Check for config syntax error
Almost all web server including Apache supports config file syntax checking. To run syntax check for config files, enter:
# httpd –t
# httpd –S

If httpd.conf is configured properly you will get “Syntax OK”. Otherwise it will display an error message.

Check Apache error log file
Checking error log will point out exact problem.

Tail –f /var/log/httpd-error.log
Egrep –I ‘warn|error’ /var/log/httpd-error.log

DNS Configuration

Apache requires working DNS client. Make sure DNS is working and ServerName is set correctly in httpd.conf

Check your hostname and set it as ServerName in httpd.conf.

Hostname –f

Check Apache, PHP, Pythong and CGI log file size. If log files are over 2GB, it will cuase problem or error 500.

Check for port 80 and 443. Make sure no other process are using port 80 and 443, if they are either stop them or assign another port for Apache.