Difference between revisions of "Create root filesystem snapshots with LVM"

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Requires=multi-user.target
 
Requires=multi-user.target
 
</pre>
 
</pre>
 +
Adapt the base target, if <tt>multi-user.target</tt> is not your default target.
  
 
Enable the new service with <tt>systemctl enable mk-lvm-snapshots.service</tt>.
 
Enable the new service with <tt>systemctl enable mk-lvm-snapshots.service</tt>.
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To get the messages of the new service use
 
To get the messages of the new service use
 
<tt>journalctl -u mk-lvm-snapshots.service</tt>.
 
<tt>journalctl -u mk-lvm-snapshots.service</tt>.
 +
 +
== Usage ==
 +
To use this functionality for a full system backup restart your system with the snapshot creation target. Mount the
 +
snapshot volume (and further volumes, if required), preferably using the read only (<tt>-o</tt>) option.
 +
Then backup your system, for example with tar as described in [[Full_System_Backup_with_tar]].

Revision as of 06:41, 27 April 2013

This article will show you how to setup LVM snapshot creation during system start. Such snapshots can be used for full system backups with minimal downtime.


Prerequisites

A system with LVM root and systemd.


Setup

During system start a clean snapshot of the root volume is created using a new service. Create /etc/systemd/system/mk-lvm-snapshots.service containing:

[Unit]
Description=make LVM snapshots
Requires=local-fs-pre.target
DefaultDependencies=no
Conflicts=shutdown.target
After=local-fs-pre.target
Before=local-fs.target

[Install]
WantedBy=make-snapshots.target

[Service]
Type=oneshot
ExecStart=/usr/sbin/lvcreate -L10G -n snap-root -s lvmvolume/root

Adapt the lvcreate command to match your root volume group and volume name.

Create a new systemd target /etc/systemd/system/make-snapshots.target with this service:

[Unit]
Description=Make Snapshots
Requires=multi-user.target

Adapt the base target, if multi-user.target is not your default target.

Enable the new service with systemctl enable mk-lvm-snapshots.service.

If the system is started with the new target, LVM snapshot(s) are created just after mounting the local filesystems. To get a grub menu entry starting this target create /boot/grub/custom.cfg based on the grub.cfg entry for your normal startup. The kernel command line is extended to start the new make-snapshots.target:

### make snapshots ###
menuentry 'Arch GNU/Linux, make snapshots' --class arch --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-core repo kernel-true-...' {
...
        echo    'Loading Linux core repo kernel ...'
        linux   /boot/vmlinuz-linux root=/dev/mapper/lvmvolume-root ro systemd.unit=make-snapshots.target
        echo    'Loading initial ramdisk ...'
        initrd  /boot/initramfs-linux.img
}

Remember to adjust custom.cfg if grub.cfg changes.

After restarting the system with this grub entry lvs should show up the newly created snapshot. To get the messages of the new service use journalctl -u mk-lvm-snapshots.service.

Usage

To use this functionality for a full system backup restart your system with the snapshot creation target. Mount the snapshot volume (and further volumes, if required), preferably using the read only (-o) option. Then backup your system, for example with tar as described in Full_System_Backup_with_tar.