Crontab in my opinion is a job scheduler, with crontab you can make some program at a specified time that you define. Now lets just started with the configuration. To know if the user that you’re using is allowed to make a crontab you must check if your user is in /etc/crontab.deny then you cannot make a crontab job.
There are several option in crontab command
crontab -e #this will enable you to make or edit your crontab job
crontab -l #this will show you the current crontab job
crontab -r #this will remove your crontab jobs
When you’re editing crontab, here is some of the syntax that will be used
* * * * * command to be executed
– – – – –
| | | | |
| | | | +—– day of week (0 – 6) (Sunday=0)
| | | +——- month (1 – 12)
| | +——— day of month (1 – 31)
| +———– hour (0 – 23)
+————- min (0 – 59)
Lets see some of the example:
- 30 4 * * 0 cp /home /backup
this means that every Sunday at 4.30 am, it will copy folder /home into /backup
- 0 1 7 7 * /sbin/reboot
this means that in july 7th at 1.00 am, the computer will be rebooted
More in crontab you can make it to execute a file that contain several commands, like this one:
- 15 4 * * 7 /home/admin/test.sh
inside /home/admin/test.sh
cd /home
find -name “*.mp3*” -print -exec /bin/rm -f ‘{}’ +
quotaoff -avug
quotacheck -avugm
quotaon -avug
repquota -a
this file will do; go to the home directory, find all the file that contain .mp3, print them, delete them, turn off the quota, check the quota, turn it on again, and give the summary of quota.
Xanadu 