Module 10

1. Module 10 Linux

2. Installing Linux • The Linux installation will go through a number of steps to complete the installation. • The Linux boot process is similar to the boot process of Windows 2000. • The file names are different but these files essentially perform the same operations in both systems.

3. Installing Linux • The installation will start once the CD is inserted and the BIOS is configured to boot from the CD. • Select the settings for the system, for example, the language to be used. Next, choose what type of mouse and keyboard are being used. • The installer will be prompted to choose the type of installation; server or workstation installation. • The next step is to partition the hard drive.

4. Installing Linux • After the drive is partitioned, the network settings must be configured and the time zone selected. • At this point the main root account and password are set up as well as any other accounts that need to be installed on the system. • The root directory is noted by “/”

5. Installing Linux • Users can logon to a Linux operating system using the Command-Line Interface (CLI), which is similar to the Windows 2000 interface. • Instead of displaying textboxes and buttons like the Windows 2000 GUI, the Linux CLI provides the user with successive text-only prompts to enter a user name and password. • The user must login with a user name and password. • Linux passwords are masked completely as they are typed, making it important to pay close attention while entering them.

6. Linux GUI • A graphical interface named "X Windows" that allows Linux to operate similar to the other GUIs. • A typical X Windows interface will look somewhat familiar to a Windows 2000 user; a mouse is used as a pointing device, there is usually a taskbar, icons represent data, and windows display information to the user. • While the sizes, shapes, and colors of these elements may vary, the basic principles are very similar to the Windows 2000 GUI. • It is possible to switch the system from X Windows to the Linux CLI using hotkeys [CTRL + ALT + (F1 - F6)].

7. Linux Shells • The Linux shells operate as a command interpreter. The "command interpreter" from the MS-DOS environment is similar. • The Linux shells function in much the same way as the command.com program functions for MS-DOS. • The user may choose from many different shells. • With Linux, a shell that suits the preferences or environment can be chosen.

8. Linux Shells • The Bourne Shell – This is known as the original UNIX shell. The program name is (sh) and is known as the bash shell in Linux systems. • The C Shell – This shell is not widely used because it is one of the more complicated shells to work with. It uses a much more complex syntax for shell programming than some of the other shells.

9. Linux Shells • The Korn Shell – This is a shell that was written by David Korn. It combines the interactive features that make the C shell popular with the easier-to-use shell programming syntax of the Bourne shell. • Bourne Again Shell –This shell was created as an enhanced extension of the Bourne Shell. This shell is referred to as the bash shell and is used for many "UNIX-like" systems, such as Linux.

10. vi Editor • The majority of all Linux administration will be done from the command line by using the various commands, configuration, and script files to perform these functions. • Often these commands, configuration, and script files will need to be edited and changed so that they will function in the manner that is suitable to the network environment. • Linux includes a powerful editing tool call the vi Editor that will allow editing of the configuration and script files as well as creation of some configuration and script files.

11. vi Editor • When vi Editor is opened and typing is attempted nothing will happen except that the system will just "beep". • This is because vi Editor is in "command" mode when first opened. • The correct command must be typed in order to enter the "edit" mode (entry mode) where entering text can begin. • Enter "edit" mode by choosing the command "i".

12. awk • The awk utility allows you to create short programs that read input files, sort data, process it, perform arithmetic on the input, and generate reports. • To put it the simplest way possible, awk is a programming-language tool used to manipulate text. • The language of the awk utility resembles the shell-programming language in many areas, although awk’s syntax is unique. • awk was initially designed to work in the text-processing arena, and the language is based on executing a series of instructions whenever a pattern is matched in the input data.

13. Adding Users • The first user account created during a Linux installation is the "root" account. • This superuser account is used by the system administrator to create all other user accounts on the system. • By default and for security reasons, no other users have the power to add users except for root.

14. Adding Users • The root user creates other Linux users with the useradd command. * User account names are case sensitive. • Once a new user account has been created, it must be given a password before the user can log on to the system. This is done in Linux with the passwd command. • User accounts can also be created with a script.

15. Managing Users Accounts • With the Linux CLI, user management is again performed through various text commands, flags, and parameters. In particular, changing a user name, changing a password, or deleting an account can be done with minimal commands. • vi and Pico are text editors that can be used to edit files.

16. Managing Users Accounts

17. Creating Groups/Adding Users • In a Linux system, only the root account (or other such superuser) has the power to create and manage groups. • These tasks are performed using simple commands for creating, renaming, or deleting groups from the system. • Most Linux users are assigned to a group during the account creation process. The following syntax is used to expand on the useraddcommand: useradd -g <group> <username> -c <real name> Sets group name Adds a comment

18. Permissions • In comparison to those of Windows 2000, the Linux system of permissions is much more intricate. • System administrators are given more control with the use of three distinct permission categories: read, write, and execute. • File and directory permissions in Linux are controlled through the use of two very important commands: chown and chmod. The chowncommand is performed by all users to specify the user and group ownership of a file or directory and follows the format: • chown <username>.<group> <filename>

19. Permissions • The chown command is performed by all users to specify the user and group ownership of a file or directory and follows the format: • chown <username>.<group> <filename> • For example: chown jdoe.executives report_01 • In this example, the user "jdoe" and the group "executives" are now the owners of the file named "report_01."

20. Permissions • The chmod CommandFile and directory ownership is an important concept in Linux because permissions are declared for both users and groups based on this ownership. • For example, if the file "report_01" allows full user access and denies all group access, then jdoe will be able to access the file, but members of the executives group will be locked out. These permissions are declared through the use of the chmod command: • chmod <mode> <filename> • For example: chmod 700 report_01

21. Permissions • The previous sample command has now granted the user all permissions (read, write, and execute), while giving its group and all other users no permissions. • This is specified in the "mode" of the command - in this case: 700. • Each digit of the number represents the three different types of users on the system. Starting from the left, • the first digit represents the user (or owner), • the middle digit represents the group, • the rightmost digit represents all other users on the system (user-group-other).

22. Permissions • The three permission types (read, write, and execute) are given numerical values as follows: • Read = 4 • Write = 2 • Execute = 1 • Example 765 • 7 = read, write, execute privileges to the owner (4 + 2 + 1) • 6 = read, write privileges to the group (4 + 2) • 5 = read, execute privileges to the all others (4 + 1)

23. Permissions • Read -Sets read permission for a file or directory. A file can be displayed or printed. A directory can have the list of its files displayed. • Write - Sets write permission for a file or directory. a file can be edited or erased. A directory can be removed. • Execute - Sets execute permission for a file or directory. If the file is a shell script, it can be executed as a program. A directory can be changed to an entered.

24. Daemons • Linux offers many processes/services which are referred to as daemons. • They enable the Operating system to provide functions like the Internet, file sharing, mail exchange, directory services, remote management, and print services. • Daemons can be loaded or unloaded into memory at anytime. • They can also be restarted without having to restart the entire system.

25. Daemons • Many Daemons can run on a Linux system at any time. Some of the common Linux Daemons are: • HTTPD – This Daemon is responsible for web browser requests. • Inetd – This daemon will wait for an incoming request to be made and then forwards that request to the appropriate Daemon. • Crond – This Daemon will run scripts at a specified time. • Syslogd – This Daemon will record information about currently running programs to the system log file.

26. HTTP • The Linux NOS is not capable of providing the HTTP daemon to users. • Instead, a separate and extremely popular web-hosting program named Apache is the common solution. • Apache provides the same HTTP Daemons for Linux that the Internet Information Services (IIS) tool does for Windows 2000.

27. FTP • While the Windows 2000 FTP service may or may not be available by default, the Linux FTP service (FTPD) needs no configuring. • This setting is found in the /etc/rc.d/init.d/xinetd . • If a system administrator wishes to disable the service, a # (pound sign) can be placed at the start of the line. Otherwise, Linux automatically starts the FTP daemon (FTPD) during the boot process, and users are able to remotely FTP to the machine at any time.

28. Telnet • Telnet allows a remote user to log in to a system for the purposes of issuing commands and accessing files via a Command Line Interface (CLI). • Telnet must be configured so that only authorized users are able to access the server. • Setting a password is often not enough.

29. Telnet • When a Daemon is configured, such as Telnet, the server is forced to "listen" for requests. • Upon discovering that a server is listening for Telnet requests, a hacker can try to use brute force to break into a system. • A brute force attack may involve using a program that guesses the password, using a dictionary as the source of its guesses. • The Telnet protocol itself is not especially secure. For example, Telnet sends usernames and passwords in clear text, which can be read by other hosts on the network. • Because of the security issues noted above, the administrator must manually enable Telnet on Red Hat Linux 7.

30. Mail Client • To set up the e-mail Daemon on Linux, the administrator will need to setup: • mail user agent (also known as the mailer) • mail transfer agent (MTA) • transport protocol. • When setting up mail on a Linux system, the administrator will first need to select which type of MTA to use. The two major MTAs are SMTP and Sendmail. Once the MTA is configured and the protocol is determined (IMAP or POP3, for example), a mailer must be configured. There are several popular mailers to choose from, such as Elm, Pine, or Netscape Messenger.

31. Scripts • The Linux operating system can also accommodate many different scripting languages. • The most common and basic of these is its built-in "shell scripting" abilities. • Shell scripting is specific to the Linux OS