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Lesson 13Maintaining and Administering a Linux System

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Title: Lesson 13Maintaining and Administering a Linux System


1
Lesson 13-Maintaining and Administering a Linux
System
2
Overview
  • Introduction to super users.
  • Exploring Linux system files, processes and
    features.
  • Managing system startup and shutdown.
  • Managing Users.

3
Overview
  • Installing application packages from a CD.
  • Installing a printer.
  • Maintaining a secure system.

4
Introduction to Super Users
  • The super user is the administrator of a Linux PC
    system.
  • The super user has enormous power, both, to
    enhance and to destroy, the integrity of a UNIX
    or Linux system.
  • It is responsible for the installation,
    operation, maintenance, repair, and security for
    the system.

5
Introduction to Super Users
  • The user name or login name of the super user is
    root.
  • The User id (uid) for the super user is 0.
  • The super users home directory is / on a UNIX
    system and /root on a Linux system.

6
Introduction to Super Users
  • Any user can switch to different user accounts,
    including the super user shell.
  • Regular users use the su command to substitute
    to any other user along with the other users
    password.
  • Super user can also substitute users by entering
    that users login name as an argument to su.

7
Introduction to Super Users
  • The super user shell can be started by passing a
    dash argument to the su command (su -).
  • The super user shell initiated in this manner has
    roots identity and full environment, including
    the home directory and the value of the USER
    variable.
  • If the correct password for root is provided, a
    child process owned by root is started.

8
Introduction to Super Users
  • The super user shell can be started without
    passing a dash argument to the su command (su).
  • The super user shell initiated in this manner
    does have roots identity and powers, but it
    retains the original users full environment.

9
Introduction to Super Users
  • The shadow file that contains login names and
    encrypted passwords for all users on the system
    is accessible only by root and by members of
    roots group.

10
Exploring System Files, Processes and Features
  • A functioning system consists of many running
    processes, often employing data located in system
    files and directories.
  • These processes determine how the system behaves.

11
Exploring System Files, Processes and Features
  • System processes.
  • System directories.
  • Mounted file systems.

12
System Processes
  • The system program, named init, has a PID of 1,
    and reads a file that contains a list of all the
    system processes that should be running.
  • If one of the processes exits, init starts a new
    one to replace it.
  • The programs that run constantly are often called
    daemons and are started when the system is
    booted.

13
System Directories
  • Files containing system data and programs reside
    in the root directory.
  • Each directory in the root directory is owned by
    the super user and has a role in making the
    system function.

14
Mounted File Systems
  • On UNIX/Linux systems, all disk storage is
    integrated into a single directory hierarchy.
  • The mount utility, when run without any
    arguments, simply displays a list of the mounted
    file systems and their mount points.
  • The file systems are referred by names of their
    hardware device, and the mount points by
    directory names.

15
Managing System Startup and Shutdown
  • The procedures for starting up and shutting down
    a UNIX/Linux system are automated, but require
    some administrative intervention.
  • The shutdown -h 30 command instructs shutdown
    to wait for 30 seconds and then halt the system.

16
Managing System Startup and Shutdown
  • The shutdown utility notifies the users of the
    impending shutdown and tells them to log off.
  • The shutdown -r now command reboots the system
    without any delay.

17
Managing System Startup and Shutdown
  • Rescuing with a boot disk.
  • Recovering if super users password is unknown.
  • Changing the state at startup.

18
Rescuing with a Boot Disk
  • A rescue boot disk can usually allow your system
    to reboot when it cannot boot on its own.
  • Almost all Linux distributions prompt you to
    create an emergency boot floppy during
    installation.
  • The boot floppy contains only the Linux kernel,
    which is just enough to get the system started
    again.

19
Recovering if Super Users Password is Unknown
  • If the root password is forgotten, then the boot
    floppy can be used to rescue a system.
  • The system can work in a state called single user
    mode. Only the super user is logged on.
  • The single user mode entrance is
    password-protected.

20
Changing the State at Startup
  • Linux can work in one of the following states
  • 0 Halt. In state 0, the system is off.
  • 1 Single user mode.
  • 2 Multi-user mode without NFS.
  • 3 Multi-user with NFS.
  • 4 Not defined.
  • 5 Graphical interface.
  • 6 Reboot.

21
Changing the State at Startup
  • When the system is booted, it automatically goes
    to one of the states 2 through 5.
  • The system administrator can change the current
    state and the default startup state of the
    system.
  • The definitions for various states are in the
    inittab file.
  • The line id3initdefault controls the init
    states that the system goes to when it is booted.

22
Managing Users
  • Adding users.
  • Adding and changing passwords.
  • Compressing and uncompressing individual files.

23
Adding Users
  • The adduser username command creates a new user
    named username and copies all default files from
    /etc/skel.
  • The passwd username command is used to add a
    password to the newuser account.
  • The /etc/passwd file has a single line entry for
    every user who has access to the system.

24
Adding and Changing Passwords
  • The super user can create new passwords for new
    users and modify passwords for existing users.
  • The /etc/shadow file is in the encrypted version
    only, so the old password cannot be recovered.
  • The only choice is to use super user powers to
    assign a new password for the user.

25
Compressing and Uncompressing Individual Files
  • The gzip and gunzip utilities compress and
    expand individual files.
  • A compressed file gets the extension .gz, which
    is removed when the file is expanded.

26
Compressing and Uncompressing Individual Files
  • Tar Archives
  • The name tar is derived from tape archive.
  • This command packs the contents of a directory
    and all its subdirectories and files into a
    single file, retaining file information such as
    permissions.

27
Compressing and Uncompressing Individual Files
  • Tar Archives (continued)
  • The tar command can also be used to compress
    large files or directories.
  • With the z option, the tar utility creates an
    archive and compresses it in one step.

28
Installing Application Packages from a CD
  • Linux includes a powerful package manager,
    developed by Red Hat, called RPM for Redhat
    Package Manager.
  • It is used to build, install, query, uninstall,
    update, and verify individual software packages
    on a system.

29
Installing Application Packages from a CD
  • An RPM package consists of an archive of files
    plus package information, including name,
    version, and description.
  • In order to access a drive, it has to be mounted
    on a directory in the root file system.

30
Installing a Printer
  • In UNIX and Linux, driver programs interpret
    standard signals (for point size, font, indent,
    and so forth) to the appropriate signal for each
    particular printer.
  • The printconf-tui utility is used to configure
    a printer.

31
Installing a Printer
  • The system starts a printer daemon program,
    called a spooler.
  • The spooler accepts jobs from users and puts them
    on a queue.
  • The print queue is a list of jobs from different
    users that are waiting to be printed.

32
Maintaining a Secure System
  • As administrators, our task is to protect the
    data from being read or copied by unauthorized
    users.
  • Physical security means protecting hardware such
    as terminals, printers, the CPU, and magnetic
    media.

33
Maintaining a Secure System
  • Data security depends on the security of the
    hardware.
  • File permissions are essential. Employing
    directory permissions to prohibit all but
    essential users from accessing a directory tree
    is the strongest defense.

34
Summary
  • The system administrator (root having super user
    powers) is responsible for the hardware, data,
    applications, users, and security of the system.
  • Many system control files are located in the /etc
    directory. They provide startup information to
    the system, to processes, and to user programs.

35
Summary
  • Partitions on hard drives can be mounted onto the
    root partition of a system so that various parts
    of the drive (or other drives) can be accessed
    through the file system.
  • Mount Lists all partitions currently mounted on
    the system.
  • The command tar cvf filename directory creates
    an archive of the files and directories in the
    tree starting at directory and names it filename.

36
Summary
  • The command tar xvf filename extracts all files
    and directories from the archive filename.
  • The command rpm -ivh packagename extracts all
    files and directories from the RPM archive
    packagename and installs them on the system.

37
Summary
  • su Starts a child super user shell with full
    root environment.
  • su Starts a child super user shell maintaining
    the users environment, not the super users.
  • Ps aux Lists all processes, including user
    names.
  • Ps -lax Lists all processes, including PID,
    UID, and PPID.
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