Help:: Listen queue overflow killing servers

Paul Macdonald paul at
Fri Jul 26 13:08:29 UTC 2019

On 26/07/2019 13:52, Robert Schulze wrote:
> Hi,
> Am 26.07.19 um 13:58 schrieb Paul Macdonald via freebsd-questions:
> I think, these processes waiting for disk i/o are actually your problem.
> Since they cannot answer further requests, they run into the listen
> queue overflow.
> You should check the processes with procstat:
> list kernel threads:
> # procstat -kk <PID>
> list open files:
> # procstat -f <PID>

One of the things we do (whihc may be bad)  is to log to a single file ( 
e.g all.sites.log, this doesn;t seem to cause problems in general , but 
i can see how if there's X child processes then they may all need write 

Is that a really bad idea? ( Often handy to have one file for differnet 
vhosts, but maybe that needs a rethink)

In this case the drive is NVMe, and there's actually  only a handful of 
sites, (Other servers have several hundreds of sites, much busy but 
don;t display  the issue)

In answer to some of the other suggestions, its not actually under high 
load ( 5000 lines in the apache log for the whole day), and system has 
16C/32T,  128GB RAM

ZFS is using a bunch of RAM as i've not limited the ARC, but there's 
27GB free currently.

I guess i actually have 2 questions

1) why are the queues filling up (i'll  revert to seperate logs to see 
if that helps, although the issue is sporadic, and first time on this box)

2)  Once the queues are over limit, is this actually unresolvable other 
than a hard reboot?

I've increased the queue size via

sysctl kern.ipc.somaxconn

to 1024 for now

but netstat -Lan still shows

tcp4  0/0/128                          x.x.x.x.443
tcp4  0/0/128                          x.x.x.x.80

thanks for assiestence


> with kind regards,
> Robert Schulze
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Paul Macdonald
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