disable_functions in PHP for added security

Setting up open_basedir is good security practice, but a user can still read files from other directories by invoking exec or other commands that run on the operating system level. We can fix this by disabling a select few commands in your php.ini file.

Open /etc/php.ini (or similar), look for disable_functions and add:

disable_functions=popen,exec,system,passthru,proc_open,shell_exec

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