yufrul

Creates bootable, rolling snapshots of btrfs root filesystems on suspend/powerdown automatically

Contents

1. Requirements & Assumptions
2. Bootable Snapshots
3. Removing Outdated Snapshots
4. Invoking on Suspend or Power-down
5. Tested on
6. Inspired by
7. License
8. Naming
9. Contact

Requirements & Assumptions

Each invocation of makesnapshot.sh creates a new snapshot based on the same time stamp on all monitored filesystems. Monitored filesystems are identified by /run/btrfs-XYZ mount-points in /etc/fstab (see below for an example). If the mount-points does not exist they are created first as well as unmounted and removed after operation.

Furthermore, it is assumes that the active filesystem which should be taken a snapshot of is actually a subvolume. For each snapshot there is a new directory on each top-level filesystem having the snapshot name.

Top-level structure:

/run/btrfs-root:
@
@2015-06-14_155234/@
@2015-06-14_164429/@
@2015-06-14_172805/@

/run/btrfs-home:
@home
@2015-06-14_155234/@home
@2015-06-14_164429/@home
@2015-06-14_172805/@home

Bootable Snapshots

After creating a new snapshot by btrfs subvolume snapshot it is modified for convenience:

• A file /SNAPSHOT-TIMESTAMP containing the time stamp is created at the root of the snapshot.
• The issue file /etc/issue is adjusted on the root filesystem snapshot (assuming subvolume name @) to contain the original text appended with the snapshot name.
• The /etc/fstab file is adjusted to let the subvol=@XYZ parameter point to the appropriate snapshot.
• In order to be able to boot into a snapshot, a custom grub submenu in /etc/grub.d/40_custom is created. It contains the modified default menuentry copied from /boot/grub/grub.cfg. To put the changes into place, update-grub is run.

Removing Outdated Snapshots

On successive runs of makesnapshot.sh it first removes outdated snapshots. In order to accomplish this it extracts the time stamp of all existing snapshots and compares them with a reference date, by default 30 days ago. If a snapshot is older it is removed by btrfs subvolume delete.

Invoking on Suspend or Power-down

Enclosed is a script onupdown.sh which can be run automatically prior to entering suspend or powerdown state. It opens up a message window to give the user a change to skip the snapshot creation and continues otherwise by running makesnapshot.sh after a delay of 10 seconds.

The snapshot script is run in a xterm window to show the terminal output which is also written to a log file /var/log/snapshot.log separately. The operation finishes by closing the xterm window after another delay of 10 seconds.

It may work with any other x-terminal-emulator programs but adjusting the default font size is rather simple with an xterm which should be available on many systems anyway (as long as there is X).

Tested on

Works for the author on XUbuntu 14.04 with / and /home on different filesystems/devices and by mounting them via subvol=@ and subvol=@home respectively.

Example /etc/fstab:

UUID=aa-bb-cc /               btrfs   defaults,<more opts>,subvol=@      0   1
UUID=aa-bb-cc /run/btrfs-root btrfs   defaults,<more opts>,noauto        0   1
UUID=cc-dd-ee /home           btrfs   defaults,<more opts>,subvol=@home  0   1
UUID=cc-dd-ee /run/btrfs-home btrfs   defaults,<more opts>,noauto        0   1

USE WITH EXTREME CARE, DATA LOSS MAY OCCUR, NO WARRANTY!

Inspired by

https://wiki.archlinux.org/index.php/Btrfs_-_Tips_and_tricks

License

GPLv3

Naming

... purely arbitrarily by running apg -m 5

Contact

Feel free to contact me for any comments, feedback or critics!