Background rsync and pid from a shell script

I have a shell script that does a backup. I set this script in a cron but the problem is that the backup is heavy so it is possible to execute a second rsync before the first ends up. I thought to launch rsync in a script and then get PID and write a file that script checks if the process exist or not (if this file exist or not). If I put rsync in background I get the PID but I don’t know how to know when rsync ends up but, if I set rsync (no background) I can’t get PID before the process finish so I can’t write a file whit PID.

I don’t know what is the best way to “have rsync control” and know when it finish.

My script

#!/bin/bash
pidfile="/home/${USER}/.rsync_repository"

if [ -f $pidfile ];
then
        echo "PID file exists " $(date +"%Y-%m-%d %H:%M:%S")
else
        rsync -zrt --delete-before /repository/ /mnt/backup/repositorio/ < /dev/null &
        echo $$ > $pidfile
        # If I uncomment this 'rm' and rsync is running in background, the file is deleted so I can't "control" when rsync finish
        # rm $pidfile 
fi

Can anybody help me?!

Thanks in advance !! 🙂

Answer

# check to make sure script isn't still running
# if it's still running then exit this script

sScriptName="$(basename $0)"

if [ $(pidof -x ${sScriptName}| wc -w) -gt 2 ]; then 
    exit
fi

• pidof finds the pid of a process
• -x tells it to look for scripts too
• ${sScriptName} is just the name of the script…you can hardcode this
• wc -w returns the word count by words
• -gt 2 no more than one instance running (instance plus 1 for the pidof check)
• if more than one instance running then exit script

Let me know if this works for you.