Using the -S option, Apache will list all configured virtual hosts (and their configuration file) and perform a syntax check:
/usr/sbin/httpd -S
httpd: (98)Address already in use
After configuring an Apache server on a CentOS 7.5 server, I tried to start the service but I got this error in return:
systemd[1]: Starting The Apache HTTP Server...
httpd[47662]: (98)Address already in use: AH00072: make_sock: could not bind to address [::]:443
systemd[1]: httpd.service: main process exited, code=exited, status=1/FAILURE
I was pretty sure that nothing was using port 443 but I did a quick check with netstat -tulpn
I double checked my config files, just to be sure that I wasn’t declaring Listen 443 twice:
# grep -ir listen
conf/httpd.conf:Listen 80
conf.d/ssl.conf:# When we also provide SSL we have to listen to the
conf.d/ssl.conf:Listen 443 https
conf.d/custom.conf:Listen 443
That’s it! I forgot to comment the directive in ssl.conf file (in this case). After this tiny fix I was able to start httpd without errors.
Creating a self-signed SSL certificate
SSL stands for secure socket layer, a web protocol used to send traffic between the client and the server in a protected and encrypted wrapper. An SSL certificate also helps users verifying the identity of the sites they’re visiting.
Prerequisites
httpdmod_ssl