This document describes the default installation of cron jobs on FreeBSD. We'll start at the top and explain the files that control the actions, then follow the chain until every end action is describe (in summary) in the final table.

The cron jobs are run by cron(8). The file controlling the execution and time of the jobs is /etc/crontab. The description of /etc/crontab can be found in the man page, crobtab(5). All jobs run as root, as is specified in /etc/crontab.

An investigation of /etc/crontab will show that every job starts by resetting the environment variables. Then:

every 5 minutes it executes /usr/libexec/atrun.
every hour it rotates the 'news' log files, if neccessary.
daily it runs 'periodic'.
weekly it runs 'periodic'.
monthly it runs 'periodic'.
every half hour it runs 'adjkerntz' to adjust the CMOS clock and adjusts time zone (when needed).

The jobs that interest us are those run by periodic(8). The utility is intended to be called by cron(8) and then execute shell scripts. The scripts are stored in a subdirectory tree under /etc/periodic. In /etc/periodic, there are four (4) subdirectories, each corresponding to the nature of the job; daily, weekly, monthly and security. The subdirectory /etc/perodic/daily has the jobs that run everyday. By the same methodology, /etc/periodic/weekly, /etc/periodic/monthly and /etc/periodic/security contain the jobs to be run weekly, monthly and for security, respectively. The time and date (if applicable) that the scripts run is define in /etc/crontab. (See crobtab(5) for an explaination on how to determine the time of execution.)

Investigating each subdirectory we will find several files that start with a three digit number and end with some text. The pre-fixed numbers determine (in SystemV style) the execution order of the files. The remainder of the filename is traditionally used as a terse description of it's function. As an example, '100.clean-disks' runs before job '110.clean-tmps'. As such, '100.clean-disks' runs first and cleans the disks. (The specific tasks are described in the table below.)

Next, before executing the task intended, the script "sources", or reads, the default configuration file. If it exists, then it is located in /etc/default/periodic.conf. This file has the DEFAULT configuration values. These default values can be over-ridden by two other files. Those files are /etc/periodic.conf and /etc/periodic.conf.local. Canonically, /etc/periodic.conf over-rides the value stored in /etc/default/periodic.conf. (NOTE: Those files stored in /etc/default/* are not intended to be edited. To change the default values use the over-ride files.)

The other file, /etc/periodic.conf.local, is intended for to work in conjunction with /etc/daily.local, /etc/weekly.local and /etc/monthly.local. These un-created directories are intended for root level cron jobs that are not installed by default.

These non-default (administrator installed) root level cron jobs are then run last by a script called 999.local. Each of the default temporal directories in /etc/periodic/ has a copy of this file. The file, 999.local, then in turn searches it's related directory for scripts. For example, /etc/perodic/daily/999.local searches the directory /etc/daily.local for scripts to run, but not before checking for values it might need for it's scripts from /etc/periodic.conf.local.

Lastly, /etc/default/periodic.conf contains the a variable named local_periodic. It, in turn, stores the locations of other directories for scripts to run. Those directories are /usr/local/etc/periodic and /usr/X11R6/etc/periodic. Those directories are intended for cron jobs needed for third-party applications. However, as of this writing, the variable local_periodic is not used, or listed, in any of the default scripts or files, with the exception /etc/default/periodic.conf.