Docker @programming.dev k2helix @lemmy.world 3mo ago

Volume empty after mounting

I have a docker compose file with a bind volume. It basically mounts /media/user/drive/media to the container's /mnt.

It works as expected when /media/user/drive/ is mounted and its media folder has the files I want the container to see.

However, as it's a network drive, the container usually tries to start before it is mounted, so it would throw the error that /media/user/drive/media doesn't exist. So I created an empty folder in /media/user/drive called media while the drive was not mounted so that at least the container starts with the volume /mnt being empty until the network drive gets mounted and all the files appear at /media/user/drive/media.

To my surprise, when the drive gets mounted, even though if I do ls /media/user/drive/media it lists the drive contents correctly, the container still sees /mnt empty.

How would I go about getting the drive files inside the docker container when it automatically starts?

12 comments

The file handle of the directory changes when you mount the nfs on it, and docker is still looking at the old file handle.

It'd probably work if you mounted nfs to a folder inside that one, or moved your docker mount one level up.

Otherwise you'll need to get your container to restart after the mount is attached. You could do this with a health check for the container that checks the files are there, and restart the container if they're not. Or you could just fix your boot order and set nfs as a dependency for docker.
- Thanks for your answer. I tried mounting it to a folder inside the one I'm using in the compose file but strangely it didn't work. So I thought that the only way that wouldn't need to delay docker start is to restart the container just after the drive has been mounted.
  
  And that's what I ended up doing as the drive mount is a systemd service and therefore I can use ExecStartPost to restart the container. That way this doesn't affect other containers and also lets this one start even if the drive has not been mounted which I want in case there's no internet connection
If the container is running under a different user then you may have some permission issues.
- Don't think it has to do with permissions as if I manually start the container after the drive gets mounted then everything goes as expected and the container has the files at /mnt
  
  Pop a script on the container to do a whoami and an ls -l on the folder
How are you mounting the network drive? On my docker machine, network drive mounts are in /etc/fstab. I've not had an issue where docker starts before everything is mounted.
- I mount it using rclone mount as a systemd service, just as they say in their guide
  
  And is docker running via a systemd service also?
  
  In that case, you can add an After= line to the docker unit file, telling it to wait until after your mount service is running: https://stackoverflow.com/questions/21830670/start-systemd-service-after-specific-service
  
  You can use systemctl edit docker to create an override file with this property: https://askubuntu.com/questions/659267/how-do-i-override-or-configure-systemd-services#659268

12 comments