I am a new Linux user. How do I restart php after editing php.ini file on Linux operating systems?

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
OR
# 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
OR
# service nginx restart
OR
# 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
OR
# 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
OR php 5 fpm:
# /etc/init.d/php5-fpm restart
OR php 7 fpm:
# /etc/init.d/php7.0-fpm restart
OR
# service php-fpm restart
OR
# service php5-fpm restart
OR
# service php7.0-fpm restart
OR
# restart php-fpm
OR
# service php-fpm restart