Chapter 4

Running a Linux System

Guide to Linux Installation and Administration 1

Objectives

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In this chapter, you will: Manage files and directories on a Linux system using basic commands Launch programs and manage corresponding software packages Add and remove features from the Linux kernel Review and change the initialization process that starts a Linux-based computer Shut down a Linux system in an orderly way

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Valued Gateway Client: Working with Linux Files and Directories

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Information in Linux is stored in files organized in directories Parent directory contains child directories and files The parent directory for all directories is the root directory All Linux configuration files are located in subdirectories of the root directory

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Standard Linux Subdirectories of the Root Directory

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Working at a Command Line

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Logging in to Linux at a text-mode console launches a command-line environment Within a graphical environment, you can a command-line window by using the xterm program The command-line window is also called a terminal emulator window

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A Command-Line Window in a Graphical Environment

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Managing Files with Command-Line Utilities The command-line environment is provided by a shell Shell: program that accepts and acts on the commands that you enter Absolute path: complete description of the directory in absolute terms Relative path: partial description of the directory relative to another location

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Managing Files with Command-Line Utilities

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Linux commands

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are case sensitive can include options and parameters Information about the date and time when an event occurred is stored in the form of a timestamp

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Commands for Managing Files and Directories

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Commands for Managing Files and Directories

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Managing Files with Command-Line Utilities

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Filenames

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Are case-sensitive Can be up to 256 characters Can include file extensions

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Managing Files with Graphical Utilities

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Linux desktop includes a file manager File manager: graphical program to display the contents of a directory and manage files and directories The file manager in Red Hat Linux 7.3 is called Nautilus To perform basic file management tasks, you can drag and drop file icons

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The Nautilus File Manager Window

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File Properties

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Each file in Linux has several basic properties:

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Type Name Size Location Timestamp Each file has the owner of the file, the group assigned to the file, and the permissions granted to access the file

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The Properties Dialog Box

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File Permissions

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File permissions define the access that the owner has granted to others on the Linux system Types of permissions:

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Read permission (r) Write permission (w) Execute permission (x) Permissions can be assigned in three different ways:

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User permission Group permission Other permissions

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File Permissions

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You can alter file ownership and file permissions using the chown and chmod commands The chmod command uses letters or numeric codes to define the file permissions assigned to a file or directory The umask command determines the file permissions assigned when you create a new file

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Commonly Used File Permission Settings

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The Permissions Tab of the Properties Dialog Box

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Running and Managing Software

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Environment variables: defined by the Linux shell so that all programs can access their values Variable: memory location used by a program to store a value The PATH environment variable includes a list of all the directories where programs on the system are located You can display values of the PATH using the echo command

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Function Libraries

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A function is a small task that a computer program performs A function library is a file that contains commonly used functions The ldd command lists the libraries that a program requires

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Using rpm to Manage Software Packages

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rpm command

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Manages all of the rpm software packages Maintains a database for all the software installed on the Linux system You can use the rpm command to query the software package database or to install or erase software packages from the system Hundreds of options are supported by the rpm command

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Using Graphical Tools to Manage Software Packages

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GNOME and KDE include graphical programs to manage software packages The GnoRPM package management utility is included with Gnome The KDE Desktop includes a package management tool called kPackage Both GmoRPM and kPackage provide menu items

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The Main Window of the GnoRPM Utility

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Using kPackage to Display Software Package Information

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Using tar Archive Files

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A tar archive is a collection of many files stored in a single file The tar command is used to create a tar archive, to extract its content, and to create backups of files on the system A tar archive has a .tar extension The resulting file after the tar command with the compression options is called a gzipped tarball

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Compression Utilities in Linux

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The Linux Kernel

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Each Linux kernel has:

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Release number Timestamp Modules

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Learning about Your Kernel

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The uname command with the –r option displays the version of your Linux kernel followed by the release number A release number is assigned by the company that prepared the Linux product A timestamp indicates the date and time when the kernel was created

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Kernel Modules

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Linux kernel modules are files containing computer code that can be loaded into the kernel or removed from the kernel Kernel modules can be automatically loaded based on the configuration set during the Linux installation The lsmod command lists the modules that are installed in the Linux kernel

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Adding and Removing Modules

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The modprobe command loads a module with any required supporting modules The rmmod command removes a module from the kernel Module parameters provide information needed by amodule to locate system resources

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Locating Modules

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The module files are stored in /lib/modules/version/kernel directory, where version id the version number of the Linux kernel on the system This directory contains subdirectories for networking-related modules, device drivers, and other module types

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The Initialization Process 1. A boot manager loads and starts the Linux kernel 2. The Linux kernel initializes hardware and then launches the init program 3. The init program launches a script based on the run level in which Linux is to operate 4. The script started by init typically runs many other scripts to launch and manage system services

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Booting the Kernel

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GRUB and LILO are the boot managers The boot manager displays a prompt listing the available operating system to launch Boot parameters instruct the Linux kernel how to operate or how to access parts of the computer system’s hardware You can add boot parameters at the boot manager selection prompt

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Configuring the Boot Manager

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You can update the configuration of a boot manager after the installation is completed The configuration file for the LILO boot manager is /etc/lilo.conf.anaconda

The configuration file for GRUB boot manager is /boot/grub/grub.conf

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Initializing System Services

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The init program is a master control program that starts other programs and scripts that initialize the system services A script is a collection of commands that are stored in a text file and executed without user intervention The init program is controlled by the /etc/inittab configuration file

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Reviewing Run Level Services

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A run level is a mode of operation in which a preconfigured set of services is activated

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The Linux Initialization Process

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Starting and Stopping System Services

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The chconfig program allows you to start and stop services when you boot Linux RedHat Linux includes a graphical utility to configure system services called serviceconf The KDE Desktop includes a similar graphical utility called ksysv

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The Service Configuration Utility

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The ksysv Graphical Services Configuration Utility

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Configuring System Services

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The initialization scripts in /etc/rc.d/init.d are provided when you install Linux Configuration details for system services scripts are located in the /etc/sysconfig directory and its subdirectories

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Shutting Down Linux

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You can shut down Linux by:

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The reboot command The halt command The shutdown command Pressing Ctrl+Alt+Del The telinit 0 command

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Summary

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Information in Linux is stored in files organized in a directory structure that begins with the root directory There are basic commands to manage files and directories Files can be compressed using tar, zip, gzip, and other utilities Read, Write, and Execute permissions for a file or directory can be assigned to the owner, to the assigned group, or to all other users on the system The rpm command is used to query the software package database or to install or erase software packages from the system

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Summary

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The Linux kernel supports loadable modules, which are managed using the lsmod, insmod, rmmod, and modprobe commands You can provide boot parameters to the Linux kernel at the boot manager selection prompt The Linux kernel starts the init program, which in turn runs several scripts based on information stored in the run level directories You can set up which services are activated at boot time using the chkconfig command or using various graphical utilities To avoid data loss, you must gracefully shut down Linux using a command such as reboot, halt, or shutdown

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