Thanks, Your strace examples are imminently more useful I just need to make sense of the output. For some reason even though it seems that host is getting the right answer it still tries the second dns server specified.
I also get: 2522 23:15:39 bind(20, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}, 16) = 0 2522 23:15:39 recvmsg(20, 0x41753ef0, 0) = -1 EAGAIN (Resource temporarily unavailable) which is a bit strange. Will investigate a bit further tomorrow when I am thinking clearly again. Regards On 1 March 2012 16:52, Hugh Brown <hbr...@divms.uiowa.edu> wrote: > > >>> strace -v -o filename host myserver.example.com >> >> Regards >> > > > strace -fvvvto filename -s 2048 <cmd> > > is my usual form of calling strace when I don't know what I want from > strace. I think you want to add a -f to follow any forked processes at the > least. > > > When I set up a bogus nameserver in my resolv.conf and strace it, I see > resolv.conf get read and then I see a > > sendmsg(20, {msg_name(16)={sa_family=AF_**INET, sin_port=htons(53), > sin_addr=inet_addr("192.168.1.**2") ... > and then later, I see a few -1 EAGAIN Resource temporarily unavailable. > > Next I see it attempt a sendmsg to the next IP in the list which gives it > an answer in a recvmsg a few lines down. > > If I put a correct nameserver back in resolv.conf and redo the strace, I > only see it attempt the first. > > So, a shortened version of strace that would just track the sendmsg call > would be > > strace -f -e sendmsg -s 2048 host myserver.example.com > > > If I don't do it with the -f flag, then I don't see the query process > happening. > > > Hugh > > ______________________________**_________________ > rhelv5-list mailing list > rhelv5-list@redhat.com > https://www.redhat.com/**mailman/listinfo/rhelv5-list<https://www.redhat.com/mailman/listinfo/rhelv5-list> > -- Gerhardus Geldenhuis
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