Red Hat Bugzilla – Bug 23712
udp sockets remain after dns reverse lookup fails
Last modified: 2016-11-24 10:07:21 EST
I have two RedHat 7.0 boxes running with the 2.2.16 SMP kernel.
Some services on both machines appear to have sockets remaining open to
the primary and secondary dns servers after a reverse lookup fails.
The first indication of the problem was when my max file descriptor limit
was reached, because of this I had increased the limit. After a bit more
investigation I noticed that when a reverse dns request is made by certain
services (ie: apache, sendmail, xinetd) and the remote authoritative host
for the reverse ip block fails, a socket is left resident in the system to
the local primary or secondary dns servers.
If the system is left unchecked, the entire machine will lockup after
roughly two days of activity on a medium load server.
The sockets are closed after the afflicted service is stopped and
I have only been able to reproduce these events on two SMP servers which
run the same hardware configurations in each. I don't have access to a
third server which runs RedHat 7 with SMP and different hardware to
completely verify the circumstances.
I have only seen one other instance of this happening in the newsgroups
and email lists. The other company affected had contacted me inregards to
the problem. After they had downgraded to RedHat 6.2, the problem was
Linux web 2.2.16-22smp #3 SMP Fri Nov 3 22:08:03 EST 2000 i686 unknown
apache compiled with egcs-2.91.66
Visual of the problem:
# netstat -an | grep '.53' | grep udp
udp 0 0 web:3129 188.8.131.52:53 ESTABLISHED
udp 0 0 web:3128 184.108.40.206:53 ESTABLISHED
udp 0 0 web:3127 220.127.116.11:53 ESTABLISHED
udp 0 0 web:3126 18.104.22.168:53 ESTABLISHED
udp 0 0 web:3125 22.214.171.124:53 ESTABLISHED
udp 0 0 web:3124 126.96.36.199:53 ESTABLISHED
# fuser -n udp 3124
# ps ax | grep 2360
2360 ? S 0:00 /usr/local/httpd/bin/httpd
# netstat -an | grep '.53' | grep udp | wc -l
Packet level visual:
14:03:40.085211 eth0 > web.efni.com.2640 > rhymes.efni.com.domain: 31440+
PTR? 188.8.131.52.in-addr.arpa. (44)
14:03:40.086942 eth0 < rhymes.efni.com.domain > web.efni.com.2640: 31440
ServFail 0/0/0 (44) (DF)
udp 0 0 184.108.40.206:2640 220.127.116.11:53
15:11:07.482324 eth0 > web.efni.com.2168 > rhymes.efni.com.domain: 54530+
PTR? 251.146.3.209.in-addr.arpa. (44)
15:11:07.484169 eth0 < rhymes.efni.com.domain > web.efni.com.2168: 54530
ServFail 0/0/0 (44) (DF)
udp 0 0 18.104.22.168:2168 22.214.171.124:53
In the two instances listed above, I had waited roughly two minutes
before checking for the socket in a netstat.
This bug is marked as glibc as I believe it was the proper place for the
report, but I could very easily have been mistaken on this..
UNIX Systems Administration
Tel: (705) 474-3364 ext. 2557
Fax: (705) 472-9202
PGP KEY: http://users.efni.com/admin/pgp/
I have the same problem which is on my machine triggered by silent releasing of
the eth0 interface (which I still don't know why it releases). After that the
open UDP sockets (by httpd especially) stay opened even when I start the eth0
I have RedHat Linux 7.0 with all recent updates applied but with kernel 2.2.18.
Machine is Celeron II 566 with ASUS CUV4X MB and 3COM ethernet card.
*** This bug has been marked as a duplicate of 18332 ***