Install Nagios Plugins on CentOS 9 Stream

This guide will walk you through how to install Nagios Plugins on CentOS 9 Stream. Nagios plugins are standalone extensions that enables Nagios to monitor databases, operating systems, services, applications, network equipment, protocols etc.

To use Nagios Plugins, you need to have installed and Setup Nagios Core server. Follow the link below to install Nagios server on CentOS 9 Stream.

Install Nagios Server on CentOS 9 Stream

Installing Nagios Plugins on CentOS 9 Stream

Once you have setup the Nagios Core server, proceed to install the Nagios plugins.

Well, there are two ways in which you can install Nagios Plugins.

1. Building Nagios Plugins from the source
2. Installing Nagios Plugins from EPEL Repos (Probably the easiest)

We will cover the two installation methods.

Install Nagios Plugins from the Source on CentOS 9 Stream

Install Required Build Tools and Dependencies

Nagios plugins are build from the source code. Hence, you need to install required build tools and dependencies.

Some of the packages below might have been installed if you followed the Nagios guide above.

dnf install -y \
    gcc \
    glibc glibc-common \
    make \
    gettext \
    automake autoconf \
    wget \
    openssl-devel

Download Nagios Plugins Source Code

You can check for any latest Nagios plugins on Nagios Plugins page.

Get the latest stable release version number and substitute the value of the VER variable below;

VER=2.4.12

Next, download Nagios plugins source code.

wget https://nagios-plugins.org/download/nagios-plugins-${VER}.tar.gz

Extract Nagios Plugins Source Code

Once downloaded, extract it by running the command below

tar xzf nagios-plugins-${VER}.tar.gz

Configure Nagios Plugins

Navigate to Nagios plugins source directory and run the configure script to adapt the plugins to the system and check for any missing dependency.

cd nagios-plugins-${VER}

./configure --with-nagios-user=nagios --with-nagios-group=nagios

Compile Nagios Plugins on CentOS 9 Stream

If there is no configuration error, proceed to compile Nagios.

Ensure that user nagios is already created before you can proceed. You might need to install NRPE agent first.

getent passwd nagios

nagios:x:974:974::/var/spool/nagios:/sbin/nologin

The compile Nagios plugins.

make

Install Nagios Plugins on CentOS 9 Stream

You can now run the command below to install Nagios Plugins.

make install

This will install default Nagios plugins under the /usr/local/nagios/libexec/ directory.

ls -1 /usr/local/nagios/libexec/

check_apt      check_dhcp      check_flexlm     check_ifoperstatus  check_load      check_nagios  check_ntp_peer  check_ping   check_sensors  check_ssl_validity  check_udp     negate
check_breeze   check_disk      check_ftp        check_ifstatus      check_log       check_nntp    check_ntp_time  check_pop    check_simap    check_ssmtp         check_ups     remove_perfdata
check_by_ssh   check_disk_smb  check_http       check_imap          check_mailq     check_nntps   check_nwstat    check_procs  check_smtp     check_swap          check_uptime  urlize
check_clamd    check_dummy     check_icmp       check_ircd          check_mrtg      check_nt      check_oracle    check_real   check_spop     check_tcp           check_users   utils.pm
check_cluster  check_file_age  check_ide_smart  check_jabber        check_mrtgtraf  check_ntp     check_overcr    check_rpc    check_ssh      check_time          check_wave    utils.sh

Restart Nagios Core service

Now restart Nagios core service.

systemctl restart nagios

After that, login Nagios Server Web interface on the browser to confirm that the localhost services and state are now being monitored.

Verify Host and Service Monitoring on Nagios Server

Navigate to Nagios Web interface and check the local host status by clicking on the Hosts under Current Status on the left panel.

Check the status of the localhost services by clicking Services under Current Status on the left panel.

If the services have not updated their status, you can force check by selecting a host from the services host lists > Schedule a check of all services on this host.

The force check!

Fix Error: Could not stat() command file ‘/usr/local/nagios/var/rw/nagios.cmd’!

If upon hitting commit button to force check services on a host, you are welcomed by the error:

You are most likely to be dealing with SELinux access controls here!

So, login to the system and check the logs for any issue;

journalctl -n 100 -f

I found this, which is really helpful on how to fix the issue;

Nov 17 11:11:50 localhost.localdomain setroubleshoot[45737]: failed to retrieve rpm info for path '/usr/local/nagios/sbin/cmd.cgi':
Nov 17 11:11:50 localhost.localdomain setroubleshoot[45737]: failed to retrieve rpm info for path '/usr/local/nagios/var/rw/nagios.cmd':
Nov 17 11:11:50 localhost.localdomain systemd[1]: Started dbus-:[email protected].
Nov 17 11:11:50 localhost.localdomain setroubleshoot[45737]: SELinux is preventing /usr/local/nagios/sbin/cmd.cgi from getattr access on the fifo_file /usr/local/nagios/var/rw/nagios.cmd. For complete SELinux messages run: sealert -l f3d4a4f5-2da0-45d9-a372-4460a40d1a2d
Nov 17 11:11:50 localhost.localdomain setroubleshoot[45737]: SELinux is preventing /usr/local/nagios/sbin/cmd.cgi from getattr access on the fifo_file /usr/local/nagios/var/rw/nagios.cmd.
                                                             
                                                             *****  Plugin catchall (100. confidence) suggests   **************************
                                                             
                                                             If you believe that cmd.cgi should be allowed getattr access on the nagios.cmd fifo_file by default.
                                                             Then you should report this as a bug.
                                                             You can generate a local policy module to allow this access.
                                                             Do
                                                             allow this access for now by executing:
                                                             # ausearch -c 'cmd.cgi' --raw | audit2allow -M my-cmdcgi
                                                             # semodule -X 300 -i my-cmdcgi.pp
                                                             
Nov 17 11:12:00 localhost.localdomain systemd[1]: dbus-:[email protected]: Deactivated successfully.
Nov 17 11:12:00 localhost.localdomain systemd[1]: setroubleshootd.service: Deactivated successfully.
Nov 17 11:13:33 localhost.localdomain sshd[45754]: Connection closed by 127.0.0.1 port 40564 [preauth]
Nov 17 11:18:33 localhost.localdomain sshd[45769]: Connection closed by 127.0.0.1 port 50120 [preauth]

How to fix this is actually provided. So let’s execute the command provided!

ausearch -c 'cmd.cgi' --raw | audit2allow -M my-cmdcgi

semodule -X 300 -i my-cmdcgi.pp

Similarly, you can check for any denied entries in the auditd logs;

tail -f /var/log/audit/audit.log | grep denied

type=AVC msg=audit(1731861535.230:725): avc:  denied  { write } for  pid=45980 comm="cmd.cgi" name="nagios.cmd" dev="vda1" ino=44536 scontext=system_u:system_r:httpd_sys_script_t:s0 tcontext=system_u:object_r:usr_t:s0 tclass=fifo_file permissive=0

You can solve as follows;

tail /var/log/audit/audit.log | grep denied | grep nagios.cmd

The generate SELinux policy module;

tail /var/log/audit/audit.log | grep denied | grep nagios.cmd | audit2allow -M apachenagioscmd

Activate the policy;

semodule -i apachenagioscmd.pp

Restart Nagios and Apache;

systemctl restart httpd nagios

You should be able to force check the services now!

There you go. You have successfully installed Nagios Plugins on CentOS 9 Stream for localhost state and and service status monitoring.

Install Nagios Plugins from EPEL Repository

It is also possible to install Nagios plugins from EPEL repository.

Install EPEL repository on CentOS 9 Stream

dnf install epel-release

Once the installation is done, you can search for the available Nagios plugins by running the command below;

dnf search nagios-plugins-*

nagios-plugins-nt.x86_64 : Nagios Plugin - check_nt
nagios-plugins-dns.x86_64 : Nagios Plugin - check_dns
nagios-plugins-all.x86_64 : Nagios Plugins - All plugins
nagios-plugins-apt.x86_64 : Nagios Plugin - check_apt
nagios-plugins-dbi.x86_64 : Nagios Plugin - check_dbi
nagios-plugins-dig.x86_64 : Nagios Plugin - check_dig
nagios-plugins-dns.x86_64 : Nagios Plugin - check_dns
nagios-plugins-fts.noarch : Nagios probes to be run remotely against FTS3 machines
nagios-plugins-log.x86_64 : Nagios Plugin - check_log
nagios-plugins-ntp.x86_64 : Nagios Plugin - check_ntp
nagios-plugins-rpc.x86_64 : Nagios Plugin - check_rpc
nagios-plugins-ssh.x86_64 : Nagios Plugin - check_ssh
nagios-plugins-tcp.x86_64 : Nagios Plugin - check_tcp
...

You can also run the command below to list all plugins.

dnf list nagios-plugins-*

You can now install the specific plugins that you require. For example, to install Nagios plugins that checks the load, http, users, processes, disk space, swap space, uptime,dns, run the command below;

dnf install nagios-plugins-{load,http,users,procs,disk,swap,nrpe,uptime,dns}

Plugins that are installed using the package manager as stored under /usr/lib64/nagios/plugins/.

ls -1 /usr/lib64/nagios/plugins/

check_disk
check_dns
check_http
check_load
check_nrpe
check_procs
check_swap
check_uptime
check_users
eventhandlers
negate
urlize
utils.sh

There you go.

In our next guide, we will discuss how to install Nagios Remote Execution Plugins for remote host monitoring.

See Other similar guides by following the link below;

Nagios SNMP Monitoring of Linux Hosts on AlienVault USM/OSSIM

How to Install Nagios Plugins and NRPE agents on CentOS 7/RHEL 7/Fedora 29

Configure Nagios Availability Monitoring on AlienVault USM/OSSIM

How to Install Nagios Plugins From Source RHEL/CentOS/Oracle Linux