Command scheduling with cron

The system schedules are setup when the package is installed, via the creation of some special directories:

/etc/cron.d
/etc/cron.daily
/etc/cron.hourly
/etc/cron.monthly
/etc/cron.weekly

To display your file you run the following command:

crontab -l

root can view any users crontab file by adding “-u username”, for example:

crontab -u skx -l  # List skx's crontab file.

1. The number of minutes after the hour (0 to 59)
2. The hour in military time (24 hour) format (0 to 23)
3. The day of the month (1 to 31)
4. The month (1 to 12)
5. The day of the week(0 or 7 is Sun, or use name)
6. The command to run

*     *     *     *     *  Command to be executed
-     -     -     -     -
|     |     |     |     |
|     |     |     |     +----- Day of week (0-7)
|     |     |     +------- Month (1 - 12)
|     |     +--------- Day of month (1 - 31)
|     +----------- Hour (0 - 23)
+------------- Min (0 - 59)

To edit your crontabe file run:

crontab -e

Examples:

# Run the `something` command every hour on the hour
0   *   *   *   * /sbin/something

# Run the `nightly` command at ten minutes past midnight every day
10  0   *   *   * /bin/nightly

# Run the `monday` command every monday at 2 AM
0   2   *   *   1  /usr/local/bin/monday

Command scheduling with cron: link

The quick and simple editor for cron schedule expressions: link