Linux+ Guide to Linux Certification, Third Edition

Linux+ Guide to Linux Certification, Third Edition

Chapter 8System Initialization

and X Windows

Objectives

• Summarize the major steps necessary to boot a Linux system

• Configure the LILO and GRUB boot loaders

• Explain how the init daemon initializes the system at boot time into different runlevels

• Configure the system to start daemons upon entering certain runlevels

Linux+ Guide to Linux Certification, 3e 2

Objectives (continued)

• Explain the purpose of the major Linux GUI components: X Windows, window manager, and desktop environment

• List common window managers and desktop environments used in Linux

• Configure X Windows settings



The Boot Process

• POST (Power On Self Test): series of tests run when computer initializes– Ensures functionality of hardware

• MBR: defines partitions and boot loader – Normally located on first HDD sector

• Boot loader: program used to load an OS• MBR might contain pointer to a partition containing

a boot loader on the first sector• Active partition: partition pointed to by MBR

– One per HDD


The Boot Process (continued)

• /boot: directory containing kernel and boot-related files

• Vmlinuz-<kernel version>: Linux kernel file• Daemon: system process that performs useful

tasks– e.g., printing, scheduling, OS maintenance

• Init (initialize) daemon: first process started by Linux kernel– Loads all other daemons– Brings system to usable state


The Boot Process (continued)

Figure 8-1: The boot process


Boot Loaders

• Primary function: load Linux kernel into memory

• Other functions:– Passing information to kernel during startup– Booting another OS: known as dual booting

• Two most common boot loaders:– GRand Unified Boot loader (GRUB)– Linux Loader (LILO)

GRUB

• More common boot loader for modern Linux

• Stage1: first major part of GRUB – Typically resides on MBR– Points to Stage1.5

• Stage1.5: loads filesystem support and Stage2– Resides in /boot/grub

• Stage2: performs boot loader functions – Displays graphical boot loader screen– Resides in /boot/grub


GRUB (continued)


Figure 8-2: GRUB boot loader screen

GRUB (continued)

• To configure, edit /boot/grub/grub.conf– Read directly by Stage2 boot loader– HDDs and partitions identified by numbers

• Format: (hd<drive#>,<partition#>)

• GRUB root partition: partition containing Stage2 boot loader and grub.conf file

• GRUB normally allows manipulation of boot loader– To prevent, enable password protection

• grub-md5-crypt command: generates encrypted password for use in grub.conf file



GRUB (continued)

• If press any key during first five seconds after the BIOS POST get graphical GRUB boot menu– Manipulate the boot process– Get a grub> prompt to enter commands

• Help screen provides list of all available commands

• grub-install command: installs GRUB boot loader– Typically for reinstallation when GRUB becomes

damaged


GRUB (continued)

Figure 8-5: Viewing help at the GRUB prompt


LILO

• Stands for Linux Loader

• Traditional Linux boot loader– No longer supported by Fedora

• Typically located on MBR

• Lilo boot: prompt appears following BIOS POST– Allows choice of OS to load at startup

• To configure, edit /etc/lilo.conf file


LILO (continued)

Table 8-1: Common /etc/lilo.conf keywords


LILO (continued)

Table 8-2: LILO error messages


LILO (continued)

• append= keyword (in /etc/lilo.conf): Useful for manually passing information to Linux kernel– Can pass almost any hardware information

• Format is hardware dependent

• Must reinstall LILO if /etc/lilo.conf file altered• lilo command: Reinstalls LILO

– -u option: Uninstall LILO


Dual Booting Linux

• Normally only one OS may be used at a time– Can use virtualization software to run multiple OSs

at the same time

• Dual booting: configuration of boot loader which allows choice of OS at boot time


Using GRUB or LILO to Dual Boot Other Operating Systems

• Easiest if Linux installed after another OS– Allows installation program to detect other OS

• Place appropriate entries in boot loader configuration file

• GRUB and LILO cannot load Windows Kernel directly– GRUB loads Windows boot loader from Windows

partition– LILO uses other= keyword to load boot loader in

appropriate partition


Using GRUB or LILO to Dual Boot Other Operating Systems (continued)

Figure 8-7: Configuring GRUB for a dual boot system


Using a Windows Boot Loader to Dual Boot Linux

• Use EasyBCD to add components to Windows boot loader– Within EasyBCD, use NeoGrub tab to modify

Windows boot loader to include Linux support– Copy contents of grub.conf into C:\NST\menu.lst

• At next boot, Windows boot loader will prompt to choose between Windows and starting the NeoGrub loader to load the Linux OS


Using a Windows Boot Loader to Dual Boot Linux (continued)

Figure 8-9: The EasyBCD program


Using a Windows Boot Loader to Dual Boot Linux (continued)

Figure 8-10: Booting Linux from a Windows boot loader


Linux Initialization

• Kernel assumes control after Linux loaded– Executes first daemon process (init daemon)

• /etc/inittab: configuration file for init daemon– Used to determine number of daemons to be loaded

• init daemon responsible for unloading daemons when the system is halted or rebooted


Runlevels

• Runlevel: defines number and type of daemons loaded into memory and executed– init daemon responsible for changing runlevels

• Often called initstates

– Seven standard runlevels

• runlevel command: displays current and most recent runlevel

• init command: change OS runlevel– telinit command: Alias to init command

Runlevels (continued)


Table 8-3: Linux runlevels


The /etc/inittab File

• Indicates default runlevel which the init daemon enters– Syntax: id:5:initdefault:

• Contains single uncommented line and series of explanatory comments


Runtime Configuration Scripts

• Runtime configuration (rc) scripts: scripts that prepare the system, start daemons and bring system to usable state– Executed by init daemon

• At boot time, run /etc/rc.d/rc.sysinit script – Initialize the hardware components, set variables,

check filesystems, and perform system tasks

• dmesg command: shows output of hardware detection and /etc/rc.d/rc.sysinit script


Runtime Configuration Scripts (continued)

• init daemon executes script for default runlevel (5) /etc/rc.d/rc5 script– Executes all files that start with S or K in the

/etc/rc.d/rc5.d directory• Each file is symbolic link to script for starting or

stopping daemon• S/K indicate Start/Kill daemon upon entering the

runlevel

• When user specifies runlevel1, init daemon runs default script but executes files in the /etc/rc.d/rc1.d directory



• Message during system initialization indicates whether each runtime configuration script has loaded successfully– Hidden by graphical boot screen display

• Use Esc key to remove the graphical screen

• Output of runtime configuration scripts is logged to the /var/log/messages file



Figure 8-11: The Linux initialization process


Configuring Daemon Startup

• Most daemons started by init daemon from symbolic links in /etc/rc.d/rc*.d directories– Point to daemon executable files in /etc/rc.d/init.d

• Most daemons accept arguments start, stop, restart– Can be used to manipulate daemons after system

startup

• service command: start, stop, or restart daemons within /etc/rc.d/init.d directory


Configuring Daemon Startup (continued)

• To add daemons to be automatically started:– Add executable to /etc/rc.d/init.d– Create appropriate links to /etc/rc.d/rc*.d

• chkconfig command: view and modify daemons that are started in each runlevel

• ntsysv utility: modifies file entries in /etc/rc.d/rc*.d directories

• Service Configuration utility: easiest way to control daemon startup by runlevel


The X Windows System: Linux GUI Components

Figure 8-15: Components of the Linux GUI


X Windows

• X Windows: core component of Linux GUI– Provides ability to draw graphical images in windows

that are displayed on terminal screen– Sometimes referred to as X server

• X client: programs that tell X Windows how to draw the graphics and display the results– Need not run on same computer as X Windows

• XFree86: OSS version of X Windows– Originally intended for Intel x86 platform


Windows Managers and Desktop Environments

• Window manager: modifies look and feel of X Windows

• Desktop environment: standard set of GUI tools– Works with a window manager to provide standard

GUI environment– Provides toolkits that speed up process of creating

new software– KDE and GNOME are most common


Windows Managers and Desktop Environments (continued)

• K Windows Manager (kwm): window manager that works under KDE

• Qt toolkit: software toolkit used with KDE• GNOME desktop environment: default desktop

environment in Fedora Linux– Metacity window manager

– GTK+ toolkit

• Can configure KDE or GNOME to use different window manager– e.g., compiz



Table 8-4: Common window managers



Figure 8-16: The KDE desktop environment



Figure 8-17: The GNOME desktop environment


Starting and Stopping X Windows

• Runlevel 5 starts GNOME Display Manager (GDM)– Displays graphical login screen– Allows user to choose the desktop environment

• .dmrc file: contains desktop environments that were manually selected in a session menu– By default, root user is not allowed to log into system

using GDM• To change this, edit /etc/pam.d/gdm and

/etc/pam.d/gdm-password files


Starting and Stopping X Windows (continued)

• For runlevel 3:– Start gdm manually, or– Use startx command

• startx command: start X Windows and Window Manager or desktop environment specified in .xinitrc file in home directory– Usually points to .Xclients-default file

Configuring X Windows

• X Windows interfaces with video hardware– Requires information regarding keyboard, mouse,

monitor, and video adapter card

• Attempts to automatically detect required information– If automatic detection fails, user needs to specify

correct hardware information manually



Configuring X Windows (continued)

• Mouse, keyboard, monitor, and video adapter card information stored in a file– /etc/X11/xorg.conf file for X.org implementation of X

Windows– /etc/X11/XF86Config file for XFree86 implementation

of X Windows– Files can be edited manually or using a program

• mouse-test command: detect mouse– Should be run as root user



• system-config-keyboard command: start the Keyboard tool in order to configure keyboard

• system-config-display command: start the Display Settings utility to configure video adapter card

• xvidtune utility: fine-tune the vsync and hsync of the video card and monitor



Figure 8-21: Selecting a keyboard layout



Figure 8-22: The Display Settings utility



Figure 8-23: Configuring video card and monitor model



Figure 8-24: Configuring dual display support



Figure 8-25: The xvidtune utility

Summary

• Boot loaders are typically loaded by the system BIOS from the MBR or the first sector of the active partition of a hard disk

• The boot loader is responsible for loading the Linux kernel and to boot other OSs in a dual boot configuration

• The GRUB boot loader uses the /boot/grub/grub.conf configuration file and the LILO boot loader uses the /etc/lilo.conf configuration file


Summary (continued)

• Seven standard runlevels are used to categorize a Linux system based on the number and type of daemons loaded in memory

• The init daemon is responsible for loading and unloading daemons when switching between runlevels

• Daemons are typically stored in the /etc/rc.d/init.d directory and loaded at system startup from entries in the /etc/rc.d/rc*.d directories


Summary (continued)

• The Linux GUI has several interchangeable components: X server, X clients, Window Manager, and optional desktop environment

• X Windows is the core component of the Linux GUI that draws graphics to the terminal screen

• You can start the Linux GUI from runlevel 3 by typing startx at a command prompt, or from runlevel 5 by using the gdm

• The hardware information required by X windows is automatically detected, but can be modified


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Linux+ Guide to Linux Certification, Third Edition