The error “gnutls_handshake() failed: Handshake failed” is fairly common among Debian system administrators dealing with web servers. It basically indicates an issue with the Transport Layer Security (TLS)/Secure Sockets Layer (SSL) handshake.
What does the error mean?
When a client/server communication is initiated, a “handshake” is exchanged for the setup of a secure connection (usually via HTTPS). GnuTLS, a secure communications library implementing SSL, TLS and DTLS protocols, is what facilitates this secure exchange of information in our Debian systems. So, if something goes wrong in the handshake process, GnuTLS throws up the error we’re discussing.
Before heading to our solutions, a note: Emacs, the extensible, customizable, self-documenting real-time display editor, is a text editor that can be specifically configured to solve SSL handshake errors. Some of the solutions below involve using emacs, while others don’t.
1. Adjust Time
Weirdly enough, incorrect system time can lead to a gnutls_handshake failure. This is because SSL certificates have their validity period defined. If your server time is not set correctly, certificate validation can fail and thus the TLS handshake fails too. Use the command “`date“` to check the current system time and adjust if necessary.
2. Upgrade GnuTLS
An outdated GnuTLS library can produce handshake errors. To solve this, upgrade the library using the following command:
sudo apt-get update
sudo apt-get upgrade gnutls-bin
3. Update Emacs
If you are facing this error while using an application that uses emacs (like git), then the problem can be resolved by updating emacs. Here are a few commands to do the same:
sudo apt-get update
sudo apt-get upgrade emacs
4. Check the SSL Certificate
Make sure that the SSL certificate of the server you are trying to access is not expired. You can check the SSL/TLS setup of the server using third party tools like SSLLabs.
5. Check for protocol mismatch
Sometimes, these errors can occur due to a mismatch in the TLS protocol used by the client and server. The server may only support a newer version of the protocol which the client doesn’t understand or vice versa. In such a case, upgrade the protocol version at the one lagging behind.
These solutions pretty much cover the usual reasons behind a gnutls_handshake error. However, keep in mind that the root cause can sometimes be very specific to your configuration or setup, and may require a deeper dig. Remember, the Debian community is your friend when you’re stuck; they certainly have been mine. Good luck!