Help:: Listen queue overflow killing servers

Paul Macdonald paul at
Fri Jul 26 12:15:32 UTC 2019


Over the past few months i've seen several boxes (4 or 5) become 
unresponsive as a result of a Listen queue overflow state.

Processes stack up, none are killable, all these are within jails and 
neither the jail can be stopped nor the server rebooted (without a power 

All are on ZFS and are std apache/php/mysql servers with nothing too exotic.

All on 12.0-RELEASE, i've only started seeing these issues recently, but 
it feels like more and more.

/var/log/messages shows tyically;

     kernel: sonewconn: pcb 0xfffff813395e3d58: Listen queue overflow: 
193 already in queue awaiting acceptance (83 occurrences)

netstat -Lan  shows

tcp4 193/0/128                          x.x.x.x.443
tcp4  193/0/128                          x.x.x.x.80

connections cannot be killed with tcpdrop ( except ssh which can!)

All processes seem to be in Disk State ( many many apache processes but 
others getting stuck too)

www      60089    0.0 0.1  196588   78328  -  DJ   21:07         1:19.54 
/usr/local/sbin/httpd -DNOHTTPACCEPT

www      93713    0.0 0.0  183576   33164  -  DJ   23:57         0:00.01 
/usr/local/sbin/httpd -DNOHTTPACCEPT

but no zombies..

last pid: 24773;  load averages:  0.00,  0.00, 0.00                   
     up 52+11:41:09  11:48:02
918 processes: 1 running, 917 sleeping
CPU:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
Mem: 107M Active, 3729M Inact, 93G Wired, 27G Free
ARC: 79G Total, 54G MFU, 23G MRU, 243M Anon, 710M Header, 1615M Other
      73G Compressed, 191G Uncompressed, 2.60:1 Ratio
Swap: 4096M Total, 4096M Free

I'd appreciate any advice as at present it looks like my only option is 
to hard power cycle these

many thanks


Paul Macdonald
Web and video hosting
t: 0131 5548070
m: 07970339546
e: paul at
40 Maritime Street

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