This problem is driving me crazy and after hours of reading and trying all possible suggested solutions I feel I have to give it a go here.
We always had problem changing the backend session timeout from default 3600 to 86440 (24 hours). Just change the settings in backend/admin don't do it. Before we upgraded Magento from 1.6.2 to 1.9.1 we managed to change timeout in varien.php and php.ini.
We have changed settings in htaccess, php.ini, varien.php and in system Magento configuration now. But I still get logged out after 1 hour (3600).
What makes it even more strange is that on the same server we made the update on our dev URL, and when sure all was working we transfered the files to the live/production URL.
On the dev, the timeout is working as we want, but not on live. And the files and settings are exactly the same.
I had a Magento expert and also my server admin looking at the files, and also for them it's a mystery. Really, what's going on?!?
-- UPDATED POST WITH INFORMATION! --
DELL PowerEdge R210 II
Processor: Intel(R) Xeon(R) CPU E31220 @ 3.10GHz
RAM:2x42GB DDR3 - 1333MHz LV
Hard Disk OS: 2x256GB DELL 10000rpm - RAID 5
Operating System: CentOS 6.5 64Bit
PHP (mod_php): 5.3.28
Magento CE 188.8.131.52 multistore