11-20-2005
$RANDOM is helpful, but there's still a 1/32000 chance that you'll have a clash within the next instant. You can also try using $$, because that is the PID, which is always increasing (up to 64k) until it restarts. But it will be a while before it cycles around, so you're (often) pretty safe using that.
Sendmail, for example, does even more elaborate filename generation for the files in its mailqueue because creating thousands of files in a short period if time is pretty easy for it. So you won't see it using such a simple algorithm. But it works for many shell script situations.
-Mike
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LEARN ABOUT CENTOS
crontabs
CRONTABS(4) Crontabs users' Manual CRONTABS(4)
NAME
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 RAN-
DOMTIME 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)
Marcela Malaova 2012-08-29 CRONTABS(4)