Running a cron job at 2:30 AM everyday

crontab -e

add:

30 2 * * * /your/command

1. To edit:

   crontab -e
   

2. Add this command line:

   30 2 * * * /your/command
   

   • Crontab Format:

     MIN HOUR DOM MON DOW CMD

   • Format Meanings and 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
   • CMD Command Any command to be executed.

3. Restart cron with latest data:

   service crond restart
   

As seen in the other answers, the syntax to use is:

  30 2 * * * /your/command
# ^  ^
# |   hour
# minute

Following the crontab standard format:

 +---------------- minute (0 - 59)
 |  +------------- hour (0 - 23)
 |  |  +---------- day of month (1 - 31)
 |  |  |  +------- month (1 - 12)
 |  |  |  |  +---- day of week (0 - 6) (Sunday=0 or 7)
 |  |  |  |  |
 *  *  *  *  *  command to be executed

It is also useful to use crontab.guru to check crontab expressions.

The expressions are added into crontab using crontab -e. Once you are done, save and exit (if you are using vi, typing :x does it). The good think of using this tool is that if you write an invalid command you are likely to get a message prompt on the form:

$ crontab -e
crontab: installing new crontab
"/tmp/crontab.tNt1NL/crontab":7: bad minute
errors in crontab file, can't install.
Do you want to retry the same edit? (y/n) 

If you have further problems with crontab not running you can check Debugging crontab or Why is crontab not executing my PHP script?.