<prgn>anacron</prgn>. Thus, you should only use this
directory for jobs which may be skipped if the system is not
running.)</p>
+ <p>
+ Unlike <file>crontab</file> files described in the IEEE Std
+ 1003.1-2008 (POSIX.1) available from
+ <url id="http://www.opengroup.org/onlinepubs/9699919799/"
+ name="The Open Group">, the files in
+ <file>/etc/cron.d</file> and the file
+ <file>/etc/crontab</file> have seven fields; namely:
+ <enumlist>
+ <item>Minute [0,59]</item>
+ <item>Hour [0,23]</item>
+ <item>Day of the month [1,31]</item>
+ <item>Month of the year [1,12]</item>
+ <item>Day of the week ([0,6] with 0=Sunday)</item>
+ <item>Username</item>
+ <item>Command to be run</item>
+ </enumlist>
+ Ranges of numbers are allowed. Ranges are two numbers
+ separated with a hyphen. The specified range is inclusive.
+ Lists are allowed. A list is a set of numbers (or ranges)
+ separated by commas. Step values can be used in conjunction
+ with ranges.
+ </p>
<p>
- The scripts or crontab entries in these directories should
+ The scripts or <tt>crontab</tt> entries in these directories should
check if all necessary programs are installed before they
try to execute them. Otherwise, problems will arise when a
package was removed but not purged since configuration files
- are kept on the system in this situation.</p>
+ are kept on the system in this situation.
+ </p>
+
+ <p>
+ Any <tt>cron</tt> daemon must provide
+ <file>/usr/bin/crontab</file> and support normal
+ <tt>crontab</tt> entries as specified in POSIX. The daemon
+ must also support names for days and months, ranges, and
+ step values. It has to support <file>/etc/crontab</file>,
+ and correctly execute the scripts in
+ <file>/etc/cron.d</file>. The daemon must also correctly
+ execute scripts in
+ <file>/etc/cron.{hourly,daily,weekly,monthly}</file>.
+ </p>
</sect>
<sect id="menus">