Cron is the daemon that can be used to schedule tasks according to time, day of the month, month, day of the week, and week.
In order to use cron you must have:
1. a package vixie-cron installed.
To check it type:
rpm -q vixie-cron
2. Daemon crond must be running. To check it type:
service crond status
To install crond on Centos type:
yum install vixie-cron
If you want to add some task to cron you must place it in the file
Sample crontab config:
SHELL=/bin/bash PATH=/sbin:/bin:/usr/sbin:/usr/bin MAILTO=root HOME=/ # For details see man 4 crontabs # Example of job definition: # .---------------- minute (0 - 59) # | .------------- hour (0 - 23) # | | .---------- day of month (1 - 31) # | | | .------- month (1 - 12) OR jan,feb,mar,apr ... # | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat # | | | | | # * * * * * user-name command to be executed 01 00 * * thu,sat root /scripts/./backupvm
Scheduled task is a script ./backupvm which is in folder /scripts. Script is starting as root at 0:01 any day of month, any month, but two days a week: THU an SAT.
On some OS distros you should use
command to edit cron tasks. You can switch to your preferred editor. For example to nano:
EDITOR=nano; export EDITOR
After run again "crontab -e" And place the task. For example we apply to start some script every minute:
* * * * * root /./vpncheck.sh >>/testlog.log
Every 2 minutes:
*/2 * * * * root /./vpncheck.sh >>/testlog.log
Every time when system starts:
@reboot root /./vpncheck.sh >>/testlog.log