host(1) & nslookup(1) hang, but name resolution ... works??!?
david at catwhisker.org
Wed Nov 28 07:17:04 PST 2007
OK; this is weird and probably rather vaguer than anyone would like.
I noticed this yesterday, but I needed to actually use my laptop at
work, so I didn't really have much opportunity to poke around. I did
some poking around this morning (on booting yesterday's CURRENT to build
today's), and here's some background and what I found:
* I normally run the laptop as a DHCP client.
* In dhclient-exit-hooks, I have a bit of code that uses the just-
acquired IP address as an argument to host(1), then parses the output
to determine a hostname to assign to the laptop. This has been
working for a very long time -- definitely as far back as FreeBSD 4.8;
probably earlier than that. It still works fine in RELENG_6 &
RELENG_7 (which I also track daily; the laptop gets a fair workout).
* I'm presently running:
FreeBSD g1-1.catwhisker.org 8.0-CURRENT FreeBSD 8.0-CURRENT #604: Tue Nov 27 07:17:37 PST 2007 root at g1-1.catwhisker.org.:/common/S4/obj/usr/src/sys/CANARY i386
which is where I first noticed the issue: the invocation of host(1)
appears to hang.
* I tried invoking host(1) from the command line; that invocation also hung.
* nslookup(1) also hung.
* I tried running tcpdump(1), then invoking host(1); there was no
indication of network traffic at all.
* I tried running host(1) under ktrace(1); running kdump(1) with "-E"
flag so I can see some timing, the output ends with:
9739 initial thread 0.010794 CALL getsockname(0x3,0xbfbfe140,0xbfbfe15c)
9739 initial thread 0.010820 RET getsockname 0
9739 initial thread 0.010837 CALL close(0x3)
9739 initial thread 0.010874 RET close 0
9739 initial thread 0.010892 CALL socket(PF_LOCAL,SOCK_STREAM,0)
9739 initial thread 0.010934 RET socket 3
9739 initial thread 0.010951 CALL close(0x3)
9739 initial thread 0.010982 RET close 0
9739 initial thread 0.012502 CALL _umtx_op(0xbfbfe0ac,0x3,0x1,0,0)
9739 initial thread 0.012535 RET _umtx_op 0
9739 initial thread 0.012552 CALL sigprocmask(SIG_BLOCK,0xbfbfe040,0x28501190)
9739 initial thread 0.012569 RET sigprocmask 0
9739 initial thread 0.012597 CALL _umtx_op(0x283168a0,0x5,0,0,0)
9739 initial thread 19.115591 RET _umtx_op RESTART
9739 initial thread 19.115650 PSIG SIGKILL SIG_DFL
As you can see, I waited about 19 seconds before killing the host(1)
process (with SIGKILL).
* Despite all of this, hostname resolution is actually working -- e.g.,
I can ping using a hostname:
g1-1(8.0-C) ping -c 2 freefall.freebsd.org
PING freefall.freebsd.org (188.8.131.52): 56 data bytes
64 bytes from 184.108.40.206: icmp_seq=0 ttl=56 time=14.120 ms
64 bytes from 220.127.116.11: icmp_seq=1 ttl=55 time=14.583 ms
--- freefall.freebsd.org ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 14.120/14.351/14.583/0.231 ms
which is a fairly useful thing, since I'm actually sending this
message from my internal mailhost (vs. my laptop). (It's also
something of which I wasn't aware yesterday at work, or I might
have been able to report this earlier.)
* Here's what ps(1) has to say:
g1-1(8.0-C) ps xwwl
UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND
1001 24683 24682 0 20 0 4500 2588 pause Is pe 0:00.06 csh
1001 24920 24683 0 44 0 5596 1896 umtxn I+ pe 0:00.01 host 172.17.1.1
* The host(1) process is not killed by SIGTERM, but SIGKILL does the job.
As noted, I'm building today's CURRENT now; if there's a change in
the behavior, I'll send a follow-up note.
I keep a local CVS repo mirror handy, and am not at all averse to
If there are other aspects of the behavior I might check on, please
let me know.
David H. Wolfskill david at catwhisker.org
Proprietary data formats obfuscate, rather than disseminate, information.
See http://www.catwhisker.org/~david/publickey.gpg for my public key.
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