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I have a Linux server on an ADSL connection, and I just noticed that sometimes I get

Connecting to example.com|xxx.xxx.xxx.122|:80... connected.
HTTP request sent, awaiting response...

when I use wget or e.g. a browser like firefox.

In the case of wget pressing CTRL-C and then try again "solves the problem", and in the case of firefox, reloading the page also makes the page load.

It seams to be random when it happens. I have tried to change the DNS to Google's DNS, but I still get the same problems there.

Question

How do I debug something like that, so I can find the source of the problem or perhaps a pattern?

Sandra
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4 Answers4

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Have you ever tried waiting to see what HTTP status code returns?

To debug this case, open 2 terminals: in the first, ssh to your server and type:

# tcpdump -vv -s0 tcp port 80 -w /tmp/example.pcap

(you can also append and src host <client_IP> to filter junk requests)

and in the second, use wget to browse your website, reproduce this problem and switch to the first terminal and press Ctrl+C.

Copy this .pcap file to the client and open with Wireshark to see what happens.

quanta
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  • This should be interesting! I haven't tried to let it time out. How long would that take for it to timeout? 10 minutes? 1 hour? – Sandra Sep 24 '11 at 15:53
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If you see:

HTTP request sent, awaiting response...

This means that the DNS works fine, that the TCP connection is in established state and the request was send. I think that the cause of your problems is the remote server that might be busy.

As @quanta said a network capture will give you better details. In Wireshark just use Follow TCP Stream to see the HTTP conversation. Pay attention to ICMP messages too.

Mircea Vutcovici
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0

Restart your Apache Server. This should solve the problem.

Abhishek Goel
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I had a very similar issue on a freshly provisioned AWS instance:

apt install would fail, claiming that it couldn't fetch some package. When I tried to fetch the package manually with wget, it would sometimes hang indefinitely, and sometimes succeed immediately (after it hanged indefinitely).

Restarting the server didn't help. Then I terminated and reprovisioned the instance, after which I didn't have the problem on the new instance.

Go figure.

Zoltán
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