commands in a container created from docker/whalesay image.
$ docker run docker/whalesay ls -l total 56 -rw-r--r-- 1 root root 931 May 25 2015 ChangeLog -rw-r--r-- 1 root root 385 May 25 2015 INSTALL -rw-r--r-- 1 root root 1116 May 25 2015 LICENSE -rw-r--r-- 1 root root 445 May 25 2015 MANIFEST -rw-r--r-- 1 root root 1610 May 25 2015 README -rw-r--r-- 1 root root 879 May 25 2015 Wrap.pm.diff drwxr-xr-x 2 root root 4096 May 25 2015 cows -rwxr-xr-x 1 root root 4129 May 25 2015 cowsay -rw-r--r-- 1 root root 4690 May 25 2015 cowsay.1 -rw-r--r-- 1 root root 54 May 25 2015 install.pl -rwxr-xr-x 1 root root 2046 May 25 2015 install.sh -rw-r--r-- 1 root root 631 May 25 2015 pgp_public_key.txt $ docker run docker/whalesay lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 14.04.2 LTS Release: 14.04 Codename: trusty However, I am unable to run a shell in a container created from this image.
$ docker run docker/whalesay bash $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES $ docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 7ce600cc9904 docker/whalesay "bash" 5 seconds ago Exited (0) 3 seconds ago loving_mayer Why did it not work? How can I make it work?
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If you have a container in the exited state and you want to start a bash associated with that container, you can use the Docker start command along with the --attach and --interactive options. This will attach a new terminal and will allow you to interact with the container easily.
To use the docker exec command, you will need a running Docker container. If you don't already have a container, start a test container with the following docker run command: docker run -d --name container-name alpine watch "date >> /var/log/date. log"
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. COMMAND will run in the default directory of the container.
To run an image inside of a container, we use the docker run command. The docker run command requires one parameter and that is the image name. Let's start our image and make sure it is running correctly. Execute the following command in your terminal.
If you docker run without attaching a tty, and only call bash, then bash finds nothing to do, and it exits. That's because by default, a container is non-interactive, and a shell that runs in non-interactive mode expects a script to run. Absent that, it will exit.
To run a disposable new container, you can simply attach a tty and standard input:
docker run --rm -it --entrypoint bash <image-name-or-id> Or to prevent the above container from being disposed, run it without --rm.
Or to enter a running container, use exec instead:
docker exec -it <container-name-or-id> bash In comments you asked
Do you know what is the difference between this and
docker run -it --entrypoint bash docker/whalesay?
In the two commands above, you are specifying bash as the CMD. In this command, you are specifying bash as the ENTRYPOINT.
Every container is run using a combination of ENTRYPOINT and CMD. If you (or the image) does not specify ENTRYPOINT, the default entrypoint is /bin/sh -c.
So in the earlier two commands, if you run bash as the CMD, and the default ENTRYPOINT is used, then the container will be run using
/bin/sh -c bash If you specify --entrypoint bash, then instead it runs
bash <command> Where <command> is the CMD specified in the image (if any is specified).
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