18.5 Objective 4: Install and
Customize a Window Manager Environment
The
selection of a desktop environment for X is a personal
decision. At a minimum, you need a window manager such as
twm to provide basic window
frames, menus, and controls. On the more elaborate side, an
integrated working environment such as KDE or GNOME offers a
rich set of applications. Regardless of how you configure your
desktop, it's important to understand some basic customization
techniques.
18.5.1 Starting X and a Default
Window Manager
Starting XFree86 can be as simple as issuing
the X command as root.
However, X alone doesn't give
you a working environment. At the very least, you also need to
start a window manager and an application and set up basic X
access authority. You may also
wish to choose from among multiple desktop environments and
window managers installed on your system.
18.5.1.1 The XFree86 startup
process
Assuming for the moment that we're not using
xdm, the process of starting X
goes like this:
-
The user issues the startx command. This is a script
provided by XFree86 and often modified by distributors and
administrators. startx is
intended as a frontend to xinit.
-
startx calls
xinit with two main
arguments:
-
An Xinitrc script, which contains
X programs to run. This script could be .xinitrc
from the user's home directory, or if that doesn't exist,
a systemwide default found in
/etc/X11/xinit/xinitrc.
-
Server options, such as X authority
information.
-
xinit
launches XFree86 and the chosen Xinitrc script.
-
XFree86 starts. Note that X itself does not
provide any applications. They appear only as the result of
the commands found in the Xinitrc script.
-
Client programs and a window manager found
in the Xinitrc script start.
The contents of startx and the system default
/etc/X11/xinit/xinitrc can vary from distribution to
distribution and can be changed by administrators to suit
local needs. They may also reference additional files, such as
/etc/X11/xinit/Xclients, to determine which programs
and window manager to run. Example
18-4 shows the contents of /etc/X11/xinit/xinitrc,
a modified version of the original distributed with XFree86.
Example 18-4. A System Default
xinitrc #!/bin/sh
# $XConsortium: xinitrc.cpp,v 1.4 91/08/22 rws Exp $
userresources=$HOME/.Xresources
usermodmap=$HOME/.Xmodmap
sysresources=/usr/X11R6/lib/X11/xinit/.Xresources
sysmodmap=/usr/X11R6/lib/X11/xinit/.Xmodmap
# merge in defaults and keymaps
if [ -f $sysresources ]; then
xrdb -merge $sysresources
fi
if [ -f $sysmodmap ]; then
xmodmap $sysmodmap
fi
if [ -f $userresources ]; then
xrdb -merge $userresources
fi
if [ -f $usermodmap ]; then
xmodmap $usermodmap
fi
# start some nice programs
(sleep 1; xclock -geometry 50x50-1+1) &
(sleep 1; xterm -geometry 80x50+494+51) &
(sleep 1; xterm -geometry 80x20+494-0) &
exec twm
In this example, resource and keyboard
mappings are set, a few applications are launched, and the
twm window manager is started.
twm is installed as a basic
default window manager on most distributions.
18.5.1.2 Customizing twm
Each of the window managers and desktop
environments has its own style of configuration. In the case
of twm, a single file called
.twmrc in the user's home directory is used. If
.twmrc doesn't exist, the system-wide default
/etc/X11/twm/system.twmrc is used. The file can
include:
Even for a basic window manager such as twm, a wide array of configuration
options is available to tailor the window manager to your
personal taste. Example
18-5 contains parts of system.twmrc, which defines
a default options menu, defops, and a submenu that
starts various X terminals.
Example 18-5. Menu
Configuration in system.twmrc menu "defops"
{
"Twm" f.title
"Netscape" f.exec "netscape &"
"Terminals" f.menu "Terms"
}
menu "Terms"
{
"Aterm" f.exec "exec aterm &"
"Kvt" f.exec "exec kvt &"
"Xterm" f.exec "exec xterm &"}
For complete information on twm, see its manpage (man twm).
|
This Objective requires that you have a
general understanding of the configuration of menus for
a window manager. You will not be required to generate
window manager configuration files for the test, but you
should be aware of the need to edit and modify them. |
18.5.2 xterm et al.
One of the most important applications
available to a system administrator working in a graphical
environment is a terminal
emulator. The standard
terminal emulator distributed with X is xterm,
which understands DEC VT and Tektronix graphics terminal
protocols. The VT behavior that is emulated includes cursor
positioning, character effects, and reverse video, among
others. In essence, an xterm is
a direct replacement for a hardware terminal.
xterm has a
large resource configuration file located in
/usr/lib/X11/app-defaults/XTerm that contains configurable menus,
fonts, colors, and actions. You may customize this file to
alter the default behavior of xterm on your system. These settings
can also be overridden by resource settings contained in your
own .Xdefaults file, located in your home directory.
|
You should be familiar with at least
one of the popular X terminal programs available on your
Linux system. Remember that some programs have
system-wide configuration files that can be used to
fine-tune their behavior and appearance.
|
18.5.3 X Libraries
Just as many
executable programs are dependent upon shared system libraries
for their execution, most X applications require a number of
X-specific libraries. XFree86 comes bundled with the necessary
set of libraries for traditional X applications. However, many
graphical programming projects are created using toolkits
whose libraries are not included in the XFree86 distribution.
In these cases, you need to install the required libraries
before programs requiring them will compile or execute.
For example, the GIMP Toolkit (GTK) is used to build
much of the GNOME desktop environment. This means that GTK
must be installed on the system in order to run GNOME applications, including The GIMP
(http://www.gimp.org/).
Library dependency issues typically occur
when you try new software. Either the compiler fails as you
attempt to build the program, or the loader fails when you try
to run a precompiled dynamic binary. In either case, you need
to locate the correct version of the libraries and install
them. It should be relatively easy to find recent versions of
the popular libraries in your distribution's package format by
visiting web sites of the library distributor or your Linux
distribution.
To manually check for library dependencies,
you may use the ldd utility, described fully in Section
14.4.
18.5.4 Remote X Clients
One of the
fundamental design elements of the X Window System is that it
is a network protocol, which allows for displays to occur
remotely across a network. Many sites employ high-powered
systems for computation and use desktop X servers (X terminals
or Linux systems, for example) for display rendering.
To send the output from an X application to a
remote machine, you need to set the display environment variable. This
variable contains a description of the output destination and
has three components:
[host]:display[.screen]
- host
-
This part of the
description specifies the remote hostname on the network. It
can be any valid hostname, fully qualified domain name, or
IP address. host is optional; the local system is
used if the host is not specified.
- display
-
This specifies which display the
output should be directed toward. A single system can manage
many displays. Note that the colon is required even if the
host is omitted.
- screen
-
This optional
parameter is used for multiheaded systems (i.e., systems
with more than one monitor) and specifies on which output
screen the application will appear.
Setting display to "point to" a
remote host display causes all subsequent X applications to be
displayed there. For example: # export DISPLAY=yourhost:0.0
# xterm
In this example, the xterm is displayed on the first
display on yourhost.
18.5.4.1 Examples
The default display on the local host: :0
The default display on a remote host: yourhost:0
Display programs on the first screen of the
second display found on the machine located at 192.168.1.2:
192.168.1.2:1.0
Display programs on the first screen of the
third display on yourhost: yourhost:2.0
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You must be familiar with the
display environment variable and how to use it
to direct X client applications to remote X servers.
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