scripts/btrfs-snapshots.sh

#!/usr/bin/env bash


    ## ## ## ## ## ## ## ## ## ## ## ## ## ##
   ##                                       ##
  ##           btrfs-snapshots.sh            ##
 ##                                           ##
 ##    Take read-only snapshots of BTRFS      ##
  ##              subvolumes                 ##
   ##                                       ##
    ## ## ## ## ## ## ## ## ## ## ## ## ## ##


##
## Information
## (don't touch unless you are me)
##

NAME="btrfs-snapshots.sh"
VERSION="0.2.0"
AUTHOR="david@socialnerds.org"
LICENSE="MIT"
DESCRIPTION="Take read-only snapshots of BTRFS subvolumes."
WEBSITE="https://git.socialnerds.org/david/scripts"
CHANGELOG=("[2023-10-26][v0.2.0] Complete rewrite"
           "[2021-01-01][v0.1.0] Initial version")


##
## Configuration
##

EXECUTABLE="$(basename $0)"
LIBRARIES="lib.sh"
DEPENDENCIES="basename dirname readlink ln mkdir rm ls date btrfs"
REQUIRE_ROOT=1

SNAP_FOLDER=".snapshots"
SNAP_PREFIX="snapshot-"
SNAP_TIMESTAMP=$(date +%Y%m%d%H%M) #add %S if you want sub-minute snapshots
SNAP_NAME="$SNAP_PREFIX$SNAP_TIMESTAMP"

# Build the Btrfs command
BTRFS_BINARY="$(command -v btrfs)"
BTRFS_OPTIONS="-q"
BTRFS_COMMAND="$BTRFS_BINARY $BTRFS_OPTIONS"

# How many snapshots should be kept?
# Can be overridden with an option flag (-s)
SNAPSHOTS=128


##
## Functions
##

# Print help information
function print_help() {
  printf "%s\n\n%s\n%b\n\n%s\n  %-21s %s\n  %-21s %s\n  %-21s %s\n  %-21s %s\n  %-21s %s\n" \
         "$DESCRIPTION" "Usage:" "$LIB_BOLD$EXECUTABLE <options> <subvolume>$LIB_CLEAR" "Options:" \
         "-s, --snapshots <int>" "Override how many snapshots to keep (default: 128)" \
         "-h, --help" "Print help screen and exit" \
         "-i, --info" "Print script information and exit" \
         "-v, --verbose" "More verbose output" \
         "-q, --quiet" "No output except errors (overrides -v)"
}

# Verify that input is a Btrfs subvolume
function is_subvolume() {
  if ! $($BTRFS_COMMAND subvolume show $1 >/dev/null 2>&1); then
    return 1
  fi
}


##
## Preflight
##

# Load BASH libraries
SCRIPT_PATH=$(readlink -f "$0")
SCRIPT_DIR=$(dirname "$SCRIPT_PATH")
for LIBRARY in $LIBRARIES; do
  if [[ -r "$SCRIPT_DIR/$LIBRARY" ]]; then
    #echo "Loading library file [$SCRIPT_DIR/$LIBRARY]"
    source "$SCRIPT_DIR/$LIBRARY"
  else
    echo "Error: Cannot load library file [$SCRIPT_DIR/$LIBRARY]"
    exit 1
  fi
done

# Check for root privileges
if ! lib_amiroot && [[ $REQUIRE_ROOT -eq 1 ]]; then
  lib_print "!You need to have root privileges"
  exit 1
fi

# Check for dependencies
MISSING_COMMANDS=$(lib_missing_commands $DEPENDENCIES)
if [[ -n "$MISSING_COMMANDS" ]]; then
  lib_print "!One or more commands missing [$MISSING_COMMANDS]"
  lib_print "Try installing them with your package manager"
  exit 1
fi


##
## Liftoff
##

while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do
  case $1 in
    -s|--snapshots)
      shift
      if lib_is_int $1; then
        SNAPSHOTS=$1
      else
        lib_print "!Input for --snapshots must be an intager"
        exit 1
      fi
    ;;
    -h|--help)
      H=1
    ;;
    -i|--info)
      I=1
    ;;
    -v|--verbose)
      V=1
    ;;
    -q|--quiet)
      Q=1
    ;;
    *)
      lib_print "!Unknown option [$1]"
      lib_print "Try --help or -h for available options"
      exit 1
      ;;
  esac
  shift
done

if [[ "$1" == '--' ]]; then
  shift
fi

if [[ $I -eq 1 ]]; then
  lib_print_info
  exit 0
elif [[ $H -eq 1 ]]; then
  print_help
  exit 0
fi

if [[ -z "$1" ]]; then
  print_help
  exit 0
else
  if is_subvolume "$1"; then
    SNAP_FOLDER="${1%/}/$SNAP_FOLDER"
    # Create $SNAP_FOLDER if it does not exist
    if [[ ! -d "$SNAP_FOLDER" ]]; then
      lib_print "?Creating snapshot folder because it does not yet exist [$SNAP_FOLDER]"
      mkdir "$SNAP_FOLDER"
    fi
    if [[ -d "$SNAP_FOLDER/$SNAP_NAME" ]]; then
      lib_print "?Skipping snapshot because it already exists. [$SNAP_FOLDER/$SNAP_NAME]"
    else
      # Take the snapshot
      #TODO: handle failed snapshot creations
      if $($BTRFS_COMMAND subvolume snapshot -r "$1" "$SNAP_FOLDER/$SNAP_NAME"); then
        lib_print "Created new snapshot [$SNAP_FOLDER/$SNAP_NAME]"
      else
        lib_print "!Error occured while creating new snapshot [$SNAP_FOLDER/$SNAP_NAME]"
        exit 1
      fi
   	  if [ -h "$SNAP_FOLDER/latest" ]; then
	    rm "$SNAP_FOLDER/latest"
	  fi
      ln -sf "$SNAP_FOLDER/$SNAP_NAME" "$SNAP_FOLDER/latest"
      lib_print "?Relinked latest to new snapshot [$SNAP_FOLDER/$SNAP_NAME]"
      # Delete old snapshots
      SNAPS=($(ls -r $SNAP_FOLDER | grep $SNAP_PREFIX))
      lib_print "?Snapshot retention is set to: $SNAPSHOTS"
      lib_print "?Existing snapshots found: ${#SNAPS[@]}"
      i=0
      for SNAP in ${SNAPS[@]}; do
        if [[ $i -ge $SNAPSHOTS ]]; then
	      if $($BTRFS_COMMAND subvolume delete "$SNAP_FOLDER/$SNAP"); then
		    lib_print "Deleted old snapshot [$SNAP_FOLDER/$SNAP]"
		  else
			lib_print "!Error occured while deleting old snapshot [$SNAP_FOLDER/$SNAP]"
			exit 1
		  fi
        fi
        i=$((i+1))
      done
    fi
  else
    lib_print "!Input does not appear to be a Btrfs subvolume [$1]"
    exit 1
  fi
fi


##
## Here be dragons
##

exit 0