-bash: nslookup: command not found in rhel, centos and Ubuntu

[root@monitor ~]# nslookup <FQDN>
-bash: nslookup: command not found

The Linux Install did not come with bind-utils pacakge, Which needs to be install in order to use nslookup. You can install bind-utils with following procedure.

Login as root.
yum install bind-utils -y


You can search for what package provides a command using the yum provides command:

yum provides '*bin/nslookup'

How to install dig, nslookup commands in Debian based server?
In ubuntu the package is  “dnsutils”
You can Search it as well:
root@ubuntu:~# apt-cache search nslookup
dnsutils - Clients provided with BIND

root@ubuntu:~# apt-get update
root@ubuntu:~# apt-get install dnsutils -y