Cron is time-based job scheduler. People who set up and maintain software environments use cron to schedule jobs (commands or shell scripts) to run periodically at fixed times, dates, or intervals.
Cron is driven by a crontab (cron table) file, a configuration file that specifies shell commands to run periodically on a given schedule. The crontab files are stored where the lists of jobs and other instructions to the cron daemon are kept. Users can have their own individual crontab files and often there is a system wide crontab file (usually in /etc or a subdirectory of /etc) that only system administrators can edit.
Linux Crontab Format
1. How to list crontab entries
2. How to edit and add crontab entries
3.Schedule a Job for Every Minute Using Cron
4.Schedule a Background Cron Job For Every 10 Minutes
5.Scheduling a Job For a Specific Time
6. Schedule a Job For More Than One Instance
00 - 0 minute
09 - 9 am
19 - 7 pm
job will run in both timings 9:00 & 19:00.
7 .Schedule a Job for Specific Range of Time
job will run from 9:00 to 19:00 every one hour.
8. Cron for visiting URL
Cron is driven by a crontab (cron table) file, a configuration file that specifies shell commands to run periodically on a given schedule. The crontab files are stored where the lists of jobs and other instructions to the cron daemon are kept. Users can have their own individual crontab files and often there is a system wide crontab file (usually in /etc or a subdirectory of /etc) that only system administrators can edit.
Linux Crontab Format
* * * * * /path-of-script
(min) (hour) (dom) (mon) (dow )
Field Description Allowed Value
MIN Minute field 0 to 59
HOUR Hour field 0 to 23
DOM Day of Month 1-31
MON Month field 1-12
DOW Day Of Week 0-6
1. How to list crontab entries
root@linuxstorage:~#crontab -l
2. How to edit and add crontab entries
root@linuxstorage:~#crontab -e
3.Schedule a Job for Every Minute Using Cron
* * * * * . /path-of-script
4.Schedule a Background Cron Job For Every 10 Minutes
*/10 * * * * /path-of-script
5.Scheduling a Job For a Specific Time
30 09 10 08 * /path-0f-scriptjob will run at Aug month(8 month) , 10 day , 9.30 time(am).
6. Schedule a Job For More Than One Instance
00 09,19 * * * /path-of-script
00 - 0 minute
09 - 9 am
19 - 7 pm
job will run in both timings 9:00 & 19:00.
7 .Schedule a Job for Specific Range of Time
00 09-19 * * * /path-of-script09 - 19 = time from 9 to 19. 9,10,11,12,13,14,15,16,17,18 & 19.
job will run from 9:00 to 19:00 every one hour.
8. Cron for visiting URL
* * * * * /usr/bin/wget http://your-website/cron.php
* * * * * /usr/bin/curl http://your-website/cron.php
* * * * * /usr/bin/wget -q -o http://your-website/cron.php
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