HowTo: Connecting to Remote X11 Host from a Mac

I want to run a remote X client on my Linux desktop (with Ubuntu and X Window System) and display that client application my Apple MacBook Pro laptop running OS X Yosemite (version 10.10.5). I was hoping that, since Mac originated from parts of the Linux / X Window world, I could simply run ssh -X user@server, but this doesn't do the trick.

Installation of XQuartz

After multiple attempts to get things working, I discovered that to use ssh with X11 Forwarding, you need to install XQuartz¹ on OS X v10.8 or above. The XQuartz project is an open-source effort to develop a version of the X.Org X Window System that runs on OS X. This is Apple's version of the X server. You need to download and install the server before using ssh with X11 forwarding. Just follow the instructions given here.

Once the install is completed, clicking on the XQuartz logo gives you a XTerm. Within the XTerm, you can run an application on the remote system using the following commands:

# execute a XTerm on the remove system and display on you local Mac
ssh -X -C user@server-ip

# execute an app on the remote system, go to background, and display on your local Mac
ssh -f -X -C user@server-ip /path/to/app-name

Where,

• user@server-ip: remote login username and password
• -f: Requests ssh to go to background just before command execution. This is useful if ssh is going to ask for passwords or passphrases, but the user wants it in the background. This is the recommended way to start X11 programs at a remote site/host.
• -X: Enables X11 forwarding.
• -C: Requests compression of all data (including stdin, stdout, stderr, and data for forwarded X11 and TCP connections).
• -c cipher: Selects the cipher specification for encrypting the session.
• -T: Disable pseudo-tty allocation.

Use compression, -C, if you think that programs are running slowly because of a lack of bandwidth or network congestion.

.Xresources or .Xdefaults?

Many X programs have user-level configuration options that can be set in the X server resource database. Depending on your version of X.Org, the most common ways to achieve persistent configuration for your X programs are to store them in either the .Xresources or .Xdefaults files which are read when X starts or when the X client starts, respectively. Both are user configurable dotfiles located in $HOME used to set X resources. These are configuration parameters for X client applications, such as:

• defining terminal colours
• configuring terminal preferences
• setting dots-per-inch (DPI), anti-aliasing, hinting and other X font settings
• changing the Xcursor theme
• theming xscreensaver
• altering preferences on low-level X applications (e.g. xclock, xeyes)

Consider the X program xterm. You want to make the background black and the foreground white. This can be achieved by passing some command line arguments to xterm:

# xterm with background black and foreground white
xterm -bg black -fg white

This is fine if you want this for only one time, but if you want it to be the default, you put it in a configuration file .Xresources or .Xdefaults as follows:

XTerm*background: black
XTerm*foreground: white

The difference between these two files are the following:

• .Xdefaults is the older method of storing X resources. This file is re-read every time an Xlib program is started. If X11 is used over the network, the file must be present on the same filesystem as the programs.
• .Xresources is newer. It is loaded with xrdb into the resource manager property of the X11 root window. Whenever any program looks up a resource, it is read straight from resource manager.

If .Xresources does not exist, Xlib falls back to the old method of reading .Xdefaults on every program startup. Note that most distributions will load .Xresources automatically if it is present, causing .Xdefaults to be ignored even if you have never run xrdb manually.

The advantage of the new method is that it's enough to call xrdb once, and the resources will be available to any program running on this display, whether local or remote. Use of .Xdefaults comes at the cost that basically all X programs needs to parse this file every time you run one. A better way is to put the configuration options in .Xresources and store the configuration in the X server’s resource database by using the xrdb command:

# intialize user configurable resources using the X server resource database utility, xrdb
xrdb -merge $HOME/.Xresources

This execution of xrdb is done automatically when you login on most Linux distributions. Also, the name .Xresources is only a convention – you can use xrdb to load any file, even .Xdefaults.

Short Digression Concerning gVim and MacVim

vi / vim / gvim has long been my standard text editor on Linux. Assuming you have the editors configured properly on the remote system, and you're using Xterm to login in, you should have no difficulty using it with XQuartz.

This easy of use made me ponder why I could never get gvim to work properly with my .vimrc resource file on my Mac, even when working within the XQuartz XTerm. A small amount of research taught me that gvim requires X.Org and I must use MacVim instead. If you’re on a Mac, you just have to use MacVim as the gvim alternative, there seems to be no way out of it. It’s basically like gvim, except for Mac OS.

To help get MacVim working, use the following articles:

• Getting MacVim to run properly on Yosemite
• Gvim or MacVim in Mac OS X
• Running MacVim in your terminal
• gvim cmdline OSX