Fix Apache failed to start (AH00072 port in use and config errors)

If systemctl start apache2 or systemctl start httpd fails, every site on the server goes down. The good news is that Apache always says why. This guide shows how to get the exact message, then fixes the causes you will meet most often: a configuration error, another program on port 80 or 443, and a certificate file that no longer exists.

Before you start

• A Linux VPS with Apache 2.4 on Ubuntu, Debian, AlmaLinux or Rocky Linux.
• SSH access with sudo.
• The service name: apache2 on Ubuntu and Debian, httpd on AlmaLinux and Rocky. The examples use apache2; swap in httpd where needed.

Step 1: Get the real error

Check the service state and the last log lines:

sudo systemctl status apache2 --no-pager
sudo journalctl -u apache2 -n 40 --no-pager

Then run Apache's own syntax check:

sudo apachectl configtest

A healthy config prints Syntax OK. Anything else names the file and line that is wrong.

Fix configuration syntax errors

A typical failure looks like this:

AH00526: Syntax error on line 12 of /etc/apache2/sites-enabled/example.com.conf:
Invalid command 'ProxyPass', perhaps misspelled or defined by a module not included in the server configuration

Read it in three parts: the file, the line, and the reason.

• Invalid command: the module for that directive is not loaded. On Ubuntu and Debian, enable it, for example sudo a2enmod proxy proxy_http. On AlmaLinux and Rocky, install the package or check /etc/httpd/conf.modules.d/.
• <VirtualHost> was not closed: a closing tag is missing or misspelled.
• DocumentRoot must be a directory: the path does not exist. Create it, or fix the typo.

After each fix, run sudo apachectl configtest again until it says Syntax OK.

Fix AH00072: address already in use

This error means another process already listens on port 80 or 443:

(98)Address already in use: AH00072: make_sock: could not bind to address [::]:80
no listening sockets available, shutting down

Find out what owns the port:

sudo ss -ltnp | grep -E ':(80|443)\s'

The last column shows the program. Common culprits:

• Nginx: both web servers want the same ports. Stop and disable the one you do not use: sudo systemctl disable --now nginx.
• A second Apache process left over: run sudo pkill -f apache2 (or httpd), then start the service again.
• A Docker container or app publishing port 80. Stop it or move it to another port.

The same error also appears when Listen 80 is written twice, for example in ports.conf and again in a site file. Search for duplicates:

sudo grep -Rn "^\s*Listen" /etc/apache2 /etc/httpd 2>/dev/null

Each port should appear once.

Fix missing or wrong certificate files

If a certificate was deleted, renamed or never issued, Apache cannot load it:

AH00526: Syntax error on line 30 of /etc/apache2/sites-enabled/example.com-le-ssl.conf:
SSLCertificateFile: file '/etc/letsencrypt/live/example.com/fullchain.pem' does not exist or is empty

Check which certificates exist:

sudo certbot certificates

If the certificate is gone, disable the HTTPS site, start Apache, then issue a new certificate:

sudo a2dissite example.com-le-ssl.conf
sudo systemctl start apache2
sudo certbot --apache -d example.com -d www.example.com

A key and certificate that do not match produce AH02565 or key values mismatch. Point SSLCertificateKeyFile at the key that belongs to the certificate.

Silence the AH00558 ServerName warning

This message is a warning, not the reason Apache failed:

AH00558: apache2: Could not reliably determine the server's fully qualified domain name

Set a global ServerName to remove it. On Ubuntu and Debian:

echo "ServerName localhost" | sudo tee /etc/apache2/conf-available/servername.conf
sudo a2enconf servername

On AlmaLinux and Rocky, add ServerName localhost near the top of /etc/httpd/conf/httpd.conf. If the service still fails after this, look for a different error further up the output.

Check it works

1. Run sudo apachectl configtest and confirm Syntax OK.
2. Start and enable the service:

   sudo systemctl enable --now apache2
   sudo systemctl status apache2 --no-pager

The status should read active (running).

1. Confirm it listens: sudo ss -ltnp | grep apache2 should show ports 80 and, if you use HTTPS, 443.
2. Load your site in a browser.

Troubleshooting

• Permission denied: AH00072 make_sock: could not bind to address: on AlmaLinux and Rocky, SELinux blocks a non-standard port. Allow it with sudo semanage port -a -t http_port_t -p tcp 8080.
• Apache starts, then stops a few seconds later: check journalctl for out-of-memory kills or a crashing module. Low-RAM servers may need MPM tuning.
• Could not open configuration file: an Include line points to a deleted file. Remove the line or restore the file.
• Starts by hand but not after reboot: the service is not enabled. Run sudo systemctl enable apache2.

Next steps

• Stop memory-related crashes: Tune Apache MPM settings.
• Re-issue HTTPS correctly: Secure Apache with Let's Encrypt.
• Read the logs in more depth: Find and read Apache access and error logs.
• Still stuck on your server? Open a ticket.