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Ogden Area Linux User Group

Book Review: X Power Tools

Presenter:Seth House
Book:X Power Tools (O'Reilly)


Version 11 came out in 1987 under the more liberal MIT license, and a vendor-neutral group called the X Consortium was formed to oversee development. Vendors used X11 sample code a starting point, then tuned specific versions for their specific needs and hardware.

In 1992 a particular implementation, X386, became popular. When it went commercial, a free version was created called XFree86. Most X innovations came from the XFree86 project over the next several years.

Starting around 1996, development stagnated for nearly four years due to internal politics and rigidity in the organization.

Control of X passed from group to group. In 1999 it was passed to The Open Group who formed

Ultimately a license dispute in 2003 caused many key developers to leave the project and move to back to the successor to the X Consortium, forming the Foundation. Development has been fast-paced since then.

X was born in 1984 at MIT.

  • 1987 — Version 11
  • 1992 — X386 became popular, gave rise to XFree86
  • 1996 — zzz
  • 1999 — formed
  • 2003 — Mass exodus to

Old X vs. New X

Old X (1984-1996)

  • Core protocol development
  • Essential extensions
  • Xt-based toolkits

New X (2000-present)

You may have noticed packages in your distro recently got small and numerous. This modularizing of X is a good thing that allows you to selectivly upgrade or change parts of X without having to recompile the whole thing (which is not for the feint of heart).

  • RENDER extension (2000)
  • Xft
  • OpenGL
  • non-Xt toolkits (GTK and qt)

The Name (Check the manpage!)


“X Windows” is generally considered used only by beginners, and is frowned on due to possible confusion with Microsoft Windows.

  • X
  • X11
  • X Window System
  • X Version 11
  • X Window System, Version 11

Nowadays “Xorg” or “X dot org” is also acceptable.



The terminology gets tricky if a user has multiple video cards or monitors using Xinerama

Generally, the user interface for one person. Keyboard, pointer, video card, and monitor.
Video card
Video card and monitor

Display Specification


Set the $DISPLAY environment variable or pass -display to a client.

Display Specification

  • A DNS hostname or IP address
  • Blank, or the word unix
  • (Rarely) DecNET or IPX/SPX designation
  • Open source operating systems use Unix domain sockets for local connections

Display Specification

  • The display number, starting at 0

Display Specification

  • Optional screen number within the display, starting at 0

Server Extensions

Off-screen rendering of windows are combined (composited) into the final screen image by hardware under control of a compositing manager. During compositing, images can be distorted, blended, and resized which makes it easy to add drop shadows, transparency, icons, and thumbnails.
Composite images such as Adobe's Flash player or anti-aliased fonts.
Displays Power Management Signalling.
OpenGL extension for X11.
Informs screen savers when to start and stop.
Rotate and resize. Notifies clients when the display is changed, and allows hot-plugging of monitors.
Enables nonrectangular windows (xeyes).
Enables complex keyboard mapping. The most poorly documented X extension.
Single-screen multimonitor support.
Allows video streams to be converted, transformed, and then overlaid on the X display. Done with hardware support and can dramatically improve video performance.
Utilized hardware support for video decompression—useful for MPEG video playback.
  • Composite
  • DPMS
  • GLX
  • SYNC
  • LBX
  • XInputExtension
  • XVideo
  • XVideo-MotionComposition

Starting a Server Manually

X :1 vt10 -config CONFIG -layout LAYOUT
  • :1
  • vt10
  • -config CONFIG
  • -layout LAYOUT

X :1 -terminate & sleep 2; DISPLAY=:1 xterm

Using a Display Manager

gdm, kdm, or xdm

  • Usually runlevel 5
  • Starts a local server
  • Authenticates
  • Starts session manager, window manager, and desktop environment
  • Either started by init or an init script.
  • Can start multiple servers (automatically or on-demand)

Config Files

X -configure writes to

The xorg.conf-4 file is a holdover from the XFree86 3.x to 4.x transition.

The files /usr/X11R6/etc/X11/xorg.conf-HOSTNAME are assumed to be on a network share, thus the file name is postfixed with a hostname.

Not needed for general configurations. X -configure

  1. File specified on the command line (must exist in the directories below)
  2. Environment variable $XORGCONFIG
  3. /etc/X11/xorg.conf-4 then /etc/X11/xorg.conf then /etc/xorg.conf
  4. /usr/X11R6/etc/X11/xorg.conf-HOSTNAME then /usr/X11R6/lib/X11/xorg.conf-HOSTNAME

xorg.conf Sections


Defines how screens and input devices are combined to form a display configuration.

Technically, this section is optional for simple configurations.

Combines one video card and one monitor to form a screen. Defines color depth and resolutions.
Characteristics of the monitor (DPMS, power saving timing, scan-rates).
Video card. Driver-specific settings, check your driver’s manpage.
One section per mouse, keyboard, etc.
  • ServerLayout
  • Screen
  • Monitor
  • Device
    • X :4 -scanpci
  • InputDevice

Virtual Screen Size (Zooming)


When changing resolution, only the displayed resolution changes, not the size of the screen image, forming a kind of virtual desktop. This is called Zooming. The virtual screen size does not need to start with the largest resolution.

Option "DontZoom" will disable Ctrl-alt + / -

By default the virtual screen size is the largest entry in the Modes entry. You can explicitly define the virtual scren size.

SubSection "Display"
    Modes "800x600" "1280x1024" "1024x768"
    Virtual  1280   1024
    Viewport 0      0

xorg.conf Optional Sections

  • Extensions (e.g. Option "Composite" "On")
  • Files (e.g. FontPath)
  • ServerFlags (e.g. zap, zoom, VT switching)
  • Module (typically optional extensions)
  • Mode or ModeLine (scan rates and signal options)
  • DRI (3d-acceleration)
    • Group (which group the device belongs to)
    • Mode (specifies file permissions for the device)

Useful Keyboard Shortcuts

  • Zap — Ctrl-alt Backspace
  • Zooming — Ctrl-alt + / -
  • Mouse keys — Shift-numlock
    • 5 or / — Left click
    • * — Middle click
    • - — Right click
    • + — Double click
    • 0 — Hold button
    • . — Release button

Changing Resolution

It’s often more useful to change both the screen resolution and the virtual screen size to eliminate scrolling. The Rotate and Resize (RANDR) extension enables this. You can also easily rotate the display with this tool.

Gnome and KDE both come with applets to access this functionality.

xrandr -q:

Screen 0: minimum 320 x 200, current 1440 x 900, maximum 1440 x 1024
default connected 1440x900+0+0 0mm x 0mm
  1440x900       60.0*
  1280x1024      75.0     70.0     60.0
  1280x960       60.0

Changing X Settings on the Fly with xset

xset q
Displays mostly settings that can be altered while the server is running such as screen saver and power management timing, keyboard repeat rates (even for individual keys), mouse acceleration, the system bell, and keyboard LED lights (recent versions of do not permit control of numlock and capslock LEDs).
  • xset q
  • xset +dpms
  • xset -r
  • xset m
  • xset b volume pitch duration
  • xset led 3
    • Options "Xleds" "1 2 3"

Useful Tools

Useful tools for diagnosing X start with the basic Xorg.0.log file (and sometimes dmesg). The X log file is self-documenting and easy to read.
To verify that your xorg.conf file is being processed correctly, consult the output from xpyinfo.
Creates ModeLines.
Useful for web developers because you can click on any pixel to get the color in 64-bit hexadecimal. (To convert to 24-bit hex just remove the first two digits from each group of four.)
  • Xorg.0.log (and dmesg)
    • xpyinfo
  • xrandr -q
  • Xnest
    • startx /usr/bin/startkde -- /usr/bin/Xnest :1
  • gtf
  • xmag
    • (3e3e, 4444, a9a9) = #3e44a9

The Clipboard

Because X is network-based the program placing data on the clipboard and the program receiving the data from the clipboard may not be on the same computer. Pasting speed is limited by network performance. Clients advertise clipboard data to other clients through the server. Data that is placed on the clipboard but never pasted is not transfered over the network. For example, Firefox may advertise that clipboard data is available in both text/plain and text/html formats. This is why clipboard data becomes unavailable once you’ve closed a client program.

  • Clients advertise clipboard data to other clients
  • Multiple formats are advertised if available
  • Pasting speed is limited by network performance


A big difference between Old X and New X is the way fonts are handled. The old font system is often called Core Fonts because fonts were handled in the X core protocols—that is, they were managed by the server, new fonts are handled by the client.

  • Core Fonts vs. RENDER, Xft, and Fontconfig
  • Install fonts to ~/.fonts or /usr/share/fonts and run fc-cache.
  • Configure font rendering with /etc/fonts/local.conf.

Remote Access

X has been a “portable, network-transparent window system” from day-one, but unless you have a specific need, just use ssh tunneling. ssh provides an enhanced version of it’s regular tunneling ability specifically for X traffic. You can set up password-less ssh using public keys and ssh-agent. An (very) improperly configured X setup can allow users to view your screen over the network.

X -nolisten tcp is a PITA.

Just use X Tunneling with SSH

ssh -X -C user@host xeyes


The Good

  • X Power Tools is a great resource for starting to really grasp X.

The Bad

  • The fonts chapter was far too Gnome and KDE focused.
  • The Session managers, desktop environments, and window managers was very light and didn’t even begin to touch the variety that exists. I still don’t know the difference between a desktop environment and a window manager.

Other notes

  • There’s a section at the end with tips on configuring X for use as a kiosk system.

X Power Tools (O'Reilly, 0-596-10195-3)