Error: Can't open display: (null) when using Xclip to copy ssh public key [closed]

DISPLAY=:0 xclip -sel clip < ~/.ssh/id_rsa.pub didn't work for me (ubuntu 14.04), but you can use :

cat ~/.ssh/id_rsa.pub

to get your public key

Based on the date of this question the original poster wouldn't have been using Windows Subsystem for Linux. But if you are, and you get the same error, the following alternative works:

clip.exe < ~/.ssh/id_rsa.pub

Thanks to this page for pointing out Windows' clip.exe (and you have to type the ".exe") can be run from the bash shell.

This was too good of an answer not to post it here. It's from a Gilles, a fellow user from askubuntu:

The clipboard is provided by the X server. It doesn't matter whether the server is headless or not, what matters is that your local graphical session is available to programs running on the remote machine. Thanks to X's network-transparent design, this is possible.

I assume that you're connecting to the remote server with SSH from a machine running Linux. Make sure that X11 forwarding is enabled both in the client configuration and in the server configuration. In the client configuration, you need to have the line ForwardX11 yes in ~/.ssh/config to have it on by default, or pass the option -X to the ssh command just for that session. In the server configuration, you need to have the line X11Forwarding yes in /etc/ssh/sshd_config (it is present by default on Ubuntu).

To check whether X11 forwarding is enabled, look at the value of the DISPLAY environment variable: echo $DISPLAY. You should see a value like localhost:10 (applications running on the remote machine are told to connect to a display running on the same machine, but that display connection is in fact forwarded by SSH to your client-side display). Note that if DISPLAY isn't set, it's no use setting it manually: the environment variable is always set correctly if the forwarding is in place. If you need to diagnose SSH connection issues, pass the option -vvv to ssh to get a detailed trace of what's happening.

If you're connecting through some other means, you may or may not be able to achieve X11 forwarding. If your client is running Windows, PuTTY supports X11 forwarding; you'll have to run an X server on the Windows machine such as Xming.

By Gilles from askubuntu