Add a section documenting the cron(8) daemon.

svn path=/head/; revision=17009

en_US.ISO8859-1/books/handbook/config/chapter.sgml

@@ -417,6 +417,100 @@ exit 0
       system boot.</para>
   </sect1>
 
+  <sect1 id="configtuning-cron">
+    <sect1info>
+      <authorgroup>
+        <author>
+	<firstname>Tom</firstname>
+	<surname>Rhodes</surname>
+	<contrib>Contributed by </contrib>
+	<!-- 20 May 2003 -->
+	</author>
+      </authorgroup>
+    </sect1info>
+    <title>Configuring the <command>cron</command> utility</title>
+
+    <indexterm><primary>Configuring the <command>cron</command> utility</primary></indexterm>
+
+    <para>One of the most useful utilities in FreeBSD is &man.cron.8;.  The
+      <command>cron</command> utility runs in the background and constantly
+      checks the <filename>/etc/crontab</filename> file.  The <command>cron</command>
+      utility also checks the <filename>/var/cron/tabs</filename> directory, in
+      search of new <filename>crontab</filename> files.  These
+      <filename>crontab</filename> files store information about specific
+      functions which <command>cron</command> is supposed to perform at
+      certain times.</para>
+
+    <para>Let us take a look at the <filename>/etc/crontab</filename> file:</para>
+
+
+    <programlisting># /etc/crontab - root's crontab for FreeBSD
+#
+# &dollar;FreeBSD: src/etc/crontab,v 1.32 2002/11/22 16:13:39 tom Exp &dollar;
+#
+SHELL=/bin/sh
+PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin
+HOME=/var/log
+#
+#minute	hour	mday	month	wday	who	command
+#
+*/5	*	*	*	*	root	/usr/libexec/atrun
+#
+# Save some entropy so that /dev/random can re-seed on boot.
+*/11	*	*	*	*	operator /usr/libexec/save-entropy
+#
+# Rotate log files every hour, if necessary.
+0	*	*	*	*	root	newsyslog
+#
+# Perform daily/weekly/monthly maintenance.
+1	3	*	*	*	root	periodic daily
+15	4	*	*	6	root	periodic weekly
+30	5	1	*	*	root	periodic monthly
+#
+# Adjust the time zone if the CMOS clock keeps local time, as opposed to
+# UTC time.  See adjkerntz(8) for details.
+1,31	0-5	*	*	*	root	adjkerntz -a</programlisting>
+
+    <para>Like most of the configuration files in FreeBSD, the <quote>#</quote>
+      character represents a comment.  Notice we have several lines here.  Each
+      line has seven fields.  The first five of these fields hold time information,
+      listed in minute, hour, day, month, and the day of the week.  Some of these
+      fields have a <quote>*</quote> character, which represents <quote>every</quote>.
+      Thus, if we look at the periodic monthly listing, we can see that it is set to
+      run at minute thirty, hour five, on the first day of every month.  Always
+      remember that time is in the twenty-four hour clock format.  You can also see
+      that this command is set to be run as <username>root</username>.</para>
+
+    <para>This is the basic set up for every <filename>crontab</filename> file,
+      although there is one thing different about this one.  Field number six, where
+      we specified the username, only exists in the <filename>/etc/contrab</filename>
+      file.  If you ever write your own <filename>crontab</filename>, which I know you
+      will if your reading this, use of this field should be avoided.</para>
+
+    <note><para>The <command>cron</command> utility cannot read shell start up files,
+      therefor absolute paths need to be used in the
+      <filename>crontab</filename>.</para></note>
+
+    <para>The final field here will define the action to be performed.  This field can
+      be have any valid command, or shell script.  So if you want a list of actions to
+      be performed, you can write a shell script to execute them.  Then define this shell
+      script in your <filename>crontab</filename>.</para>
+
+    <sect2 id="configtuning-installcrontab">
+      <title>Installing a <filename>crontab</filename></title>
+
+      <para>To install your freshly written <filename>crontab</filename>, just
+	use the <command>crontab</command> utility.  The most common usage is:</para>
+
+      <screen>&prompt.root; <userinput>crontab crontab</userinput></screen>
+
+      <para>There is also an option to list installed <filename>crontab</filename> files,
+	just pass the <option>-l</option> to <command>crontab</command> and look
+	over the output.</para>
+
+    </sect2>
+  </sect1>
+
   <sect1 id="configtuning-rcNG">
     <sect1info>
       <authorgroup>