JulienB: /* Usage */

2013-07-08T08:21:54Z

‎Usage

JulienB: creation

2013-04-10T14:20:03Z

creation

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On Linux systems, when it's a matter of programming periodic tasks, the utility of choice is: ''cron''.

==Installation==
* It should be done by default on your APF. If not:
<pre class="host">
$ make busybox-menuconfig
</pre>
<pre class="config">
Miscellaneous Utilities --->
[*] crond
[ ] Support option -d to redirect output to stderr
[ ] Report command output via email (using sendmail)
(/var/spool/cron) crond spool directory
[*] crontab
</pre>

==First usage==
* Create a script on your APF to automatically start cron daemon at each boot, for example ''/etc/init.d/S50crond'':
<source lang="bash">
#!/bin/sh

case "$1" in
start)
echo -n "Starting crond: "
mkdir -p /var/spool/cron/crontabs
start-stop-daemon -S -q -b -m -p /var/run/crond.pid --exec /usr/sbin/crond
[ "$?" -eq 0 ] && echo "OK" || echo "KO"
;;

stop)
echo "Stopping crond"
start-stop-daemon -K -q -p /var/run/crond.pid
[ "$?" -eq 0 ] && echo "OK" || echo "KO"
;;

restart)
$0 stop
$0 start
;;

*)
echo "Usage: $0 {start|stop|restart}"
exit 1
;;
esac

exit 0

</source>

* Give it executable rights:
<pre class="apf">
# chmod a+x S50crond
</pre>

==Usage==
* When cron daemon is started you can ask it to do periodic tasks with the help of "crontabs". To edit a crontab do:
<pre class="apf">
# crontab -e
</pre>
* crontabs format is given here: http://en.wikipedia.org/wiki/Cron#Examples
* for example to log something every minute of every hour of every day of every month of every year then type:
<pre class="apf">
* * * * * logger -t CRON "Hello World !"
</pre>
* then by looking at /var/log/messages you should see your message printed each minute:
<pre class="apf">
# tail -f /var/log/messages
...
Apr 9 21:42:01 armadeus cron.info crond[573]: crond: USER root pid 605 cmd logger -t CRON "Hello World !"
Apr 9 21:42:01 armadeus user.notice CRON: Hello World !
...
Apr 9 21:43:01 armadeus cron.info crond[573]: crond: USER root pid 607 cmd logger -t CRON "Hello World !"
Apr 9 21:43:01 armadeus user.notice CRON: Hello World !
</pre>
* another example to poweroff your APF everyday at midnight (if your APF can control its power supply):
<pre class="apf">
0 0 * * * poweroff
</pre>
* By defaults crontabs are stored in ''/var/spool/cron/crontabs/'' and therfore are lost when you powerdown the APF (''/var'' in in RAM on APF).

==Links==
* http://en.wikipedia.org/wiki/Cron

@@ Line 78: / Line 78: @@
 0 * * * poweroff
 </pre>
-* By defaults crontabs are stored in ''/var/spool/cron/crontabs/'' and therfore are lost when you powerdown the APF (''/var'' in in RAM on APF).
+* By defaults crontabs are stored in ''/var/spool/cron/crontabs/'' and therefore are lost when you powerdown the APF (''/var'' is located in RAM by default on APF).
 ==Links==
 * http://en.wikipedia.org/wiki/Cron

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