Fedora Linux

/etc/cron.hourly	Hourly	:01 past each hour	Send/receive netnews
/etc/cron.daily	Daily	4:02 a.m. every day	Analyze web logs, rotate logs, delete old temporary files, monitor cryptographic certificate expiry, update installed software
/etc/cron.weekly	Weekly	4:22 a.m. every Sunday	Clean up old yum packages, index manpages
/etc/cron.monthly	Monthly	4:42 a.m. on the first day of every month	(None defined)

Many Fedora packages install files into these directories to schedule tasks; for example, the webalizer package installs /etc/cron.daily/00webalizer to set up automatic web log analysis.

If a task is not performed because the system is off at the scheduled time, the task is performed at the next boot or the next regularly scheduled time, whichever comes first (except for hourly tasks, which just run at the next scheduled time). Therefore, the regularly scheduled maintenance tasks will be still be executed even on a system that is turned on only from (say) 8:00 a.m. to 5:00 p.m. on weekdays.

6.4.2. How Does It Work?

The cron server daemon executes tasks at preset times. The crontab files created with the crontab command are stored in a text file in /var/spool/cron .

There is also a system-wide crontab file in /etc/crontab and additional crontab files, installed by various software packages, in /etc/cron.d . These crontab files are different from the ones in /var/spool/cron because they contain one additional field between the time values and the command: the name of the user account that will be used to execute the command.

This is the default /etc/crontab file installed with Fedora Core:

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/
# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly

The entries in this file execute the scripts in the directories listed in Table 6-8 . Note that the sixth field is root , meaning that these scripts are executed with root permission.

The files in /etc/cron.d may also be executed by the anacron service during system startup ( anacron takes care of running jobs that were skipped because your computer was not running at the scheduled time). The files /var/spool/anacron/cron.daily , /var/spool/anacron/cron.monthly , and /var/spool/anacron/cron.weekly contain timestamps in the form YYYYMMDD recording when each level of task was last run.

The default /etc/anacrontab looks like this:

# /etc/anacrontab: configuration file for anacron
# See anacron(8) and anacrontab(5) for details.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
1 65 cron.daily run-parts /etc/cron.daily
7 70 cron.weekly run-parts /etc/cron.weekly
30 75 cron.monthly run-parts /etc/cron.monthly

The three entries at the end of this file have four fields, specifying the minimum number of days that must have elapsed since a command was last run before it is run again, the number of minutes after anacron is started that the command should be executed, the anacron label (corresponding to the timestamp filename in /var/spool/anacron ), and the command to be executed. If the specified number of days has elapsedfor example, the weekly tasks have not been executed in more than a weekthe anacron service starts the appropriate tasks after the specified delay (so, in this example, weekly tasks would be executed approximately 70 minutes after system boot).

6.4.3. What About...

6.4.3.1. ...daylight savings time?

In many parts of the world, daylight savings time , or summer