Wednesday, September 20, 2006


Nifty MDB tidbits

This stuff is actually kind of fun to play with. Yesterday, one of my colleagues was trying to figure out the option to ps to get it to display the actual time of day something was started, when it was started long enough ago that it only displays the month and day. I did some random poking with MDB (output slightly modified for formatting purposes. The 64-bit address is the proc structure.):
server# mdb -k
Loading modules: [ unix krtld genunix specfs dtrace 
cpu.AuthenticAMD.15 ufs ip sctp usba fcp fctl qlc 
lofs md cpc fcip random crypto zfs logindmux ptm nfs ]
> ::ps ! grep sshd
R   1298      1   ffffffff8166b150 sshd
R   6701   1298   fffffe82ca7d98f8 sshd
R   6727   6701   fffffe81b3205230 sshd
R  25827   1298   fffffe80eb61a6c8 sshd
R  25857  25827   fffffe82c7be5a20 sshd
R   8479   1298   fffffe82c7bdb988 sshd
R   8485   8479   fffffe80ec1296f8 sshd
> ffffffff8166b150::print -t proc_t ! grep time
 [ ... ]
            time_t tv_sec = 2006 Sep  7 15:00:44
 [ ... ]
(This was obviously just random poking and not necessarily the most efficient way to get this information.)
And here was a nifty problem that I ran across. We'd lost contact with a Solaris 8 server -- ssh gave a connection refused, and there was no response on the console. Someone dropped it to the ok prompt and ran 'sync' to get a core dump. I was looking at the core dump and noticed this:
server# mdb -k unix.0 vmcore.0
Loading modules: [ unix krtld genunix ip usba lofs 
random nfs ptm ]
> ::ps -f ! grep ssh
Z    428      1    0000030004938048 /usr/local/sbin/sshd
Hmm, sshd is a zombie, so it makes sense that there's no response on port 22. What about the console?
> ::ps -f ! grep ttymon
R   1152      1   0000030003f54040 /usr/lib/saf/ttymon
Z   1144      1   0000030004cf1540 /usr/lib/saf/ttymon 
         -g -h -p server console login:  -T sun -d /de
Hmm, that's odd. If the console ttymon died, init should have restarted it. That's what inittab says. So I look at init:
> ::ps -f ! grep init
Z      1      0      0000030001b81528 /etc/init -

Ayup, that would be a problem. If init's a zombie itself, it's not likely to be doing its job of restarting ttymon.

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