scripts to initiate a backup from a source Synology NAS

do_backup.sh

#!/bin/sh
# this script will initiate a backup from a source Synology NAS
# 'challenges'
# - there's no blocking means to run a backup task (i.e. a command to start a
#   backup task and not return until it's complete); instead we only have
#   asynchronous actions to start a task and then later check state
# - it takes some period of time to actually start the task, i.e. starting a
#   backup and immediately checking backup state will likely (incorrectly)
#   return "not running"
# - there appears to be no way to actually tell if the backup succeeded or not,
#   other than inspecting the log file (sigh)
#   - the synobackup.log file access permissions are borked on DSM 7 (not
#     sufficient to just be in the `log` group)
#   - thus the user this script runs as needs to be in the `wheel` group so as
#     to be able to sudo without a password (ref. /etc/sudoers),
#     e.g. for the user `offsite`:
#     synogroup --memberadd wheel offsite
#     (will also need to be in `administrators` in order to ssh)
#
# - the synobackup utility requires the 'task id', however there is no simple
#   way of determining the task ID for a task created via the UI
#   - prior to Hyperbackup 4.1.0 the task ID was listed in
#     /usr/syno/etc/synobackup.conf ('ini' format, unparseable)
#     however that file no longer exists and the task ID appears to be
#     indeterminable.
#     - fortunately it appears to be simply an index starting from 1,
#       incremented whenever a new task is created; moreover passing an invalid
#       task id appears to have no harm
#       i.e. invoke synobackup with a task ID of 1, increment until you see
#       (in the UI) the job you want to run actually start

TASK_ID="$1"

HOSTNAME="$(hostname)"

log () {
  echo "$(date) [${HOSTNAME}] $*"
}

if [ $# -eq 0 ]; then
  echo "usage: $0 <task id>" >&2
  exit 1
fi

# synobackup does not provide any means to check whether
# a backup worked (e.g. result of last backup); have to resort to
# monitoring the log...
# - don't want the whole log, only what's added during our run
# - intermingle log output with ours, "FYI"
logfile=$(mktemp)
# shellcheck disable=SC2024 # just want to run tail elevated, not > file
sudo tail -n0 -f /var/log/synolog/synobackup.log > "$logfile" &
logpid=$!

_exit() {
  log "exiting"
  # stop the log tail (wait to suppress shell "Terminated" messsage)
  # by design, sudo will not relay signals that were sent by the same process
  # group (see sudo doc); so run the kill in a new session
  setsid kill "$logpid" && wait "$logpid" 2>/dev/null
  # did it work? ugh
  rc=1
  if ! grep -q -i started "$logfile"; then
    log "failed to start?"
  else
    grep -q -i success "$logfile"
    rc=$?
    if [ $rc -ne 0 ]; then
      log "failed?"
    fi
  fi
  # what happened? (if anything)
  log "synobackup.log:"
  cat "$logfile"
  rm "$logfile"
  exit "$rc"
}
trap _exit EXIT

# no sudo, plain ol' admins can kick off a backup...
/usr/syno/bin/synobackup --backup "${TASK_ID}" --type image
case $? in
  0)
    log "backup task ID ${TASK_ID} started"
	;;
  153)
    log "backup task  ID ${TASK_ID} already running?"
    exit 1
    ;;
  *)
    log "failed to start backup task  ID ${TASK_ID}"
    exit 1
    ;;
esac

is_backup_running() {
  # synobackup's exit status is backwards:
  #   0 (i.e. success/true) if not running
  #   1 (i.e. error/false) if running
  if /usr/syno/bin/synobackup --is-backup-restore-running; then
    return 1
  fi
  return 0
}

# can take a moment before synobackup reports the task state, so sleep up front
# "give up"logic: things don't always go to plan:
#   wait till the backup ends; increasing intervals, to a total of ~30 hrs
for s in $(seq 90 15 1800) -1; do 
  if [ "${s}" -lt 0 ]; then
    log "failed to report stop"
    exit 2
  fi
  sleep "$s"
  if ! is_backup_running; then
    break
  fi
  log "in progress"
done

pull_backup.sh

#!/bin/sh
# this script will initiate a backup from a source Synology NAS
# - before deploying this script via the Synology task scheduler: the backup
#   source's ssh host key needs to be recorded in ~/.ssh/known_hosts; to do so
#   - as the user that will run this script in the Synology task scheduler -
#   invoke this script with any argument, e.g. sudo ./pull_backup.sh nasadmin@100.x.x.x
# - this script needs to be run as root so as to be able to call shutdown
# - invoke with arg1 as target username@host; arg2 as the backup script on the target
#   - in turn, the backup script requires the synobackup task ID
#   e.g.
#   sudo $0 nasadmin@100.x.x.x ./do_backup.sh 3

HOSTNAME="$(hostname)"

log () {
  echo "$(date) [${HOSTNAME}] $*"
}


ssh_with_args() {
  # adjust as needed
  ssh "$SSH_TARGET" \
    -o ControlMaster=auto -o ControlPersist=5m -o ControlPath=~/.ssh/cm-%r@%h:%p \
    "$@"
}

if [ $# -eq 0 ]; then
  echo "usage: $0 user@host dobackup_script [dobackup_script args]" >&2
  exit 1
fi

SSH_TARGET="$1"
shift

# if invoked with just one argument, do a "ssh host key scan" and exit
# note: synology doesn't provide ssh-keyscan...
if [ $# -eq 0 ]; then
  ssh_with_args -o StrictHostKeyChecking=no exit
  exit
fi

# shutdown will be suppressed if, when the backup ends:
# - anyone is logged in via ssh
# - this file is present:
NOSHUTDOWN="$0.noshutdown"

do_shutdown() {
  # return true if shutdown should proceed
  [  -e "${NOSHUTDOWN}" ] && return 1
  who --short | grep -q '.' && return 1
  return 0
}

# can take a moment for ssh to get going (e.g. VPN/tunnel to establish)
for s in $(seq 30 15 90) -1; do
  if [ "${s}" -lt 0 ]; then
    log "failed to connect (ssh)"
    exit 1
  fi
  if ssh_with_args true; then
    log "connected"
    break
  fi
  log "waiting to connect"
  sleep "$s"
done

if ! ssh_with_args "$@"; then
  log "failed"
  exit 1
fi

log "success"
# shutdown ignores arguments; certainly time; so DIY
# this is important: need to provide opportunity to fix things
if do_shutdown; then
  log "shutting down"
  # leave the pending shutdown run in the background, so as to let any email report/etc go out
  nohup sh -c 'sleep 300 && shutdown --poweroff' >/dev/null &
fi