In /etc/php5/apache2/php.ini

as someone already can upload phpshell it will not do too much…

disable_functions = exec, shell_exec, system, popen, passthru, escapeshellarg, escapeshellcmd, proc_close, proc_open, ini_alter, dl, popen, show_source, set_time_limit, php_uname, phpinfo, diskfreespace, disk_total_space, disk_free_space, get_current_user, posix_uname