Ubuntu系统下Docker data-root配置重启后失效的问题求助

I see you're running Docker installed via Snap on Ubuntu 20.04, and you've hit a common quirk with Snap-managed services: when you manually switch the Docker data root to /dockerdata (via daemon.json or modifying docker.service), it sticks after a manual Docker restart—but after a full system reboot, Docker reverts to the Snap default path /var/snap/docker/common/var-lib/docker. Let's break down why this happens and fix it permanently.

Why this happens #

Snap packages run in an isolated sandbox, and Snap's built-in service manager handles starting Docker on system boot. It doesn't respect system-level daemon.json or modified docker.service files you set up—instead, it loads its own default configuration unless you explicitly configure Snap-specific Docker settings. Your manual restart works because you're temporarily bypassing Snap's initial startup logic.

Permanent solutions for Snap Docker #

Method 1: Use Snap's dedicated Docker config file (Recommended) #

This is the simplest, most "Snap-native" way to lock in your custom data directory:

1. Stop the Docker Snap service first:

   sudo snap stop docker
   

2. Create the config directory for Snap's Docker instance (if it doesn't exist):

   sudo mkdir -p /var/snap/docker/current/config/
   

3. Create a daemon.json in this Snap-specific directory to set your custom data root:

   sudo tee /var/snap/docker/current/config/daemon.json <<EOF
   {
     "data-root": "/dockerdata"
   }
   EOF
   

4. Ensure the /dockerdata directory has the correct permissions (Docker requires root access):

   sudo chown -R root:root /dockerdata
   sudo chmod -R 700 /dockerdata
   

5. Start the Docker Snap service again:

   sudo snap start docker
   

6. Verify the change took effect:

   docker info | grep "Docker Root Dir"
   

   You should see /dockerdata listed. Reboot your system and run the verify command again—this time the setting will persist.

Method 2: Switch to systemd management (Optional) #

If you prefer using standard systemd to manage Docker instead of Snap's service manager, you can disable the Snap-managed Docker and set up a custom systemd service:

1. Stop and disable the Snap Docker service:

   sudo snap stop docker
   sudo snap disable docker
   

2. Create a systemd service file at /etc/systemd/system/docker.service with the following content (note the --data-root /dockerdata flag):

   [Unit]
   Description=Docker Application Container Engine
   Documentation=https://docs.docker.com
   After=network-online.target firewalld.service
   Wants=network-online.target
   
   [Service]
   Type=notify
   ExecStart=/snap/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock --data-root /dockerdata
   ExecReload=/bin/kill -s HUP $MAINPID
   TimeoutSec=0
   RestartSec=2
   Restart=always
   StartLimitBurst=3
   StartLimitInterval=60s
   LimitNOFILE=infinity
   LimitNPROC=infinity
   LimitCORE=infinity
   TasksMax=infinity
   Delegate=yes
   KillMode=process
   
   [Install]
   WantedBy=multi-user.target
   

3. Reload systemd and enable the new service:

   sudo systemctl daemon-reload
   sudo systemctl enable --now docker
   

4. Verify the configuration, then reboot to confirm it persists.

Context from your environment #

Looking at your docker version and docker info output:

• You're running Docker Engine - Community 19.03.12, installed via Snap (evidenced by the original default path)
• After manual restart, your Docker Root Dir correctly shows /dockerdata—the issue is exclusively Snap overriding this setting on system boot

Method 1 is the best approach since it works within Snap's ecosystem, but Method 2 gives you more control if you're accustomed to systemd service management.

内容的提问来源于stack exchange，提问作者uruloki