concerning dovecot settings for high volume server

[Rajesh M]

----- Original Message -----
From: Tony Morehen [mailto:tmorehen at ajmconsulting.ca]
To: dovecot at 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 = </var/qmail/control/servercert.pem
> ssl_dh_parameters_length = 2048
> ssl_key = </var/qmail/control/servercert.pem
> userdb {
>    args = cache_key=%u quota_template=quota_rule=*:backend=%q
>    driver = vpopmail
> }
> protocol imap {
>    imap_client_workarounds = delay-newmail
>    mail_plugins = " quota imap_quota"
> }
> protocol pop3 {
>    pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
>    pop3_fast_size_lookups = yes
>    pop3_lock_session = no
>    pop3_no_flag_updates = yes
> }
>
>
> 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 at ns1 log]# cat /proc/sys/kernel/pid_max
49152

[root at 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