crontab

Cron
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
02 minutes after an hour

22 4 * * 0 root run-parts /etc/cron.weekly

To run /root/script/backup at 23:00, every day, enter
# crontab -e
0 23 * * * /root/script/backup

Run foo job very weekday (MON-Fri) at 6am, enter:
0 6 * * 1-5 /root/script/backup

1 0 * * * printf > /www/apache/logs/error_log



* * * * * command to be executed
┬ ┬ ┬ ┬ ┬
│ │ │ │ │
│ │ │ │ │
│ │ │ │ └───── day of week (0 - 7) (Sunday=0 or 7)
│ │ │ └────────── month (1 - 12)
│ │ └─────────────── day of month (1 - 31)
│ └──────────────────── hour (0 - 23)
└───────────────────────── min (0 - 59)

-------------------

1. Scheduling a Job For a Specific Time
10th June 08:30 AM

Please note that the time field uses 24 hours format. So, for 8 AM use 8, and for 8 PM use 20.

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

2. Schedule a Job For More Than One Instance (e.g. 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 wee

3. Schedule a Job for Specific Range of Time (e.g. Only on Weekdays)

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)


How to View Crontab Entries?

ramesh@dev-db$ crontab -l
@yearly /home/ramesh/annual-maintenance
*/10 * * * * /home/ramesh/check-disk-space

[Note: This displays crontab of the current logged in user]


How to Edit Crontab Entries?
ramesh@dev-db$ crontab -e
@yearly /home/ramesh/centos/bin/annual-maintenance
*/10 * * * * /home/ramesh/debian/bin/check-disk-space
~
"/tmp/crontab.XXXXyjWkHw" 2L, 83C


Edit Root Crontab entries
Login as root user (su – root) and do crontab -e as shown below.

root@dev-db# crontab -e


Schedule a Job for Every Minute Using Cron.
 * * * * * CMD

 Schedule a Background Cron Job For Every 10 Minutes.
 */10 * * * * /home/ramesh/check-disk-space

 Schedule a Cron Job Beginning of Every Month using @monthly
 @monthly /home/ramesh/suse/bin/tape-backup


Installing Crontab From a Cron File
Instead of directly editing the crontab file, you can also add all the entries to a cron-file first. Once you have all thoese entries in the file, you can upload or install them to the cron as shown below.

ramesh@dev-db$ crontab -l
no crontab for ramesh

$ cat cron-file.txt
@yearly /home/ramesh/annual-maintenance
*/10 * * * * /home/ramesh/check-disk-space

ramesh@dev-db$ crontab cron-file.txt

ramesh@dev-db$ crontab -l
@yearly /home/ramesh/annual-maintenance
*/10 * * * * /home/ramesh/check-disk-space