Generally, you shouldn't need to change your php.ini, but if you do (like in ISPCOnfig3 setups), this page is to share tips & tricks about Tiki-related configs.
You have to place your custom php.ini file in your Tiki root folder.
Keep in mind that some servers have two different php.ini files, one for php scripts used through a web server and browser, and another one for php scripts being run in the commadn line (CLI). These 2 are common locations for those 2 php.ini files (in Debian GNU/Linux servers):
; if you want to reduce CPU usage, set it to off ; if you want to limit traffic, set to on zlib.output_compression = Off max_execution_time = 60 ; Maximum execution time of each script, in seconds max_input_time = 60 ; Maximum amount of time each script may spend parsing request data memory_limit = 256M ; 128M is PHP's default value. If you still get blank pages, raise it. ; realpath_cache_size determines the size of the cache used by PHP used each time it references a file ; The size value should be increased for Tiki as the default is only 16K ; see http://www.php.net/manual/en/ini.core.php#ini.realpath-cache-size realpath_cache_size = 64k ; The time to live value defaults to 120 seconds so can be increased on stable sites, e.g. ; realpath_cache_ttl = 360
memory_limit=128M upload_max_filesize=10M post_max_size=11M max_execution_time=90
Add on 2015-11-23:
Since php 5.3 you can use .user.ini in stead of php.ini,
Since php 5.5 it is also necessary!! For example on site5.com as they explain here: http://kb.site5.com/php/how-to-make-custom-php-changes-using-a-user-ini-file/ (see the link for more information)