How to create a Nagios Core contact and contact group

Nagios Core routes alert recipients through contact objects and contact groups. A contact stores the person, mailbox, notification periods, and notification commands, while a contact group gives host and service definitions a stable recipient name that can stay the same when team membership changes.

On Ubuntu and Debian package installs, the main configuration reads packaged sample contacts from /etc/nagios4/objects/contacts.cfg and extra local snippets from /etc/nagios4/conf.d. Keeping new contact objects in a separate file under /etc/nagios4/conf.d makes validation and rollback easier than editing the packaged sample file directly.

The sample contact inherits generic-contact, so the packaged notification periods, options, and email notification commands remain active. The host or service notification period and state filters still decide whether Nagios sends a message for a given event. Replace the sample address with the real mailbox, attach the group to the host or service that should notify it, and run a controlled notification test after the configuration loads.

Steps to create a Nagios Core contact and contact group:

Confirm that the local object directory is loaded by Nagios Core.
```
$ grep '^cfg_dir=/etc/nagios4/conf.d' /etc/nagios4/nagios.cfg
cfg_dir=/etc/nagios4/conf.d
```
Current Ubuntu and Debian packages include /etc/nagios4/conf.d by default. Add a cfg_dir or cfg_file entry first when your installation stores local objects somewhere else.
Related: How to add a Nagios Core object configuration directory
Create a local object file for the contact and group.
```
$ sudoedit /etc/nagios4/conf.d/ops-contact.cfg
```

Add the contact and contact group definitions.

define contact {
    use                             generic-contact
    contact_name                    ops-primary
    alias                           Primary Operations Contact
    email                           ops-primary@example.net
}
 
define contactgroup {
    contactgroup_name               linux-admins
    alias                           Linux Administrators
    members                         ops-primary
}

generic-contact supplies the notification periods, notification options, and packaged email notification commands. Use the real mailbox or distribution list for email.

Create or edit the monitored object that should notify the new group.
```
$ sudoedit /etc/nagios4/conf.d/web01-contact-target.cfg
```
Use the existing host or service file when the object is already defined. Nagios object names must stay unique across all loaded configuration files.

Related: How to add a host in Nagios Core
Related: How to add a service check in Nagios Core

Assign the contact group to the host or service.

define host {
    use                             linux-server
    host_name                       web01.example.net
    alias                           Web 01
    address                         192.0.2.10
    contact_groups                  linux-admins
}

contact_groups sets the recipient group for that object. Include any existing groups that should keep receiving alerts, and use the same directive inside a service definition when only one service should notify linux-admins.

Validate the Nagios Core configuration.

$ sudo nagios4 -v /etc/nagios4/nagios.cfg
Nagios Core 4.4.6
##### snipped #####
Reading configuration data...
   Read main config file okay...
   Read object config files okay...

Running pre-flight check on configuration data...

Checking objects...
	Checked 8 services.
	Checked 2 hosts.
	Checked 1 host groups.
	Checked 0 service groups.
	Checked 2 contacts.
	Checked 2 contact groups.
##### snipped #####
Total Warnings: 0
Total Errors:   0

Things look okay - No serious problems were detected during the pre-flight check

Zero errors confirm that ops-primary, linux-admins, and the object using contact_groups linux-admins all parse together.
Related: How to validate the Nagios Core configuration

Reload the nagios4 service to load the new object definitions.
```
$ sudo systemctl reload nagios4
```
Ubuntu and Debian package installs use the nagios4 unit. Use the local service name or source-install control script when Nagios Core was installed outside the package layout.
Related: How to manage the Nagios Core system service
Confirm that Nagios Core remains active after the reload.
```
$ sudo systemctl is-active nagios4
active
```
Check /var/log/nagios4/nagios.log or the journal if the service is not active after the reload.
Related: How to check Nagios Core logs
Trigger a controlled notification for the object that uses the new group.

The test should send to the mailbox behind ops-primary and record the notification against the host or service that references linux-admins.
Related: How to test Nagios Core notifications