How can I set cron to run certain commands every one and a half hours?

Question

How can I set cron to run certain commands every one and a half hours?

Answer 1

#! /bin/sh

# Minute Cron
# Usage: cron-min start
# Copyright 2014 by Marc Perkel
# docs at http://wiki.junkemailfilter.com/index.php/How_to_run_a_Linux_script_every_few_seconds_under_cron"
# Free to use with attribution

# Run this script under Cron once a minute

basedir=/etc/cron-min

if [ $# -gt 0 ]
then
   echo
   echo "cron-min by Marc Perkel"
   echo
   echo "This program is used to run all programs in a directory in parallel every X minutes."
   echo
   echo "Usage: cron-min"
   echo
   echo "The scheduling is done by creating directories with the number of minutes as part of the"
   echo "directory name. The minutes do not have to evenly divide into 60 or be less than 60."
   echo
   echo "Examples:"
   echo "  /etc/cron-min/1      # Executes everything in that directory every 1  minute"
   echo "  /etc/cron-min/5      # Executes everything in that directory every 5  minutes"
   echo "  /etc/cron-min/13     # Executes everything in that directory every 13 minutes"
   echo "  /etc/cron-min/90     # Executes everything in that directory every 90 minutes"
   echo
   exit
fi

for dir in $basedir/* ; do
   minutes=${dir##*/}
   if [ $(( ($(date +%s) / 60) % $minutes )) -eq 0 ]
   then
      for program in $basedir/$minutes/* ; do
     if [ -x $program ]
     then
        $program &> /dev/null &
     fi
      done
   fi
done

Answer 2

Two lines in the crontab. Along the lines of:

0 0,3,6,9,12,15,18,21 * * * /usr/bin/foo
30 1,4,7,10,13,16,19,22 * * * /usr/bin/foo

Answer 3

*/10 * * * * root perl -e 'exit(time()%(90*60)>60)' && command

90 — it is one and a half hour in minutes

"> 60" — I give to cron ability to delay the start of script during a minute

Also with help of this hack you can set any period with a minute resolution

For example start the script every 71 minutes

* * * * * root perl -e 'exit(time()%(71*60)>60)' && command