How to install X Window System XQuartz on macOS for ssh X11 forwarding

Can’t load X11 after OS X Yosemite upgrade

You need to delete / remove existing XQuartz server and reinstall it again.

Step 1 – Download and install X Window XQuartz on macOS

Visit this page and download XQuarz server for macOS. Once downloaded the XQuarz package, install the server by double clicking the package icon in your Downloads folder. Please follow the instructions on-screen to complete the installations:

Installing X Window XQuartz on macOS using brew command

Another option is to install Homebrew on macOS to use the brew package manager as follows using the Termaial app:
brew install --cask xquartz

Want to run graphical programs remotely from a Linux server? You need XQuartz on your Mac and can be installed using the brew

Step 2 – Reboot your Mac

You need to reboot the Mac to work it correctly. Otherwise, you will get various warnings or errors. Click on the Apple icon and then Restart. Another option is to type the following command using Termaial app:
sudo reboot

Step 3 – ssh X11 forwarding syntax for macOS

A tunneling protocol is a network protocol which encapsulates a payload protocol, acting as a payload protocol. Reasons to tunnel include carrying a payload over an incompatible delivery network, or to provide a secure path through an untrusted network. SSH is frequently used to tunnel insecure traffic over the Internet in a secure way. Simply type the following command to use X over ssh:

ssh -X user@RemoteserverNameHere
x-app-name-here &

OR

ssh -X userName@Server-Ip-Address-Here
x-window-app-name-here &

Step 4 – Enables and use trusted X11 forwarding

A small number of X11 GUI apps may require the use of -Y option instead of -X.

The syntax is:

ssh -Y user@server-ip
app-name &

Trusted X11 forwardings are not subjected to the X11 SECURITY extension controls. From the ssh man page:

X11 forwarding should be enabled with caution. Users with the ability to bypass file permissions on the remote host (for the user’s X authorization database) can access the local X11 display through the forwarded connection. An attacker may then be able to perform activities such as keystroke monitoring. For this reason, X11 forwarding is subjected to X11 SECURITY extension restrictions by default. Please refer to the ssh -Y option and the ForwardX11Trusted directive in ssh_config(5) for more information.

Step 5 – Run graphical programs remotely from a Linux or BSD server on macOS

The main advantage of using xterm instead of the built-in Terminal app is that xterm works without rebooting your Mac.

XQuartz.app itself comes with xterm (Terminal). You can use that app too apart from built-in Terminal app. To run X11 Forwarding on Mac:

1. Run XQuartz.app Applications.
2. Then right click on the XQuartz icon in the dock and select Applications > Terminal:
   
3. You should see a new xterm terminal windows
4. Finally, use the xterm app and ssh into the Linux or BSD server:
   ssh -X UserName@your-server-ip-here
   OR
   ssh -Y UserName@home-wan-linux.cyberciti.biz
5. Then type app name such as:
   xeyes
   

Examples

In this example, I am going login to the Linux based nas01 server as a user called nixcraft using macOS Terminal app itself:
$ ssh -X nixcraft@nas01
OR
$ ssh -X nas01
You will see XQuartz server in the Dock i.e. a new XQuartz icon sits at the bottom of side of your screen as follows:

Fig.01: X11.app ( XQuartz ) loaded at the Dock

Animated gif 01: X11 Forwarding on OS X v10.8+. This demo was tested on OS X 10.9 i.e. Mavericks and Linux remote server.

Edit your ~/.ssh/config file and append the following line and you wouldn’t need pass the -X option to ssh command:

ForwardX11 yes

Finally, you can run ssh in the background after running a GUI app as follows:

ssh user@server -f -X app-Name
ssh nixcraft@nas01 -f -X gpass
ssh nixcraft@nas01 -f -X xeyes

Troubleshooting

Is X11 forwarding still not working on your Mac? Try these tips on your Linux or BSD/Unix server:

1. Make sure xauth is installed on your Linux/BSD server. Use the type command/command command:
   type -a xauth
command -V xauth
2. After login using ssh client, you must see the DISPLAY variable set by ssh client. Without this variable X11 forwarding will never work. For instance:
   echo "$DISPLAY"
3. Finally, run the following command and make sure X11 forwarding is enabled on your SSHD server:
   sudo sshd -T | grep -i X11
4. If not enabled edit the /etc/ssh/sshd_config and set those option:
   sudo vim /etc/ssh/sshd_config
   Append the following settings:
   x11forwarding yes
5. It would be best if you reloaded sshd server as per your OS. For example:# Debian/Ubuntu Linux server #
sudo systemctl restart ssh.service
# RHEL/CentOS Linux user run: #
sudo systemctl restart sshd.service

Troubleshooting ssh X11 Forwarding issues on Linux and BSD Unix servers

Summing up

You learned how to install X Window XQuartz on macOS to enable and use X forwarding with ssh command. See the following man pages:
man ssh
man sshd
man sshd_config
man ssh_config