The cron daemon can help you run programs on an automated regular basis. Red Hat Linux configures standard cron jobs through /etc/crontab , configured by time period in directories such as /etc/cron .hourly and /etc/cron.weekly . Users can configure their own cron jobs with the crontab command; each user s configuration is stored in the /var/spool/cron directory. cron security is governed by the /etc/cron.allow and /etc/cron.deny files.
The at command is like cron , except it can help you run jobs on a onetime basis. The batch command is a variation of at that runs a specified job when the demands on your system are below 80 percent of capacity. Similar to cron , at command security is governed by the /etc/at.allow and /etc/at.deny files.
Another key to administering Linux is based on log files. Standard Linux log files are configured in /etc/syslog.conf and located in the /var/log directory. System logs help you trace detected hardware and analyze login activity. Daemon logs can help you monitor when daemons such as crond , httpd , and smbd are used. Other log files are available for tasks such as monitoring currently installed RPMs, secure connections, news servers, and more.
Everyone who administers a Linux computer needs to know several basic process and user management commands. The ps , top , and kill commands help you find and kill processes that are out of control. The who command can identify currently logged-in users. The nice and renice commands enable you to prioritize critical jobs.
In the following chapter, you ll extend your knowledge of Linux administration by learning the commands you need to back up all or part of your system.