Monitor remote linux machines

Sometimes, the status such as disk usage of remote machines needs to be monitored. There are two ways to do that - by SSH connection of the nagios server, or by installing NRPE daemon on the machine that needs monitoring. The following demonstrate how to use NRPE to monitor the status of a remote machine.

 

Configure remote machine

In the first step, the nagios plugins must be installed on the remote host so that all the checks commands will working on the remote host.

 

useradd nagios

passwd nagios

./configure

make

make install

chown nagios:nagios /usr/local/nagios

chown nagios:nagios /usr/local/nagios/libexec

 

Next is to install xinetd using yum.

 

Next install nrpe by the following command:

 

tar xzf nrpe-2.12.tar.gz

cd nrpe-2.12

./configure

make all

make install-plugin

make install-daemon

make install-daemon-config

make install-xinetd

 

Edit the /etc/xinetd.d/nrpe file and add the IP address of the monitoring server to the only_from directive.

 

only_from        = 10.0.11.5

 

Add the following entry for the NRPE daemon to the /etc/services file.

 

nrpe            5666/tcp                #NRPE

 

Now restart xinetd service

 

service xinetd restart

 

If everything worked a netstat -st | grep nrpe should output the following:

 

tcp            0            0    *:nrpe    *:*            LISTEN

 

Now open up the firewall for nrpe service

 

iptables -I INPUT -p tcp -m --dport 5666 -j ACCEPT

 

or, if using cetos/Redhat/fedora

 

iptables -I RH-Firewall-1-INPUT -p tcp -m tcp -dport 5666 -j ACCEPT

 

Note: After setting up the only_from directive for xinetd, the local nrpe plugin would not be able to inspect the setting of local files.

 

For systems with out compiling environment, we need to build rpm packages from systems that has one, a simple method is to use the rpmbuild utility.

 

Put the nagios-plugins and nrpe source pakcage in one folder and use the following commands to build respective rpm packages:

rpmbuild -tb nrpe*

rpmbuild -tb nagios-plugins*

Building of nagios-plugins rpm package need perl-Net-SNMP package which could be found in dag repo. By default, the rpm pacakge built can be found in /usr/src/redhat/RPMS/i386 folder if the rpm package is compiled for i386 systems, for 64bit systems, the folder is x86_64.

 

After building the package, nrpe can be installed by rpm -i command. By default the configuration file would be located at /etc/nagios folder instead of /usr/local/nagios/etc.

 

 

 

Configure the nagios server

 

On the nagios server the nrpe plugin needs to be installed.

 

tar xzf nrpe-2.12.tar.gz

cd nrpe-2.12

./configure

make all

make install-plugin

 

Now we can check if NRPE is working by

 

/usr/local/nagios/libexec/echeck_nrpe -H sophia

 

If everything works, the nrpe version would pop out.

 

Next step is to define the nrpe command in the object file commands.cfg

define command{
    command_name    check_nrpe
    command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -c  $ARG1$
    }

 

Sample commands that can be used by NRPE are

command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10
command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20
command[check_hda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/hda1
command[check_zombie_procs]=/usr/local/nagios/libexec/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/local/nagios/libexec/check_procs -w 150 -c 200

For security reasons the nrpe should not be configured to allow command arguments unless absolute nessessay.

The following sample services were added in the testing to monitor vavious aspects of the remote machine sophia.

define service{
    use            generic-service
    host_name        sophia.blueprint.org
    service_description    SSH
    check_command        check_ssh
    }

define service{
    use            generic-service
    host_name        sophia.blueprint.org
    service_description    CPU Load
    check_command        check_nrpe!check_load
    }

define service{
    use            generic-service
    host_name        sophia.blueprint.org
    service_description    Current Users
    check_command        check_nrpe!check_users
    }

define service{
    use            generic-service
    host_name        sophia.blueprint.org
    service_description    /dev/hda1 Free Space
    check_command        check_nrpe!check_hda1
    }

define service{
    use            generic-service
    host_name        sophia.blueprint.org
    service_description    Total Processes
    check_command        check_nrpe!check_total_procs
    }

define service{
    use            generic-service
    host_name        sophia.blueprint.org
    service_description    Zombie Processes
    check_command        check_nrpe!check_zombie_procs
    }

 

Monitor remote windows machines

Windows machines can be monitored through nagios by installing a monitoring daemon NSclient++.

 

Install NSclient++ on Windows machine

 

NSclient++ can be downloaded from http://trac.nakednuns.org/nscp/. To install NSclient++ extract the zip file to C:\nsclient and type:

 

nsclient /install

 

Open the services manager and make sure the NSClientpp service is allowed to interact with the desktop (see the ’Log On’ tab of the services manager). If it isn’t already allowed to interact with the desktop, check the box to allow it to.

 

Edit the NSC.INI file (located in the C:\NSClient++ directory) and make the following changes:

• Uncomment all the modules listed in the [modules] section, except for CheckWMI.dll and RemoteConfiguration.dll
• Optionally require a password for clients by changing the ’password’ option in the [Settings] section.
• Uncomment the ’allowed_hosts’ option in the [Settings] section. Add the IP address of the Nagios
• server to this line, or leave it blank to allow all hosts to connect.
• Make sure the ’port’ option in the [NSClient] section is uncommented and set to ’12489’ (the default port).

 Now starts the nsclient service by:

nsclient++ /start

To configure the nagios server, just include windows.cfg in the nagios configuration and make changes to windows.cfg using the template.

 

 

Monitor routers and switches

wrgt (oss.oetiker.ch/mrtg) is a plotter for the the network usage. In Centos 5.1 wrgt can be installed through yum.

The format for mrgt is mrtg <mrtgcfgfile>, wheremartgcfgfile is the configuration file for mrtg. A cfg generation tool called cfgmaker is installed with mrtg and it can be used to generate the config file for mrtg to use.

 

cfgmaker --global 'WorkDir: /home/nagios/mrtg' --global 'Options[_]: growright,bits' --ifref=ip public@10.0.11.1

 

The --ifref parameter is important because it sets the chriteria that differenciates the ports, other values include nr,ip,eth,descr,name,type.

 

copy the file to /home/nagios/mrtg folder and change the owner to nagios

 

The mrtg has to be executed continuously, add the following lines to the crontab of usr nagios so that mrtg executes every 1 minutes:

 

crontab -u nagios -e

 

Then add the following line in the editor opened:

 

*/1 * * * * env LANG=C /usr/bin/mrtg /home/nagios/mrtg.cfg --logging /var/log/mrtg.log

 

After the above configuration, one mrtg is excuted, logfiles for the bandwiths of defferent ports of the router will be generated in the /home/nagios/mrtg folder and the filename is in the format of <router address>_<port address>.log this can be used in the check_local_mrtgtraf plugin for checking bandwith of different ports.

    host_name    ecklie        ; The name we're giving to this switch