Month: January 2017

My webspace provider offers a simple ssh access to upload and download files. One cannot install any software there and has a limited set of commands. I wanted to check the free space on that server because it often runs out of free space and then new uploads fail.

The script on the server

The server does not have a “quota” command and “df” is about the whole filesystem, not just about my webspace. So I used “du -ms .” to check how much data is saved in my webspace. I have creates a small shell script “checkfreespace.sh” and saved it on the server:

#!/bin/bash
export USEDSPACE=`du -ms . | sed "s/[^0-9]*//g"`;
if [ "$USEDSPACE" -lt "9000" ] ; then echo "OK - $USEDSPACE MB used" ; exit 0; else echo "CRITICAL - $USEDSPACE MB used"; exit 2; fi

It checks if less than 9000MB are used and returns “OK” with exit code 0. Otherwise it returns “CRITICAL” with exit code 2. These are keywords that are used by Nagios.

SSH configuration

Then it is necessary to make it possible to login using public key authentication (so that Nagios does not need a password).

1. Use “chsh nagios” to set the shell of nagios to “/bin/bash”.
2. Use “su – nagios” to switch to the home directory of nagios.
3. Create a key pair if necessary e.g. using

   ssh-keygen -t rsa -b 4096 -C your@email.com

   in the .ssh directory of the nagios user and change the owner to the nagios user if necessary.

4. Append the contents of the file .ssh/id_rsa.pub to the file .ssh/authorized_keys on the server.
5. Use “chsh nagios” to set the shell of nagios back to “/bin/false”.

Nagios configuration

Finally you have to configure Nagios. Add this to the commands.cfg file:

define command{
	command_name	check_my_free_space
	command_line	/usr/lib/nagios/plugins/check_by_ssh -H ssh.yourserver.com -l yourusername -C "bash checkfreespace.sh" -t 30
	}

Afterward you have to use this new command in your services file, e.g. add this:

define service {
        service_description             Free webspace;
        check_command                   check_my_free_space
        use                             generic-service;
        host_name  android.calengoo.com;
        notification_interval           0 ; set > 0 if you want to be renotified
        normal_check_interval           60
}