Nagios Support Forum

Questions around nrpe. We see a lot of these error messages

Feb 3 13:58:49 xx-xx-001 nrpe[53960]: Error: (use_ssl == true): Request packet version was invalid!
Feb 3 13:58:49 xx-xx-001 nrpe[53960]: Could not read request from client 10.2.36.191, bailing out...
Feb 3 13:58:49 xx-xx-001 nrpe[53960]: INFO: SSL Socket Shutdown.

We don’t use SSL so why would this be happening?

More info:

The check_nrpe on the server is version 4

root@xx-xx-001 0 14:03:31 /usr/local/nagios/etc # /usr/local/nagios/libexec/check_nrpe --version
NRPE Plugin for Nagios
Version: 4.0.3

The nrpe version on the clients are version 3 with no updates to version 4 available.

root@xx-xx-001 0 14:00:57 /var/log # yum info nrpe
Loaded plugins: product-id, rhnplugin, search-disabled-repos, subscription-manager
This system is receiving updates from RHN Classic or Red Hat Satellite.
eus-custom-repo_c | 871 B 00:00:00
Installed Packages
Name : nrpe
Arch : x86_64
Version : 3.2.0
Release : 6.el7
Size : 356 k
Repo : installed
From repo : eus-epel-7_2018-07-11
Summary : Host/service/network monitoring agent for Nagios
URL : http://www.nagios.org
Licence : GPLv2
Description : Nrpe is a system daemon that will execute various Nagios plugins
: locally on behalf of a remote (monitoring) host that uses the
: check_nrpe plugin. Various plugins that can be executed by the
: daemon are available at:
: http://sourceforge.net/projects/nagiosplug
:
: This package provides the core agent.

Available Packages
Name : nrpe
Arch : x86_64
Version : 3.2.1
Release : 8.el7
Size : 261 k
Repo : eus-epel-77_2020-02-24
Summary : Host/service/network monitoring agent for Nagios
Licence : GPLv2
Description : Nrpe is a system daemon that will execute various Nagios plugins
: locally on behalf of a remote (monitoring) host that uses the
: check_nrpe plugin. Various plugins that can be executed by the
: daemon are available at:
: http://sourceforge.net/projects/nagiosplug
:
: This package provides the core agent.

Apparently newer versions of the NRPE receiver will straight-up reject packets from version 3 of the Nagios NRPE client:

NRPE daemon should no longer accept packets from version 3, and the client should never accept packets unless they match the packet version that was sent.
-- madlohe (NagiosEnterprises/nrpe@5ed18d75)

As far as why it's reporting SSL = true when you disabled SSL, I'd need to inspect your configuration to determine what's going on. Seems like the only way to disable SSL on the receiver side is to run nrpe with the -n flag. What's the output from the following command?

Woah thats a bit of a worry as we have version 3 on receivers and 4 on the server..

Regarding SSL this is the output of the ps command:
/usr/sbin/nrpe -c /etc/nagios/nrpe.cfg -d

Does that error go away if you pass a -3 to the check?
Or: