Free Up Docker Space: Relocate /var/lib/docker Using Symlinks & Config

Because the initial system partition is small, the root (/) partition cannot accommodate Docker's default storage located at /var/lib/docker. Over time this fills up, causing space issues. The article explains three ways to relocate Docker's storage to a larger disk.

1. Use a Symbolic Link

Check the current Docker root directory:

# Default storage location
$ sudo docker info | grep "Docker Root Dir"

Stop Docker, move the directory, and create a symlink pointing to the new location:

# Stop Docker service
$ systemctl stop docker
# or
$ service docker stop

# Move the existing data
$ mv /var/lib/docker /data/docker

# Create the symbolic link
$ ln -sf /data/docker /var/lib/docker

2. Specify the Storage Path with Daemon Options

Set the --graph (or -g) option in Docker’s configuration file to point to the new directory. The file location differs by distribution:

Ubuntu: /etc/default/docker CentOS: /etc/sysconfig/docker Example configurations:

# CentOS 6 (SELinux enabled)
OPTIONS=--graph="/data/docker" --selinux-enabled -H fd://

# CentOS 7 (modify systemd unit)
$ vi /usr/lib/systemd/system/docker.service
ExecStart=/usr/bin/dockerd --graph /new-path/docker

# Ubuntu (SELinux not enabled)
OPTIONS=--graph="/data/docker" -H fd://

Reload the daemon and restart Docker:

# Reload systemd configuration
$ sudo systemctl daemon-reload
# Restart Docker
$ sudo systemctl restart docker.service

For Docker 1.12+ you can also edit or create /etc/docker/daemon.json:

{
  "registry-mirrors": ["http://7e61f7f9.m.daocloud.io"],
  "graph": "/new-path/docker"
}

3. Create a Systemd Drop‑In File

Place a drop‑in file at /etc/systemd/system/docker.service.d/docker.conf to override the default ExecStart line:

# Define new storage location
$ sudo vi /etc/systemd/system/docker.service.d/docker.conf
[Service]
ExecStart=/usr/bin/dockerd --graph "/data/docker" --storage-driver=devicemapper

After saving, reload and start Docker:

# Reload daemon
$ sudo systemctl daemon-reload
# Start Docker
$ sudo systemctl start docker

Verify the new root directory with docker info.

Reference

https://blog.51cto.com/forangela/1949947