Dovecot service stops with the error: "Warning: service(pop3-login): process_limit (100) reached, client connections are being dropped"

Created:

2017-05-24 17:46:53 UTC

Modified:

2017-08-08 13:18:51 UTC

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Dovecot service stops with the error: "Warning: service(pop3-login): process_limit (100) reached, client connections are being dropped"

Symptoms

Dovecot service stops with a differnet time interval.

A huge amount of same errors can be found in the /var/log/maillog:

May 24 13:25:38 mdimail9 dovecot: master: Warning: Killed with signal 15 (by pid=25795 uid=0 code=kill)
May 24 13:25:55 mdimail9 dovecot: master: Warning: Killed with signal 15 (by pid=25926 uid=0 code=kill)
May 24 13:27:26 mdimail9 dovecot: master: Warning: Killed with signal 15 (by pid=26222 uid=0 code=kill)

 

Also, before the killing of the processes above the following error also can be found:

May 24 13:13:04 mdimail9 dovecot: master: Warning: service(pop3-login): process_limit (100) reached, client connections are being dropped
May 24 13:13:04 mdimail9 dovecot: master: Warning: Killed with signal 15 (by pid=23093 uid=0 code=kill)

The following errors may be observed in /var/log/maillog:

May 26 03:48:27 thor dovecot: pop3-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=10.10.10.10, lip=20.20.20.20, session=<WomZiGNQD81ItjsF>

May 26 03:48:27 thor dovecot: pop3-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=10.10.10.10, lip=20.20.20.20, session=<Z5iZiGNQEc1ItjsF>

May 26 03:48:27 thor dovecot: pop3-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=10.10.10.10, lip=20.20.20.20, session=<v6mZiGNQQc5ItjsF>

Cause

A number of dovecot processes on the system is higher than its current limit.

Resolution

1. Execute the command 

# ps -aux | grep dovecot | grep -v grep | wc -l
250

when the service dovecote fails next time in order to identify the service load.

2. Increase the value default_process_limit according to the service needs. Add 

default_process_limit = 300

to the end of the dovecot configuration file /etc/dovecot/dovecot.conf.

3. Start the dovecot service:

# service dovecot start

Note: If you face following warnings:

# service dovecot restart
Stopping Dovecot Imap: [ OK ]
Starting Dovecot Imap: doveconf: Warning: service auth { client_limit=1000 } is lower than required under max. load (1100)
doveconf: Warning: service anvil { client_limit=1000 } is lower than required under max. load (1103)
Warning: service auth { client_limit=1000 } is lower than required under max. load (1100)
Warning: service anvil { client_limit=1000 } is lower than required under max. load (1103)

add 

default_client_limit = 1200

to the end of the /etc/dovecot/dovecot.conf file.

Restart the dovecot service:

# service dovecot start

Note: If you face the following warning:

# service dovecot restart
Stopping Dovecot Imap: [ OK ]
Starting Dovecot Imap: Warning: fd limit (ulimit -n) is lower than required under max. load (1024 < 1200), because of default_client_limit

add

ulimit -n 1300

to the end of the /etc/sysconfig/dovecot file.

Restart the dovecot service:

# service dovecot start

4. If the service dovecot stops with the similar error in the /var/log/maillog it is needed to increase the default_process_limit value even more (according to the step 1). 

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