Setting up cron
jobs using crontab.
This guide will show you how to setup a conjob
using the crotab.
To install a cronjob, you will want to follow the following steps.
1. Enter username into following file:
user@UnixBox ~# vi /etc/cron.allow
Note: Be sure there is a blank line at the end of the file. You can always use a different text editor but this guide is showing it using vi.
2. Run crontab command:
- if you are logged in as root:
user@UnixBox ~# crontab -e -u username
Note: Here the username is the username owner of the cronjob.
- if you are logged in as the username that will be owner of the crontab:
user@UnixBox ~# crontab -e
Note: This can be executed as any user including the root if you are going to set a cronjob owned by the root.
The following is the syntax of the crontab:
[minute] [hour] [day of month] [month] [day of week] COMMAND
| field |
allowed values
|
| minute
|
0-59
|
| hour
|
0-23
|
| day of month
|
1-31
|
| month
|
1-12
|
| day of week
|
0-7 (0 or 7 is Sun)
|
You should prepend the COMMAND with nice.
nice is a program
that gives a given command a given priority. The default is 10. The
range is from -20 to 20 with -20 being the highest priority.
Here is an example of running a nice'd command in the
www/cgi-bin directory of a user every day at 11 PM (2300).
0 23 * * *
nice ~/www/cgi-bin/command
~/ = current users home directory.. You should not have to,
but you
can also use ~username/ to further specify the given user. This is
useful in case a process is launched by another user.
The "nice" option is used to limit the amount of resources
that
a cronjob can use. In some instances, you do not want to use the nice
option. If the user is making calls to the perl library within their
script, you would want to replace "nice" with "perl". This is difficult
to determine unless you can recognize within their script that they are
making calls to the perl library. If in doubt, just leave the cronjob
to run as nice, and if the customer reports that their cronjob is not
running properly, then change it to "perl".
For PHP scripts, you do not want to use nice. It is normally
better to specify the path to the php binary before the path
to the script. For example, replace "nice" with
"/usr/bin/php".
|
