The PHP User On Linux
Reading or writing a file using PHP is quite a common practice, but it can often fall cause programs to fall flat on their face if the proper user privileges are not in place. Although this is not a problem on Windows machines due to the lack of a proper security model, but on Linux machines you need to make sure your scripts can run with the correct permissions.
First you must determine what the name of the user and group is. On OS X the default is "www" for both user and group. If you are using Apache then the user and group information is kept in the http.conf file. Look for a couple of lines that look like this, this is the default settings for Apache 2.2.