crontabs man page

crontabs — configuration and scripts for running periodical jobs

Synopsis

run-parts [--list|--test]<directory>

Description

Crontabs is a historical name for the run-parts script and the system crontab. The run-parts script runs all executables in the specified directory. Run-parts runs all executables in the specified directory. The execution of files can be allowed or denied by creating file jobs.allow or jobs.deny which worked similar as other allow/deny config files. The file must be created in the specified directory.

--list
print names of all files (not limited to executables), but don't run them. This option can't be used with test option.
--test

print names of files, which would be run.

Randomization of jobs can be configured in the /etc/sysconfig/run-parts file. To enable randomization of jobs, set the RANDOMIZE parameter to 1 and set the RANDOM parameter to an integer which determines a random seed. Additionally, you may configure the RANDOMTIME parameter (again, by specifying an integer) to provide an additional level of randomization. Jobs are not randomized when the RANDOM and RANDOMTIME parameters are set to 0. Values in these two parameters must be set to 1 or larger to provide a good enough randomization.

Randomization of cron jobs can be useful for shared networks, where multiple cron jobs executed at once can cause spikes in traffic, especially during daily jobs. With randomized jobs, the workload is evenly distributed throughout the day.

Example of Configuration File

RANDOMIZE=1
RANDOM=4
RANDOMTIME=8

Historically the crontab file contained configuration which called run-parts on files in cron.{daily,weekly,monthly} directories. These jobs are now run indirectly through anacron to prevent conflicts between cron and anacron. That means the anacron package has to be installed if the jobs in these directories should be running. Refer to the anacron(8) how to limit the time of day of the job execution.

Example

/etc/cron.daily/jobs.deny could contain for example 0logwatch which forbid execution of this script.

See Also

anacron(8), crontab(5)

Referenced By

run-parts(4) is an alias of crontabs(4).

2012-08-29 Marcela Mašláňová Crontabs users' Manual