Could not connect to socket /var/imap/socket/lmtp: Connection refused by localhost

[Eugene M. Zheganin]

Hi.

On 17.01.2017 19:09, Andy Dorman via Info-cyrus wrote:
>
> I am not an expert by any means and I hope someone corrects me if I 
> make a bad suggestion...but I have two questions:
>
> 1. It sounds like you have a heavily used server, so why do you have 
> Cyrus listening on both "localhost:lmtp" AND a unix socket 
> "/var/imap/socket/lmtp"?
>
> From the log entry it looks like your MTA uses a unix socket. Unless 
> you have something else (mail clients or other MTAs running on your 
> Cyrus server?) that need to communicate via the localhost:lmtp port, 
> you could comment out the unneeded lmtp service line and save those 
> resources.
Well, on one hand you are right, seems like noone uses network lmtp 
connections, but on the other hand how can the idle processes save 
resources ? They only can save the memory, which doesn't seem to be the 
problem. However, I will try you advice.
>
> 2. You say "increasing this value can make the situation even worse". 
> Which value?  There are 5 values on those two lines that you could 
> increase.  And by "even worse" do you mean even more refused connections?
The maxchild number.
>
> While I am not a Cyrus guru, I have seen my share of overloaded mail 
> servers and if you are running into a disk IO limit, adding more 
> processes fighting over a limited resource is very likely to make 
> things worse.  So you should also confirm a hardware limitation is not 
> at play here.
Yup, this is exaclty what happens when increasing the maxchild number: 
more messages start to bounce. And yes, the disks iops seems to be the 
limiting factor. So, are there any other approaches besides scaling out 
the disks iops ?

Thanks.
Eugene.