Nagios Support Forum

I am getting the Command not defined error when accessing remote client

It certainly has something to do with arguments because check_apt command works correctly.

ALL other checks return STATUS Unknown

I have followed the guide at https://support.nagios.com/kb/article.php?id=515 to install the NRPE from source on my nagios server. When I test NRPE locally, I get version
NRPE v3.2.1

if I run it returns
Usage:
check_users -w <users> -c <users>

if I run it returns the number of users logged on.

Not sure what else to do.

I always us the single quoted arguments syntax like in your example.
/usr/local/nagios/libexec/check_nrpe -H <remoteip> -c check_users -a '-w 5 -c 10'
You say the command above works, so what's the check_nrpe, command syntax and output that doesn't work?