Apple Mac OS X Server manual Terminating Commands, Scheduling Tasks

Important: As the root user, you have sufficient privileges to do things that can cause your server to stop working properly. Don’t execute commands as the root user unless you know what you’re doing. Logging in as an administrator user and using sudo selectively might prevent you from making unintended changes.

Terminating Commands

To terminate the currently running command, enter Control-C. This keyboard shortcut sends an abort signal to the command. In most cases this causes the command to terminate, although commands may install signal handlers to trap this signal and respond differently.

Scheduling Tasks

You can create scheduled tasks using the cron tool. cron is a daemon that executes scheduled commands from a crontab file. The cron tool searches the /var/cron/tabs folder for crontab files that are named after accounts in /etc/passwd, and loads the files into memory. cron also searches for crontab files in the /etc/crontab folder, which are in a different format. cron then cycles every minute, examining all stored crontab files and checking each command to see if it should be run in the current minute.

When commands execute, any output is mailed to the owner of the crontab file or to the user named in the MAILTO environment variable in the crontab file, if such exists. When a crontab file has been modified, cron needs to be restarted. crontab is the program used to install, deinstall, or list the tables used to drive the cron daemon. Each user can have their own crontab file.

To configure your crontab file, use the crontab -ecommand. This displays an empty crontab file.

An example of a configured crontab file:

SHELL=/bin/sh

PATH=/bin:/sbin:/usr/bin:/usr/sbin

HOME=/var/log

#min	hour	mday	month wday		command
30	18	*	*	1-5	/usr/local/vscanx folder-name
50	23	*	*	0	/usr/local/vscanx --summary folder-name
15	10	*	*	6	/usr/local/vscanx --load /usr/local/conf1 /uz
45	8	*	*	1	/usr/local/vscanx --f /usr/local/biglist

Listed below is an explanation of the crontab structure shown above.

The following crontab entry schedules a scan operation to run and produce a summary at 18:30 every day, Monday through Friday:

30 18 * * 1-5 /usr/local/vscanx folder-name

Chapter 1 Executing Commands

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