btrfs snapshot automation script

btrfs_backup.service

# systemd main unit file for btrfs incremental snapshotting
[Unit]
Description=Execute btrfs snapshot routine for given volumes

[Service]
Type=oneshot
ExecStart=/usr/local/bin/btrfs_backup /home 48    # Choose partition mount point and num backups to keep here

btrfs_backup.sh

#!/bin/sh
# MolarFox 2021
# Shell script to run basic btrfs snapshot backup routine on a btrfs volume - does not perform incremental sending to external btrfs partition

# btrfs_backup.sh <btrfs_volume> <num_backups_to_keep>

# Expects base directory of btrfs (sub)volume to be backed up in argv[1] / $1
# Expects number of recent backups to keep in argv[2] / $2

pacman -Q > /root/installed_packages            # keep a list of installed stuff, in case fresh re-install needed (for arch linux, replace w/ package manager for whichever distro)

backup_name=$(date --utc | sed -r 's/ /_/g')    # name backup by current UTC time

# Run the backup
btrfs subvolume snapshot -r $1 $1/.snapshots/$backup_name

# Delete all but the newest n backups in the snapshots directory
old_backups=$( ls -1t $1/.snapshots | head -n -$2 )

if [ $(echo -n $old_backups | grep -c '^') -gt 0 ]      # if there are backups to delete
then
        while IFS= read -r line; do     # iterate and delete the backup subvolumes
                btrfs subvolume delete $1/.snapshots/$line
        done <<< $old_backups
fi

btrfs_backup.timer

# systemd timer unit file for btrfs incremental snapshotting
[Unit]
Description=Run btrfs snapshot on selected drives every 5 mins

[Timer]
OnBootSec=5min
OnUnitActiveSec=5min    # modify these to change snapshot frequency
RandomizedDelaySec=20

[Install]
WantedBy=timers.target