Hello guys.
Possible this topic was there already, just I dont know how to correctly search for it.
I migrated central distribution site from checkmk appliance into checkmk build on ubuntu linux.
What we realized after is, that there are some issues with “nullmailer” email.
On appliance the setting is easy - but how to set it on linux system?
You have to configure a smarthost or relay host for nullmailer.
try sudo dpkg-reconfigure -plow nullmailer (if nullmailer is installed)
On a normal Linux system, Checkmk by default just uses the locally installed MTA, be it nullmailer, postfix, sendmail, exim, … To configure that MTA is up to the Linux admin, using the tools and config files of their distribution. See the docs for a more detailed explanation:
thanks both.
of course i know that there must be some mail system enabled.
on this linux host is the postfix working, which have as mailname in /etc/mailname set lets say “domain” (there was hostname@domain - which led to format central@hostname@domain - which mail server didnt likes - but as i removed hostname@ and there remain only a domain in that mailname - it at least now feed the teams channel)
all emails by default are send with “whatever@domain”.
so far all is good.
issue is, that site is called “Central” and in past on appliance the nullmailer was set as on picture ^^ nagios-central@domain.
After migration to linux based system from appliance - it send only as “Central@domain” now after update of mailname was made. And I am looking for the solution / config location where i can rename it back to nagios-central (without renaming site) as the “Central” is correct for sitename, but not for “from” field for this nullmailer.
Hope I was able to explain it a little better.
You got me confused with the reference to nullmailer … Checkmk itself does not include nullmailer or any other MTA, it just uses mail (heirloom-mailx) as a client to talk to the local MTA (nullmailer in the appliance, postfix in your case).
In your notification rules, you can set the From address and display name for the outgoing notification mails.
Or you could set up an address mapping in your local postfix, see Postfix Address Rewriting
Thanks Martin.
Possible i will end with address maping on Postfix.
What I dont understand is that on appliance all local emails can be set quickly and easily thru web interface, while on linux based installation its not “easy” or “easily to be found” 
As well I know about the “from” and “display name” which are possible to change in the Wato for every rule created … just this rule which was on appliance is not visible on wato notification section - if it was, its easy as well.
its not even possible to adjust the “From” on the global settings in wato.
Checkmk itself is the same in both setups, relying on the MTA in the underlying system, be it the appliance or a “normal” Linux system.
The appliance is meant for people without Linux knowledge. It’s like a “Checkmk-specific Linux distribution”, ready to use. Looks like tribe29 did a good job there and have offered an easy interface for the MTA configuration. Of course it helps that nullmailer is a rather simple MTA that doesn’t have too many features anyway.
If you have a Linux server running a general-purpose Linux distribution that you install and administrate yourself, then you need to configure your MTA yourself as well. With the tools/methods your distribution offers. You could also use nullmailer instead of postfix, but that’s your own decision.
What your screenshot of the Global settings shows is the fallback address – that’s a destination address, not a from. Totally unrelated.
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