Hi,
After upgrading Dovecot from version 2.2.27 to 2.3.9.2, we are sporadically seeing lots of these errors in the error log on many of our servers:
imap-login: Error: master(imap): net_connect_unix(imap) failed: Resource temporarily unavailable - http://wiki2.dovecot.org/SocketUnavailable
The issue is causing significant delays and/or timeouts on login.
From what I can tell, this happens because the imap-login service is unable to connect to the imap service socket, however I am unable to identify the root cause of the issue.
We have increased the client_limit for the stats service, as described in the upgrade document at (https://wiki2.dovecot.org/Upgrading/2.3). It is set to the same value as the process_limit for imap service.
System CPU usage does not appear to be saturated. The CPU usage sits at around 50% when these errors appear.
We have doubled the number of file descriptors after upgrading from 2.2.27. It was previously set to 16392 (which worked fine):
~# cat /proc/pidof dovecot/limits | grep "open files"
Max open files 30000 30000 files
We have tried increasing default_process_limit and default_client_limit from the default 1000 to 3000, but this has no effect.
Current configuration (with irrelevant parts removed):
~# doveconf -n
default_client_limit = 3000 # these were raised after upgrading in attempt to remedy default_process_limit = 3000 default_vsz_limit = 512 M [...] service imap-login { client_limit = 1250 inet_listener imap { port = 143 } inet_listener imaps { port = 993 ssl = yes } process_limit = 16 process_min_avail = 16 service_count = 0 vsz_limit = 512 M } service imap { client_limit = 1 process_limit = 20000 } service stats { client_limit = 20000 } [...]
We appear to be nowhere near the 20000 process_limit set for the imap service. We are also not seeing any warnings being logged with regards to the process_limit.
~# doveadm who -1 | wc -l 8765
~# doveadm process status | grep "^imap " | wc -l 7583
~# ps aux | grep "dovecot/imap" | wc -l 7449
~# doveadm process status | grep -v "^imap " name pid available_count total_count idle_start last_status_update last_kill_sent stats 19875 12384 582387 0 1578305489 0 pop3-login 19868 1000 0 0 1578061504 0 pop3-login 19867 1000 0 0 1578061503 0 pop3-login 19866 1000 0 0 1578061502 0 pop3-login 19865 1000 0 0 1578061503 0 pop3-login 19864 1000 0 0 1578061503 0 pop3-login 19853 1000 0 0 1578061504 0 pop3-login 19852 1000 0 0 1578061504 0 pop3-login 19851 1000 0 0 1578061504 0 pop3-login 19849 1000 0 0 1578061503 0 pop3-login 19847 1000 0 0 1578061503 0 pop3-login 19846 1000 0 0 1578061503 0 pop3-login 19845 1000 0 0 1578061503 0 pop3-login 19844 1000 0 0 1578061503 0 pop3-login 19843 1000 0 0 1578061503 0 pop3-login 19842 1000 0 0 1578061503 0 pop3-login 19839 1000 0 0 1578061502 0 log 19841 2973 27 0 1578061502 0 imap-login 19873 666 14942 0 1578305488 0 imap-login 19872 523 32792 0 1578305489 0 imap-login 19871 316 62876 0 1578305489 0 imap-login 19870 167 78332 0 1578305489 0 imap-login 19869 118 97989 0 1578305489 0 imap-login 19863 0 184726 0 1578305489 0 imap-login 19862 0 193094 0 1578305489 0 imap-login 19861 0 186800 0 1578305487 0 imap-login 19860 675 17806 0 1578305487 0 imap-login 19859 0 169446 0 1578305489 0 imap-login 19858 0 143517 0 1578305489 0 imap-login 19857 0 119215 0 1578305488 0 imap-login 19856 0 151958 0 1578305489 0 imap-login 19855 483 47036 0 1578305488 0 imap-login 19854 1 185240 0 1578305489 0 imap-login 19840 567 23859 0 1578305485 0 config 19874 2967 124482 0 1578305489 0 auth 19885 2967 124185 0 1578305489 0 anvil 10017 967 7567 0 1578305463 0
-- Eirik