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

docker-default-directory.md

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