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<link rel=stylesheet href="style.css" type="text/css">
<title>collectl - Running as a Service</title>
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<body>
<center><h1>Running As A Service</h1></center>
<p>
Assuming collectl has been installed from the rpm kit, it has been
configured to be run as a service, but disabled from automatically
starting at boot. To enable it, simply
<i>chkconfig collectl on</i>, noting that by default collectl is
configured to collect most data.
To see what the specific subsystems are, execute <i>collectl -V</i>
and look at the daemon default values for <i>-s</i>. You should then look at
the <i>DaemonCommands</i> string /etc/collectl.conf to see if any changes to
-s have been explictly set. At the time of this writing, collectl has been
further configured to add slab and process data to the base defaults.
<p>
Further inspection of this command string will show the daemon has also been
configured to write all its data to a set of compressed text files in
<i>/var/log/collectl</i>, which was created when the kit was installed. To verify
collectl will properly run as a service, you can execute the command
<i>/etc/init.d/collectl start</i> (or as a shortcut on a redhat system use
the command <i>service collectl start</i>) and examine the <i>log</i> file in /var/log/collectl
for the startup (and hopefully no termination) messages as well as the appearance
of either a <i>raw</i> or <i>raw.gz</i> data file in that same directory.
Note that since the output is buffered, the data file will probably have a length of
0 until the buffer fills or the flush interval passes, which is currently set to 60 seconds,
which ever comes first. Or the command <i>/etc/init.d/collectl flush</i> is executed.
<p>
In order to write its output as a compressed file, the perl <i>Compress</i> module
must be present as it is with newer perl distributions. If not present
you should install it, otherwise you will get messages warning you that compression is not
installed.
<p>
To change any behaviors of the daemon such as the flush interval, output file
location, etc., simply change the <i>DaemonCommands</i> line in
<i>/etc/collectl.conf</i>, which specifies the actual command string collectl is passed at
startup. Use care in setting this string as incorrect settings may cause collectl
to abnormally exit and if it does, you should examine the <i>log</i> file for
messages.
<p>
<center>
<b><i>caution about pipes in DaemonCommands</i></b>
<p>
<table width="80%">
<tr><td>Since some of the filters can include pipes, one might choose the use the perl form of
<i>"abc|def|xyz"</i> when using them interactively, having to use quotation marks to
prevent the shell from acting on them. However if you include the quotes in the
<i>DaemonCommands</i> line, the filters will not work correctly as collectl will see
the quotes as part of the filter itself.</td></tr>
</table>
</center>
<p>
<b>One-time modification of runtime parameters</b>
<p>
If you want to change the way collectl runs as a daemon for a specific instance, you can
pass the normal collectl switches to the start script as its second parameter (more on the
first parameter later). For example, to start collectl with a monitoring interval of
15 seconds, just start it as follows:
<p>
<pre>
/etc/init.d/collectl start '-i 15'
</pre>
<p>
The next time it is started (or restarted) it will use its default values.
<p>
<b>Running multiple instances of a collectl daemon</b>
<p>
By default, collectl only supports running a single instance of a daemon and it you try to
start a second you will get an error message. However, there may be times you really want to
run a second instance, most typically if you want to collect a subset of data at a different
monitoring interval, and to do this one uses an alternative syntax which prefaces the
parameters with a string such as <i>test</i> as in the following example:
<p>
<pre>
/etc/init.d/collectl start test -i15
</pre>
<p>
Also note in this example quotes weren't needed because there were no spaces in the second
argument. In this case a process named <i>collectl-test</i> will be created and use the
argument -i15. You must be careful when using this format because if you leave off the
second argument you'd actually start the main process with the invalid switch of </i>test</i>.
<p>
To perform other operations on this second instance, such as <i>stop</i> or <i>flush</i>, simply
add the <i>test</i> qualifier to the command. If you want to restart one of these instances be
sure to include the appropriate arguments because you must use the 2 argument form of the command.
This syntax was also chosen to assure the user does use additional switches because without them
you'd essentially be running an identical copy of the default configuration.
<table width=100%><tr><td align=right><i>updated Sep 5, 2013</i></td></tr></colgroup></table>
</body>
</html>
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