Do i need to create a account for nagios user in linux

What I use:

  su - nagios -s /bin/bash

Which changes to the nagios user with the nagios user's environment using the shell "/bin/bash"

This message indicates that the account has been disabled by setting its shell (probably to /sbin/nologon). You can still run commands with that user's privileges if you want to; there are many ways to do this. For example, you can use su:

su nagios -s /bin/bash

Or you can use sudo:

sudo -u nagios <command>

The trick is just to get around running the user's default shell. Other things like cron jobs or suid programs which use this account, and certainly nagios, will work fine; the message only means that the user can't log in and get a shell.