Help:: Listen queue overflow killing servers

Robert Schulze rs at
Fri Jul 26 13:19:45 UTC 2019


Am 26.07.19 um 15:08 schrieb Paul Macdonald via freebsd-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)

like I already mentioned: if a webserver process is stuck in disk-wait,
this process will probably not answer any further requests, so the
listen backlog will fill up.

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

again: your problem are the webserver processes in disk-wait. This
process state is uninterruptible, processes in this state cannot be
killed. A process simply reaching somaxcon will not interfere with

> I've increased the queue size via
> sysctl kern.ipc.somaxconn
> to 1024 for now

You will not solve your problem by increasing somaxconn. You have to
figure out why these processes are stuck in disk i/o (see previous hints
about procstat).

Robert Schulze

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