PHP is associated with either your web-server or external FastCGI process manager. In most cases you just need to restart web-server such as Apache / Nginx / Lighttpd depending on your system and software.
Restart PHP by restarting your web-server
Type the following command as per your web-server.
Restart Apache for php service
If you are using Apache web server type the following command to restart the php:
# /etc/init.d/apache2 restart
# apache2ctl restart
See how to restart Apache Web Server on Ubuntu Linux for more information.
Restart Nginx for php service
If you are using Nginx web-server type the following command to restart nginx:
# /etc/init.d/nginx restart
# service nginx restart
# nginx -s reload
Restart Lighttpd for php service
If you are using Lighttpd web-server type the following command to restart lightpd:
# /etc/init.d/lighttpd restart
# service lighttpd restart
Restart PHP-FAM Fastcgi for PHP service
If you are running php via PHP-FAM fastcgi manager, use any one of the following as per your version of Linux/Unix:
# /etc/init.d/php-fpm restart
# /etc/init.d/php5-fpm restart
# service php-fpm restart
# service php5-fpm restart
# restart php-fpm