I would build on the nice script by Ignacio Nunez Hernanz:
#!/bin/bash
#
# Script that creates BTRFS snapshots, manually or from cron
#
# Usage:
# sudo btrfs-snp <dir> (<tag>) (<limit>) (<seconds>) (<destdir>)
#
# Copyleft 2017 by Ignacio Nunez Hernanz <nacho _a_t_ ownyourbits _d_o_t_ com>
# GPL licensed (see end of file) * Use at your own risk!
#
# Based on btrfs-snap by Birger Monsen
#
# More at https://ownyourbits.com
#
function btrfs-snp()
{
local BIN="${0##*/}"
local DIR="${1}"
local TAG="${2:-snapshot}"
local LIMIT="${3:-0}"
local TIME="${4:-0}"
local DST="${5:-.snapshots}"
## usage
[[ "$*" == "" ]] || [[ "$1" == "-h" ]] || [[ "$1" == "--help" ]] && {
echo "Usage: $BIN <dir> (<tag>) (<limit>) (<seconds>) (<destdir>)
dir │ create snapshot of <dir>
tag │ name the snapshot <tag>_<timestamp>
limit │ keep <limit> snapshots with this tag. 0 to disable
seconds │ don't create snapshots before <seconds> have passed from last with this tag. 0 to disable
destdir │ store snapshot in <destdir>, relative to <dir>
Cron example: Hourly snapshot for one day, daily for one week, weekly for one month, and monthly for one year.
cat > /etc/cron.hourly/$BIN <<EOF
#!/bin/bash
/usr/local/sbin/$BIN /home hourly 24 3600
/usr/local/sbin/$BIN /home daily 7 86400
/usr/local/sbin/$BIN /home weekly 4 604800
/usr/local/sbin/$BIN / weekly 4 604800
/usr/local/sbin/$BIN /home monthly 12 2592000
EOF
chmod +x /etc/cron.hourly/$BIN"
return 0
}
## checks
local SNAPSHOT=${TAG}_$( date +%F_%H%M%S )
[[ ${EUID} -ne 0 ]] && { echo "Must be run as root. Try 'sudo $BIN'" ; return 1; }
[[ -d "$SNAPSHOT" ]] && { echo "$SNAPSHOT already exists" ; return 1; }
mount -t btrfs | cut -d' ' -f3 | grep -q "^${DIR}$" || {
btrfs subvolume show "$DIR" | grep -q "${DIR}$" || {
echo "$DIR is not a BTRFS mountpoint or snapshot"
return 1
}
}
DST="$DIR/$DST"
mkdir -p "$DST"
local SNAPS=( $( btrfs subvolume list -s --sort=gen "$DST" | awk '{ print $14 }' | grep "${TAG}_" ) )
## check time of the last snapshot for this tag
[[ "$TIME" != 0 ]] && [[ "${#SNAPS[@]}" != 0 ]] && {
local LATEST=$( sed -r "s|.*_(.*_.*)|\\1|;s|_([0-9]{2})([0-9]{2})([0-9]{2})| \\1:\\2:\\3|" <<< "${SNAPS[-1]}" )
LATEST=$( date +%s -d "$LATEST" ) || return 1
[[ $(( LATEST + TIME )) -gt $( date +%s ) ]] && { echo "No new snapshot needed for $TAG"; return 0; }
}
## do it
btrfs subvolume snapshot -r "$DIR" "$DST/$SNAPSHOT" || return 1
## prune older backups
[[ "$LIMIT" != 0 ]] && \
[[ ${#SNAPS[@]} -ge $LIMIT ]] && \
echo "Pruning old snapshots..." && \
for (( i=0; i <= $(( ${#SNAPS[@]} - LIMIT )); i++ )); do
btrfs subvolume delete "$DIR/${SNAPS[$i]}"
done
echo "snapshot $SNAPSHOT generated"
}
btrfs-snp "$@"
# License
#
# This script is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This script is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this script; if not, write to the
# Free Software Foundation, Inc., 59 Temple Place, Suite 330,
# Boston, MA 02111-1307 USA
Relevant usage info:
# btrfs-snp
Usage: btrfs-snp <dir> (<tag>) (<limit>) (<seconds>) (<destdir>)
dir │ create snapshot of <dir>
tag │ name the snapshot <tag>_<timestamp>
limit │ keep <limit> snapshots with this tag. 0 to disable
seconds │ don't create snapshots before <seconds> have passed from last with this tag. 0 to disable
destdir │ store snapshot in <destdir>, relative to <dir>
Your upgrade alias would need to look like this:
btrfs-snp / syschanges 3 600 && ... which generates a snapshot with the tag syschanges in /.snapshots, but not if there is already one in the last 5 minutes, and keeps maximum 3 of these.
This gives you a 5-minute window to do repeat operations without cluttering, for example, if you want to install from different repos or ppas in one install step, not only upgrades.
Then, you can use and restore these snapshots as per btrfs best practice.
