nagios - memory configuration

Question

I am trying to configure nagios to perform memory check on a ubuntu server. I already have the basic configuration but when a try to start nagios, the following error message is displayed:

Service check command 'check_mem' specified in service 'Current Memory Usage' for host 'xxxx' not defined anywhere!

Besides commands.cfg, is there any possible place to define the command to be executed?

Thanks in advance, Best regards!

Answer 1

Rui:

ok, that's much clearer. The answer is that NAGIOS can take any valid configuration statement in any of its configuration files, and there can be an unlimited number of these. I have a NAGIOS server with 136 config files; any of those could contain a command definition.

So if you have a running configuration that has it defined somewhere, but not in commands.cfg, then the bad news is it could be in any of its config files, and these can be anywhere.

If I wanted to find it, I'd look in nagios.cfg to see what directories the config files live in, then automate the process of finding it, perhaps with

find /config/directory1 /config/directory2 /you-get-the-idea  -type f -exec grep check_mem {} /dev/null \;

and see what matches that finds.

Answer 2

most probably you want to use nagios nrpe server on monitored machine and define what plugin should execute this check.

btw maybe you should rather check swap usage?

Answer 3

I couldn't find a decent script for checking memory so I wrote the following. I use it with nrpe as suggested above.

Service definition on the server in the host config:

define service {
       use                     generic-service
       host_name               <hostname>
       service_description     Memory Usage
       check_command           check_nrpe_1arg!check_memory
}

This needs to be defined in /etc/nagios/nrpe.cfg on the client, amended for the values you want to check for:

command[check_memory]=/usr/lib/nagios/plugins/check_memory.sh -w 85 -c 90

Example output:

#:~$ ./check_memory.sh -w 80 -c 90
Memory OK. 44% used.


#:~$ ./check_memory.sh -w 40 -c 50
Memory WARNING. 44% used.

The script:

#!/bin/bash
#
# Script to check memory usage on Linux. Ignores memory used by disk cache. 
#
# Requires the bc command
#
print_help() {
    echo "Usage:"
    echo "[-w] Warning level as a percentage" 
    echo "[-c] Critical level as a percentage" 
    exit 0
}

while test -n "$1"; do
    case "$1" in
        --help|-h)
            print_help
            exit 0
            ;;
        -w)
            warn_level=$2
            shift
            ;;
        -c)
            critical_level=$2
            shift
            ;;
        *)
            echo "Unknown Argument: $1"
            print_help
            exit 3
            ;;
    esac
    shift
done

if [ "$warn_level" == "" ]; then
    echo "No Warning Level Specified"
    print_help
    exit 3;
fi

if [ "$critical_level" == "" ]; then
    echo "No Critical Level Specified"
    print_help
    exit 3;
fi


free=`free -m | grep "buffers/cache" | awk '{print $4}'`
used=` free -m | grep "buffers/cache" | awk '{print $3}'`

total=$(($free+$used))

result=$(echo "$used / $total * 100" |bc -l|cut -c -2)

if [ "$result" -lt "$warn_level" ]; then
    echo "Memory OK. $result% used."
    exit 0;
elif [ "$result" -ge "$warn_level" ] && [ "$result" -le "$critical_level" ]; then
    echo "Memory WARNING. $result% used."
    exit 1;
elif [ "$result" -gt "$critical_level" ]; then
    echo "Memory CRITICAL. $result% used."
    exit 2;
fi

Answer 4

The problem is nagios server can't find check_nrpe_1arg's define. There are somewhere else you can define commands, e.g nagios-plugins

Here, I solve the problem by define command in plugins

deploy@code:/etc/nagios-plugins/config$ pwd
/etc/nagios-plugins/config
deploy@code:/etc/nagios-plugins/config$ cat check_nrpe.cfg 
# this command runs a program $ARG1$ with arguments $ARG2$
define command {
    command_name    check_nrpe
    command_line    /usr/lib/nagios/plugins/check_nrpe -H $HOSTADDRESS$ -c $ARG1$ -a                 $ARG2$
}


# this command runs a program $ARG1$ with no arguments
define command {
    command_name    check_nrpe_1arg
    command_line    /usr/lib/nagios/plugins/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}

To use check_nrpe or check_nrpe_1arg, you must make sure /usr/lib/nagios/plugins/check_nrpe exist. In debian system, you can install package nagios-nrpe-plugins on the nagios server.