PLESK

mkdir -p /usr/local/psa/admin/conf/templates/custom/domain
cp /usr/local/psa/admin/conf/templates/default/server.php /usr/local/psa/admin/conf/templates/custom
cp /usr/local/psa/admin/conf/templates/default/domain/nginxDomainVirtualHost.php /usr/local/psa/admin/conf/templates/custom/domain
cp /usr/local/psa/admin/conf/templates/default/domain/nginxForwarding.php /usr/local/psa/admin/conf/templates/custom/domain

Modify server.php:
remove Header add X-Powered-By PleskLin

Modify nginxDomainVirtualHost.php:
remove add_header X-Powered-By PleskLin;

Rebuild configuration files:
/usr/local/psa/admin/sbin/httpdmng --reconfigure-all

https://support.plesk.com/hc/en-us/articles/115000385274-How-to-remove-modify-the-X-Powered-By-header-

NON PLESK

On Debian, Ubuntu or Linux Mint:
$ sudo vi /etc/apache2/apache2.conf

On CentOS, Fedora, RHEL or Arch Linux:
$ sudo vi /etc/httpd/conf/httpd.conf

ServerSignature Off
ServerTokens Prod

The first line ‘ServerSignature Off’ makes Apache2 web server hide Apache version info on any error pages.



On Debian, Ubuntu, or Linux Mint:
$ sudo vi /etc/php5/apache2/php.ini

On CentOS, Fedora, RHEL or Arch Linux:
$ sudo vi /etc/php.ini

expose_php = Off

Finally, restart Apache2 web server to reload updated PHP config file. Now you will no longer see “X-Powered-By” field in HTTP response headers.