session_start hangs

Question

since a few hours our server hangs every time you do a session_start.

For testing purposes i created a script which looks like this:

<?php
session_start();
?>

Calling it from the console hangs and it can't even be stopped with ctrl-c, only kill -9 works. The same for calling it via Apache. /var/lib/php/session/ stays empty but permissions are absolutely fine, www can write and also has read permissions for all parent folders.

According to the admins there were no changes made on the server and there is no special code registered for sessions. The Server is CentOS 4 or 5 and yesterday everything was working perfectly. We rebooted the server and updated PHP, but nothing changed.

I've ran out of ideas, any suggestions?

UPDATE

We solved this problem by moving the project to another server, so while the problem still exists on one server there is no immediate need for a solution anymore. I will keep the question open in case someone has an idea for others having a similar problem in the future, though.

Answer 1

There are many reasons for that, here are a few of them:

A. The session file could be opened exclusively. When the file lock is not released properly for whatever reason, it is causing session_start() to hang infinitely on any future script executions. Workaround: use session_set_save_handler() and make sure the write function uses fopen($file, 'w') instead of fopen($file, 'x')

B. Never use the following in your php.ini file (entropie file to "/dev/random"), this will cause your session_start() to hang:

<?php
ini_set("session.entropy_file", "/dev/random");
ini_set("session.entropy_length", "512");
?>

C. session_start() needs a directory to write to.

You can get Apache plus PHP running in a normal user account. Apache will then of course have to listen to an other port than 80 (for instance, 8080).

Be sure to do the following things: - create a temporary directory PREFIX/tmp - put php.ini in PREFIX/lib - edit php.ini and set session.save_path to the directory you just created

Otherwise, your scripts will seem to 'hang' on session_start().

Answer 2

If this helps:

In my scenario, session_start() was hanging at the same time I was using the XDebug debugger within PHPStorm, the IDE, on Windows. I found that there was a clear cause: Whenever I killed the debug session from within PHPStorm, the next time I tried to run a debug session, session_start() would hang.

The solution, if this is your scenario, is to make sure to restart Apache every time you kill an XDebug session within your IDE.