php - session_start hangs -

since few hours our server hangs every time session_start.

for testing purposes created script looks this:

<?php session_start(); ?> 

calling console hangs , can't stopped ctrl-c, kill -9 works. same calling via apache. /var/lib/php/session/ stays empty permissions absolutely fine, www can write , has read permissions parent folders.

according admins there no changes made on server , there no special code registered sessions. server centos 4 or 5 , yesterday working perfectly. rebooted server , updated php, nothing changed.

i've ran out of ideas, suggestions?

update

we solved problem moving project server, while problem still exists on 1 server there no immediate need solution anymore. keep question open in case has idea others having similar problem in future, though.

there many reasons that, here few of them:

a. session file opened exclusively. when file lock not released whatever reason, causing session_start() hang infinitely on future script executions. workaround: use session_set_save_handler() , make sure write function uses fopen($file, 'w') instead of fopen($file, 'x')

b. never use following in php.ini file (entropie file "/dev/random"), cause session_start() hang:

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

c. session_start() needs directory write to.

you can apache plus php running in normal user account. apache of course have listen other port 80 (for instance, 8080).

be sure following things: - create temporary directory prefix/tmp - put php.ini in prefix/lib - edit php.ini , set session.save_path directory created

otherwise, scripts seem 'hang' on session_start().