Chapter 7. The X Window System

Each package which is compliant to Freedesktop.org's xdg menu system installs its menu data provided by "*.desktop" under "/usr/share/applications/". Modern desktop environments which are compliant to Freedesktop.org standard use these data to generate their menu using the xdg-utils package. See "/usr/share/doc/xdg-utils/README".

The following (re)configures an X server.

# dpkg-reconfigure --priority=low x11-common

	Note
	Recent Linux kernels have good graphics and input device supports with DRM, KMS, and udev. X server is rewritten to use them. So "/etc/X11/xorg.conf" is usually not present on your system. These parameters are configured by the kernel. See "fb/modedb.txt" in the Linux kernel documentation.

For the large high resolution CRT monitor, it is a good idea to set the refresh rate as high as your monitor can handle (85 Hz is great, 75 Hz is OK) to reduce flicker. For the LCD monitor, slower standard refresh rate (60Hz) is usually fine due to its slow response.

	Note
	Be careful not to use too high refresh rate which may cause fatal hardware failure of your monitor system.

There are several ways of getting the "X server" (display side) to accept connections from an "X client" (application side).

On a system where "/etc/X11/Xsession.options" contains a line "allow-user-xsession" without preceding "#" characters, any user who defines "~/.xsession" or "~/.Xsession" is able to customize the action of "/etc/X11/Xsession" by completely overriding the system code. The last command in the "~/.xsession" file should use form of "exec some-window/session-manager" to start your favorite X window/session managers.

If this feature is used, the selection of the display (or login) manager (DM), session manager or window manager (WM) by the system utility is ignored.

Here are new methods to customize the X session without completely overriding the system code as above.

The selection of the display (or login) manager (DM), session manager or window manager (WM) by the system utility is respected.

These configuration files should not have "exec …" nor "exit" in them.

The use of "ssh -X" enables a secure connection from a local X server to a remote application server.

Set "X11Forwarding" entries to "yes" in "/etc/ssh/sshd_config" of the remote host, if you want to avoid "-X" command-line option.

Start the X server on the local host.

Open an xterm in the local host.

Run ssh(1) to establish a connection with the remote site as the following.

Secure X terminal via the Internet, which displays remotely run entire X desktop environment, can easily achieved by using specialized package such as ldm. Your local machine becomes a secure thin client to the remote application server connected via SSH.

aptitude(8) helps you find additional fonts easily.

Since Free fonts are sometimes limited, installing or sharing some commercial TrueType fonts is an option for a Debian users. In order to make this process easy for the user, some convenience packages have been created.

You'll have a really good selection of TrueType fonts at the expense of contaminating your Free system with non-Free fonts.

Font name such as "VL PGothic" with "P" is a proportional font which corresponds to the fixed width "VL Gothic" font.

Here is a list of basic office applications (LO is LibreOffice).

Here is a list of basic utility applications which caught my eyes.

The modern Desktop Environments (GNOME, KDE, …) offer different clipboard system for the cut, copy, and paste using the left mouse button and keys (CTRL-X, CRTL-C, and CTRL-V).

xmodmap(1) is a utility for modifying keymaps and pointer button mappings in the X Window System. To get the keycode, run xev(1) in the X and press keys. To get the meaning of keysym, look into the MACRO definition in "/usr/include/X11/keysymdef.h" file (x11proto-core-dev package). All "#define" statements in this file are named as "XK_" prepended to keysym names.

Most traditional X client programs, such as xterm(1), can be started with a set of standard command line options to specify geometry, font, and display.

They also use the X resource database to configure their appearance. The system-wide defaults of X resources are stored in "/etc/X11/Xresources/*" and application defaults of them are stored in "/etc/X11/app-defaults/*". Use these settings as the starting points.

The "~/.Xresources" file is used to store user resource specifications. This file is automatically merged into the default X resources upon login. To make changes to these settings and make them effective immediately, merge them into the database using the following command.

$ xrdb -merge ~/.Xresources

See x(7) and xrdb(1).

	Warning
	Never start the X display/session manager under the root account by typing in root to the prompt of the display manager such as gdm3 because it is considered unsafe (insecure), even when you plan to perform administrative activities. The entire X architecture is considered insecure if run as root. You must always use the lowest privilege level possible, like a regular user account.

Easy ways to run a particular X client, e.g. "foo" as root is to use sudo(8) etc. as the following.

$ sudo foo &

$ sudo -s
# foo &

$ gksu foo &

$ ssh -X root@localhost
# foo &

	Caution
	Use of ssh(1) just for this purpose as above is waste of resource.

In order for the X client to connect to the X server, please note the following.

The gksu package (popcon: V:56, I:291) is a specialized GTK+ GUI package for gaining the root privileges. It can be configured to use su(1) or sudo(8) as its backend depending on the "/apps/gksu/sudo-mode" gconf key. You can edit gconf key using gconf-editor(1) (menu: "Applications" → "System Tools" → "Configuration Editor").