lock

#!/bin/bash

# This file will act as a mutex lock to ensure that only one
# instance of a command will be running at a time. It uses a lock
# file to check if another instance of the command is already
# running. If not, we create the lock file and "obtain" the lock.
# The lock file contains this process's PID. If the lock file
# exists, but that PID is not running, we assume the lock is
# free.

# Define constants
LOCKFILE="/share/Web/bin/epic-shelter/backup.lock"
# This is the location of my puch notification scripts. They use
# pushover.com to send a notification using cURL. Becuase they
# contain API keys, they're not a part of the public repo.
PUSH_NOTIFICATION_DIRECTORY="/share/Web/bin/push_notifications/backups"

# If there is a lockfile AND that PID is still active
if [ -e ${LOCKFILE} ] && kill -0 `cat ${LOCKFILE}`; then
  # Push a notification that the backup did not start...
	$PUSH_NOTIFICATION_DIRECTORY/push-high \
		"Backup not started" \
		"A backup is already running. Check for an undeleted lockfile?"
  # And exit
	exit
fi

# make sure the lockfile is removed when we exit and then claim it
trap "rm -f ${LOCKFILE}; exit" INT TERM EXIT
echo $$ > ${LOCKFILE}

# do stuff
/share/Web/bin/epic-shelter/backup-videos
/share/Web/bin/epic-shelter/backup-plex-db
/share/Web/bin/epic-shelter/backup-photos

# Delete the lock file
rm -f ${LOCKFILE}