Linux: cron jobs

Linux cron tab format

MIN HOUR DOM MON DOW CMD

Field	Description	Allowed Value
MIN	Minute	0-59
HOUR	Hour	0-23
DOM	Day of Month	1-31
MON	Month	1-12
DOW	Day of the week	0-6
CMD	Command	Any command to execute

view/edit crontab

$ crontab -l → To view crontab
$ crontab -e → Edit crontab
$ crontab -u otherusername -e → Edit other user crontab

=== Schedule a job every 5 minutes

*/5 * * * * /home/ramesh/backup.sh

Schedule a job for a specific day

example: 10th June 08:30 AM.

30 08 10 06 * /home/ramesh/full-backup

• 30 – 30th Minute
• 08 – 08 AM
• 10 – 10th Day
• 06 – 6th Month (June)
• * – Every day of the week

Schedule a job twice a day

00 11,16 * * * /home/ramesh/bin/incremental-backup

• 00 – 0th Minute (Top of the hour)
• 11,16 – 11 AM and 4 PM
• * – Every day
• * – Every month
• * – Every day of the week

Schedule a job during working hours

00 09-18 * * * /home/ramesh/bin/check-db-status

• 00 – 0th Minute (Top of the hour)
• 09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
• * – Every day
• * – Every month
• * – Every day of the week

Schedule a job during working hours excluding Saturday and Sunday

00 09-18 * * 1-5 /home/ramesh/bin/check-db-status

• 00 – 0th Minute (Top of the hour)
• 09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
• * – Every day
• * – Every month
• 1-5 -Mon, Tue, Wed, Thu and Fri (Every Weekday)

Cron jobs special codes

Keword	Equivalent
@yearly	0 0 1 1 *
@daily	0 0 * * *
@hourly	0 * * * *
@reboot	Run at startup.

@yearly /home/ramesh/red-hat/bin/annual-maintenance
@monthly /home/ramesh/suse/bin/tape-backup
@daily /home/ramesh/arch-linux/bin/cleanup-logs "day started"
@reboot CMD

Adding paths to cron jobs

Add the following line to crontab to specify the location of the scriptss (/home/user/scripts)
This will allow to avoid having to type the full path to the script

PATH=/bin:/sbin:/usr/bin:/usr/sbin:/home/user/scripts