nagios4 command not found

In this troubleshooting guide we learn how to fix nagios4 command not found error message

Introduction

When you run more command in linux terminal / console, you get the following error message

nagios4: command not found

or when using sudo you get the following error message

sudo: nagios4: command not found

In Ubuntu nagios4 is provided by nagios4-core package.

nagios4-core is:

Nagios is a monitoring and management system for hosts, services and networks. The package contains the nagios4 monitoring daemon.

Nagios’ features include:

Monitoring of network services (via TCP port, SMTP, POP3, HTTP, NNTP, PING, etc.)
Plugin interface to allow for user-developed service checks
Contact notifications when problems occur and get resolved (via email, pager, or user-defined method)
Ability to define event handlers to be run during service or host events (for proactive problem resolution)
Web output (current status, notifications, problem history, log file, etc.)

To fix this problem, we can install more using the command below.

sudo apt-get -y install nagios4-core

This command might take some time to finish depending on your machine internet connection.

You can also use apt command to install nagios4-core.

sudo apt -y install nagios4-core

Or if you have aptitude installed you can use the following command.

sudo aptitude install nagios4-core

In this tutorial we learn how to fix nagios4 command not found error in Ubuntu / Debian / Kali Linux or Raspbian distribution.