The X Window System

• Computer Systems Lab Documentation
  • 1 Frequently Asked Questions
    • 1.8 The X Window System
      • 1.8.1 How do I change the screen resolution on the computer I'm using?
      • 1.8.2 How do I lock the display?
      • 1.8.3 How do I change my background?
      • 1.8.4 How do I use X from home?
      • 1.8.5 How can I get my X and/or motif application to compile and link properly?
      • 1.8.6 Why can't I find X application on my Red Hat computer?
      • 1.8.7 How do I use the numeric keypad in X with applications like vi or matlab?
      • 1.8.8 How do I get rid on these can't alloc color for Color messages?
      • 1.8.9 Can my X display be configured for more than 256 colors (8 bits)?

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1.8.1 How do I change the screen resolution on the computer I'm using?

The command xsetres can only be used on X86 machines. Note: This means that anyone on an instructional computer will not be able change the screen resolution.

The location of xsetres should be given already in your path; however, if there is a problem the program can be found in /s/std/bin.

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1.8.2 How do I lock the display?

The command xlock will lock your workstation. xlock has a large number of options. You should consult the xlock man page (type man xlock) for more information on these.

When you return to the workstation, move the mouse or press a key. You will be asked to enter your password to regain access to the workstation.

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1.8.3 How do I change my background?

You can change the background on your computer to a specific color, or you can use a picture.

To change your background to a solid color, use the command xsetroot -solid [color]. Valid color names can be found in /s/X11/lib/X11/rgb.txt or by using the showrgb program.

To change your background to a picture, use the command xv -root [name] -quit, where name is the picture you want to use. Any picture format that can be viewed using the xv viewer is acceptable. Warning: The more complex the picture, the more time it will take to repaint your computer screen after moving things around.

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1.8.4 How do I use X from home?

Note: This listing is not meant to be comprehensive. If you have more questions, please reference the manual that came with your X server.

We don't allow non-CS hosts to start X sessions on any CS workstations. If you want to run an X application on a CS workstation from outside the department use secure telnet or ssh to log into the CS workstation.

Set your DISPLAY environment variable to point to your X server, where [machine] is the name of your home computer.

• Using the C shell (csh, tcsh): setenv DISPLAY [machine]:0.0
• Using the Bourne shell (sh): DISPLAY=[machine]:0.0; export DISPLAY

Note: If your X server requires the XDM-AUTHORIZATION-1 or MIT-MAGIC-COOKIE-1 type authorization, you will need to forward those credentials to your CS account. Try man xauth for more information.

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1.8.5 How can I get my X and/or motif application to compile and link properly?

Note: The xmkmf program will automatically add all the required paths and libraries you may need in your build. We therefore strongly encourage it's use wherever possible. The following information is provided for situations where xmkmf cannot be used.

Make sure you have the correct paths specified. If you are building X applications, you need to add /s/X11R6/include to the include search path and /s/X11R6/lib to the library search path. If you are using motif application, you also need to add /s/motif/include and /s/xpm/include to your include path and /s/motif/lib and /s/xpm/lib to your library path. Most compilers will prefer the shared versions of these libraries. Check your compiler documentation to ensure that the syntax you choose will include the required paths both at link time and at run time.

Make sure that you have all the required libraries. Each application will vary in the libraries that it requires. Some of the X and motif libraries you may need are listed below (along with some examples of functions that are defined in each library. The list is not exhaustive, but may help you identify needed libraries:

Library	Link syntax	Symbol Example	Component
libX11	-lX11	(Always included)	Core X
libXau	-lXau	XauReadAuth	X
libXaw3d	-lXaw3d	XawInitializeWidgetSet	X
libXIE	-lXIE	XieFloConvertFromRGB	X
libXext	-lXext	XShapeCombineMask	X
libICE	-lICE	IceProcessMessages	X
libSM	-lSM	SmcDeleteProperties	X
libXm	-lXm	XmCreateCommandDialog	Motif
libMrm	-lMrm	MrmFetchWidget	Motif
libXpm	-lXpm	xpmParseColors	pixmaps
libsocket	-lsocket -lnsl	getpeername	solaris

Note: The CSL does not provide programming consulting services. If you are having trouble building your application, you will need to seek help from the man system, these faqs, the author of the package, and other sources.

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1.8.6 Why can't I find X application on my Red Hat computer?

In Red Hat, X applications are installed in a different location than on other architectures. Running the newdots program will correct the problem by updating all your 'dot' files to the current version, which includes the path for the Red Hat X applications. Alternatively, if you feel comfortable editing your 'dot' files, you can add /usr/X11R6/bin to the end of your path in your $HOME/.cshrc file.


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1.8.7 How do I use the numeric keypad in X with applications like vi or matlab?

This is a terminal capabilities problem. When the application (vi, matlab, etc.) starts, it enables an "Application keypad" mode, which causes the keypad keys to generate escape sequences instead of ascii numbers.

The recommended workaround for this problem is:

• Start your application (vi, matlab, etc.)
• Hold down 'ctrl+middle mouse button'
• (de-)select the option titled 'Enable Application Keypad'
• Be sure numlock is active, then use the keypad.

You will need to re-select this option each time you run the application.


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1.8.8 How do I get rid on these can't alloc color for Color messages?

Usually, this is caused when netscape is using too many colors, and not enough are available for other applications. There are several solutions:

• Start netscape with the option `-ncols 128` (or some other number). This will limit netscape to 128 colors. This is how netscape is currently configured for new users who start netscape from fvwm (the default window manager). You can always start netscape from the command line with this option. Running the newdots command will update your fvwm configuration file to the current default, which includes this netscape option (newdots will update all your dot files to the current defaults, so be sure this is what you want before doing it). You can also update your window manager configuration file by hand, if you know how to do that, and add this option.

• Start netscape with the option `-install`. This will cause netscape to run with a private color map. This allows netscape to have more colors, but the display colors change as you select and deselect the netscape window.

Any application (not just netscape) that uses too many colors will cause this problem. The solution is always to get the application to use fewer colors. The method to do this will vary from application to application.

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1.8.9 Can my X display be configured for more than 256 colors (8 bits)?

In general no. Most of the video cards we have are not capable of running 24 bit (true-color) modes at usable numbers of pixels. Also, there are known driver problems running displays in a 1280x1024x24bit mode even on the few cards that have enough memory for this mode.

16 bit display modes are incompatible with some X applications (the applications cannot open their windows). For this reason, we don't run any displays at 16 bit depth.


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