(partially solved, see UPDATE1, import/export issue)
I recently pulled an image from docker hub, named
amd64/ubuntu:latest. I modified it slightly on my Desktop machine, which is Ubuntu 20.04. The image I downloaded is also and image of Ubuntu 20.04, as I could verify by checking the
/etc/lsb-release file inside the container.
The modifications were minor: I installed zsh, compiled vim and compiled sshd (because installing packages for those two takes much more space). Everything worked inside the container. I then created another image from that modified container, removed the container and started a new one from the modified image with this command:
$ docker run -dit --name=myubuntu20 local/ubuntu:March07_2022
This would work with no problem, and I would then start sshd daemon on it (while not common to call sshd this way, it does work):
$ docker exec myubuntu20 bash -c 'service ssh start'
I made /etc/init.d/ssh in the container as simple as possible only containing these two lines:
So everything worked and I was able to connect normally via ssh.
THEN I decide to test this image on another machine, namely Ubuntu 21 VirtualBox installation. I save the image as a .tgz archive and import it inside the Ubuntu 21 Machine - exactly as per Docker documentation, naming it the same as the image on my Desktop machine. Attempts to run the image on Ubuntu 21 failed though. Here’s what I tried on Ubuntu 21 Virtual Box (all of these work on Ubuntu 20 Desktop):
$ docker run -dit --name=myubuntu20 local/ubuntu:March07_2022 docker: Error response from daemon: No command specified. # RESULT: container is not created at all.
Fine, I read the docs, let’s try adding something as a command:
$ docker run -dit --name=myubuntu20 local/ubuntu:March07_2022 /bin/sh -c 'echo hello' 86cca2e49ee136c52145788f8883af159d53e99ea5ce52e3fc58469a6310121d docker: Error response from daemon: OCI runtime create failed: container_linux.go:380: starting container process caused: exec: "/bin/sh": stat /bin/sh: no such file or directory: unknown.
This time, a container had been created, but not started. I tried different commands apart form
/bin/sh and I double checked - it does exist inside the container, so the file is there. I tried
/usr/local/sbin/sshd - all with the same result as above.
At present time, I find it not likely that this is due to VirtualBox, but perhaps I am being wrong. I’m currently installing Ubuntu 20 on it to try and run it there and will also try running on another hardware and not inside a Virtual machine. However, it does seem very strange this should even happen.
Docker versions are exactly the same on both machines:
$ /usr/bin/dockerd --version Docker version 20.10.12, build 459d0df $ docker --version Docker version 20.10.12, build e91ed57
They also seem to be running with the same configuration parameters, as I haven’t changed much, so the output is THE SAME for both machines:
$ ps aux | grep '[d]ocker' root /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
(process ids and other irrelevant info is stripped)
Could anyone please give me a hint at what’s going it? Perhaps saving and/or importing images is broken?
UPDATE 1 (partially solved)
Yes, it appears to be an export/import issue, because when I simply uploaded the image to Docker Hub and pulled it on another machine - it worked. Still remains the question, why is the export/import broken? Should repo name be exactly the same upon import or is there something else? Again, the commands used were all as per documentation:
$ docker image save local/ubuntu:March07_2022 -o ubuntu.tgz # on Ubuntu 20 $ docker import ubuntu.tgz local/ubuntu:March07_2022 # on Ubuntu 21