How To Lock Cron Job From Overruning In Linux

Just donwload http://www.unixwiz.net/tools/lockrun.c

# compile it
$ gcc lockrun.c -o lockrun
$ sudo cp lockrun /usr/bin/

# add to cron job e.g in single line

*/5 * * * * /usr/bin/lockrun --lockfile=/var/run/mcron.lockrun -- /usr/bin /mcron.sh

# -- before name of cronjob is necessary