Permanently Change the Root Data Directory in Docker

This article explains how to permanently switch the default root data directory /var/lib/docker/ to a different directory.

Background information

The /var/lib/docker directory stores all images, volumes from Docker and can grow significantly depending on how many containers are used. The directory is structured as follows:

root@js-checkmk-02:/var/lib/docker# ls
buildkit  containers  engine-id  image  network  overlay2  plugins  runtimes  swarm  tmp  volumes

You can see that it is used if you, for example, verify the status with df -h:

root@js-checkmk-02:/var/lib/docker# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            3.9G     0  3.9G   0% /dev
tmpfs           794M  684K  794M   1% /run
/dev/sda1        47G  3.8G   41G   9% /
tmpfs           3.9G     0  3.9G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
/dev/sda15      124M   12M  113M  10% /boot/efi
tmpfs           794M     0  794M   0% /run/user/0
tmpfs           794M     0  794M   0% /run/user/1000
overlay          47G  3.8G   41G   9% /var/lib/docker/overlay2/a6a4203cef42815c7187f584436e5eb9dff385e3ca9c92d597a38806b9dc255d/merged

Configuration

First, docker must be stopped, which has immediately influence on all active containers. In addition, we install the tool rsync.

root@js-checkmk-02:/# systemctl stop docker && apt install rsync

After this, it must be communicated to Docker where to find the new data root:

# Create directory if it has not been created yet
root@js-checkmk-02:/# mkdir -p /root/docker/root

# Daemon-Datei anlegen in /etc/docker
root@js-checkmk-02:/# nano /etc/docker/daemon.json

# Please add the following into the file, then adjust your path and store it. In this example, we change it to /root/docker/root

{
   "data-root": "/root/docker/root"

}

Next, the whole content of the old docker-root-directory is copied into the new data-root-directory and then the old /var/lib/docker directory is renamed to /var/lib/docker.old.

rsync -aP /var/lib/docker/ "/root/docker/root"
cp -rp /var/lib/docker/* "/root/docker/root"
mv /var/lib/docker /var/lib/docker.old

After that, Docker can be restarted and it should be verified if all containers still function:

systemctl start docker

If everything functions, the old data-root-directory can be deleted:

rm -rf /var/lib/docker.old

Author: Jonas Sterr Jonas Sterr has been working for Thomas-Krenn for several years. Originally employed as a trainee in technical support and then in hosting (formerly Filoo), Mr. Sterr now mainly deals with the topics of storage (SDS / Huawei / Netapp), virtualization (VMware, Proxmox, HyperV) and network (switches, firewalls) in product management at Thomas-Krenn.AG in Freyung.

Translator: Alina Ranzinger Alina has been working at Thomas-Krenn.AG since 2024. After her training as multilingual business assistant, she got her job as assistant of the Product Management and is responsible for the translation of texts and for the organisation of the department.