Below example shows how to create a systemd script to mount a disk under a specific path on reboot automatically.
1. Check the filesystem UUID using the command “blkid”.
# blkid /dev/sdb /dev/sdb: UUID="5813cd72-ff30-44bc-a7a3-27c68fe3e6c7" UUID_SUB="ccd243dc-1481-403f-aa51-1502a95cdf2f" TYPE="btrfs"
2. We need to create a new mount unit to mount the filesystem. Mount units must be named after the mount point directories they control. For Example: the mount point /var/lib/docker must be configured in a unit file var-lib-docker.mount. For details about the escaping logic used to convert a file system path to a unit name, see manpage of systemd.unit.
# vi /etc/systemd/system/var-lib-docker.mount [Unit] Description=Docker mount [Mount] What=/dev/disk/by-uuid/5813cd72-ff30-44bc-a7a3-27c68fe3e6c7 Where=/var/lib/docker Type=btrfs Options=defaults [Install] WantedBy=multi-user.target
The option for “What” can be UUID, LABEL, path to disk
3. Enable the systemd unit to be started after boot.
# systemctl enable var-lib-docker.mount
4. The below docker service script is modified to make sure that the service should be only started after the mount service is called.
# cat /usr/lib/systemd/system/docker.service [Unit] Description=Docker Application Container Engine Documentation=https://docs.docker.com After=network.target docker.socket var-lib-docker.mount ### Added mount unit for docker service to wait Requires=docker.socket ...
5. Reboot the node and check for the status of the mount service unit.
# shutdown -r now
# systemctl status var-lib-docker.mount ● var-lib-docker.mount - Docker mount Loaded: loaded (/etc/systemd/system/var-lib-docker.mount; enabled; vendor preset: disabled) Active: active (mounted) since Tue 2016-06-07 02:06:07 IST; 54s ago Where: /var/lib/docker What: /dev/sdb Process: 416 ExecMount=/bin/mount /dev/disk/by-uuid/5813cd72-ff30-44bc-a7a3-27c68fe3e6c7 /var/lib/docker -n -t btrfs -o defaults (code=exited, status=0/SUCCESS) Jun 07 02:06:07 OL7-docker-TD systemd[1]: Mounting Docker mount... Jun 07 02:06:07 OL7-docker-TD systemd[1]: Mounted Docker mount.
6. Check for the mount point in the “mount” command.
# mount | grep docker /dev/sdb on /var/lib/docker type btrfs (rw,relatime,seclabel,space_cache)
The mount unit cannot be added to be part of another service operation. Available systemd Unit Types:
| Unit Type File | Extension | Description |
|---|---|---|
| Service unit | .service | A system service. |
| Target unit | .target | A group of systemd units. |
| Automount unit | .automount | A file system automount point. |
| Device unit | .device | A device file recognized by the kernel. |
| Mount unit | .mount | A file system mount point. |
| Path unit | .path | A file or directory in a file system. |
| Scope unit | .scope | An externally created process. |
| Slice unit | .slice | A group of hierarchically organized units that manage system processes. |
| Snapshot unit | .snapshot | A saved state of the systemd manager. |
| Socket unit | .socket | An inter-process communication socket. |
| Swap unit | .swap | A swap device or a swap file. |
| Timer unit | .timer | A systemd timer. |