How to check in a bash script if something is running and exit if it is

Question

I have a script that runs every 15 minutes but sometimes if the box is busy it hangs and the next process will start before the first one is finished creating a snowball effect.

Answer 1

This is how I do it in one of my cron jobs

lockfile=~/myproc.lock
minutes=60
if [ -f "$lockfile" ]
then
  filestr=`find $lockfile -mmin +$minutes -print`
  if [ "$filestr" = "" ]; then
    echo "Lockfile is not older than $minutes minutes! Another $0 running. Exiting ..."
    exit 1
  else
    echo "Lockfile is older than $minutes minutes, ignoring it!"
    rm $lockfile
  fi
fi

echo "Creating lockfile $lockfile"
touch $lockfile

and delete the lock file at the end of the script

echo "Removing lock $lockfile ..."
rm $lockfile