How to check Apache configuration
You need to restart your Apache service for any changes you made to the config file to be effective. It is then crucial for your to test your Apache config for errors before restarting as it could cause the Apache service to fail to start and disrupt the availability of your hosted websites.
Apache has a built-in feature to test the validity of the config file that you can use to test your config files for errors or warnings. You can repeatedly check the configuration files until all the errors and warnings are gone before restarting the service.
You can use both apachectl and httpd tool to test your Apache configuration from the terminal.
Steps to test Apache configuration without restarting service:
Launch your preferred terminal application.
Edit Apache configuration file using your preferred text editor.
$ sudo vi /etc/apache2/apache2.conf
Test configuration file syntax using Apache binary.
$ sudo apachectl configtest AH00543: apache2: bad user name username Action 'configtest' failed. The Apache error log may have more information.
Use -t option instead of configtest if you're using httpd or apache and not apachectl
Continue editing and testing your Apache configuration until no error is reported by the configtest option.
$ sudo apachectl configtest Syntax OK
Restart Apache service for the changes to take effect.
$ sudo systemctl restart apache2 # Ubuntu, Debian, openSUSE and SLES $ sudo systemctl restart httpd # CentOS and Red Hat
Related: How to manage Apache service