Cron

  • Idea: daemon which executes commands periodically. F.e.: quotacheck

  • File /etc/crontab (contains 8 fields):

# setting environment variables

SHELL = /bin/bash 

PATH = /sbin:/bin:/usr/sbin:/usr/bin 

MAILTO = root 

HOME = / 

# run-parts 

0 * * * * root run-parts /etc/cron.hourly 

0 1 * * * root run-parts /etc/cron.daily 

0 1 * * 0 root run-parts /etc/cron.weekly 

0 2 1 * * root run-parts /etc/cron.monthly 

cron.* are directories containing scripts to be executed hourly, daily, weekly or monthly

Note: run-parts execute all the scripts in a directory
#DescriptionRange
1Minute0-59
2Hour0-23
3Day of Month1-31
4Month1-12
5Day of Week0-6 (0 for Sun)
6User
7Reserved Word run-parts or command
8Scripting Directory or empty

Example (running quotacheck weekly)

  • One of both:

    1. add the following script in the directory /etc/cron.weekly:

      /sbin/quotacheck -g && exit 0

    2. add the following line in /etc/crontab:

      0 1 * * 0 root /sbin/quotacheck -g