rsync-snapshot

#!/bin/dash

user_id="$(\id -u)" || exit $?

[ "$user_id" != 0 ] && \
  printf '%s\n' "$0: Permission denied." 'Need root access.' && \
  exit 2

backup_dir='/root/backup'
target_snapshot='/'
exclude_file='./exclude.list'
device="${dev:-nvme0n1p3}"

[ ! -z "$dry_run" ] && dry_run='--dry-run'

[ ! -z "$1" ] && {
  echo "Mounting /dev/$device at $backup_dir"
  mount --mkdir /dev/$device $backup_dir || exit $?
}

list_snapshot="$(\find $backup_dir/ -mindepth 1 -maxdepth 1 -type d | sort -nr)" || exit "$?"

[ ! -z "$list_snapshot" ] && \
  prev_snapshot="$(printf '%s\n' "$list_snapshot" | head -1)/snapshot/"

current_date="$(date +'%F_%H-%M-%S')"

unmount_dev() {
  echo "Unmounting /dev/$device"
  umount -l /dev/$device
}

rsync_cmd() {
  rsync \
    -a \
    --delete \
    --numeric-ids \
    --exclude-from="$exclude_file" \
    --sparse \
    --info=progress2,stats2 \
    $dry_run \
    $* || {
    local rsync_exit_code="$?"
      unmount_dev
      exit $rsync_exit_code
    }

    unmount_dev
}

backup() {
  # so that we can create the log file.
  # seems like `--mkpath` comes after creating log file.
  [ -z "$dry_run" ] && \
    \mkdir -p "$backup_dir/$current_date" && \
    log_file="--log-file=$backup_dir/$current_date/changes.log"

  if [ ! -z "$prev_snapshot" ]; then
    echo "Hard link $prev_snapshot"
    rsync_cmd \
      --link-dest="$prev_snapshot" \
      --mkpath $log_file \
      "$target_snapshot" "$backup_dir/$current_date/snapshot/"

  else
    rsync_cmd \
      --mkpath $log_file \
      "$target_snapshot" "$backup_dir/$current_date/snapshot/"
  fi
}

restore() {
  if [ ! -z "$1" ]; then
    local grep_snapshot
    grep_snapshot="$(printf '%s\n' "$list_snapshot" | \grep $1)" || {
      local exit_code="$?"
      [ "$exit_code" = 1 ] || exit "$exit_code"
    }

    [ ! -z "$grep_snapshot" ] && selected_snapshot="$grep_snapshot/snapshot/"

  else
    selected_snapshot="$prev_snapshot"
  fi

  # after update the system,
  # we need to reexecute systemd manager after restore from snapshot before
  # update.
  # also, check whether we are in chroot environment or not before reexecute
  # or reload systemd.
  # reference on arch linux:
  # - /usr/share/libalpm/scripts/systemd-hook
  # - /usr/bin/checkservices
  if [ ! -z "$selected_snapshot" ]; then
    echo "Restoring from $selected_snapshot"
    rsync_cmd "$selected_snapshot" "$target_snapshot"

    if $(stat -c %d:%i / /proc/1/root/ | awk -v RS= '{exit $1 != $2}') && \
      [ -d /run/systemd/system ] && \
      command -v systemctl >/dev/null && \
      [ -z "$dry_run" ]; then

      if grep -qF '(deleted)' /proc/1/maps; then
        echo 'Restart systemd system...'
        systemctl --system daemon-reexec || exit $?
      else
        echo 'Reload systemd system...'
        systemctl --system daemon-reload || exit $?
      fi

    else
      echo 'Skipping systemd restart/reload'
      exit
    fi

  else
    echo 'There is no snapshot, nothing to restore.'
    unmount_dev
    exit 1
  fi
}

ls() {
  [ ! -z "$list_snapshot" ] && {
    printf '%s\n' "$list_snapshot" | sed --expression='s/[a-z/]//g'
  }
  unmount_dev
}

remove() {
  {
    {
      [ ! -z "$1" ] || {
        echo 'Please specify snapshot to remove.'
        unmount_dev
        exit 1
      }
    } && {
      [ -d "$backup_dir/$1" ] || {
        echo "Snapshot $1 not found."
        unmount_dev
        exit 1
      }
    }
  } && {
    echo "Removing snapshot $backup_dir/$1"
    \rm -r "$backup_dir/$1"
    echo "Removed"

    unmount_dev
  }
}

case "$1" in
  backup)
    backup
    ;;
  restore)
    restore "$2"
    ;;
  ls)
    ls
    ;;
  rm)
    remove "$2"
    ;;
  *)
    printf "Usage:
- [dry_run=1] [dev=sda1, check lsblk] $0 backup
- [dry_run=1] [dev=sda1, check lsblk] $0 restore [year-month-date_hour-minute-second]
- $0 ls
- $0 rm year-month-date_hour-minute-second\n"
    ;;
esac