cron

[maxwas]

Hi all,

I have a Fedora 11 box and I am confused about cron, where exactly do I enter the cron jobs?

For example, I have a job that needs to run every half hour.

Thanks

Max

[Rubberman]

See the crontab command. Here is the manpage:

CRONTAB(1)                                                          CRONTAB(1)

NAME
       crontab - maintain crontab files for individual users (ISC Cron V4.1)

SYNOPSIS
       crontab [-u user] file
       crontab [-u user] [-l | -r | -e] [-i] [-s]

DESCRIPTION
       Crontab is the program used to install, deinstall or list the tables used to drive the cron(8) daemon
       in ISC Cron.  Each user can have their own crontab, and though these are files in /var/spool/ ,  they
       are  not intended to be edited directly. For SELinux in mls mode can be even more crontabs - for each
       range. For more see selinux(8).

       If the cron.allow file exists, then you must be listed therein in order to be  allowed  to  use  this
       command.   If the cron.allow file does not exist but the cron.deny file does exist, then you must not
       be listed in the cron.deny file in order to use this command.  If neither of these files exists, only
       the super user will be allowed to use this command.

OPTIONS
       -u     It  specifies  the  name  of  the  user whose crontab is to be tweaked.  If this option is not
              given, crontab examines "your" crontab, i.e., the crontab of the person executing the command.
              Note  that  su(8)  can  confuse crontab and that if you are running inside of su(8) you should
              always use the -u option for safety’s sake.  The first form of this command is used to install
              a new crontab from some named file or standard input if the pseudo-filename "-" is given.

       -l     The current crontab will be displayed on standard output.

       -r     The current crontab will be be removed.

       -e     This  option  is  used to edit the current crontab using the editor specified by the VISUAL or
              EDITOR environment variables.  After you exit from the editor, the modified  crontab  will  be
              installed automatically.

       -i     This  option  modifies  the  -r option to prompt the user for a ’y/Y’ response before actually
              removing the crontab.

       -s     It will append the current SELinux security context string as  an  MLS_LEVEL  setting  to  the
              crontab  file  before  editing  /  replacement  occurs - see the documentation of MLS_LEVEL in
              crontab(5).

SEE ALSO
       crontab(5), cron(8)

FILES
       /etc/cron.allow
       /etc/cron.deny

STANDARDS
       The crontab command conforms to IEEE Std1003.2-1992 (‘‘POSIX’’).  This  new  command  syntax  differs
       from previous versions of Vixie Cron, as well as from the classic SVR3 syntax.

DIAGNOSTICS
       A fairly informative usage message appears if you run it with a bad command line.

AUTHOR
       Paul Vixie <vixie@isc.org>

[aetiv]

You really should avoid editing the file directly and instead use the crontab command. It will verify things are being entered properly.

[STanner]

Not exactly sure about fedora 11, but with Redhat ES 4.5-5.x there are a couple of ways to enter a cron job depending on which RPM's are installed (anacron, vixie-cron) and how often you want the job to run.

It's a bit frustrating, as different RPM packages will choose different methods for adding cron jobs, making you search to see where a process is being called. Anyways...

For a 5 min interval, you can:
- Add the job file to /etc/cron.d
- Add the entry to the users cron file : /var/spool/cron/crontabs/$user$ (not recommended, but still done fairly often).
- Use the crontab command as described earlier
- Add an entry to /etc/crontab

[fatra2]

Hi there,

A cron entry for your purpose is quite simple. If you want your job to run every half hour, you could do something like this:

0,30 * * * * /usr/bin/theProg differentOptionsw whatNext
or
15,45 * * * * /usr/bin/theProg differentOptionsw whatNext

"theProg" will run every half hour. You need to know that if your computer is not running, cron will not look back in the past.

Cheers

[vkv]

Create a file

touch file

edit that file and add the schedule and save the file

Then user crontab command

crontab file

or crontab -u username file (Cron job for particular user)

This should work

[scm]

What's wrong with using crontab -e? And crontab -l to view the jobs that are setup?

[vkv]

Yeah that also works.

I was just explaining one method.

crontab -e and crontab -l works great

[fatra2]

Hi there,

What's wrong with using crontab -e? And crontab -l to view the jobs that are setup?

You are absolutely right. crontab -e will let you directly edit the crontab file. But, with this command, you enter the vim text editor. If you don't know it, or don't feel comfortable with it, you are better of with something else.

Cheers