Chris Tyler - Fedora Linux

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).

In many parts of the world, daylight savings time , or summer time , shifts the local time by one hour through the spring and summer months. In most jurisdictions in North America, the local time jumps from 2:00 a.m. to 3:00 a.m. during the spring time change and from 3:00 a.m. to 2:00 a.m. during the autumn time change. The spring time change has been held on the first Sunday in April, but that will change (experimentally) to the second Sunday in March in 2007. The fall time change has been held on the last Sunday in October, which will change to the first Sunday in November in 2007. If the changes do not result in significant energy savings, governments may revert to the traditional dates.

This means that there is no 2:30 a.m. local time on the day of the spring time change, and that 1:30 a.m. local time happens twice on the day of the fall time change.

crond was written to take this issue into account. Jobs scheduled to run between 2:00 and 3:00 a.m. during the spring time change will execute as soon as the time change occurs, and jobs scheduled to run between 1:00 and 2:00 a.m. during the autumn time change will be executed only once.

The environment variable EDITOR can be used to specify a different editor, such as emacs , joe , or mcedit . You can set this variable temporarily by assigning a value on the same command line as the crontab command:

$ EDITOR= joe crontab -e

It may be useful to edit your ~/.bash_profile and add this line to permanently specify a different editor:

export EDITOR= mcedit

When executed without any arguments, the crontab command will read the crontab configuration from the standard input. You can use this feature to load the configuration from a file:

$ crontab < /tmp/newcrontab

To see the current crontab configuration, use the -l option:

$ crontab -l

# Backup ~chris/oreilly/ to bluesky:~chris/backup/ as a tar archive

30 0,12 * * * /usr/local/bin/bluesky-backup-oreilly

# Update the local rawhide repository

0 5 * * * /usr/local/bin/rawhide-rsync

Putting these features together, you can create a simple script to edit a crontab configuration:

#!/bin/bash

# addtmpclean :: add a crontab entry to clean ~/tmp daily

(crontab -l ; echo "30 4 * * * rm -f ~/tmp/*")|crontab

 The manpages for cron , crontab(1) , crontab(5) , anacron , and anacrontab

Fedora, like most Linux and Unix systems, makes no distinction between server and client systems. In fact, many Fedora systems participate in both roles, both serving and consuming information.

It should come as no surprise, then, that Fedora Core ships with a full complement of software for serving everything from web pages and email to files and printer connections. These server packages are based on open standards and interoperate with other platforms, so you can use a Fedora system to serve Windows, Mac, Linux, or Unix clients.

Most Fedora servers are extensively configurable. Configuration information is stored in text files, but the format of the text files varies, and the information in those files goes by different names directives , statements , parameters , or options depending on the program. Red Hat has developed convenient graphical configuration tools for most of the server configuration files.

Services are programs that constantly run in the background. Services can start automatically when the system starts, but not all services are configured this way by default (see Lab 4.6, "Managing and Configuring Services").

It also might be necessary to adjust your firewall or SELinux configuration to use the services discussed in this chapter (see Chapter 8 for more information).

Fedora can be configured to use Samba to serve files and printers to a wide range of Windows systems using Microsoft-compatible protocols.

Samba can be configured to work with a wide range of Windows versions and to serve resources in many different ways. This lab is focused on sharing files and printers with Windows XP systems in a small workgroup, which is a common scenario in home and small-business networks.