Schedule A Unix Cron Job

Filed in archive on September 8, 2006

When scheduling a cron job each column indicates a different time period:

minute hour [Day of Month] [Month] [Day of Week]

Thus, to schedule a job to run at 5 minutes after every hour:

5 * * * * /job

every five minutes:

0-59/5 * * * * /job

some versions of cron allow the abbreviation: */5 * * * * /job

every hour on the hour:

0 * * * * /job

On the first of every month (at 1 am):

0 1 1 * * /job

---

Field Meaning

1 Minute (0-59)

2 Hour (2-24)

3 Day of month (1-31)

4 Month (1-12, Jan, Feb, ...)

5 Day of week (0-6) 0 = Sunday, 1 = Monday, ... or Sun, Mon, etc)

6 Command to execute

Some versions of cron allow an extra field before the command to
specify the user that the command will run as.

---

35 2 * * * root tar czf /usr/local/backups/daily/abc.tar.gz /abc >/dev/null 2>&1
This will run tar czvf /usr/local/backups/daily/abc.tar.gz /abc at 2:35am every day.
The > /dev/null 2>&1 part means to send any standard output to /dev/null and
to redirect standard error (2) to the same place as the standard output (1).
Basically it runs the command without any output to a terminal.