from the bash prompt, type the following:
locate php.ini
this will give you the location(s) that php.ini is found in. If it returns nothing and you are sure php is installed on the linux box, execute this command (you might not have permissions):
updatedb
simply put, updatedb will update the linux references (at least for the purposes of the locate command) to all the files on the linux box. after updatedb is run... might take a while to run... execute the locate php.ini file again and it will find it.