The man behind the Linux:

          Linus ntorvalds the finish developer of the Linux was born in 1969 in helsinki.

INTRODUCTION:

2. Cornerstone of the Linux effort has been the peer review, that not only the software but the source code itself is subjected to.

4. Linux is customizable like no other software.

5. Support- One of the stated plus points of commercial software is that there's a structured support program that you can avail of. But reality is often different. Those of you who have had occasion to ask for help would know that often it's not from the structured support programs, but from non-structured ones like user groups and Internet news groups that you get more precise and faster help.

6. Linux doesn't need the latest, fastest, hardware to run on.

7. And last but not the least, because it's free.

Red Hat Linux and Debian Linux are not different.

Linux is essentially safe,secure and robust.

Security: class C2 is a rating granted by the Natinal Computer Security Center (NCSC) for software that have been evaluated against the Defence Trusted Computer System Evaluation Criteria (TCSEC).

C2 security class requires individual logon with password and an audit mechanism.

LINUX ARCHITECTURE:

          Inner most layer is  kernel. This is the heart of the operating system, the part of the implements that primtive system calls that form the basis of the system.

          On top of the kernel are various libraries that implement high level functions. These can be critical functions such as the ANSI standad  C library or a specialised library such as one to manipulate JPEG encoded image files.

           Linux applications are typically  built on top of the functions provided by libraries.

User interface:

          Linux supports many different libraries for user interfaces. Some of the more common ones are briefly described here.

Text mode:- Simple output of ASCII routines such as printf. The traditional approach for simple Unix type file commands.
Curses/temcap:- Text-based,but with yhe ability to position ythre cursor anywhere,change colours get individual key presses and generate simple line graphics. This works with various types of serial terminals as well as the linux text console and inside an xterm window.

Svgalib:- A library that provides simple graphics routines (drawing pixels,lines etc) works by directly accessing the videocard.

X11:- The standard for portable distributed windowing applications. The low-level X libraries tend to hard to use.

LINUX DIRECTORIES:

/

|---bin

|---boot

|---dev

|---etc

|---home

|       |-----user1

|       |-----user2

|       |-----user3

|

|---lib

|---lost+found

|---mnt

|      |-----cdrom

|      |-----floppy

|      |-----zip
|---proc

|---root

|---sbin

|---tmp

|---usr

|     |------x11r6

                 |------bin

                 |-----include

                 |-----lib

                 |-----man

                 |-----share

|    |-----bin

|    |-----dict

|    |-----doc

              |----howto

|    |-----etc

|    |-----include

|    |-----info

|    |-----lib

|    |-----local

               |-----bin

               |-----doc

               |-----etc

               |-----include

               |-----lib

               |-----man

               |-----sbin

               |-----share

               |-----src|

     |-----man

     |-----sbin

     |-----share

     |-----src

|----var

|        |-----log

|        |-----spool

|        |-----mail

File and Directory permissions:

                   read, write,execute.

For each file and directory,the rwx permission may be seperately for each of the following classes of users.

User(U) à user who owns the file /directory.

Group(G) à several users purposely lumped together so that they can share

acess  to each others files.

Others(O) à the remainder  of the authorised users of the system. 

- - -                       0 0 0                       0

- - x                      0 0 1                       1

- w -                      0 1 0                       2

- w x                     0 1 1                       3

r  - -                      1 0 0                       4

r – x                     1 0 1                         5

r w -                     1 1 0                       6

r w x                     1 1 1                       7

RULES FOR LINUX COMMANDS:

2.     Linux commands can only be entered at the shell prompt.

3.     Linux command lines must end with a return.

4.     More than one option can be included with most of the commands.

GETTING ONLINE HELP:

Special keys and control characters:

Ctrl –u        erases the entire command line.

Ctrl –s        stops the flow of output to display.

Ctrl –w       erases the last word on the cmd line.

Ctrl –c        interrupts a command or process in progress and returns to the command line.

Ctrl –z        suspends a command or process in progress.

Ctrl –d        generates an end-of file charecter.

Ctrl -\          quits a program and saves an image of the program in a file called core for later debugging.

Setup and status commands:

logout                   end of linux session.

passwd                 change password by prompting old and new passwords.

stty                       set terminal option.

date                      display or set the date.

finger                    display information about users.

ps                         display information about processes.

env                       display or change current environment.

File and directory commands:

cat                        concatenate and display files.

cat/etc/profile       shows the default console profile for all users.

more                     paginator allows u to browse through  a text file.

less                       a more versatile paginator than more,lets u scroll both up

                             and down,either line by line or pagewise.

mv                        move or rename files.

cp                         copy files.

rm                        remove files.

ls                          lists contents of directories.

mkdir                   make directory.

rmdir                    remove direrctory.

cd                         change working  directory.

pwd                      print working directory.

du                         summarize disk usage.

chmod                  change mode(access permission) for a file or directory.

file                        determine the type of file.

quota –v               displays the current usage for this account.

Editing tools:

pico                      simple text editor.

diff                       shows the difference between the contents of two files.

grep                      search a file for a pattern.

sort                       sort and collate  lines of a file.

wc                        count lines,words and charecters in a file.

look                      look up a specified words in the system directory.

awk                      pattern scanning and processing language.

emacs                   advanced text editor.

vi                          screen oriented a display editor.

Formatting and printing commands:

lpq                        view printer queue.

lpr                        send file to printer queue to be printed.

lprm                     remove job from printer to spooling queue.

enscript                converts textfiles to postscript format for printing.

lprloc                    locations,names of printers,printer costs.

pacinfo                 current billing info for this account.

Program controls,pipes and filters:

Jobs                      lists background jobs.

Sleep                    suspend execution of an interval

Kill                       terminate a process.

Nice                      run a command at low priority.

Renice                  alter priority of running process.

&                          run process in background when placed at end of command line.

>                           redirect the output of a command into a file.

<                           redirect the file to the input of a command.

|                            pipe the output of one command into another.

There are several reasons for reducing the size of a file. The two most common are to save space or, if we are transferring the file across a network, to save transmission time.  To compress a file, enter the command gzip and the file name.

                              $  gzip  mydata

                              $  ls

                               mydata.gz

To decompose a file, use the gzip with the –d option or the command gunzip. These commands will decompress a compressed file with the .gz extension and replace it with a decompressed version with the same root name, but without the .gz extension. When we use gunzip, we do not even have to type in the .gz extension.

                        $  gunzip  mydata.gz

                        $  ls

                           mydata

Suppose we want to display or print the contents of a compressed file without first having to decompressed it. The command zcat will generate a decompressed version of a file and send it to the standard output. We can redirect this output to a printer or display a utility such as more.

                                   $    zcat  mydata.gz   |more

          We can also compress archive tar file. This returns file extensions .tar.gz.

                    $   gzip   myarch.tar

                    $  ls

                     myarch.tar.gz      

          We can also use the compress and uncompress commands to create compressed files. They  generate a file that has a .Z extensions and  use a different compression format than gzip.

LINUX APPLICATIONS:

We can set permissions on a file or directory to control access by other users. A file or directory can be set for read,  write, and execute  permissions. Either the user, group, and other users can have access. The command chmod sets these permissions, and the ls commad with  the–l option lists files and directories with the current permissions.

          Different storage devices such  each contain their own file system that we can mount and access. We can access CD-ROMs, floppy disks, and hard disk partitions.  We can also mount MS-DOS hard drive partitions anc access them directly from our Linux system.  By placing an entry for a file system in the /etc/fstab file, we can have a file system mounted automatically when we boot. If we are on a network, mount  and access file systems on a remote server.