I've got a Joomla website located at www.mysdomain.com/site1/. I can't install extensions because Joomla can't write to the tmp folder. The tmp folder does have the right permissions drwxr-xr-x 2 web1 client1 4096 Apr 9 10:38 tmp. SuEXEC is enabled, and so is fast-cgi. What is the problem here? Any ideas? Can't I have a Joomla installation inside a "sub-folder" ?
Yes, you can have Joomla inside a sub folder. You probably do not have correct log and tmp folder settings in Joomla. Check out the path to those from configuration.php file and see if those folders actually exist and have write permissions for the correct user and group. (Check suPHP/suExec user and group.)