Nagios Support Forum

After rhel8 to rhel9 update, nagios client is not connecting. Message on ui is:
CHECK_NRPE: Receive header underflow - only -1 bytes received (4 expected

Hello @soigan23,

I often see this error when there is an SSL mismatch and the handshake is unable to be completed. If the daemon is expecting SSL to be used and the plugin is used with the --no-ssl or -n flag, then this error is often the result.

What is the result of the following command (if run from the monitoring server)? - Emmett

Hi Emmett,

[root@prod-mon-n1 ~]# /usr/lib64/nagios/plugins/check_nrpe -H prod-nlog-n1
NRPE v4.1.2

[root@prod-mon-n1 ~]# /usr/lib64/nagios/plugins/check_nrpe -n -2 -H prod-nlog-n1
CHECK_NRPE: Receive header underflow - only -1 bytes received (4 expected).
[root@prod-mon-n1 ~]#

This is fixed by adding
define command {
command_name check_nrpe_v2
command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$ -t 50
}

in /etc/nagios/objects/commands.cfg file

and creating new cfg files in /etc/nagios/objects for upgraded vms and adding these new config files in /etc/nagios/nagios.cfg

Hi @soigan23,

I'm glad you found a fix, because NRPE sometimes has the vaguest error messages. Just for my notes, what did the old command definition for check_nrpe look like?

Thanks,
- Emmett