On 9/12/2015 10:51 PM, Rajesh M wrote:

----- Original Message ----- From: Tony Morehen [mailto:tmorehen@ajmconsulting.ca] To: dovecot@dovecot.org Sent: Sat, 12 Sep 2015 17:57:27 -0400 Subject: Re: concerning dovecot settings for high volume server

You may be running up against Linux system/user limits. Run $ cat /proc/sys/kernel/pid_max and $ ulimit -a That should give some insight into your problem.

On 12/09/2015 2:53 PM, Rajesh M wrote:

...

hi

centos 6 64 bit

hex core processor with hyperthreading ie display shows 12 cores 16 gb ram 600 gb 15000 rpm drive

we are having around 4000 users on a server

i wish to allow 1500 pop3 and 1500 imap connections simultaneously.

need help regarding the settings to handle the above

imap-login, pop3-login imap pop3 service settings

i recently i got an error imap-login: Error: read(imap) failed: Remote closed connection (process_limit reached?)

my current dovecot config file

# 2.2.7: /etc/dovecot/dovecot.conf # OS: Linux 2.6.32-431.23.3.el6.x86_64 x86_64 CentOS release 6.5 (Final) auth_cache_negative_ttl = 0 auth_cache_ttl = 0 auth_mechanisms = plain login digest-md5 cram-md5 default_login_user = vpopmail disable_plaintext_auth = no first_valid_gid = 89 first_valid_uid = 89 log_path = /var/log/dovecot.log login_greeting = ready. mail_max_userip_connections = 50 mail_plugins = " quota" managesieve_notify_capability = mailto managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave namespace { inbox = yes location = prefix = separator = . type = private } passdb { args = cache_key=%u webmail=127.0.0.1 driver = vpopmail } plugin { quota = maildir:ignore=Trash quota_rule = ?:storage=0 } protocols = imap pop3 service imap-login { client_limit = 256 process_limit = 400 process_min_avail = 4 service_count = 0 vsz_limit = 512 M } service pop3-login { client_limit = 1000 process_limit = 400 process_min_avail = 12 service_count = 0 vsz_limit = 512 M } ssl_cert =

thanks very much,

rajesh

this is the first time i got this message since past over an year. the error went away as soon as i restarted dovecot.. surprisingly this happened in the night ie off-office hours.

here are the values i got

also could you provide me the settings for the limits if wish to handle around 1500 simultaneous connections of pop3 and imap each ?

the current values are as follows

[root@ns1 log]# cat /proc/sys/kernel/pid_max 49152

[root@ns1 log]# ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 127047 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 127047 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited

thanks rajesh

I'm no expert but it is my understanding that the binding limit would be the lower of pid_max or max user processes ie 49152. From that you would subtract 300 (reserved system pids) and the number of non-dovecot processes.

Dovecot itself uses about 6 base processes (/usr/sbin/dovecot -F; dovecot/anvil; dovecot/log; dovecot/config; dovecot/auth; dovecot/ssl-params) plus one processes for each logged-in pop3 and imap mailbox. That's one process for each pop3 account but potentially multiple imap mailboxes per imap account if the imap client is using idle to monitor multiple imap mailboxes for changes.

Assuming 10 mailboxes per simultaneous imap account, that would be 15000 processes, well below max_pid. I'd say that your problem does not appear to arise from system limits. Perhaps someone else could point you in a different direction.