Using Init.d

/etc/init.d/apache2 restart

sudo /etc/init.d/apache2 restart

sudo service apache2 restart

For a graceful restart, replace restart with reload.

For CentOS and RHEL servers

service httpd restart

Using Systemctl

systemctl restart apache2.service

Using Apachectl

sudo apachectl -k restart

sudo apachectl -k graceful