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I have a shell script that I use to monitor loading times and response codes on my live server cluster. It runs a total of 250 iterations every 5 minutes, distributed across 10 servers and 6 sites. It uses curl with the -w flag to return pertinent information which is then parsed by my shell script:

curl -svw 'monitor_load_times %{time_total} %{http_code}' -b 'server=$server' -m 15 -o /dev/null $url 2>&1

This information is then parsed by a graphing script that can display a number of different responses. However, curl will occasionally return a response code of "000". When this happens, it seems to happen multiple times at once despite being distributed over many iterations:

Error code graph

What I'm trying to work out is if this is a client-side issue that's skewing my results or if it's actually indicative of a server-side problem affecting my entire cluster. Does 000 mean that the connection was dropped? Database entries corresponding to curl iterations with that response code return "0.000" for the time_total value. All of the search results I've found for curl returning a code of 000 are related to HTTPS being unsupported, but all of my test URLs are HTTP.

(The spike in 500 errors is a completely unrelated issue that affected my servers last night.)

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After some more searching, it seems that 000 is intended to indicate that the connection timed out. However, when I see this while running directly from the command line, the curl commands exit almost immediately (more quickly than 200 responses) rather than hanging as you'd expect. Still trying to determine if this issue is client-side or server-side. –  Mikkel Dec 7 '12 at 22:59

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