Updated OMD and Check_MK Agent returns Null

check-mkmonitoringnagios

I updated OMD to the current version using the following:

omd update <site>

Everything appears to update fine, but now my servers with the check_mk agent installed show (null) and I do not have current data. Here is a weird bit: it will inventory the services just fine, so the agent is working on the server to some extent. I have also attempted:

check_mk -II
check_mk -R

But that, too, did not work. If I spin up a new site and add one of the servers, it inventories fine, so I find it odd that an existing site is having issues getting updated information. I am hoping somebody can help me with this issue.

Thank you in advance!

Best Answer

does this also happen if you do

cmk -v server_host_name

or will that correctly return a status? If it works fine, there's two routes to look into:

Precompiling of checks is broken cmk -R does do that, but maybe it actually failed. I'd try cmk --debug -R (most of cases, this should be the issue) and even if that came out OK, I'd also delete the precompiled checks from var/check_mk/precompiled
A non-working nagios core (omd status), or issue with the config of it. (i.e. if you'd use livecheck or mod_gearman and this stopped working, or if the check result files aren't read any more...)

In any case, check the Nagios logfiles for this and the --debug -v flag to check_mk will also help you.

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Nginx – Reverse proxy with URL rewrite issues for check_mk and nginx

This is like WAY too late, but I stumbled upon this and ended up figuring it out. This has to be in your location block:

proxy_pass_header Authorization;
proxy_set_header X-Real-IP  $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_http_version 1.1;
proxy_set_header Connection "";
proxy_buffering off;
proxy_request_buffering off;
client_max_body_size 0;
proxy_read_timeout  36000s;
proxy_redirect off;
proxy_ssl_session_reuse off;
proxy_hide_header x-frame-options;

It may be a little more than needed, but it's what worked for me. Best of luck!

IPv6 to IPv4 – How to Change Check_mk Agent Listening

On Linux, the v6 sockets are dual stack by default, but this is platform specific behavior. Of course applications can still do AF_INET sockets, and would have to if v6 is not in the kernel. Beware, without v6 some apps may no longer work in their default configurations.

but on machines, where ipv6 is deaktivated for security reasons, it does not work.

Do not disable IPv6 completely on a host. You already broke a thing, and pretending it does not exist is not secure. Avoid adding to technical debt.

Instead, leave IPv6 enabled on hosts and manage your network. Just to name some basics, RA guard and other first hop security, firewall rules, and manage A or AAAA records in DNS. An IPv6 implementation is not required, but actually securing a network requires knowledge of both.

Best Answer

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Nginx – Reverse proxy with URL rewrite issues for check_mk and nginx

IPv6 to IPv4 – How to Change Check_mk Agent Listening

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