This is the default output of the munin load plugin.

I’ve patched it to add a permanent blue line indicating the number of cpu of the server. The resulted graph looks like this :

You can download the patched plugin here. It is tested with Linux and FreeBSD.

Playing with memory_limit in PHP, we wanted to know the average memory usage per php-cgi process. This is easily calculated with our best friend awk.

First, get the number of php running processes:

# ps aux | grep php-cgi | grep -v grep | wc -l
126

Then, use awk to calculate the average memory usage for these processes:

# ps aux | grep --exclude=grep php-cgi | grep -v grep | awk 'BEGIN{s=0;}{s=s+$6;}END{print s/126;}'
33987.8

The number used in the calculation is the field RSS given by ps. The ps manual page says:

rss: resident set size, the non-swapped physical memory that a task has used (in kiloBytes)

You can also calculate the total memory used by all php-cgi processes:

# ps aux | grep --exclude=grep php-cgi | grep -v grep | awk 'BEGIN{s=0;}{s=s+$6;}END{print s;}'
4302028

If you need to watch the trend of this average memory usage, a little shell loop does the trick:

# while [ 1 ]; do ps aux | grep --exclude=grep php-cgi | grep -v grep | awk 'BEGIN{s=0;}{s=s+$6;}END{print s/126;}'; sleep 2; done
34401.3
34405.1
34408.4
34409.4
34414.2
34417

Use of uninitialized value in eval {block} exit at /usr/sbin/munin-node line 456, <CHILD> line 8.

What a great error message

After digging into Google results, I found it was just a problem with host_name variable in the configuration. Default value is hostname.localdomain. I’ve replaced it with a valid hostname and it works!

Nothing was written in the logs to say that there was a problem.

To avoid future problems, I wrote an alert for monit.

In my crontab, I’ve added the following job:

*/5 * * * *       root    touch /tmp/check_cron

This job will update the timestamp of the file /tmp/check_cron every 5 minutes.

And in monit configuration (/etc/monit/monitrc), I’ve added the following alert:

check file check_cron with path /tmp/check_cron
        if timestamp > 10 minutes then alert

If the crontab is not working, monit will send you an alert email like this:

Subject: monit alert --  Exists check_cron

Exists Service check_cron 

	Date:        Thu, 27 Nov 2008 21:21:53 +0100
	Action:      alert
	Host:        myhost
	Description: 'check_cron' file exist

Your faithful employee,
monit