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Welcome to Linux. A quick overview of some ideas and commands of most frequent use to programmers using Linux. Two interface options. The ‘modern’ graphical desktop interface: Objects are represented as colorful icons Users operate mainly by clicking the mouse

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Welcome to linux l.jpg

Welcome to Linux

A quick overview of some ideas and commands of most frequent use to programmers using Linux

Two interface options l.jpg
Two interface options

  • The ‘modern’ graphical desktop interface:

    • Objects are represented as colorful icons

    • Users operate mainly by clicking the mouse

    • It’s ‘intuitive’ (like Macintosh or Windows)

  • The ‘legacy’ command-line interface:

    • Objects are accessed by their file-names

    • Users operate by typing in commands

    • It’s flexible and powerful, but demands knowledge!

Toggle between interfaces l.jpg
Toggle between interfaces

  • If your workstation is configured for the Graphical Desktop Interface by default (also known as ‘runlevel 5’), it is easy to switch to the Command-Line Interface by typing a keystroke-combination:

    <CNTRL><ALT>-Fn (for n = 1, 2, ..., 6)

  • You can return to your Graphical Desktop by typing: <ALT>-F7

All linux s objects are files l.jpg
All Linux’s objects are ‘files’

  • All ordinary files are sequences of ‘bytes’

  • Some store data, others store programs

  • Also there are some ‘special’ files (such as ‘directories’, device-files, and pseudo-files)

  • Each file has a unique name

  • Each file has a specific ‘owner’

  • Each file has a set of ‘access permissions’

File permissions l.jpg
File ‘permissions’














r = ‘read access’ (1 = yes, 0 = no)

w = ‘write access’ (1 = yes, 0 = no)

x = ‘execute access’ (1 = yes, 0 = no)

Bitmap-example: 110-100-100

Octal representation: 0644

ASCII-representation: rw-r--r--

Directory tree l.jpg
Directory Tree








Linux organizes its hundreds of thousands of files into a tree-like hierarchy.

For a current Linux installation (such as Fedora Core 5), the topmost directory

(named ‘/’) will typically contain only about two-dozen sub-directories.

Directory tree7 l.jpg
Directory Tree













The ‘/home’ directory contains a sub-directory for each authorized user.

Directory tree8 l.jpg
Directory Tree











compressed kernel

The ‘/boot’ directory contains the files and directories that are needed

to select, load, decompress, and begin executing the Linux kernel

Directory tree9 l.jpg
Directory Tree












The ‘/etc’ directory stores files concerned with the system’s configuration-options.

Directory tree10 l.jpg
Directory Tree











The ‘/bin’ directory contains about a hundred of the most necessary and basic

binary-executables (such as the programs which implement the minimal set of

commands you need for system-recovery in the unlikely event of a ‘crash’ ).

Directory tree11 l.jpg
Directory Tree













The ‘/usr’ directory contains about a dozen sub-directories which organize the

vast majority of the various kinds files needed for a useful work-environment.

Together these sub-directories contain tens of thousands of files and programs.

Directory tree12 l.jpg
Directory Tree











The ‘/var’ directory contains about two-dozen sub-directories that pertain to

various value-added resourses (such as system log-files or users’ email).

Unique filenames l.jpg
Unique filenames

  • To give each file a name that’s unique, the directory-tree hierarchy is utilized:









The online manual l.jpg
The online ‘manual’

  • Linux offers online documentation for all of its commands (and for its library functions)

  • You type ‘man <command-name>’ to view the relevant page of this online manual

  • Example: $ man ls # view ‘ls’ options

  • Some commands have numerous options that are explained (but seldom illustrated)

Command usage examples ls l.jpg
Command-usage examples: ‘ls’

  • The ‘LiSt’ command: $ ls

    • $ ls # files in present working directory

    • $ ls / # files in the topmost (‘root’) directory

    • $ ls ~ # files in YOUR home-directory

    • $ ls –l # files with their attributes

    • $ ls –a # files (‘all’ including the ‘hidden’ ones)

    • $ ls *.c # files having the ‘.c’ filename-suffix

    • $ ls * # files in every immediate sub-directory

    • $ ls .. # files in the parent-directory

    • $ ls my* # files whose names begin with ‘my’

My own top 30 commands l.jpg
My own ‘top-30’ commands

  • cd # Change Directory

  • cp # CoPy file (or files)

  • mv # MoVe file (or files)

  • rm # ReMove file (or files)

  • rename # RENAME a file (or files)

  • who # who else is using station

  • mkdir # MaKe a new DIRectory

  • rmdir # ReMove DIRectory

My top 30 continued l.jpg
My “top-30” (continued)

  • scp # Secure CoPy

  • ssh # Secure Shell

  • lpr # Line-Printer

  • cat # conCATenate file(s)

  • grep # global reg-expr printer

  • uname -r # shows kernel-release

  • ln –s # creates a ‘soft’ link

My top 30 continued18 l.jpg
My “top-30” (continued)

  • vi # VIsually edit a text file

  • gcc # Gnu C Compiler

  • g++ # Gnu C++ compiler

  • as # Assembler

  • ld # Linker

  • make # compile-and-link script

  • objdump -d # disassemble program

My top 30 continued19 l.jpg
My “top-30” (continued)

  • tar # uncompresses a file

  • diff # compares two textfiles

  • exit # terminates a user-session

  • time # time a program’s execution

  • chmod # change file’s access-mode

  • su # Substitute User

  • more # view textfile page-at-a-time

Recommend keeping a journal l.jpg
Recommend keeping a ‘journal’

Some notes I find useful for reference…

  • For extracting a new Linux kernel release

    • $ tar –xvf linux-

  • For combining several files of a new project

    • $ tar –cvf linux- *

Some practice exercises l.jpg
Some practice exercises…

  • Switch from your Graphical Desktop to a Text-Mode Console Interface (6 choices)

  • Switch from one text-console to another

  • Login to that console

  • Type the ‘ls’ command

  • Log out from that console

  • Return to your Graphical Desktop

Some exploration exercises l.jpg
Some exploration exercises…

  • Use ‘cat’ to look at one of the hidden files in your own ‘home’ directory, like this:

    $ cat .bash_history

  • Use ‘ls’ to look at the names of all the files in your own ‘Desktop’ directory, like this:

    $ ls -a Desktop

  • Use ‘cd’ to change your current directory to the ‘root’ directory, like this:

    $ cd /

An advanced exercise l.jpg
An ‘advanced’ exercise

  • Create a subdirectory named ‘bin’ in your own home directory, like this:

    $ cd ~ # ‘~’ is your home-directory

    $ mkdir bin # creates ‘bin’ sub-directory

  • Copy a program-file from a class-website, then compile it, move the executable into your ‘~/bin’ subdirectory, and finally execute it, like this:

    $ cp /home/web/cruse/cs630/dump.cpp .

    $ g++ dump.cpp -o dump

    $ mv dump bin

    $ dump dump.cpp