Change docker's default /var/lib/docker to different directory on Ubuntu

docker-default-directory

1. Take a backup of docker.service file.
   $ cp /lib/systemd/system/docker.service /lib/systemd/system/docker.service.orig

2. Modify /lib/systemd/system/docker.service to tell docker to use our own directory 
   instead of default /var/lib/docker. In this example, I am using /p/var/lib/docker
   
   Apply below patch.

   $ diff -uP -N /lib/systemd/system/docker.service.orig /lib/systemd/system/docker.service
   --- /lib/systemd/system/docker.service.orig	2018-12-05 21:24:20.544852391 -0800
   +++ /lib/systemd/system/docker.service	2018-12-05 21:25:57.909455275 -0800
   @@ -10,7 +10,7 @@
    # the default is not to use systemd for cgroups because the delegate issues still
    # exists and systemd currently does not support the cgroup feature set required
    # for containers run by docker
  -ExecStart=/usr/bin/dockerd -H unix://
  +ExecStart=/usr/bin/dockerd -g /p/var/lib/docker -H unix://
   ExecReload=/bin/kill -s HUP $MAINPID
   TimeoutSec=0
   RestartSec=2

3. Stop docker service
   $ systemctl stop docker
4. Do daemon-reload as we changed docker.service file   
   $ systemctl daemon-reload
5. rsync existing docker data to our new location   
   $ rsync -aqxP /var/lib/docker/ /p/var/lib/docker/
6. Start docker service   
   $ sysctl docker start

You should be consistent and start the docker service using the following command:

systemctl start docker

nice shot

this didn't work for me so I went with /etc/docker/daemon.json solution.

Worked for me.

thanks, works on ubuntu20.04, docker19.03

use —data-root in Docker version 19.03.1

This works

Worked.

Moreover, for systemctl spot docker:

Sometimes docker has socket running to be active. You have to also stop it with

systemctl stop docker.socket

Then, check if docker is not running with

systemctl status docker
AND
ps aux | grep -i docker | grep -v grep -----> if you don't have outputs here, it means docker is stopped, otherwise it needs to be stopped.

this is al fun and games until your package manager updates the docker.service file and suddenly everything breaks.

You are going to get a very nasty surprise when docker updates :)

Try this?

1. sudo systemctl edit docker
2. Add JUST this (using your example):

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -g /p/var/lib/docker -H unix://

I found a great explanation here, which explains better than I can: https://askubuntu.com/questions/659267/how-do-i-override-or-configure-systemd-services

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -g /p/var/lib/docker -H unix://

Your option -g /p/var/lib/docker doesn't work for me. But a:

sudo /var/lib/dockerd --help

revealed that there is a option --data-root. After copying all the contents from /var/lib/docker to /data/var/lib/docker (/data is my new directory pointing to some new bigger virtual disk as I am running fedora 37 in libvirt) and after modify the systemd's override via:

sudo systemctl edit docker

and pasted the following content:

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd --data-root /data/var/lib/docker/ -H fd:// --containerd=/run/containerd/containerd.soc

it works perfect.

Pay attention: The value for --data-root has to end with a slash "/". The first shot didn't work as I missed it. After appending the "/" it worked.

Regards

EDIT
Of course the sequence of editing is as follows:

1. sudo systemctl stop docker
2. sudo systemctl status docker #check that docker is relay inactive
3. sudo cp -r /var/lib/docker /directory-for--data-root
4. sudo systemctl edit docker
5. change and save the override with values like above "ExeStart= ...." (yes ExecStart is needed two times, 1. to reset, 2. with new value)
6. sudo systemctl deamon-reload
7. sudo systemctl start docker
8. be happy

@pumuugel82 it's worked for me, thank you

@pumuugel82 #6. sudo systemctl deamon-reload <---- daemon spelling correction :-)