The "No xauth program; cannot forward with spoofing" error occurs when you try to forward X11 connections over SSH and the xauth program is not available on the remote system.
X11 forwarding allows you to display X11 applications running on the remote system on your local system, through an SSH connection. To enable X11 forwarding, you need to set the ForwardX11 option in your ssh configuration, or pass the -X or -Y option to the ssh command when connecting to the remote system.
However, in order for X11 forwarding to work, the xauth program must be installed on both the local and the remote system. xauth is a utility that is used to manipulate the X authorization database, which is used to authenticate X11 clients to the X11 server.
If the xauth program is not available on the remote system, you will see the "No xauth program; cannot forward with spoofing" error when you try to forward X11 connections over SSH.
To fix this error, you need to install the xauth program on the remote system. On most Linux distributions, you can install xauth by running the following command:
sudo apt-get install xauth
On macOS, you can install xauth by running the following command:
brew install xauth
Once xauth is installed on the remote system, you should be able to forward X11 connections over SSH without getting the "No xauth program; cannot forward with spoofing" error.
Keep in mind that you may also need to install an X11 server on your local system in order to display the X11 applications running on the remote system. On most Linux distributions, you can install an X11 server by running the following command:
sudo apt-get install xorg
On macOS, you can install an X11 server by installing the XQuartz package from the XQuartz website:
Once you have installed an X11 server on your local system, you should be able to forward X11 connections over SSH and display the X11 applications running on the remote system on your local system.