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      Apache Configuration Error AH00526: Syntax error



      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 AH00526: Syntax error message occurs when there is a typo or misconfigured setting somewhere in your Apache configuration files. It is a generic error that can be indicative of a number of underlying problems.

      The error can be detected using apachectl configtest before an invalid configuration is loaded. It can also be found using the systemctl and journalctl commands. In the latter two cases, Apache will be unable to run because of the error.

      If you have detected the error using apachectl then skip to the Troubleshooting Using the Built in apachectl Command section of this tutorial. Otherwise, the next section will explain how to use systemctl to troubleshoot the error.

      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 AH00526 error is to check Apache’s status with systemctl. It is important to understand if the error affects the running process, or if it is preventing Apache from starting up.

      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 AH00526: Syntax error message, you should receive output that is similar to the following:

      Output

      ● apache2.service - The Apache HTTP Server Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled) Drop-In: /lib/systemd/system/apache2.service.d └─apache2-systemd.conf Active: failed (Result: exit-code) since Wed 2020-07-15 13:45:49 UTC; 1min 37s ago . . . Jul 15 13:45:49 f17f01056c5b systemd[1]: Starting The Apache HTTP Server... Jul 15 13:45:49 f17f01056c5b apachectl[15860]: AH00526: Syntax error on line 2 of /etc/apache2/sites-enabled/000-default.conf: Jul 15 13:45:49 f17f01056c5b apachectl[15860]: Invalid command 'SSSLCertificateFile', perhaps misspelled or defined by a module not included in the server configuration Jul 15 13:45:49 f17f01056c5b apachectl[15860]: Action 'start' failed. Jul 15 13:45:49 f17f01056c5b apachectl[15860]: The Apache error log may have more information. Jul 15 13:45:49 f17f01056c5b systemd[1]: apache2.service: Control process exited, code=exited status=1 Jul 15 13:45:49 f17f01056c5b systemd[1]: apache2.service: Failed with result 'exit-code'. Jul 15 13:45:49 f17f01056c5b systemd[1]: Failed to start The Apache HTTP Server.

      In this case, Apache is not running because of the syntax error. The error is caused by an extra S character at the beginning of the SSSLCertificateFile line in the /etc/apache2/sites-enabled/000-default.conf file. The correct directive should be SSLCertificateFile, so editing the file to fix the directive name in this example would resolve the error and allow Apache to start.

      The systemctl output in this example also includes some lines from the systemd journal. If your output indicates a specific line in your configuration file is generating the syntax error, you can skip the journalctl and apachectl configtest troubleshooting steps. Instead, you can go directly to the file to inspect and edit the erroneous line to resolve the error.

      If your output does not give specific information about the error location in Apache’s configuration files, you will need to examine journalctl output from the systemd logs. The following section explains how to use journalctl to troubleshoot an AH00526 error.

      Troubleshooting with journalctl logs

      If your systemctl output does not include specifics about an AH00526 syntax error, you can 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 you have an AH00526 error in your Apache configuration, look through the journalctl command output for lines like the following:

      Output

      -- Logs begin at Tue 2019-11-05 21:26:44 UTC, end at Tue 2020-06-09 15:13:01 UTC. -- . . . Jun 09 15:12:28 f17f01056c5b apachectl[3157]: AH00526: Syntax error on line 3 of /etc/apache2/sites-enabled/000-default.conf: Jun 09 15:12:28 f17f01056c5b apachectl[3157]: Invalid command 'SSLCertificateFile', perhaps misspelled or defined by a module not included in the server configuration . . .

      The first line of output is the AH00526 error. Since this error is a general error related to an invalid setting or a typo in a configuration file, the next line explains what caused the error. In this case it is a directive called SSLCertificateFile, which will only be valid if the ssl module is enabled.

      If you encounter an AH00526 error that is related to an invalid SSLCertificateFile directive, you can resolve it by enabling the ssl module and then restarting Apache to make the error go away.

      For Ubuntu and Debian systems, run the following to enable the module:

      • sudo a2enmod ssl
      • sudo systemctl restart apache2.service

      On CentOS and Fedora systems, ensure that the mod_ssl package is installed, and then load the module by adding it to Apache’s /etc/httpd/conf.modules.d directory in a file like this:

      • sudo yum install mod_ssl
      • echo "LoadModule ssl_module modules/mod_ssl.so" | sudo tee > /etc/httpd/conf.modules.d/00-ssl.conf
      • sudo systemctl restart httpd.service

      Once the module is referenced by Apache and you restart it using the command that is appropriate to your Linux distribution, the server will start up if there are no more errors in the configuration.

      However, if there are more errors, Apache and systemctl status will continue to report them and attempt to explain why the server cannot be started. systemctl will output failure messages like this on Ubuntu and Debian systems:

      Ubuntu & Debian Output

      Job for apache2.service failed because the control process exited with error code.
      See "systemctl status apache2.service" and "journalctl -xe" for details
      

      And on CentOS, Fedora, and RedHat derived systems, a failed startup message will be similar to the following:

      CentOS and Fedora Output

      Job for httpd.service failed because the control process exited with error code.
      See "systemctl status httpd.service" and "journalctl -xe" for details.
      

      When Apache will still not start because of errors, using the apachectl configtest command can be the most efficient and effective way to diagnose issues. The next section will explain how to use the utility to resolve an AH00526 error that is again related to an invalid SSLCertificateFile directive.

      Troubleshooting with apachectl

      To troubleshoot an AH00526 error with Apache’s apachectl utility, you can test your Apache configuration using the configtest sub-command. This tool will parse your Apache files to determine whether it’s valid and, if not, locate incorrect settings in the Apache configuration.

      The apachectl configtest command is useful for catching syntax errors before reloading apache with a new configuration. This test can help you to avoid service outages in the event of a misconfigured setting in your Apache files.

      The following example configuration test command will return an AH00526 Syntax error message, and explains that the likely problem is that Apache is referencing an empty SSLCertificateFile:

      • sudo apachectl configtest

      Output

      AH00526: Syntax error on line 3 of /etc/apache2/sites-enabled/000-default.conf: SSLCertificateFile: file '/etc/ssl/certs/example.com.pem' does not exist or is empty

      In this example output, the /etc/ssl/certs/example.com.pem file does not exist as the error message notes. Adding an SSL/TLS certificate to the file, or removing the directive will resolve the issue.

      A successful apachectl configtest invocation should result in output like this:

      Output

      Syntax OK

      Conclusion

      In this tutorial you learned how to troubleshoot an Apache AH00526 syntax error. The first step when investigating any Apache error is to examine the server’s status with systemctl status apache2, or systemctl status httpd depending on your Linux distribution. From there, you can determine whether Apache is running correctly, or if it is unable to start because of the error.

      After you have determined Apache’s status, you can diagnose it further using journalctl to examine the systemd logs for the process. You can also use the apachectl configtest command to check the configuration files for errors directly.



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



      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:

      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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      Apache Configuration Error AH00558: Could not reliably determine the server’s fully qualified domain name



      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 AH00558: Could not reliably determine the server's fully qualified domain name message is generated when Apache is not configured with a global ServerName directive. The message is mainly for informational purposes, and an AH00558 error will not prevent Apache from running correctly.

      In this tutorial you will learn how to detect an AH00558 message using the methods described in the How to Troubleshoot Common Apache Errors tutorial at the beginning of this series. You will also learn how to set a ServerName directive to resolve the message.

      If you have already determined that your Apache server is affected by an AH00558 message and you would like to skip the troubleshooting steps, the Setting a Global ServerName Directive step at the end of this tutorial explains how to resolve the message.

      Troubleshooting Using systemctl

      The first step when you are troubleshooting an AH00558: Could not reliably determine the server's fully qualified domain name message is to check Apache’s status using systemctl. The output from systemctl will in many cases contain all the information that you need to resolve the message.

      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 Fedora, and RedHat-derived 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.

      You should receive output that is similar to the following:

      Output

      ● apache2.service - The Apache HTTP Server Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled) Drop-In: /lib/systemd/system/apache2.service.d └─apache2-systemd.conf Active: active (running) since Wed 2020-07-29 14:30:03 UTC; 33min ago Process: 34 ExecStart=/usr/sbin/apachectl start (code=exited, status=0/SUCCESS) Main PID: 46 (apache2) Tasks: 55 (limit: 2344) CGroup: /system.slice/apache2.service ├─46 /usr/sbin/apache2 -k start ├─47 /usr/sbin/apache2 -k start └─48 /usr/sbin/apache2 -k start Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Starting The Apache HTTP Server... Jul 29 14:30:03 68e2cf19f3f1 apachectl[34]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Started The Apache HTTP Server.

      The highlighted line that contains the AH00558 message is the important one. Essentially, it informs you that Apache couldn’t find a valid ServerName directive in its configuration file, so it will use the first IP address it detects. In this example, it’s the server’s public IP address: 172.17.02. If you are troubleshooting an AH00558 message, the IP address that is detected may be different, or it may be a human readable DNS name.

      If your systemctl output contains an auto-detected value of any IP address or hostname, skip to the last section of this tutorial, Setting a Global ServerName Directive to resolve the issue. In that section you will configure Apache with a safe default ServerName value using the IP address for localhost: 127.0.0.1.

      If your systemctl output does not indicate a value that you can use for the ServerName directive, the next section of this tutorial explains how to examine the systemd logs using journalctl to locate an AH00558 message.

      Troubleshooting Using journalctl

      To examine the systemd logs for Apache you will use the journalctl command. When invoking journalctl, there are two specific flags that will help you locate specific messages if there is a large volume of log entries.

      The first flag that you will add to the journalctl invocation is the --since today flag. It 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.

      The second flag that you will use is the same --no-pager option that you used with systemctl, which will output the entire log to your screen at once.

      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

      If your Apache server is generating an AH00558 message, look through the journalctl command output for lines like the following:

      Output

      -- Logs begin at Wed 2020-07-29 14:30:02 UTC, end at Wed 2020-07-29 14:45:03 UTC. -- . . . Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Starting The Apache HTTP Server... Jul 29 14:30:03 68e2cf19f3f1 apachectl[34]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message Jul 29 14:30:03 68e2cf19f3f1 systemd[1]: Started The Apache HTTP Server.

      The second line of output is the AH00558 message. The line includes the server’s public IP address, which is the address that Apache automatically detects and sets as a default at runtime. With this message as confirmation of an AH00558 error, you can proceed to the Setting a Global ServerName Directive to resolve the issue.

      Otherwise, the next section explains how to diagnose an AH00558 error message using the apachectl command.

      Troubleshooting using apachectl

      An AH00558: Could not reliably determine the server's fully qualified domain name error can be detected using Apache’s apachectl utility. With apachectl you can catch messages like these before reloading or restarting Apache, and you can avoid having to search through systemctl and journalctl logs to locate errors.

      To check your Apache configuration for an AH00558 message, run the following command:

      • sudo apachectl configtest

      You should receive output like the following if your server is affected by an AH00558 error message:

      Output

      AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message Syntax OK

      As with the previous sections in this tutorial that used systemctl and journalctl to locate AH00558 messages, the line that contains the AH00558 message, highlighted in the previous example, is the important one. Again note that the IP address 172.17.0.2 in this example may be different on your server.

      The next section of this tutorial explains how to set the ServerName directive to resolve AH00558 error messages.

      Setting a Global ServerName Directive

      To resolve an AH00558: Could not reliably determine the server's fully qualified domain name error message, you will need to add a ServerName directive to your Apache configuration. Apache uses the ServerName directive to map incoming HTTP requests to an IP address or DNS hostname using VirtualHost directives in order to handle requests for multiple sites using a single server.

      The error message notes that a global ServerName directive should also be set. Doing so will ensure that Apache can gracefully handle incoming requests that do not map to a VirtualHost without generating additional errors.

      For maximum compatibility with various Apache configurations, use the value of 127.0.0.1 for your global ServerName directive. You can use a different IP address or DNS name that corresponds to your server’s configuration if you need to, but it is safest to use 127.0.0.1.

      On Ubuntu and Debian-derived systems, open the /etc/apache2/apache2.conf file with root privileges using nano or your preferred text editor:

      • sudo nano /etc/apache2/apache2.conf

      Add a line containing ServerName 127.0.0.1 to the end of the file:

      /etc/apache2/apache2.conf

      . . .
      # Include the virtual host configurations:
      IncludeOptional sites-enabled/*.conf
      
      # vim: syntax=apache ts=4 sw=4 sts=4 sr noet
      ServerName 127.0.0.1
      

      On CentOS, Fedora, and RedHat-derived systems, open the /etc/httpd/conf/httpd.conf file with root privileges using nano or your preferred text editor:

      • sudo nano /etc/httpd/conf/httpd.conf

      Add the ServerName 127.0.0.1 line to the end of the file:

      /etc/httpd/conf/httpd.conf

      . . .
      # Supplemental configuration
      #
      # Load config files in the "/etc/httpd/conf.d" directory, if any.
      IncludeOptional conf.d/*.conf
      ServerName 127.0.0.1
      

      Save and close the file when you are finished. If you used nano, do so by pressing CTRL + X, Y, and then ENTER.

      Once you have added the ServerName directive to your configuration, run apachectl to test that the configuration is valid.

      • sudo apachectl configtest

      A successful apachectl configtest invocation should result in output like this:

      Output

      Syntax OK

      You can now restart Apache using the appropriate systemctl restart command for your Linux distribution.

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

      • sudo systemctl restart apache2.service

      On CentOS, Fedora, and RedHat-derived systems use this command to restart Apache:

      • sudo systemctl restart httpd.service

      After you restart Apache, the AH00558 error message will no longer appear in your logs. You can confirm the messages are silenced by running any of the three systemctl, journalctl, or apachectl commands that are demonstrated in this tutorial.

      Conclusion

      In this tutorial you learned about AH00558: Could not reliably determine the server's fully qualified domain name error messages. While these messages do not prevent Apache from running, they can be resolved by setting a global ServerName directive.

      You learned how to search for AH00558 error messages using the systemctl, journalctl, and apachectl commands. Finally, you learned how to edit your Apache configuration on various Linux distributions to silence the messages.

      If you would like to learn more about how Apache uses ServerName directives, the Apache documentation about Name-Based Virtual Hosts explains the directive in more detail.



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