I am using CentOS / RHEL / Fedora Linux server and I would like to restart my httpd server after making some changes to httpd.conf file. How do I restart httpd service?

You can use the service or systemctl command to restart httpd server. Another option is use /etc/init.d/httpd service script.

Restart Httpd Server on RHEL/CentOS 7.x/8.x

Use the systemcl command command as follows:
sudo systemctl start httpd
sudo systemctl stop httpd
sudo systemctl restart httpd
sudo systemctl status httpd

Task: Start httpd server:

Login as root user and type the following commands on RHEL/CentOS version 5.x/6.x or older:
# service httpd start

Task: Restart httpd server:

# service httpd restart

Task: Stop httpd server:

# service httpd stop
Please note that restart option is a shorthand way of stopping and then starting the Apache HTTPd Server. You need to restart server whenever you make changes to httpd.conf file. It is also good idea to check configuration error before typing restart option:
# httpd -t
# httpd -t -D DUMP_VHOSTS
Sample output:

Syntax OK

Now restart httpd server:
# service httpd restart
Where,

• -t : Run syntax check for config files
• -t -D DUMP_VHOSTS : Run syntax check for config files and show parsed settings only for vhost.

/etc/init.d/httpd script option

You can also use following command:
# /etc/init.d/httpd restart
# /etc/init.d/httpd start
# /etc/init.d/httpd stop

A note about Debian / Ubuntu Linux (older version)

Type the following command under Debian / Ubuntu Linux:
# /etc/init.d/apache2 restart
# /etc/init.d/apache2 stop
# /etc/init.d/apache2 start
You can also use service command under Debian / Ubuntu Linux:
# service apache2 restart
# service apache2 stop
# service apache2 start

If you are using the systemd based latest version of Debian/Ubuntu Linux

Try the following command:
sudo systemctl start apache2
sudo systemctl stop apache2
sudo systemctl restart apache2
sudo systemctl status apache2