I recently encountered a problem with a phpBB3 site. After the site was moved around (from one domain to another), all the sudden nobody can log in to the site any more. To be accurate, log in itself actually worked, and I could see my user name displayed on the top right after I logged in. But as soon as I clicked on any link, I was kicked out (my user name disappeared from the top right). This happens to all users in the system, including the admins.

After hours of research and testing, I was almost certain it was a setting problem. I needed to set cookie domain correctly. But I can’t log in to the system as admin, the only way to do this is to mess with the database.

So I logged in to the server, started mysql in command line, (You can use phpMyAdmin interface if you have one.) and ran following commands:

update phpbb3_config set config_value='.domain.com' where config_name='cookie_domain';

update phpbb3_config set config_value='/path' where config_name='cookie_path';

Make sure there is no trailing slash after the cookie path.

Important clear out the cache before you test to see if this works. I wasted at least half an hour search for more solutions before I realized that my changes to the config were not even take effect because of cache. I went into the cache folder under phpBB3 installation, and removed the cache file for phpBB3 config. (filename has ‘config’ in it or something similar.)