Moving the Docker Root Directory

I was using GitLab on an in-house cloud server.
However, a build that had been working fine until just before suddenly failed when I tried to rebuild it.

Upon investigation, I found that the cause was insufficient local disk space...

# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        7.8G     0  7.8G   0% /dev
tmpfs           7.8G     0  7.8G   0% /dev/shm
tmpfs           7.8G  817M  7.0G  11% /run
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/sda7        98G   97G  1.8G  100% /
/dev/sda1       494M  136M  358M  28% /boot
/dev/sda2       400G   51G  350G  13% /dat
/dev/sda3       300G  136G  165G  46% /log
/dev/sda5       100G  2.9G   98G   3% /sw
tmpfs           1.6G     0  1.6G   0% /run/user/1000
tmpfs           1.6G     0  1.6G   0% /run/user/0

I can see that the capacity of /dev/sda7 is insufficient.

The documentation mentioned that it was a 2TB RAID when I took over...
Am I misunderstanding the concept of RAID?

Changing Docker Settings

To move the root directory, you need to change the Docker settings.

If you installed from the official Docker repository, create and modify the /etc/docker/daemon.json file.

# /etc/docker/daemon.json
{
  "data-root": "/dat/docker"
}

I created this file.

After that, restarting Docker will change the root directory.

sudo systemctl restart docker

If There Are Existing Docker Volumes

If you have existing volumes, you need to move those volumes to the new directory.

To replicate all the information, use the rsync command.

rsync -av /var/lib/docker /dat/docker

If the Volume Size Is Large

In my case, the volume was about 45GB, and since I was working at night, I proceeded with the replication in the background.
I also planned to check the logs, so I used a terminal multiplexer to work in the background.

tmux

rsync -av /var/lib/docker /dat/docker

Press Ctrl + b and then d to continue working in the background.

# If you haven't closed the terminal, open the last session
tmux attach-session

# If you closed the terminal and want to check again
tmux ls # Check the session list
tmux attach -t 0 # Connect using the session number

TODO

[ ] Regularly back up Docker volumes