Solving gnutls_handshake() failed: Handshake failed on Debian Web Servers

Whether you’re an experienced system administrator or a beginner managing web servers, encountering the "gnutls_handshake() failed: Handshake failed" error can be a frustrating experience. This error is generally an indication of an issue during the SSL/TLS handshake process, which could be due to a variety of reasons such as misconfiguration, outdated software, or certificate problems. In this post, we’ll go through the steps you can take to troubleshoot and fix this error on a Debian system, utilizing the power of tmux for multitasking.

<h2>Understanding the Handshake Error</h2>
Before diving into the solutions, it’s important to understand what the GNU TLS handshake error means. The GnuTLS library is a secure communications library that implements SSL, TLS, and DTLS protocols. When you encounter this error, it means that the handshake, which is the initial step to establish a secure connection, failed due to problems with verifying the SSL/TLS certificate or agreeing on the encryption.

<h2>Using tmux for Troubleshooting</h2>
<code>tmux</code> is a terminal multiplexer that allows you to have several terminal sessions within a single window. It is ideal for keeping sessions alive and running multiple commands simultaneously without losing your progress if you disconnect.

To start a new tmux session, simply enter:

“`bash
tmux
“`

If you want to detach from the tmux session and leave it running in the background, you can press <kbd>Ctrl</kbd>+<kbd>b</kbd> followed by <kbd>d</kbd>. Re-attach to the session anytime by typing:

“`bash
tmux attach
“`

<h2>Step 1: Check the Certificate Validity</h2>
First, ensure that the certificate is valid and has not expired. Use the <code>openssl</code> command to check the validity of the SSL/TLS certificate:

“`bash
openssl s_client -connect yourdomain.com:443 -servername yourdomain.com
“`

Examine the output for the certificate’s expiration date and issuer. If the certificate has expired or was not issued by a trusted authority, this might be the root cause of the handshake failure.

<h3>Step 2: Verify Configuration Files</h3>
If the certificate is valid, the next step is to check the web server's configuration files for any mistakes or misconfigurations related to SSL/TLS settings. For Apache or Nginx, these configurations can be found at:

– For Apache:
“`bash
/etc/apache2/sites-available/default-ssl.conf
“`

– For Nginx:
“`bash
/etc/nginx/sites-available/yourdomain.com
“`

Ensure that the paths to the certificate and private key are correctly specified and that the server is listening on port 443.

<h3>Step 3: Update the GnuTLS Library and Dependencies</h3>
Outdated software can often be the cause of handshake errors. Update your Debian system along with the GnuTLS library to ensure you have the latest bug fixes and security updates:

“`bash
sudo apt-get update && sudo apt-get upgrade
“`

<h3>Step 4: Disable Problematic Ciphers and Protocols</h3>
Sometimes, handshake errors arise due to certain ciphers or protocols not being supported or being insecure. Edit the web server configuration to disable outdated or insecure protocols like SSLv2 or SSLv3 and ensure that only strong ciphers are being used.

<h3>Step 5: Check Logs for Detailed Error Messages</h3>
The error logs can provide more detailed insight into what is causing the handshake to fail. For Apache and Nginx, you can check the logs at:

– For Apache:
“`bash
/var/log/apache2/error.log
“`

– For Nginx:
“`bash
/var/log/nginx/error.log
“`

Look for any messages related to SSL or TLS and address the specific issues reported.

<h3>Step 6: Test the Configuration</h3>
After making changes to the configuration files or updating the system, it's important to test the web server's configuration:

– For Apache:
“`bash
sudo apache2ctl configtest
“`

– For Nginz:
“`bash
sudo nginx -t
“`

If the configuration test passes, you can restart the web server to apply the changes:

– For Apache:
“`bash
sudo systemctl restart apache2
“`

– For Nginz:
“`bash
sudo systemctl restart nginx
“`

<h2>Conclusion</h2>
By following these steps and using tmux to manage your sessions, troubleshooting the "gnutls_handshake() failed: Handshake failed" error should be more manageable. Remember that keeping your Debian system and web server configurations

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