MacOS Time Machine helper

README.md

MacOS High Sierra Timemachine helper

Adapted from the posting at https://forums.macrumors.com/threads/automatically-unmount-external-hd-after-time-machine-backup.1057661/#post-26190076

Personally, I run this hourly via crontab, with something like:

$ crontab -l
0 * * * * /bin/sh /absolute/path/to/macos_timemachine_helper/timemachine_helper.sh "My Backup Drive"

with /absolute/path/to and My Backup Drive adjusted accordingly.

timemachine_helper.sh

#!/bin/sh
# Check for a backup today, if none then mount the Time Machine volume
# and wait for Time Machine to run.  When the backup is over, unmount
# the Time Machine volume and exit.

# Set these variables or else
# for TMVOLUME ls -l /Volumes/ and paste the entire path including spaces in the
# quotes replace 'backup drive' below, TMFREQ is how recently you care to look
# for a backup

set -x

TMVOLUME=${1:?The name of the backup drive must be provided!}
TMFREQ=${2:-12h}

DISKUTIL=/usr/sbin/diskutil
LOCKFILE="/tmp/$(basename $0).lock"

TMUUID="$($DISKUTIL info "$TMVOLUME" | grep 'Volume UUID' | cut -f 2 -d ':'| awk '{$1=$1};1')"

function check_log() {
  log show --style syslog  --predicate 'senderImagePath contains[cd] "TimeMachine" AND eventMessage contains[cd] "Backup completed successfully"' --info --last $TMFREQ| grep -v 'Filtering\|Timestamp'
}

function do_mount() {
  # See if the Time Machine volume is mounted
  # and if it isn't, mount it.
  while ! test_dir; do
    $DISKUTIL mountDisk "$TMUUID"

    if test_dir; then
      echo "Mounted..."
      break
    else
      echo "Failed to mount? Will try again in 10 seconds."
      sleep 10
    fi
  done
}

function test_dir() {
  local DIR="/Volumes/$TMVOLUME"
  test -d "$DIR"
  local RESULT=$?

  if [ $RESULT == "0" ]; then
    echo "$DIR exists."
  else
    echo "$DIR doesn't exist."
  fi

  return $RESULT
}

function do_unmount() {
  # Unmount the Time Machine volume and exit
  while test_dir; do
    $DISKUTIL unmountDisk "$TMUUID"

    if test_dir; then
      echo "Unmounted..."
      break
    else
      echo "Failed to unmount? Will try again in 10 seconds."
      sleep 10
    fi
  done
}

function mount_backup_and_unmount() {
  if ! check_log; then
    # No backup yet today.
    do_mount

    # Wait a while for Time Machine to wake up and do a backup
    while ! check_log; do
      sleep 300
    done
  fi

  # Backup completed (or none necessary), unmount the Time Machine volume if
  # mounted and exit
  do_unmount
}

if shlock -d -f $LOCKFILE -p $$; then
  mount_backup_and_unmount
  rm $LOCKFILE
fi