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 ServerLoaded: 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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