Tutorial

Apache Network Error AH00072: make_sock: could not bind to address

ApacheNetworking
Part of the Series: Common Apache Errors

This tutorial series explains how to troubleshoot and fix some of the most common errors that you may encounter when using the Apache web server.

Each tutorial in this series includes descriptions of common Apache configuration, network, filesystem, or permission errors. The series begins with an overview of the commands and log files that you can use to troubleshoot Apache. Subsequent tutorials examine specific errors in detail.

Introduction

An Apache AH00072: make_sock: could not bind to address error message is generated when there is another process listening on the same port that Apache is configured to use. Typically the port will be the standard port 80 for HTTP connections, or port 443 for HTTPS connections. However, any port conflict with another process can cause an AH00072 error.

The error is derived from the underlying operating system system’s network stack. The issue is that only a single process can be bound to a port at any given time. If another web server like Nginx is configured to listen on port 80 and it is running, then Apache will not be able to claim the port for itself.

To detect a port conflict with Apache, you will need to examine systemctl and journalctl output to determine the IP address and port that are causing the error. Then you can decide how to resolve the issue, whether it is by switching web servers, changing the IP address that Apache uses, the port, or any combination of these options.

Troubleshooting with systemctl

Following the troubleshooting steps from the How to Troubleshoot Common Apache Errors tutorial at the beginning of this series, the first step when you are troubleshooting an AH00072: make_sock: could not bind to address error message is to check Apache’s status with systemctl.

If systemctl does not include output that describes the problem, then the last section of this tutorial, Troubleshooting Using journalctl Logs explains how to examine the systemd logs to find the conflicting port.

The output from systemctl status will in many cases contain all the diagnostic information that you need to resolve the error. It will include the IP address that Apache is using, as well as the port that it is attempting to bind to. The output will also indicate how long Apache has been unable to start so that you can determine how long the issue has been affecting Apache.

On Ubuntu and Debian-derived Linux distributions, run the following to check Apache’s status:

Ubuntu and Debian Systems
  • sudo systemctl status apache2.service -l --no-pager

On CentOS and Fedora systems, use this command to examine Apache’s status:

CentOS and Fedora Systems
  • sudo systemctl status httpd.service -l --no-pager

The -l flag will ensure that systemctl outputs the entire contents of a line, instead of substituting in ellipses () for long lines. The --no-pager flag will output the entire log to your screen without invoking a tool like less that only shows a screen of content at a time.

Since you are troubleshooting an AH00072: make_sock error message, you should receive output that is similar to the following:

Output
● httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled) Active: failed (Result: exit-code) since Tue 2020-07-28 13:58:40 UTC; 8s ago Docs: man:httpd.service(8) Process: 69 ExecStart=/usr/sbin/httpd $OPTIONS -DFOREGROUND (code=exited, status=1/FAILURE) Main PID: 69 (code=exited, status=1/FAILURE) Status: "Reading configuration..." Tasks: 213 (limit: 205060) Memory: 25.9M CGroup: /system.slice/containerd.service/system.slice/httpd.service Jul 28 13:58:40 e3633cbfc65e systemd[1]: Starting The Apache HTTP Server… Jul 28 13:58:40 e3633cbfc65e httpd[69]: (98)Address already in use: AH00072: make_sock: could not bind to address [::]:80 Jul 28 13:58:40 e3633cbfc65e httpd[69]: (98)Address already in use: AH00072: make_sock: could not bind to address 0.0.0.0:80 Jul 28 13:58:40 e3633cbfc65e httpd[69]: no listening sockets available, shutting down Jul 28 13:58:40 e3633cbfc65e httpd[69]: AH00015: Unable to open logs Jul 28 13:58:40 e3633cbfc65e systemd[1]: httpd.service: Main process exited, code=exited, status=1/FAILURE Jul 28 13:58:40 e3633cbfc65e systemd[1]: httpd.service: Failed with result 'exit-code'. Jul 28 13:58:40 e3633cbfc65e systemd[1]: Failed to start The Apache HTTP Server.

Note that your output may be slightly different if you are using an Ubuntu or Debian-derived distribution, where the name of the Apache process is not httpd but is apache2.

This example systemctl output includes some highlighted lines from the systemd journal that describes the AH00072 error. These lines, both of which begin with (98)Address already in use: AH00072: make_sock: could not bind to address, give you all the information about the AH00072 error that you need to troubleshoot it further, so you can skip the following journalctl steps and instead proceed to the Troubleshooting with ss and ps Utilities section at the end of this tutorial.

If your systemctl output does not give specific information about the IP address and port or ports that are causing the AH00072 error, you will need to examine journalctl output from the systemd logs. The following section explains how to use journalctl to troubleshoot an AH00072 error.

Troubleshooting Using journalctl Logs

If your systemctl output does not include specifics about an AH00072 error, you should proceed with using the journalctl command to examine systemd logs for Apache.

On Ubuntu and Debian-derived systems, run the following command:

  • sudo journalctl -u apache2.service --since today --no-pager

On CentOS, Fedora, and RedHat-derived systems, use this command to inspect the logs:

  • sudo journalctl -u httpd.service --since today --no-pager

The --since today flag will limit the output of the command to log entries beginning at 00:00:00 of the current day only. Using this option will help restrict the volume of log entries that you need to examine when checking for errors.

If Apache is unable to bind to a port that is in use, search through the output for lines that are similar to the following log entries, specifically lines that contain the AH00072 error code as highlighted in this example:

Output
-- Logs begin at Tue 2020-07-14 20:10:37 UTC, end at Tue 2020-07-28 14:01:40 UTC. -- . . . Jul 28 14:03:01 b06f9c91975d apachectl[71]: (98)Address already in use: AH00072: make_sock: could not bind to address [::]:80 Jul 28 14:03:01 b06f9c91975d apachectl[71]: (98)Address already in use: AH00072: make_sock: could not bind to address 0.0.0.0:80 Jul 28 14:03:01 b06f9c91975d apachectl[71]: no listening sockets available, shutting down

This output indicates two AH00072 errors. The first of these explains that Apache cannot bind to the [::]:80 address, which is port 80 on all available IPv6 interfaces. The next line, with the address 0.0.0.0:80, indicates Apache cannot bind to port 80 on all available IPv4 interfaces. Depending on your system’s configuration, the IP addresses may be different and only show individual IPs, and may only include IPv4 or IPv6 errors.

Even though your own system may have different conflicting interfaces and ports, the errors will be similar to the output shown here. With output from journalctl you will be able to diagnose the issue using ss in the following section of this tutorial.

Troubleshooting with ss and ps Utilities

To troubleshoot an AH00072 error you need to determine what other process is listening on the IP address and port that Apache is attempting to use. Most modern Linux distributions include a utility called ss which can be used to gather information about the state of a system’s network sockets.

In the previous journalctl section, something was already bound to the IPv4 and IPv6 addresses on port 80. The following command will determine the name of the process that is already bound to an IPv4 interface on port 80. Ensure that you substitute the port from the error message if it is different from 80 in the following command:

  • sudo ss -4 -tlnp | grep 80

The flags to the ss command alter its default output in the following ways:

  • -4 restricts ss to only display IPv4-related socket information.
  • -t restricts the output to tcp sockets only.
  • -l displays all listening sockets with the -4 and -t restrictions taken into account.
  • -n ensures that port numbers are displayed, as opposed to protocol names like ‘httporhttps`. This is important since Apache may be attempting to bind to a non-standard port and a service name can be confusing as opposed to the actual port number.
  • -p outputs information about the process that is bound to a port.

With all of those flags, you will receive output like the following:

Output
LISTEN 0 511 0.0.0.0:80 0.0.0.0:* users:(("nginx",pid=40,fd=6))

The first three fields are not important when troubleshooting an AH00072 error so they can be ignored. The important fields are the fourth (0.0.0.0:80), which matches the journalctl error that you discovered earlier, along with the last users:(("nginx",pid=40,fd=6)), specifically the pid=40 portion.

If you have an AH00072 error that is related to an IPv6 interface, repeat the ss invocation, this time using the -6 flag to restrict the interfaces to the IPv6 network stack like this:

  • sudo ss -6 -tlnp |grep 80
Output
LISTEN 0 511 [::]:80 [::]:* users:(("nginx",pid=40,fd=7))

Again, substitute the port number in question from your journalctl output if it is different from the highlighted 80 given here.

In both these cases of IPv4 and IPv6 errors, the ss output indicates that there is a program with process ID 40 (the pid=40 in the output) that is bound to the 0.0.0.0:80 and [::]:80 interfaces respectively. This process is preventing Apache from starting since it already owns the port. To determine the name of the program, use the ps utility like this, substituting the process ID from your output in place of the highlighted 40 value in this example:

  • sudo ps -p 40

You will receive output that is similar to the following:

Output
PID TTY TIME CMD 40 ? 00:00:00 nginx

The highlighted nginx in the output is the name of the process that is listening on the interfaces. Now that you have the name of the program that is preventing Apache from starting, you can decide how to resolve the error. You could stop the nginx process, reconfigure nginx to listen on a different interface and port, or reconfigure Apache to avoid the port collision.

It is important to note that the process may be different from nginx and the port and IP addresses may not always be 0.0.0.0 or [::] if you are diagnosing an AH00072 error. Oftentimes, different web servers and proxies will be in use on the same server. Each may be attempting to bind to different IPv4 ports and IPv6 interfaces to handle different web traffic. For example, a server that is configured with HAProxy listening on the IPv4 loopback address (also referred to as localhost) on port 8080 will show ss output like this:

Output
LISTEN 0 2000 127.0.0.1:8080 0.0.0.0:* users:(("haproxy",pid=545,fd=7))

It is important to combine systemctl output, or journalctl output that indicates specific IP addresses and ports, with diagnostic data from ss, and then ps to narrow down the process that is causing Apache to fail to start.

Conclusion

In this tutorial you learned how to troubleshoot an Apache AH00072 make_sock: could not bind to address error message on both IPv4 and IPv6 interfaces. You learned how to use systemctl to examine the status of the Apache server and try to find error messages. You also learned how to use journalctl to examine the systemd logs for specific information about an AH00072 error.

With the appropriate error messages from the logs, you then learned about the ss utility and how to use it to examine the state of a system’s network sockets. After that you learned how to combine process ID information from ss with the ps utility to find the name of the process that is causing Apache to be unable to start.

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