Cannot activate Jetpack on my server

I’m trying to install Jetpack after a successful install, but Jeckpack throws an error about site not being publicly accessible:

site_inaccessible

Error Details: The Jetpack server was unable to communicate with your site [IXR -32300: transport error: http_request_failed Operation timed out after 15001 milliseconds with 0 bytes received]

Been checking Jetpack/WordPress support forums for some options, XMLRPC is enabled

XML-RPC server accepts POST requests only.

Trying curl to fetch the data & it’s successful in making the connection

curl -i -L –data ‘test’ ‘https://jetpack.wordpress.com/jetpack.register/1’

HTTP/1.1 400 Bad Request
Server: nginx
Date: Wed, 14 Dec 2011 13:40:59 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Connection: close
Vary: Cookie
X-hacker: If you’re reading this, you should visit automattic.com/jobs and apply to join the fun, mention this header.
X-Pingback: http://jetpack.wordpress.com/xmlrpc.php
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Last-Modified: Wed, 14 Dec 2011 13:40:59 GMT
Cache-Control: no-cache, must-revalidate, max-age=60
Pragma: no-cache

I don’t use W3 Total Cache plugin, which seems to cause problems with many users.

How can I get it to activate?

I’m running on WordPress 3.3

You may not have enough processes running.

To test, try creating a file sleeper.php:

<?php
sleep(5);
echo "Working fine\n";

And then run this from the cli:

curl -m 6 http://example.com/sleeper.php & curl -m 6 http://example.com/sleeper.php & wait

If there is only one process it will print out something like this:

Working fine
curl: (28) Operation timed out after 6001 milliseconds with 0 bytes received

Notes/credits: I received this test from my colleague Pyry Hakulinen while working on WordPress.com support. It should work as a basic test and starting point to troubleshoot the “Operation timed out after 15001 milliseconds with 0 bytes received” error.