Re: "Resource temporarily unavailable", systemd and your FAQ Webpage

[Nicola Nye via Info-cyrus <info-cyrus@xxxxxxxxxxxxxxxxxxxx>]

Thanks Stephan!

I will fold your information into the FAQ as this is a topic which comes up semi regularly on the list. 

   Nicola

On Fri, Dec 16, 2016, at 07:54 PM, Stephan Lauffer via Info-cyrus wrote:

Hello!

While testing 2.5 we struggled over (known) problems like this...:

  ...ssh can't fork process to run service imaps/ipv4: Resource 

temporarily unavailable

I searchd... and I found your FAQ...

  https://cyrusimap.org/imap/faqs/o-toomanyprocesses.html

...and this "tcp_keepalive = 1" hint was doing a good job, but not 

fixing our problem completely. Less processes as without this setting 

but too many at all.

Btw we have a murder with 5 backends and each has about 5k mboxes. 

With 2.4 we have about 400 imapd processes on the backends (in normal 

state) and about 800 on the proxy. Peaks raises this values for sure.

But we still wasn't able to get over a limit of about 500 imapds on 

our new system which is running 2.5. Yesterday night I found our 

problem:

  SYSTEMD

(and not cyrus-imapd-2.5, but 2.5 was running with systemd here...)

I guess there may be more people out there which may be interested in 

a solition (we will add fixes to our systemd scripts of our suse bulds 

soon, see  

https://build.opensuse.org/package/show/home:nixda:devel/cyrus-imapd).

The first problem there is:

Systemd does not care about your /etc/security/limits.conf

The second problem is:

Systemd comes with a new limit called "TasksMax". You will find this 

limit f.e. in /etc/systemd/system.conf as "DefaultTasksMax=512". But 

you will NOT find this limit in "cat /proc/`cat 

/var/run/cyrus.pid`/limits".

The solution is to add a file with a systemd override for this 

service. F.e. use the systemctl edit <sevice> command... (like 

"systemctl edit cyrus-imapd.service") or place a file in 

/etc/systemd/system/cyrus-imapd.service.d/override.conf with f.e.:

[Service]

TasksMax=2048

LimitNOFILE=10000

The LimitNOFILE is just a guess... maybe you may not need this here.

After setting this override you will see a status information about 

your process count and limit like this:

  # systemctl status cyrus-imapd.service

● cyrus-imapd.service - The Cyrus IMAP and POP Mail Server

    Loaded: loaded (/usr/lib/systemd/system/cyrus-imapd.service; 

enabled; vendor preset: disabled)

  Drop-In: /etc/systemd/system/cyrus-imapd.service.d

            └─override.conf

    Active: active (running) since Thu 2016-12-15 20:51:17 CET; 12h ago

  Main PID: 12901 (master)

    Tasks: 326 (limit: 2048)

[...]

What about adding a short hint to your faq? Yes, it is not a cyrus 

problem. And yes, a sysadmin should know... but... I guess systemd in 

depth may not be good known as the old ulimit thing and if you are 

searching in the web 99% of the hits deal with ulimit.

--

Liebe Gruesse, with best regards

Stephan Lauffer

Pedagogical University Freiburg - Germany

http://www.ph-freiburg.de/zik/

Fon/ Fax: +49 761 682 -559/ -486

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