[ale] nslookup works, ping doesn't ???

[Greg Freemyer]

On Tue, Jan 19, 2010 at 3:00 PM, Brian Pitts <brian at polibyte.com> wrote:
> On 01/19/2010 02:28 PM, Greg Freemyer wrote:
>> I can ping local machines by IP.
>>
>> I can do:
>> nslookup yahoo.com 127.0.0.1
>> and
>> nslookup yahoo.com 10.0.1.44   (my desired primary dns server)
>>
>> Both those give the expected result.
>>
>> But "ping yahoo.com" comes back with unknown host.
>>
>> What gives?
>>
>> fyi: resolv.conf is not used in this distro.  I see 10.0.1.44 as my
>> nameserver down in /etc/sysconfig/network/config, but I don't know if
>> it is working.
>
> You could strace ping and see everywhere it checks for name resolution
> info. EG on my box it's reads resolv.conf, nsswitch.conf, host.conf, and
> hosts, then does a dns lookup using the server in my resolv.conf file.
> You can even see the data sent and received in the sendto() and
> recvfrom() calls, although tcpdump would make that easier to read.
>
Brain,

Good thought.

It does some basic stuff and quickly opens and closes resolv.conf.

Then it seems to interrogate "/var/run/nscd/socket"  (I don't know
what that is):

socket(PF_FILE, 0x80801 /* SOCK_??? */, 0) = 4
connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = 0
send(4, "\2\0\0\0\r\0\0\0\6\0\0\0hosts\0", 18, MSG_NOSIGNAL) = 18
poll([{fd=4, events=POLLIN|POLLERR|POLLHUP}], 1, 5000) = 1 ([{fd=4,
revents=POLLIN|POLLHUP}])
recvmsg(4, {msg_name(0)=NULL, msg_iov(2)=[{"\2\0\0\0|\255", 6},
{"\1\0\0\0D\th\267", 8}], msg_controllen=0,
msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 0
close(4)                                = 0
socket(PF_FILE, 0x80801 /* SOCK_??? */, 0) = 4
connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = 0
send(4, "\2\0\0\0\4\0\0\0\n\0\0\0yahoo.com\0", 22, MSG_NOSIGNAL) = 22
                                                       ^^^^^^^^^^^
this is the only attempt to resolve that I saw

poll([{fd=4, events=POLLIN|POLLERR|POLLHUP}], 1, 5000) = 1 ([{fd=4,
revents=POLLIN|POLLHUP}])
read(4, "\2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0",
32) = 32
close(4)                                = 0
write(2, "ping: unknown host yahoo.com\n", 29ping: unknown host yahoo.com
) = 29
exit_group(2)                           = ?