Setting up "CRON" Jobs in Linux
If you want to use the emacs editor for editing cron jobs, then, set the following in your "/home/user/.bash_profile"
EDITOR=emacs
Then, to edit cron jobs
$ crontab -e
You may want to put in the following header
#MINUTE(0-59) HOUR(0-23) DAYOFMONTH(1-31) MONTHOFYEAR(1-12) DAYOFWEEK(0-6) Note 0=Sun and 7=Sun
#
#14,15 10 * * 0 /usr/bin/somecommmand >/dev/null 2>&1
The sample "commented out command" will run at 10:14 and 10:15 every Sunday. There will be no "mail" sent to the user because of the ">/dev/null 2>&1" entry.
$ crontab -l
The above will list all cron jobs. Or if you're root
$ crontab -l -u <username>
$ crontab -e -u <username>
Reference "man 5 crontab":
The time and date fields are:
field allowed values
----- --------------
minute 0-59
hour 0-23
day of month 1-31
month 1-12 (or names, see below)
day of week 0-7 (0 or 7 is Sun, or use names)
A field may be an asterisk (*), which always stands for ``first-last''.
Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. The specified range is inclusive. For example, 8-11 for an ``hours'' entry specifies execution at hours 8, 9, 10 and 11.
Lists are allowed. A list is a set of numbers (or ranges) separated by commas. Examples: ``1,2,5,9'', ``0-4,8-12''.
Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".
Note, you can run just every 5 minutes as follows:
*/5 * * * * /etc/mrtg/domrtg >/dev/null 2>&1
To run jobs hourly,daily,weekly or monthly you can add shell scripts into the
appropriate directory:
/etc/cron.hourly/
/etc/cron.daily/
/etc/cron.weekly/
/etc/cron.monthly/
Note that the above are pre-configured schedules set in "/etc/crontab", so if you want, you can change the schedule. Below is my /etc/crontab:
$ cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/
# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly