LINUX Basics

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LINUX Basics
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LOGIN and LOGOUT
This is how a Linux login screen looks like.
There will be a login prompt where the user will
be asked to enter his Account or User Name.
For security purposes, each account will have a
password which is asked by the operating system
every time a user wants a login. As the user
enter the password, the characters typed will not
be printed on the screen.
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LOGIN and LOGOUT

• If a user has a valid account name
  and the correct password is entered, Linux will
  display its prompt (usually the dollar sign, )
  to indicate that it is ready to receive
  commands/instructions.
• A user may opt to change his password.
  This may be achieved by typing passwd at the
  prompt.
• passwd
• Changing password for harriet
• harriets Old password
• harriets New password
• Enter the new password again
• It is advised that users change their
  password from time to time. Also note that Linux
  is case sensitive. An upper case letter is
  different from the lower case.
• To quit a session, a use logs-out by
  pressing ltCTRLgt - ltDgt or typing either exit or
  logout

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LINUX COMMAND FORMAT

• Most Linux commands have the following format
• Command_name optionarguments
• A user types in the name of the command to
  be executed followed by the options (option are
  generally preceded by a dash or minus sign) and
  then followed by the arguments. Options
  determine how the command will be executed while
  arguments are the data to be processed by the
  command.
• Note
• Some commands do not require the use of options
  and/or arguments. Examples of such are the
  passwd and clear commands.

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Command Usage and Principle

• Separation - each component of Linux command
  should be separated a space.
• Example
• ls -l test.txt
• Order - The position of the components of an
  Linux command should not be interchanged. The
  order should always be
• Example
• ls -l test.txt
• Multiple Option - The rule of separation can be
  applied in case of multiple options. An option
  should be preceded by a space.
• Example
• ls -l -C -d sample.doc

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Basic Commands

• Commands are entered either by typing the name
  of the commands at the Linux prompt. The command
  is executed by pressing the ltentergt or ltreturngt
  key.
• The date command is used if the user wants to
  know the current date and time. Only the system
  administrator can change the system date and
  time.
• Example date
• Mon Oct 6 192450 PST 1996
• Typing clear at the prompt followed by the
  ltentergt or ltreturngt key will simply clear the
  screen. This is similar to cls command in DOS.

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Basic Commands

• Typing who command is used to determine the
  users currently logged in the system. The output
  will give the user name together with the TTY or
  terminal number (the exact terminal being used)
• Example who
• root tty4
• user3 tty9
• user1 tty2
• Typing whoami command is used to determine the
  users currently logged-in at a particular
  terminal. For example if someone happens to see
  a terminal left on with someone logged in, typing
  whoami at the prompt will give the name of the
  user currently logged-in.
• Example whoami
• user

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Basic Commands

• The finger command displays information about
  the users currently logged on to the system.
• Example
• finger harriet
• Login name harriet
• Directory /home/harriet Shell /bin/bash
• Last login Thu 22 052610 (PHT) on 0
• This cal command gives the user the calendar for
  the current month and year. The cal year command
  will give the user the whole calendar for the
  year specified. Same with the cal month year
  command, it will give the calendar for the
  specific month and year.
• The bc command will enable user to access binary
  calculator.

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Sample

• ls command
• The ls (list) command list the name of files in
  a given directory. Typing ls without any option
  and argument at the prompt (followed by an
  ltentergt key) gives the user a listing of the
  files in columns and in alphabetical order.
• Example
• ls
• shapes quiz1.doc mike.let
• test tymi.doc sample1

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Command Usage and Principle

• Multiple Arguments - The rule of separation
  should also be applied in case of multiple
  options. Each argument is listed but separated
  from each other with a space.
• Example
• ls -l sample doc.txt test
• Multiple Commands - Several commands maybe
  entered at a single Linux prompt. In such cases,
  each command unit is delimited by a semi-colon
  (). The commands will then be executed
  consecutively.
• Example
• ls ls -a

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Command and Option

• The l option gives a long listing of the files.
  It consists of 8 columns
• First Security Access Modes
• Second Number of Links
• Third Owner of this file and directory
• Fourth Group where owners belong
• Fifth Size of Files
• Sixth Date the file was last modified
• Seventh Time the file was last modified
• Eight Name of the File or Directory
• Example
• ls -l
• -r-xr-xr-x-l user1 staff 42 Jan 13 1100
  harriet.txt

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Command and Option

• The a option gives a listing of the files
  including hidden files (those which starts with a
  .)
• Example
• ls -a
• profile.sh_history quiz.doc
• Command and Argument
• Example
• ls sample
• arithmetic
• Command,Option and Argument
• Example
• ls -l sample.c
• -rw -r--r--2 tymi staff July 29 1130 sample.c

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Common Usage and Principle

• Wild Cards
• Asterisk () - The asterisk wild card will
  match any number of characters that occur at the
  designated position in the pattern.
• Example
• ls ch
• chapter5 champ charie_text
• ls er
• october system.ver
• Note
• In DOS . represents all files (any name and
  extension). This is not applicable in Linux
  since it does not follow the concept of file
  extension. Instead . will be interpreted as
  any file with a period in its filename. To
  represent all files in Linux, just simply type .

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Wildcards

• Question Mark (?) - Like in DOS, the question
  mark will match any single character
• Example
• ls ?ark
• mark lark 5ark
• Square Brackets - The square brackets are
  similar to the question mark in the sense that it
  will match any single character. However,
  options may be specified if the square brackets
  are used. Reverse listings can also be done by
  using
• Example
• ls letter246.doc
• letter2.doc letter4.doc letter6.doc
• ls memo_a-c.doc
• memo_a.dco memo_b.doc memo_c.doc

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Linux Documentation
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Manual Pages

• Manual Pages
• Commands and system calls
• Viewed a page at a time
• Search for keywords
• man Command
• man command
• Output section of manual for commands,
  subroutine, and files.
• Manual information consists of
• PURPOSE (one-line description)
• SYNTAX (command syntax)
• DESCRIPTION
• FILES (associated files)
• RELATED INFORMATION
• BUGS (odd behavior)

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Linux Files and Directories
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File

• File
• A collection of data
• A stream of characters
• No structure is imposed by the operating
  system
• - the user is free to structure and interpret the
  contents of a file in whatever way it is
  appropriate.

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File Types

• File Types
• Ordinary
• Text or code data
• No particular internal format
• Directory
• A table of contents
• Special Files
• Represents hardware or logical devices
• Found in directory /dev

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Directory

• Directory
• Unique type of file that contains only the
  information needed to access files or other
  directories.
• Each directory contains a file or subdirectory
  name and its associated inode number
• The pwd command can be used to find out what
  your current directory is

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Linux Filenames

• Should be descriptive of the contents
• Should only use alphanumeric characters,
  UPPERCASE, lowercase, number, , _at_, _
• Should not be the same as a system command
• Are case sensitive
• Starting with a . are hidden from the normal ls
  commands
• The maximum number of characters for a filename
  is 255

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Linux File Types

• The / (root) directory contains many directories
  that are critical in the operations of the system
• The /usr directory contains system programs and
  installed licensed program packages
• The /home directory contains user login
  directories and files
• The /var directory contains files and logs that
  dynamically change
• The /tmp directory will hold files that are
  temporarily needed or created by applications and
  programs.

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Hierarchical Structure
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Pathnames

• Pathnames
• A sequence of filenames, separated by slashes
  (/), that describes the path, or route, the
  system must follow to locate a file in the file
  system.
• Two types
• Absolute - start from / (the root directory)
• Relative - start from the current working
  directory
• Examples
• /home/tymi/.sh_history (Absolute)
• doc/sample (relative)
• ./harriet/quiz1 (relative)