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Has anyone ever seen this before? Note that this happens not only with, but with every domain I try. It's a wireless connection (WEP), but I'm not sure how that would be relevant:

$ curl -v
# This takes about 60s to return
* getaddrinfo(3) failed for
* Couldn't resolve host ''
* Closing connection #0
curl: (6) Couldn't resolve host ''

$ wget
--2011-11-28 14:44:08--
Resolving failed: Name or service not known.
wget: unable to resolve host address `'

$ ping
PING ( 56(84) bytes of data.
64 bytes from ( icmp_req=2 ttl=54 time=136 ms
64 bytes from ( icmp_req=3 ttl=54 time=34.0 ms
64 bytes from ( icmp_req=4 ttl=54 time=34.3 ms
64 bytes from ( icmp_req=5 ttl=54 time=42.5 ms
64 bytes from ( icmp_req=6 ttl=54 time=44.7 ms
64 bytes from ( icmp_req=7 ttl=54 time=34.5 ms
--- ping statistics ---
8 packets transmitted, 6 received, 25% packet loss, time 7007ms
rtt min/avg/max/mdev = 34.063/54.376/136.026/36.758 ms

$ host has address has address has address has address has address has address mail is handled by 30 mail is handled by 40 mail is handled by 50 mail is handled by 10 mail is handled by 20

$ host
Using domain server:
Aliases: has address has address has address has address has address has address mail is handled by 40 mail is handled by 50 mail is handled by 10 mail is handled by 20 mail is handled by 30

$ cat /etc/resolv.conf 
# Generated by NetworkManager

$ cat /etc/hosts       localhost
::1             localhost

$ netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface         UG        0 0          0 wlan0       UG        0 0          0 lo   U         0 0          0 wlan0

Basically any application, including Firefox, can't work to do name lookups. What's more, if I take the wifi offline and plug in an ethernet cable, everything is fine.

share|improve this question
Maybe add some more info - is it just curl ? What about wget, browsers, ping etc. ? – Sandman4 Nov 28 '11 at 8:39
I see you marked an answer but what exactly was the issue and solution? Was it an SELinux problem? – Belmin Fernandez Nov 28 '11 at 17:10
The "solution" was just that the network appears to be right-gibbled. I'm not running any SELinux on the laptop and the "network" is just managed by a crappy store-bought wifi router. That answer was the one to help me figure out that I was dropping packets all over the place, so I figured it was something I couldn't solve and gave that guy the credit. Why, do you have a better idea? – Daniel Quinn Nov 29 '11 at 14:20
up vote 5 down vote accepted

Perhaps you have some very weird and restrictive SELinux (or grsecurity...) rules in place?

If not, try strace -o /tmp/wtf -fF curl -v and try to spot from /tmp/wtf output file what's going on.

share|improve this answer
Looks like it's the wifi connection itself. The output file is FULL of stuff like this: 9344 poll([{fd=3, events=POLLIN|POLLPRI|POLLRDNORM|POLLRDBAND}], 1, 1000) = 0 (Timeout) – Daniel Quinn Nov 28 '11 at 10:44
@Daniel Quinn, can you post output of /tmp/wtf? – Sachin Divekar Nov 28 '11 at 10:44
Here's the output: – Daniel Quinn Nov 28 '11 at 12:49
Hmm, looks like it's doing the query to Can you do "host" for sanity? Basically, DNS lookup specifically against your DNS server. – cjc Nov 28 '11 at 12:57
Done (added it to the question). And that works just fine -- which makes sense since issuing host without a server argument works correctly as well. It looks like it's just actual HTTP calls too, since ICMP (mostly, it drops the first ping) works. – Daniel Quinn Nov 28 '11 at 13:00

Using this:

I found a key command that helped me troubleshoot:

[root@localhost ~]# wget -6 URL Failed

[root@localhost ~]# wget -4 URL Worked

It's something to do with the default ipv6 stack that's causing problems with certain utils. Disable ipv6 to resolve.

share|improve this answer

I had the same problem - host, nslookup resolves ok, curl - can't on the same hostnames.

After tcpdumping communication I found that curl tries to establish TCP (in addition to UDP) connection to DNS port, which was closed in my router. After tcp port 53 was enabled curl started to work flawlessly.

Another strange thing is that this problem does not surface if dns server is regular bind installation. If I use embedded into router DNS server, curl suddenly tries to use TCP ports even if it already received (!) answer via UDP 2ms before. I suppose this is bug.

share|improve this answer

Check your /etc/nsswitch.conf. If the hosts line says something like

hosts:      files dns

I'm as confused as you. But if it says something like

hosts:      files

then the fact that DNS is working (see output of host command) won't help curl, which is doing name resolution via the standard OS libraries, which have been told not to use the DNS.

share|improve this answer
Hmm. I hadn't thought of that, but I just checked and it says files dns so I guess that's not it :-( – Daniel Quinn Nov 28 '11 at 8:49

I had this same problem on my VE (running on my laptop) today, and found it quite surprising. Dig and NSlookup works, but curl fails.

So for instance:

# curl -v
* getaddrinfo(3) failed for
* Couldn't resolve host ''
* Closing connection #0
curl: (6) Couldn't resolve host ''

But when I saw David T's post here, I decided to try it with curl. So while this fails:

# curl -6
curl: (6) Couldn't resolve host ''

This succeeds:

# curl -4
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<H1>301 Moved</H1>
The document has moved
<A HREF="">here</A>.

The -6 specifies that curl uses IPv6 and the -4, to use IPv4. I get the same errors when using wget, so definitely some problems with the IPv6 stack on the Host.

All the other modifications to the nsswitch.conf file and other BIND conf files did not help as the problem is not with this utilities.

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Was your curl installation smooth? If possible try re-installing curl.

Try curl -v to get more verbose output for debugging.


curl -v dnserror.test
* getaddrinfo(3) failed for dnserror.test:80
* Couldn't resolve host 'dnserror.test'
* Closing connection #0
curl: (6) Couldn't resolve host 'dnserror.test'

Are you getting similar output?

share|improve this answer
Exactly the same :-( I've updated the question with the output. – Daniel Quinn Nov 28 '11 at 9:35

There could be an error in your /etc/resolv.conf file that nslookup tolerates but curl does not.

The question asked was "How is it possible that I can do a host lookup but not a curl?"

This is possible because curl uses getaddrinfo() to resolve the FQDN, whereas nslookup does not. Instead, I believe nslookup parses /etc/resolv.conf using some other function or library, or via its own custom code. I did not look at source code to verify this, but you can prove it by adding whitespace in front of the nameserver token in /etc/resolv.conf. nslookup can parse this but getaddrinfo() cannot.

Example /etc/resolv.conf

If your resolv.conf has this error, or other errors that are tolerated by nslookup but not getaddrinfo(), then you can resolve an FQDN with nslookup, but you will not be able to use curl on that FQDN.

Fix: as root, edit /etc/resolv.conf and remove any leading whitespace on the nameserver line.

share|improve this answer
The strace output shows DNS queries being sent without receiving replies. That does not support the hypothesis of a parsing error on /etc/resolv.conf. However it is possible the recursor is faulty and using a different recursor might help. – kasperd Jan 18 at 19:47

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