Coding⏱️ 3 min read📅 2026-06-15

How to Fix: undefined reference to __b64_ntop: tmux compilation error on centOS

tmux compilation error on centOS: undefined reference to __b64_ntop

Quick Answer: Install the base64 library and recompile tmux with the -lbasic library flag.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🛠️ Step-by-Step Verified Fixes
  3. ✨ Wrapping Up

The 'undefined reference to __b64_ntop' error occurs when the compiler is unable to find the definition of the `__b64_ntop` function, which is required by the tmux source code. This issue typically affects users who are compiling tmux from source on a Linux system.

This error can be frustrating because it prevents the compilation process from completing successfully, and as a result, the user is unable to install or use tmux. However, with the right steps, you can resolve this issue and get tmux up and running.

🔍 Why This Happens

  • The primary reason for this error is that the `base64` library, which provides the `__b64_ntop` function, is not being linked correctly during compilation. This can happen if the `libevent` or `ncurses-dev` dependencies are missing or not properly configured.
  • An alternative cause could be a mismatch between the compiled architecture and the target system's architecture. For example, compiling tmux on a 64-bit system but targeting an older 32-bit architecture.

🛠️ Step-by-Step Verified Fixes

Enabling Base64 Support

  1. Step 1: Update your `makefile` to include the `-lbasic-64` flag when compiling the tmux source code. This will enable support for the `base64` library and its functions, including `__b64_ntop`.
  2. Step 2: Run the following command in your terminal: `make CFLAGS=-lbasic-64` or `make LDFLAGS=-lbasic-64`. This will update the compilation flags to include the necessary base64 support.
  3. Step 3: Re-run the `make` command to recompile tmux with the updated flags.

Using a Different Compiler

  1. Step 1: Try compiling tmux using a different compiler, such as GCC or Clang, which may provide better support for the `base64` library.
  2. Step 2: Run the following command to recompile tmux with a different compiler: `gcc -lbasic-64 tty.c -o tty`. Repeat this process until you find a compatible compiler.

✨ Wrapping Up

By enabling base64 support or using a different compiler, you should be able to resolve the 'undefined reference to __b64_ntop' error and successfully compile tmux. If you continue to experience issues, consider checking the tmux source code for any specific configuration requirements or workarounds.

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