Cron is a Unix, Solaris utility that allows scheduling of tasks tasks, which run in the background at regular intervals. These tasks are often termed as cron jobs and Crontab (CRON TABle) is a file which contains the schedule of cron entries to be run and at specified times.
This document covers following aspects of Unix cron jobs
1. Who can execute Crontab?
You can execute crontab if your name appears in the file /usr/lib/cron/cron.allow.
If the above file does not exist, you can use crontab if your name does not appear in the file /usr/lib/cron/cron.deny.
If only cron.deny exists and is empty, all users can use crontab. If neither file exists, only the root user can use crontab. The
All users can use crontab if only cron.deny exists and is empty.
If neither file exists, only the root user can use crontab.
2. Crontab Commands
crontab -e : Edit your crontab file, or create one if it doesn’t already exist.
crontab -l : Display your crontab file.
crontab -r : Remove your crontab file.
crontab -v : Display the last time you edited your crontab file. (This option is only available on a few systems.)