Issue dovecot Error "Timeout waiting for handshake response"

[enduser]

Server operating system version

AlmaLinux 9.5

Plesk version and microupdate number

18.0.68 Update #2

Hi all,

We have been running our Plesk server for a long time without issues, hosting many users. However, sometimes when there are numerous IMAP connections, including from webmail, the performance slows down significantly and ultimately results in an "internal server error." Below are the errors encountered when this issue arises.

Apr 24 10:52:13 server-a dovecot[65476]: imap(87285): Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:13 server-a dovecot[65476]: imap(87284): Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:13 server-a dovecot[65476]: imap(87287): Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:14 server-a dovecot[65476]: imap-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:17 server-a dovecot[65476]: pop3: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:17 server-a dovecot[65476]: imap: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:18 server-a dovecot[65476]: pop3-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:19 server-a dovecot[65476]: imap-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:22 server-a dovecot[65476]: pop3: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:22 server-a dovecot[65476]: imap: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:23 server-a dovecot[65476]: pop3-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:24 server-a dovecot[65476]: imap-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:27 server-a dovecot[65476]: pop3: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:27 server-a dovecot[65476]: imap: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:28 server-a dovecot[65476]: pop3-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:29 server-a dovecot[65476]: imap-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:32 server-a dovecot[65476]: pop3: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:32 server-a dovecot[65476]: imap: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:33 server-a dovecot[65476]: pop3-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:34 server-a dovecot[65476]: imap-login: Error: conn unix:stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:35 server-a postfix-local[87520]: 6F414D2ABD0: process '/usr/libexec/dovecot/dovecot-lda -d "$DELIVERED_TO" -a "${ORIGINAL_RECIPIENT:-$DELIVERED_TO}"' stderr : lda([email protected]): Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:36 server-a postfix-local[87536]: BDA59D2A9B9: process '/usr/libexec/dovecot/dovecot-lda -d "$DELIVERED_TO" -a "${ORIGINAL_RECIPIENT:-$DELIVERED_TO}"' stderr : lda([email protected]): Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:38 server-a dovecot[65476]: pop3: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response
Apr 24 10:52:38 server-a dovecot[65476]: imap: Error: conn unix:/var/run/dovecot/stats-writer (pid=65473,uid=0): Timeout waiting for handshake response

After we restart the server, it will be fine for short time, but soon it will repeat the problem again.

Any clues and solutions? Many thanks

 

[Sebahat.hadzhi]

Hello, @enduser . Kindly execute the following commands:

systemctl status dovecot
journalctl -xu dovecot

and let us know what's the output.

Likely this can help, but I want to make sure what's the root cause of the issue.

 

[enduser]

Thank you Sebahat.hadzhi.

I have checked all the /var/qmail/mailnames/*/*/Maildir/dovecot.index.cache files, and the largest one is 63 MB. Based on this, I suspect that the default_vsz_limit doesn't help. Am I correct?

For "journalctl -xu dovecot", the output are all about users' login records, the most valued records are in my first post.

For "systemctl status dovecot", attached

 

[Sebahat.hadzhi]

Thank you. I don't think the file size is directly related to memory used and the default_vsz_limit. Anyhow, if that's the issue a more specific error/warning would most likely have been logged. At this point, I don't see anything in the logs that would hint what exactly the issue is.

How's the memory consumption of the server when the issue occurs? If you haven't noticed any issue with insufficient memory. I would suggest to try increasing the default_client_limit parameter to test if there's any positive impact:

• https://support.plesk.com/hc/en-us/...t-limit-is-lower-than-required-under-max-load