btrfs_snapshot.sh - create snapshot for btrfs mountpoints/volumes (and send to another btrfs backup directory)

btrfs_snapshot.sh

#!/bin/bash
# v. 2023.06.29

MOUNTPOINTS=('/home' '/')
SNAPSHOTDIRNAME='.snapshots'
# snapshots in SNAPSHOTDIRNAME
RETAINSNAPS=2

# send to BACKUPDIR: yes or no
SENDTOBACKUP=no
# optional, set SENDTOBACKUP=yes
BACKUPDIR='/mnt/backup'
# snapshots in BACKUPDIR (if SENDTOBACKUP=yes)
RETAINBACKS=7


function is_btrfs {
        local FS=$(stat -f --format=%T "$1")
        [ "$FS" = "btrfs" ] && return 0
        return 1
}

function is_btrfs_volume {
        findmnt -rn  "$1" | grep "subvol=" > /dev/null 2>&1 && return 1 # return false if path is mountpoint
        btrfs subvolume show "$1" > /dev/null 2>&1 && return 0
        return 1
}

function is_btrfs_mountpoint {
        findmnt -rn  "$1" | grep "subvol=" > /dev/null 2>&1 && return 0
        return 1
}

function create_snapshot {
        local mountpoint=$1
        local snapdir="$SNAPSHOTDIRNAME"
        local date=$(date +%Y%m%d-%H%M%S)
        local snaproot
        local vol
        local isbtrfsvolume
        local snapcount
        local lastvol
        local allsnapsarray
        local snapstoremovecount

        if [[ "$SENDTOBACKUP" == "yes" ]]; then
            if ! is_btrfs "$BACKUPDIR" ; then
                echo \"$BACKUPDIR\" is not a btrfs!! Exit.
                exit 1
            fi
        fi

        if [[ "$mountpoint" != "/" ]]; then mountpoint=${mountpoint%/}; fi; # remove trainling slash for any dir except root (/)


        # find btrfs volume name for path
        if is_btrfs_volume "$mountpoint"; then
                vol=$mountpoint
                echo \"$mountpoint\" is volume
        elif is_btrfs_mountpoint "$mountpoint"; then
                vol=$(findmnt -rn  "$mountpoint" | awk -F "subvol=" 'NR==1 {print $2}')
                echo \"$mountpoint\" is mountpoint
        else
            echo \"$mountpoint\" is not a btrfs mountpoint or volume!! Exit.
            exit 1
        fi

        if [[ "$vol" == "/" ]]; then
                vol='@btrfsroot'
        else
                vol="${vol:1}" # remove lead slash
                vol="${vol//'/'/__}" # replace slashes by __
        fi

        echo "mp: $mountpoint"
        echo "vol: $vol"

        snaproot="${mountpoint}/${snapdir}"
        mkdir -p "$snaproot" > /dev/null 2>&1

        btrfs sub snap -r "${mountpoint}"  "${snaproot}/@snp_${vol}_ro_${date}" || exit 1

        if [[ "$SENDTOBACKUP" == "yes" ]]; then
                snapcount=$(ls "$snaproot" | grep "@snp_${vol}_ro" | wc -l)
                if [[ "$snapcount" == "1" ]]; then
                        btrfs send  "${snaproot}/@snp_${vol}_ro_${date}" | btrfs receive "$BACKUPDIR"
                else
                        lastvol=$(ls "$snaproot" | grep "@snp_${vol}_ro" | tail -2 | head -n -1)
                        btrfs send -p "${snaproot}/${lastvol}"  "${snaproot}/@snp_${vol}_ro_${date}" | btrfs receive "$BACKUPDIR"
                fi

                if [ "$RETAINBACKS" -gt  "0"  ]; then
                        allbacksarray=($(ls "$BACKUPDIR" | grep "@snp_${vol}_ro"))
                        if [ "$RETAINBACKS" -lt  "${#allbacksarray[@]}" ]; then
                                backstoremovecount=$(( ${#allbacksarray[@]} - $RETAINBACKS ))
                                for ((i=0;i<$backstoremovecount;i++)); do
                                        btrfs subvolume delete "${BACKUPDIR}/${allbacksarray[$i]}"
                                done
                        fi
                fi

        fi

        if [ "$RETAINSNAPS" -gt  "0"  ]; then
            allsnapsarray=($(ls "$snaproot" | grep "@snp_${vol}_ro"))
            if [ "$RETAINSNAPS" -lt  "${#allsnapsarray[@]}" ]; then
                snapstoremovecount=$(( ${#allsnapsarray[@]} - $RETAINSNAPS ))
                for ((i=0;i<$snapstoremovecount;i++)); do
                    btrfs subvolume delete "${snaproot}/${allsnapsarray[$i]}"
                done
            fi
        fi


        echo ""
}


for mp in ${MOUNTPOINTS[*]}; do
        create_snapshot "$mp"
done