viz-snapshot

etc_default_viz_snapshot

# viz-snapshot defaults file.
BTRFS_ROOT_DEV='/dev/mapper/root'
BTRFS_SUBVOLS='system/awesome-root data/awesome-home-viz'

usr_local_sbin_viz-snapshot

#!/bin/sh
# btrfs snapshot script.
# By Viz, Apr 11, 2017

# exit the script on failure.
set -e

# load defaults.
[ -f "/etc/default/viz/snapshot" ] && source "/etc/default/viz/snapshot"
BTRFS_ROOT_DEV=${BTRFS_ROOT_DEV:-/dev/mapper/root}

# create a temporary directory for mount the btrfs root.
TMP_MNT="$(mktemp -u)"
[ -e "$TMP_MNT" ] && {
         echo "[!] Error: directory \"${TMP_MNT}\" already exists!" >&2
         exit 1
       }
mkdir -p "$TMP_MNT"
[ ! -d "$TMP_MNT" ] && {
         echo "[!] Error: failed to create \"${TMP_MNT}\" directory!" >&2
         exit 1
       }

# mount the btrfs root.
mount -t btrfs "$BTRFS_ROOT_DEV" "$TMP_MNT"
echo "[+] btrfs root is mounted successfully."

# get current time as tag.
TAG="$(date '+%F_%H:%M')"
echo "[+] set snapshot tag to \"${TAG}\"."

# snapshot all configured sub-volumes.
pushd "$TMP_MNT" >/dev/null
for SUBVOL in $BTRFS_SUBVOLS; do
  [ -z "$(ls -A "$SUBVOL" 2>/dev/null)" ] && {
    echo "[-] empty sub-volume found: \"${SUBVOL}\", skip." >&2
    continue
  }

  [ -e "${SUBVOL}-${TAG}" ] && {
    echo "[-] snapshot target path has been occupied, skip." >&2
    continue
  }

  btrfs subvolume snapshot "$SUBVOL" "${SUBVOL}-${TAG}"
  echo "[+] btrfs snapshot has taken for sub-volume \"${SUBVOL}\"."
done
popd >/dev/null
echo "[+] all btrfs snapshot has taken."

# unmount the btrfs root and cleanup.
umount -l "$TMP_MNT"  # not a bug: let it fail if failed to unmount.
rmdir "$TMP_MNT"      # not a bug: let it fail if the directory is not empty.

# done.
echo "[+] done."