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.

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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.

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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.

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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.

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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.

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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.

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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.

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Exploring System Files, Processes and Features

• System processes.
• System directories.
• Mounted file systems.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Managing Users

• Adding users.
• Adding and changing passwords.
• Compressing and uncompressing individual files.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.