Mastering Red Hat Linux 9 [Electronic resources] نسخه متنی

Understanding the Configuration Files

Several important configuration files and executable programs are related to the Linux X Window. Most of you know the command that starts the X Window from a command-line interface:

# startx

This program refers to other configuration files and programs, in the /etc/X11/xinit and /usr/X11R6/ bin directories. The /etc files can be customized for individual users, as hidden files in their home directories.

By far, the most important X Window configuration file is /etc/X11/XF86Config; we’ll discuss that file in some detail later in this section.

startx

There are three basic ways to get into the Linux GUI. You can edit the id variable in /etc/inittab to start in runlevel 5 when you boot Linux, or you can go into runlevel 5 from the text console with the init 5 command. (More information on /etc/inittab and init are available in Chapter 11.) Either of these methods brings you to one of the graphical login interfaces described earlier.

A third method is to run the startx command. This is actually an executable file in the /usr/X11R6/ bin directory. You can open startx in any text editor. The start of this file is shown in Figure 15.18.

Figure 15.18: The startx file

As you can see, this script includes several variables. It first looks for .xinitrc and .xserverrc files in the home directory of the requesting user. If these files aren’t available, it uses defaults in the /etc/X11/xinit directory.

The defaultclient and defaultserver are the default X Client and the default X Server; the default xterm client is used if you use switchdesk to make twm your default desktop. The other variables are intentionally left empty; if you’re comfortable with programming code, you’ll be able to see how these variables are assigned.

More X Windows

It’s possible to run different X Windows, locally and remotely. As described in Chapter 03, the X Window gets its own virtual console. If you’re in a text screen and the GUI is running, you can access it with the Ctrl+Alt+F7 command.

If you have enough memory, you can run a second X Window in your local computer. The startx -- :1 command opens a second GUI, which you can access with the Ctrl+Alt+F8 command.

If you want to try a GUI application from another computer, set that computer to accept X commands from the remote computer. Disable your firewall, and let the remote computer in with the xhost +computername or xhost +remoteipaddr command. (remoteipaddr represents the IP address of the remote computer.) Then you can log into the remote computer and start a command such as gimp --display youripaddr:0.0 or xclock -display youripaddr:0.0.

The display switch is not consistent; with some commands such as xclock, it requires only one dash (-display); other commands such as gimp require a double-dash (--display). If in doubt, run the command with the -h switch such as xclock -h or gimp -h.

/etc/X11

The /etc/X11 directory contains a number of important configuration files and directories. Table 15.1 describes each of the files and subdirectories.

Local Configuration Files

You can set up X Window configuration files in users’ home directories. As you’ve seen earlier, startx looks for two of them for settings to start the Linux X Window: ~/.xinitrc and ~/.xserverrc. The dot hides these filenames in your home directory.

As described earlier, Red Hat does not use the xserverrc file. Thus, the key configuration file is ~/.xinitrc, which also calls several other files in the home directory.

The other key files are ~/.Xclients and ~/.Xclients-default, which switchdesk modifies so startx knows the desktop you want. If you’re interested in how these files work, read them for yourself. Use the switchdesk command as described earlier to set a different default desktop and see what that does to ~/.Xclients-default.

xinitrc

When the startx command starts your X Server, it needs to call up fonts, keyboard settings, and default X Clients.

The xinitrc file is an executable shell script. You can use the default in the /etc/X11/xinit directory, or you can customize it, change its name to .xinitrc, and store it in your own home directory. The following is a detailed analysis of the default xinitrc file:

#!/bin/sh
# © 1999-2003 Red Hat, Inc.
userresources=$HOME/.Xresources
usermodmap=$HOME/.Xmodmap
userxkbmap=$HOME/.Xkbmap
sysresources=/etc/X11/Xresources
sysmodmap=/etc/X11/Xmodmap
sysxkbmap=/etc/X11/Xkbmap

These first lines represent the other configuration files needed through the rest of the script. You’ll see in a moment that if the user* variable files aren’t available, xinitrc uses just the sys* files.

# merge in defaults
if [ -f "$sysresources" ]; then
xrdb -merge "$sysresources"
fi
if [ -f "$userresources" ]; then
xrdb -merge "$userresources"
fi

These lines start by applying the $sysresources file, /etc/X11/Xresources. If there’s a valid $userresources file (~/.Xresources), the settings from each file are combined.

# merge in keymaps
if [ -f "$sysxkbmap" ]; then
setxkbmap `cat "$sysxkbmap"`
XKB_IN_USE=yes
fi
if [ -f "$userxkbmap" ]; then
setxkbmap `cat "$userxkbmap"`
XKB_IN_USE=yes
fi

These lines serve the same purpose as the previous stanzas, except they apply to the noted Keyboard Map files, based in Xkbmap. However, that file doesn’t normally exist in Red Hat Linux and are therefore ignored. In xinitrc, this is followed by a stanza related to a Sun Microsystems X Server, which Red Hat does not use and therefore also ignores. This is followed by:

# xkb and xmodmap don’t play nice together
if [ -z "$XKB_IN_USE" ]; then
if [ -f "$sysmodmap" ]; then
xmodmap "$sysmodmap"
fi
if [ -f "$usermodmap" ]; then
xmodmap "$usermodmap"
fi
fi
unset XKB_IN_USE

This stanza checks for an Xmodmap file in /etc/X11/xinit, or a hidden version in your home directory. If it exists, it’s used in place of the aforementioned Xkbdmap file. But remember, that file doesn’t normally exist in Red Hat Linux.

# run all system xinitrc shell scripts.
for i in /etc/X11/xinit/xinitrc.d/* ; do
if [ -x "$i" ]; then
. "$i"
fi
done

This stanza runs basic shell scripts in the noted directory, /etc/X11/xinit/xinitrc.d. These scripts can include files such as xinput and xmbind, which are described later.

if [ -f $HOME/.Xclients ]; then
[ -x /usr/bin/ssh-agent -a -z "$SSH_AGENT_PID" ] &&
 exec ssh-agent $HOME/.Xclients || exec $HOME/.Xclients
elif [ -f /etc/X11/xinit/Xclients ]; then
[ -x /usr/bin/ssh-agent -a -z "$SSH_AGENT_PID" ] && 
exec ssh-agent /etc/X11/xinit/Xclients || exec /etc/X11/xinit/Xclients
else

These commands check for default clients in the Xclients file. They also set up an authentication agent for SSH, if previously configured. See Chapter 23 for more information.

       xclock -geometry 100x100-5+5 &
xterm -geometry 80x50-50+150 &
if [ -x /usr/bin/netscape -a -f /usr/share/doc/HTML/indexl ]; then
netscape /usr/share/doc/HTML/indexl &
fi
if [ -x /usr/X11R6/bin/fvwm2 ]; then
exec fvwm2
else
exec twm
fi
fi

These commands set up default clients if no Xclients file is available. You might note that this stanza includes Netscape, which is no longer included with the Red Hat Linux CDs. This stanza also uses xclock, a generic Linux GUI clock, and xterm, a generic command-line interface window.

You can also create your own .xinitrc file in your home directory. Make sure to use the appropriate chmod command to make that file executable. For example, you could add the following information to .xinitrc:

#!/bin/bash
xclock &
xterm &
gimp &
exec twm

This file starts with #!/bin/bash, which assumes that the commands that follow are based on the bash shell. The remaining commands start the standard Linux graphical clock (xclock), a basic terminal command-line interface (xterm), and The GIMP (gimp), the GNU Image Manipulation Program. Finally, the code starts a simple window manager interface known as twm (twm). The result starts the programs with twm, as shown in Figure 15.19.

Figure 15.19: What you can do with.xinitrc

Xresources

There is normally an .Xresources file in users’ home directories, as well as a default Xresources in /etc/X11. The default file goes through a series of steps to find your preferred desktop. Generally, if GNOME or KDE is not available, Xresources looks for a .wm_style file in your home directory that might call for an older window manager.

But these are details; the standard .Xresources file in your home directory sets a color scheme for basic X Clients in your GUI.

XF86Config

The /etc/X11/XF86Config file contains the main configuration settings for the X Server. Whenever you start a Linux GUI, the basic settings for resolution, pitch, graphics drivers, monitors, keyboards, and mice or other pointing devices are configured through this file. This file includes several major sections described here.

The first line in a file tells you if XF86Config was created through Anaconda:

# XFree86 4 configuration created by pyxf86config

or redhat-config-xfree86

# XFree86 4 configuration created by redhat-config-xfree86

Many of the directives in XF86Config are listed in Table 15.2. The following subsections correspond to the typical sections that you might see in your XF86Config file.

ServerLayout

The ServerLayout section binds various InputDevice(s) and the Screen, which includes the combined configuration for the monitor and video card. The example shown here is in effect a summary of the configuration on my computer:

Section "ServerLayout"
Identifier     "Default Layout"
Screen    0    "Screen0" 0 0
InputDevice    "Mouse0" "CorePointer"
InputDevice    "Keyboard0" "CoreKeyboard"
InputDevice    "DevInputMice" "AlwaysCore"
EndSection

In other words, this particular ServerLayout section combines the settings of Screen0, Mouse0, DevInputMice, and Keyboard0, as configured through Anaconda, the Red Hat Linux installation program.

Files

The Files needed by your X Server relate to colors and fonts. The example here is taken from my computer:

Section "Files"
RgbPath    "/usr/X11R6/lib/X11/rgb"
FontPath   "unix/:7100"
EndSection

To translate, this Files section notes the location of RGB style colors for display. It also lists the standard TCP/IP port for the X Font Server, xfs. RGB (Red Green Blue) is the traditional standard for color graphics.

Module

The module commands load font and server extension modules. The font modules shown below are straightforward; they load the Freetype (True Type clone) and Type1 fonts. A full list of available modules is shown in the /usr/X11R6/lib/modules directory.

Section "Module"
Load "dbe"
Load "extmod"
Load "fbdevhw"
Load "dri"
Load "glx"
Load "record"
Load "freetype"
Load "type1"
EndSection

InputDevice

An InputDevice is anything that a user directly touches to send information to a computer. Also known as a Human Interface Device (HID), these devices are primarily keyboards and mice, but can include trackballs, touchpads, and more. As you can see below, there’s a separate InputDevice section for each component.

Section "InputDevice"
Identifier "Keyboard0"
Driver     "keyboard"
Option     "XkbRules" "xfree86"
Option     "XkbModel" "pc105"
Option     "XkbLayout" "us"
EndSection

This first InputDevice specifies your keyboard, using the driver by the same name. The basic keyboard rules specify a layout, which conforms to those associated with the XFree86 Server. The model is associated with a standard 105-key keyboard, in a standard U.S. layout.

Section "InputDevice"
Identifier "Mouse0"
Driver     "mouse"
Option     "Protocol" "IMPS/2"
Option     "Device" "/dev/psaux"
Option     "ZAxisMapping" "4 5"
Option     "Emulate3Buttons" "no"
EndSection

The next InputDevice specifies a mouse, using a PS/2 connection. The device driver file is /dev/psaux, which is often linked to /dev/mouse. ZAxisMapping represents the up and down motion of a mouse wheel, which in this case corresponds to standard mouse buttons 4 and 5. These buttons aren’t available on all mice. Button 4 corresponds to a scroll wheel on a three-button mouse. Button 5 corresponds to a button on the side of the mouse. If you have more than one mouse or pointing device, there may be another InputDevice section.

Monitor

The Monitor section summarizes the basic settings associated with your monitor. The following settings from my computer are fairly straightforward; they identify the monitor model, the DisplaySize in millimeters, and the horizontal sync and vertical refresh rates. The dpms option represents the power-saving settings standard.

Section "Monitor"
Identifier  "Monitor0"
VendorName  "Monitor Vendor"
ModelName   "S/M 955DF"
DisplaySize 360    270
HorizSync   30.0 - 85.0
VertRefresh 50.0 - 160.0
Option      "dpms"
EndSection

It’s possible to configure two different monitors; each monitor gets its own section with customized settings. The monitor and video card together gets its own Screen section, as we describe later in this chapter.

Device

The main device that supports any GUI is the video card. The following section identifies a specific card, with driver, and associated video RAM.

Section "Device"
Identifier  "Videocard0"
Driver      "i810"
VendorName  "Videocard vendor"
BoardName   "Intel 810"
VideoRam    16384
EndSection

If you have more than one video card, each card gets its own separate section in your XF86Config file.

Screen

The Screen section combines the applicable video card (Device) and monitor settings from their respective sections. The name associated with the Device and Monitor lines is taken from their Identifier variables.

Section "Screen"
Identifier "Screen0"
Device     "Videocard0"
Monitor    "Monitor0"
DefaultDepth   24
SubSection "Display"
Depth    16
Modes   "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth    24
Modes   "800x600" "640x480"
EndSubSection
EndSection

It’s the combined video card and monitor that gets a dot pitch (Depth) and resolution (Modes). The following section configures two different SubSection "Display" stanzas. Note that each stanza has one Depth and possibly overlapping Modes.

DRI

The Direct Rendering Interface (DRI) takes advantage of the 3D acceleration available with higher-end video cards. It’s associated with games as well as the higher-end graphics required for movies and computer-aided design models. The following DRI section is simple:

Section "DRI"
Mode     0666
EndSection

The 0666 is associated with read and write file permissions, for all users. If you specify a group in /etc/group, you can limit 3D rendering access. For example, if there is a galley group in /etc/ group, you could limit access with the following stanza:

Section "DRI"
Group    "galley"
Mode     0666
EndSection