How To Fix Apache Not Accepting Incoming Connections On Port 80?

Verifying Apache Installation and Status

To start troubleshooting, check if Apache is installed on your CentOS server. Run this command:

yum list installed | grep httpd

This shows if Apache is installed. If it's not listed, install it:

yum install httpd

Check the status of the Apache service:

systemctl status httpd

This command shows if Apache is running or stopped. If it's not running, start it:

systemctl start httpd

systemctl enable httpd

Examining Apache Configuration Files

Review the main Apache configuration file, httpd.conf. Open it with a text editor:

nano /etc/httpd/conf/httpd.conf

Look for the "Listen" directive. It should be set to:

Listen 80

This tells Apache to listen on port 80 for incoming connections. If it's not there or set to a different port, add or change this line.

After making changes, save the file and restart Apache:

systemctl restart httpd

These steps help you check that Apache is installed, running, and set to listen on port 80.

Analyzing Network Connections

To check which ports are open and listening for connections, use the netstat command:

netstat -tulpn

This command shows all TCP and UDP ports that are currently listening. Look for a line similar to:

tcp    0    0 :::80     :::*    LISTEN    -

This indicates that a process (likely Apache) is listening on port 80 for all IP addresses.

If you don't see this line, Apache might not be running or might be set to listen on a different port.

sudo systemctl status httpd

Examining Firewall Rules

CentOS uses iptables for its firewall. To view the current iptables rules, run:

sudo iptables -L

Look for rules that might block incoming traffic on port 80. A typical output might look like:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED 
ACCEPT     icmp --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     tcp  --  anywhere             anywhere            state NEW tcp dpt:ssh 
REJECT     all  --  anywhere             anywhere            reject-with icmp-host-prohibited 

In this example, there's no rule allowing traffic on port 80. The last line rejects all other incoming connections, which could be blocking access to your web server.

If you don't see a rule allowing traffic on port 80, this could be the reason for the connection issues.

Modifying Firewall Rules

To fix the connection issue, add a rule to allow incoming connections on port 80. Use this command:

sudo iptables -I INPUT 4 -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT

This adds a new rule at position 4 in the INPUT chain, allowing new TCP connections on port 80.

After adding the rule, save the iptables configuration:

sudo service iptables save

This keeps the new rule active after server reboots.

sudo iptables -L -n -v

ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            state NEW tcp dpt:80

Restarting Apache Service

After modifying the firewall rules, restart Apache to apply the changes:

sudo systemctl restart httpd

Check the status of Apache after the restart:

sudo systemctl status httpd

This command shows if Apache is running without errors. Look for "Active: active (running)" in the output.

If you see errors, review the Apache error logs:

sudo tail -f /var/log/httpd/error_log

This helps identify problems preventing Apache from starting correctly.

Confirming External Access

After changing your firewall rules and restarting Apache, test if the server accepts incoming connections on port 80 from external sources.

To test external access:

1. Connect from a remote location:

   • Use a different network (mobile data, another Wi-Fi network)
   • Ask someone to try accessing your server

2. Use telnet to test port 80 access:

   • From a remote machine, run:

     telnet your_server_ip 80

   • If successful, you'll see a blank screen or a connection message
   • If it fails, you'll get a "Connection refused" error

3. Test with a web browser:

   • Open a web browser on a different device or network
   • Enter your server's IP address or domain name in the address bar
   • If Apache works correctly, you should see the default Apache test page or your website

If you can access the server externally on port 80, the problem is solved. If not, check your firewall rules and Apache configuration for mistakes.

Test from multiple locations if possible, as some networks might have their own firewalls or restrictions.

curl -I http://your_server_ip