Fundamental of Computers
& Information Technology
Unit -V
MICROSOFT DISK OPERATING
SYSTEM -Microsoft Disk Operating System (MS-DOS) is
the most popular single user operating in the world. Microsoft Corporation of
USA had released it in august 1981. It includes a number of utilities that have
become common place on most PCs; disk compression, memory management,
anti-virus, backup, disk optimization. Earlier these utilities were brought
separately from third party vendors who were selling them long before DOS 6. An
operating system is the overseer (Supervisor, Manager) of the computer. In
general, an operating system is a collection of the programs that manage system
resources and aid in the development and execution of application programs. IBM (International Business Machines), the
pioneer in computer manufacturer, adopted and promoted MS-DOS for its range of
personal computers. Even many other hardware vendors found it useful and
compatible for their machines and with this MS-DOS gained so much popularity that
it became a defacto operating system for micros.
Every
operating system has a version number that allows you to keep track of whether
or not the software you are running is the latest version and also of the
current capabilities supported by different versions. Every version number is
broken down into two parts, a major and minor version number. In the case of
DOS version 1.0, for example, 1 is the major version number while 0 is the
minor version number.
First
version of MS-DOS was a refined version of an OS developed by Tim Peterson of
Seattle Computers, which he had named as QDOS (Quick and Dirty Operating
System) as he had developed it in record two months and could not introduce
some good functions of process management and memory management into it. After
the release of first version of MS-DOS, every time some refinement is made, a
new version of it is launched. The latest version of MS-DOS available in the
market is 7.x.
An
operating system is an interface between the user and the computer system.
DISK DRIVES
Most of
the personal computers work with disks.
PCs, PC-XTs, PC-ATs work with floppy drives and hard disk drives.
PCs (Personal Computer) have one or two floppy disk
drives.
PC-XTs (Extended Technology) have one or two floppy disk
drives and hard disk drive. Speed and capabilities of XTs are the same as that
of a PC.
PC-ATs (Advanced Technology) have one or two floppy disk
drives and a hard disk drives with advanced microprocessor chip which is much
more faster and capable of performing complex functions.
Floppy Disk Drive (FDD) – The mechanism, which handles a
floppy disk, is called Floppy Disk Drive. All operations on a floppy disk (e.g.
reading from a floppy disk or writing on it) are performed by a floppy disk
drive. The FDD consists of a read –write head, which moves to and fro on a
rotating floppy disk to perform read, or write operations. Each FDD is given an
identification letter. The first FDD is called drive A and if there is second
FDD also, it is called drive B.
Hard Disk Drive (HDD) - The hard disk drive (HDD) is also
called a Winchester Disk Drive. The HDD is group of some platters, each having
a read/ write arm for it. The HDD is responsible for all operations
(reading/writing) performed on a hard disk. The hard disk is given an
identification letter drive C. One hard disk can be partitioned into several
parts. Each partition forms a logical disk. If a hard disk has been
partitioned, then first partition is called drive C, second as drive D, third
as drive E, and so on.
FAT File -A FAT file system is a specific type of computer file system architecture
and a family of industry-standard file systems utilizing it.The FAT file system
is a legacy file system which is simple and robust.[3] It offers good performance even in very light-weight
implementations, but cannot deliver the same performance, reliability and
scalability as some modern file systems. It is, however, supported for
compatibility reasons by nearly all currently developed operating
systems for personal
computers and many home
computers, mobile devices and embedded
systems, and thus is a well suited format for data exchange between
computers and devices of almost any type and age from 1981 through the present.
LOADING OF DOS INTO MAIN MEMORY (BOOTING)
Loading
of DOS into main memory involves loading of three essential files of DOS viz.
IO.SYS also called (IBMBIO.COM), MSDOS.SYS also called (IMDOS.COM) and
COMMAND.COM into the main memory. Loading these files into main memory is
called booting up (which means getting ready) of the computer. The booting up
process is a step-by-step process as follows:
1. As soon as the machine is switched on, POST (Power on
Self Test) is performed which checks for integrity of all components (CPU, RAM,
IO devices etc) of a computer system. If any component is found faulty, an
error message is displayed.
2. A chip called ROM-BIOS (Read Only Memory – Basic Input
Output System) is read and executed. Then a check is performed for DOS files
presence in the following order. (1. First in A drive, if found there, DOS is
loaded from drive A. 2 If not found in A drive, then C drive is scanned for DOS
files availability. If DOS files are found in C drive, Then DOS is loaded from
C drive.)
3. If DOS files are found in a drive, its very first
sector (called boot sector) is read which stores a small program called
bootstrap loader in which instructions for booting up process are stored. The
bootstrap loader is then loaded into main memory and its instruction are
executed.
DOS System Files
The computer loads
three basic files called MS DOS.SYS, IO.SYS and Command.Com. These are the
three system files which are needed to
load DOS.
FILES AND FILE NAMING CONVENTIOS
Any information,
which is to be stored on the computer’s secondary storage, would be stored as a
file. A file is a collection of logically related information e.g. a file
containing all details about mid-term exams, a file containing monthly sales
data etc. Each file stored on the system is given a name. The file name has two
parts: primary file name and secondary file name (also called extension). A
primary file name consists of one to eight (1-8) characters in length. File
extension consists of a period followed by zero to three (0-3) characters.
Extensions are optional, but it is better to use them, as they are useful for
describing the contents of a file. For instances, all document files can be
given an extension. Doc. The primary file name and file extension can have any
characters other than following:
[] \ /: < >
+ “ =? |
Extension .exe specifies that it is an executable file,
.bas specifies it is BASIC program file, .PAS specifies that it is Pascal file
and so on. Therefore, extension can be used for better understanding of
filename.
TYPES OF DOS COMMANDS
There are
two types of dos commands.
Internal Commands
External Commands
Internal Commands: The internal commands are loaded into memory when DOS is booted.
Internal commands are always available for your use, although they are not seen
when you display the disk directory of filenames on your screen. In other words, DOS commands for which the
specification is available within the shell (COMMAND.COM) are called internal
commands. Some common internal commands are:
COPY, DEL, DIR,CLS, DATE, TIME, PATH,REN, TYPE, DIR, MD,
CD, RD
External
Commands: External commands are conventional
programs. These files can be deleted, copied and even renamed. Their filenames
are displayed when DIR lists a directory on the screen. In other words, DOS
commands for which specification is not internally available in COMMAND.COM are
called External commands. The specifications for these commands are made
available to the shell through external specifications files e.g. FORMAT is an
external command and its specification are available in FORMAT.COM, for
DISKCOPY external command, specification file is DISKCOPY.COM and so on. For
Example: CHKDSK, XCOPY, PRINT, ATTRIB
DIRECTORY STRUCTURE OF MS-DOS
In an office, the file cabinet is
divided into shelves, shelves into boxes, boxes into drawers etc. and files are
kept in them. Similar types of files are grouped and kept in the same drawer or
box or shelf. In the same way, files on disks are stored. The disk is divided
into subdirectories; each subdirectory can further be divided into sub
subdirectory and so on. DOS files with some similarity are grouped together and
a directory is formed for them under which they are kept.
WILD CARDS
Two special characters ‘?’ (Question
mark) and ‘*’ (asterisk) are called wildcards in DOS. They are useful in MS-DOS
command lines because they give flexibility in specifying paths and files.
The? Wild
Card
A question mark (?) in a filename or
file name extension means that any one or none character can occupy that
position. For instance
Memo? Doc would represent
Memo.doc
Memo3.doc
Memo4.doc
Memo7.doc and so on
The *
Wildcard
The *(asterisk) replaces any number
of characters .For instance
A*.exe would represent
Ab.exe
Abc.exe
Ans.exe
Answer.exe
Ans2.exe
As A*.exe
means A followed by any number of characters (but length should not exceed
eight in number) and extension .exe
Command
Prompt:- When you first switch on IBM PC computer,
you will see some coded information displayed by DOS 6. This information tells
the configuring of your computer. When the information stops you will see the
following:
C:\>
This is the
command prompt. The flashing underscore next to the command prompt is called
the cursor. The cursor shows the place on the screen where the command will
appear as you type it.
Dir: This command is used to list files under a directory.
SYNTAX C:\>dir
Dir command
lists names of all the files and subdirectories under the current working
directory.
Dir also
lists the drive’s volume label and volume serial number
Directory
names are shown with <DIR> entries in the directory listing. The ‘.’ And
‘.’ default entries in the directory listing denote current directory and
parent directory respectively that store information about current directory
and its parent directory. File information is displayed in five columns
1st
Column gives the primary name of the file.
2nd
Column gives the extension of the file.
3rd
Column gives the file size i.e. number of bytes stored in the file.
4th
Column gives the last-updation-date i.e. date on which the file was modified
/updated last.
5th
Column gives the last-updation-time i.e. time at which the file was updated
last.
As the
monitor size is 25*80 i.e. 25 rows and 80 columns, only 20 file names can be
displayed in one go, on the screen as first 3 rows display volume label, volume
serial number and directory’s path name and last 2 rows display total number of
bytes occupied and number of free bytes. If there are more than 20 files in the
directory being listed, the screen is scrolled up and first few file names
cannot be viewed. To view the directory-listing page wise i.e. one screen at a
time, the command used is
SYNTAX C:\>dir/p
Dir/w – It display width wise. The wide display lists up to five files
per line.
SYNTAX C:\>dir/w
Dir/on – It display sorted order of primary name
SYNTAX C:\>dir/on
Dir/oe – It display sorted order of extension
SYNTAX
C:\>dir/oe
Dir/od – It display sorted order of date
SYNTAX
C:\>dir/od
Dir/ad – It display only directories
SYNTAX C:\>dir/ad
Dir/ah – It display only hidden files
SYNTAX C:\>dir/ah
Dir/o-s – It display first files then second directory
SYNTAX
C:\>dir/o-s
Dir/os – It display first directory then second files
SYNTAX C:\>dir/os
Dir/l – It display all files and directory in small letter
SYNTAX C:\>dir/l
Dir/s – It display the directory listing of all sub directories a sub
subdirectories under the directory being listed.
You can also
display the files of other directories as well. This can be done by specifying
a path. A path tells DOS where a particular file is located. For example you
want to see the of abc directory.
SYNTAX C:\>Dir\abc
CD – This command changes your working directory to the directory you
specify.
SYNTAX C:\>Cd
<Dir name>
C:\>Cd ABC
CD. . – Makes the parent directory of working directory as working
directory.
CD\ - Makes root directory as the current working directory.
MD – This command is used to create a subdirectory.
SYNTAX C:\>Md
<Dir name>
C:\>Md ABC
RD – This command is used to delete a directory, which is empty (i.e.
with no files under
It and no directories under it except for two directories. And.) .
The directory being removed
should not be the current working directory.
SYNTAX C:\>Rd abc
File
Commands
File commands are those commands,
which operate on files.
COPY – This command is used for copying one or more files from one
location to
Another. The structure of COPY
command is
C:\> COPY Source pathname
Destination pathname
C:\> COPY C:\student\abc.txt
C:\student\Sandeep
C:\>COPY C:\Students\abc A:\
C:\>COPY A:\abc C:\Students
DEL – This Command is used for deleting the specified files.
C:\>Del <File Name>
C:\>Erase <File Name> /p
/p switch causes del or erase to
prompt you before a file is actually deleted. If /p
Is specified, file name is displayed
and confirmation is asked as Delete Y/N? If
You press Y; file is deleted, if N,
delete operation is canceled.
REN
(RENAME) – This command is used for renaming
file(s)
C:\>Ren Filename1 Filename2
Where filename1 is old filename and
filename2 is new file name.
TYPE – This command is used to display the contents of specified
filename. Type
Command works for one file only at a time.
C:\>Type <File Name>
BREAK – This command can be used to stop an activity.
C:\> Break
Ctrl+C
CLS – This command clears the screen.
C:\>Cls
When used this command clears the screen, leaving only MS-DOS PROMPT
and a cursor.
DATE – This command displays or sets the system date.
C:\>Date
TIME – This command allows one to enter or change the system time.
C:\> Time
PROMPT – This command changes the MS-DOS prompt. Mostly when you start
your computer, you get either C:\> or A:\> as the prompt. To change the
prompt to disk, give the following command.
C:\>Prompt Sandeep
SandeepPrompt $P$G
VER – This Command display the version number of MS-DOS you are working
upon.
C:\>Ver
VOL – This command display the disk volume label and serial number, if
they exist
C:\>Vol
EDIT – This command is used to change a file contents i.e. add, delete
in a file.
C:\>Edit <file name>
PATH – This command displays or sets a command search path. The PATH
command is used to tell DOS which directories it should search to find
programs. If a directory is listed in the path, you don’t have to change to
that directory to use a command or to start a program, which is stored under
that directory.
SYNTAX: Path [drive:] [path] [;
[drive] [path]…]
C:\>Path=C:\dbase;
c:\dos
The search path is the path of directories, which MS-DOS searches
for executable
File after its search in the working directory is over. Executable
files are files
With extensions .com or .exe or .bat. By default no path is set. The
maximum
Length of a search path can be 127 characters.
DOSKEY – Doskey is a special utility program, that gives you more control
over the
Command prompt. You can
edit the command line, recall the old command
For reuse or editing with the
help of DOSKEY. Each time the user enters a command, the command added to
DOSKEY’s command buffer.
SYNTAX: C:\> Doskey
MOVE – Move command helps you to move one or more files to the location
you
Specify. The move command can also be used to rename directories.
SYNTAX: C:\> Move <Source Path> <Destination Path>
SYNTAX: C:\> Move abc.txt
C:\student\xyz
DISKCOMP – This command compares two floppy disks and performs a
track-by-track
Comparison. Diskcomp
only works for similar double density with double density and high density with
high-density floppy disks and not for hard disks.
SYNTAX: C:\> diskcomp
drive1: drive2
C:\>diskcomp a: b:
C:\>diskcomp a: a:
Will first
prompt you to insert source diskette in a drive and after some time, it will
ask you to remove source diskette and insert the target diskette in A drive.
This command is used in single FDD systems.
DISKCOPY – This command makes the exact replica of source floppy disk in the
destination floppy disk. Diskcopy formats the target disk before copying.
Diskcopy works only for floppy disk and not for a hard disk.
SYNTAX: C:\> Diskcopy a: a:
FORMAT – This useful command formats a disk for use with MS-DOS. The
FORMAT command creates a new root directory and file allocation table for the
disk. It also checks for bad sectors on the disk. In order to make a new disk
usable, it must be formatted using FORMAT command.
Formatting
means creating and marking new tracks and sectors on a disk. If the disk being
formatted already contains information, it will be lost, as FORMAT will
recreate the tracks and sectors.
Tracks
are concentric circles on a disk and each sector is further divided into
smaller sections called sectors. The number of tracks on a disk and number of
sectors on a track depend upon the disk type and its capacity. The storage unit
On a disk is
a sector. A read/write head reads or
writes some fixed number of sectors (known as cluster) at a time.
The
outermost track is given number 0; next track is number 1, next 2 and so on.
Track 0 is reserved for the disk information. The system area consists of three
parts: Boot area, directory area and
File Allocation Table (FAT)
Boot area
contains the bootstrap loader if the disk is bootable (i. e. it contains three
system files IO.SYS, MSDOS.SYS and COMMAND.COM).
Directory
area stores the names of files stored under the root directory. It also stores
the starting cluster number of files it contains.
File
Allocation Table is a table that stores all the clusters numbers which contain
information of a file e.g. if a file ENTRY.DBF has an entry in the root
directory and its starting cluster number is 3. The rest of the information of
ENTRY.DBF is stored in clusters 5, 9, 10, 15, 16, 19, 20. Therefore the
information sequence (cluster – chain) for ENTRY.DBF is cluster number 3 - >
5 - >9 - > 10 - > 15 - > 16 -> 19 -> 20 EOF.
SYNTAX: C:\> Format a:
SYNTAX: C:\>Format a:/s
The /S switch
copies the system files to the floppy and makes it bootable.
This command
specifies that you want to format the disk in drive A. When you press ENTER,
the following message appears:
Insert new
diskette for drive A:
And press
ENTER when ready
As it formats the disk, MS-DOS
displays the percentage of the disk that has been formatted. When the format is
complete, the following message appears.
Volume
label(11 characters, Enter for none)?
LABEL – This command creates, changes or deletes the volume label on a
disk. Label is upto 11 characters.
SYNTAX: C:\>Label
MORE – It displays the output one screen at a time.
SYNTAX: C:\> Dir | More
C:\> Type abc.doc |
More
SYS – This command transfers MS-DOS system files (IO.SYS, MSDOS.SYS and
COMMAND.COM) to the specified drive’s disk.
SYNTAX: C:\> SYS A:
Will transfer the system files to
the disk in drive A and make it bootable.
PRINT – This command prints a text file.
SYNTAX: C:\> Print abc.bio
C:\>Type abc.bio>prn or dir>prn
TREE – This command graphically displays the path of each directory and
sub-directory on the given drive.
SYNTAX: C:\>Tree
/f
displays the names of the files in each directory.
XCOPY – Xcopy is kind of a super version of Copy command available with
the all Dos version 3.2 and hence. This command copies directories, their
sub-directories, and files (except hidden and system files) to the specified
destination.
SYNTAX: C:\> Xcopy C:\student\abc
c:\student\xyz\abc /s
(/S copies
all the subdirectories also)
BATCH
PROCESSING (FILE) - You may often find yourself
repeatedly typing the same sequence of commands to perform some common task.
With MS-DOS, you can put this command sequence into a special file called batch
file, and then run the whole sequence of commands by simply typing the name of
the batch file. MS-DOS performs these “batches” of commands just as if you had
typed them from keyboard. This is called batch processing. Batch files are text
files with .bat extension containing MS-DOS commands.
SYNTAX: C:\> Copy Con A.bat
Dir
Dir/p
Dir/on/p
Dir/oe/p
Date
Time
F6
If you want
to run the batch file, just type the primary name of batch file at command
prompt..
For
example- C:\>A
CHKDSK
(SCANDISK) – The CHKDSK command can be used to
check a hard disk or floppy disk for directory entries or the file allocation
table. In most cases, these errors are repairable. These are not errors that
you have made, but rather flaws that arise over time as a result of disk aging.
With regular use of CHKDSK you can identify and repair disk errors before they
become unmanageable.
SYNTAX: C:\> chkdsk a:
SORT – In order to view the file list in alphabetical order, you must
have the sort.exe file in the current directory or in the path given by you.
Sort is an external command.
SYNTAX: C:\> Dir | Sort | More
If you have
too many files to fit on one screen, you will desire to make the listing pause
after each screen. Use the following command.
C:\>Dir | Sort | More
FDISK – The command is used to define disk partitions on a DOS fixed
disk. Fdisk directs DOS to divide your fixed disk into logical collections of
cylinders called partitions. If the disk is partitioned, different operating
systems can be kept on fixed disk. The Fdisk command permits user to add,
change, display, or delete disk partitions.
SYNTAX: C\> Fdisk
FIND – If you want to find all the lines, which contain a particular
group of characters in a file, you can do this with the Find command. Find is
an external command.
SYNTAX: C:\> Find “Hello”
Friend.txt
This will
display all the lines in the file, which contain the word Hello.
BACKUP – It is extremely necessary to have more than one copy of your
important files. This can be done by using the Backup command. A backup is an
exact copy of the data and programs on your hard disk. If something happens to
the original copy, you can use the backup to restore the data and programs. The
backup command can be used to copy from the Hard Disk to Floppy disk only and
not vice versa. Also it erases all the data previously stored on the floppy
disk. Backup is an external command.
SYNTAX: C
:\>Backup c:\docs a:
RESTORE – The copied data from a hard disk to floppies using Backup command
cannot be retrieved by using the Copy command This data can only be retrieved
by using the Restore command. Only the files, which were copied using the
Backup command, can be retrieved by the restore command.
SYNTAX:
C:\> Restore A: C:\docs
ATTRIB – Attrib allows you to display or change the current file
attributes. Attributes, which are allowed under DOS r (read-only), h (hidden)
and s (system)
+H – Sets the
file as a Hidden file. –H Clears the Hidden File attribute.
SYNTAX:
C:\> Attrib abc +h
APPEND – Defines the data file search path that DOS will use each time it
fails to locate a file in the current directory or in a specified directory.
When DOS
cannot find a data file as specified or in the current directory, it searches
to see if the user has defined a data file search path. The DOS APPEND command
will allow you to define disk drives and subdirectories to be included in this
path.
SYNTAX:
C:\> Append C:\wordroc
C:\> Append c:\; d:\; a:\
MODE – The command is used to specify device characteristic i.e. a
parallel printer’s mode of operation is set. A graphic/colour display adapter’s
mode of operation is set.
SYNTAX:
C:\> Mode LPT1: 80,6,P
This command
will set parallel printer1 to print 80 characters per line with 6 lines printed
per vertical inch.
C:\>Mode 40
This command
sets the display width to 40 characters per line.
HELP – It displays short summaries of command syntax. Invoke the HELP
command without parameter to list all the standard DOS line and batch commands.
SYNTAX:
C:\>Help
DELTREE – The command deletes an entire directory that contains files;
sub-directories or both files and subdirectories you will like to use this
command when you want to delete an entire directory without having to empty it
first.
SYNTAX:
C:\>Deltree <Directory Name>
ECHO – The command is used in batch files to display or suppress batch
command messages.
Echo On/Off
On – Enables
the display of batch command as they execute.
Off –
Disables the display of batch commands as they execute.
REM – Display a message during the execution of a batch file. Message
is the character string whose length can be only upto 123 characters. Message
is displayed only if ECHO is ON.
CALL-This commands invokes a second batch file from within a currently
running batch file, then returns to the original batch file.
SYNTAX CALL[drive:\path\]batch file
Call requires
the name of another batch file. For example
@ECHO OFF
CALL ABC
DEL
C:\BOOK\*.BAK
XCOPY
C:\BOOK\*.* A:/M/S
The
AUTOEXEC.BAT File:-The AUTOEXEC.BAT file is the
most important batch file in your system. It is located in your root directory,
this file is read automatically when you boot your PC. This file is useful
because it executes a sequence of commands, like setting the path and prompt,
etc. as soon as the computer is switched on.
The CONFIG.SYS File:- When you start your computer, DOS carries out
certain commands which configure your hardware and reserve space in memory for
information processing. The file containing these commands is called
CONFIG.SYS. This file helps in enhancing the performance of your PC.
There are two types of files in DOS
- Executable
Files
- Non-
Executable
Executable
Files—Executable files are files that are run or execute directly on the PC.
Extension of these files is .EXE, .COM and .BAT. COM and .EXE are in the Binary Code (Machine
language) while .BAT files are made in Simple Words. Batch files are the set of
instruction.
Non-Executable Files—Non executable files are files in
which data, information or program are stored which could not be run directly.
Non-executable files are many types and extension of these files may be
anything. Like .DOC, .TXT, .BMP, .TIF etc
Concepts of Free/Open Source and Proprietary software
The term open
source refers to software whose source code — the medium in which
programmers create and modify software — is freely available on the Internet;
by contrast, the source code for proprietary commercial software is usually a
closely guarded secret.
The most well-known example of
open source software is the Linux operating system, but there are open source
software products available for every conceivable purpose.
Open source software is
distributed under a variety of licensing terms, but almost all have two things
in common: the software can be used without paying a license fee, and anyone
can modify the software to add capabilities not envisaged by its originators.
A standard is a technology specification whose
details are made widely available, allowing many companies to create products
that will work interchangeably and be compatible with each other. Any modern
technology product relies on thousands of standards in its design — even the
gasoline you put in your car is blended to meet several highly-detailed
specifications that the car’s designers rely on.
For a standard to be considered
an open standard, the specification and rights to implement it must
be freely available to anyone without signing non-disclosure agreements or
paying royalties. The best example of open standards at work is the Internet —
virtually all of the technology specifications it depends on are open, as is
the process for defining new ones.
An Application Programming Interface (API) is a feature of a software application that
allows other software to inter-operate with it, automatically invoking its
functionality and exchanging data with it. The definition of an API is a form of technology standard. The
term open API doesn’t yet have a universally accepted
definition, but it’s generally expected to be “open” in the same manner as an
open standard.
The common theme of “openness”
in the above definitions is the ability of diverse parties to create technology
that interoperates. When evaluating your organization’s current and anticipated
software needs, consider a solution’s capability to interoperate as an
important criterion. To extend the value of your technology investment, select
a software solution that is based on open standards and APIs that facilitate interoperability and has the
capability for direct integration between various vendors’ products.
Linux
Linux: - Before knowing the
Linux, you must know about the Unix. Unix is the most versatile and popular
operating system found today on scientific and high-end workstations. Linux is a project initiated to create a
working version of UNIX on Intel-based machine, more commonly referred to as
IBM PC-compatible computers that most people are familiar with. Linux is an
open-source operating system enhanced and backed by thousands of programmer’s
worldwide. It is a multi-tasking operating system that was originally designed
to be used on personal computers. The name “Linux” is derived from its inventor
Linus Torvalds. Linus was a student at the University of Helsinki, Finland in
early 1990s when he wrote the first version of an Unix-like kernel as a toy
project. He later posted the code on the Internet and asked programmers across
the world to help him build it into a working system. The result was Linux.
Torvalds holds the copyright but permits free distribution of the source
code. Today, there are thousands of
software developers around the world contributing software to the open source
community that feeds the Linux initiative. Because the source code for the
software is freely available, anyone can work on it, change it, or enhance it.
Linux
is basically a UNIX clone, which means that with Linux you get many of the
advantages of UNIX. Linux is multitasking, means that you can run multiple
programs at the same time, and each program seems to process continuously.
Other system, such as Microsoft Windows 3.1, allows you to run multiple
programs, but when you switch from one program to another, the first program
typically stops running. Microsoft’s Windows 98 and Windows NT are more like
Linux because they allow preemptive multitasking. Linux allows you to start a file transfer,
print a document, copy a floppy, use a CD-ROM and play a game-all at the same
time.
Linux
is fully multi-user capable, which means that more than one person can log in
to and use the system at the same time. Although the multi-user feature may not
be very useful at home, it gives many people in a corporate or university
setting access to the same resources at the same time yet eliminates the need
to duplicate expensive machines. If you
have heard Linux described as a free version of UNIX, there is good reason for
it. Although much of the code for Linux started from scratch, the blueprint for
what the code would do was created to follow POSIX (Portable Operating System
Interface for UNIX) standards. POSIX is a computer industry operating system
standard that every major version of UNIX complied with.
Linux
grew within a culture of free exchange of ideas and software. Like UNIX, the
focus was on keeping communications open among software developers. In the
1980s and 1990s, while Microsoft flooded (busy) the world with personal
computers running DOS and Windows operating system, power users demanded more
from an operating system. They want such systems that could run on networks,
support many users at once (multi-user), and run many programs at once
(multitasking). DOS and Windows did not cut it. On the other hand, UNIX grew
out of a culture where technology was king and marketing people were hard to
find. Bell Laboratories in Murray Hill, New Jersy, was a think tank where ideas
came first and profits were somebody else’s problem. A quote from Dennis
Ritchie, co-creator of UNIX, sums up the spirit that started NIX. In that
spirit, the first source code of UNIX was distributed free to universities.
Like Linux, the availability of UNIX source code made it possible for a diverse
population of software developers to make their own enhancement to UNIX and
share them with others.
Basic Features of Linux: - No matter what
version of Linux you use, the piece of code common to all is the Linux Kernel.
Although the kernel can be modified to include support for the features you
want, every Linux kernel can offer the following features:
·
Multi-user: -Linux is the multi-user operating system. Not only you can have
many user accounts available on a Linux system, you can also have multiple
users logged in and working on the system at the same time. If users want, They
can have their own environments arranged the way they want such as, their own
home directory for storing files and their own desktop interface (with icons,
menus, and applications arranged to suit them). User accounts can be
password-protected, so that users can control who has access to their
applications and data.
·
Multitasking: - It also has the features of Multitasking. In Linux, it is possible
to have many programs running at the same time, which means that not only can
you have many programs going at once, but that the Linux operating system can
itself have programs running in the background. Many of these system processes
make it possible for Linux to work as a server, with these background processes
listening to the network for request to log in to your system, view a Web page,
print a document, or copy a file. These background processes are referred to as
daemons.
·
Graphical user interface (X
Window System): - Linux is a GUI based system. The
powerful framework for working with graphical applications in Linux is referred
to as the X Window System (or simply X).
X handles the functions of opening X-based graphical user interface
applications and displaying them on an X server process (the process that
manages your screen, mouse, and keyboard). On top of X, you use an X-Based
desktop environment to provide a desktop image and windows manager to provide
the look and feel of your GUI (icons, window frames, menus, and colors, or a
combination of those items called themes). There are several desktop
environment and several desktop managers to choose from.
·
Hardware Support: - You can organize (configure) support for almost every type of
hardware that can be connected to a computer. There is support for floppy disk
drives, CD-ROMs, removable disks (such as DVDs and pen drives), sound cards,
tape devices, video cards, and most anything else you can think of. As device
interfaces, such as USB and FireWire, have been added to computers, support for
those devices has been added to Linux as well. (Most hardware manufacturers
don’t provide Linux drivers with their peripheral devices and adapter cards.
Although most popular hardware will be supported eventually in Linux, it can
sometimes take a while for a member of the Linux community to write a driver.)
·
Networking Connectivity: - To connect your Linux system to a network, Linux offers support
for a variety of local area network (LAN) cards, modems and serial devices. In
addition to LAN protocols, such as Ethernet (both wired and wireless), all the
most popular upper level networking protocols can be built-in. The most popular
of these protocols is TCP/IP. Other protocols, such as IPX (for Novell
networks) and X.25 (a packet-switching network type that is popular in Europe),
are also available.
·
Network Servers: - A variety of software packages are available that enable you to
use Linux as a print server, file server, FTP server, mail server, Web server,
news server, or workgroup server.
·
Application Support: - Because of compatibility with POSIX (Portable Operating System
Interface for UNIX) and several different application programming interfaces
(APIs), a wide range of freeware and shareware software is available for
Linux.
Advantage of Linux: - Linux has many advantages. When compared to
different commercially available operating system, the best properties of Linux
are its price, its reliability and the freedom it gives you. Linux is the most
popular free operating system that is widely available. Most people know that
its initial price is free. However, when people talk about Linux’s
affordability, they are usually thinking of its total cost, which includes no
licensing fees and the capability of using inexpensive hardware and compatible
free add-on applications. Although commercial operating system tend to
encourage upgrading to later hardware. Linux does not require that (although
faster hardware and larger disks are nice to have).
In
terms of reliability, Linux is more reliable than most desktop-oriented
operating system. This is especially true if you rely on your computer system
to stay up because it is a Web server or a file server. (You don’t have to
reboot every time you change something).
Because you can get the source code, you are free to
change any part of the Linux system, along with any open source software that
comes with it, in any way that you choose. Unlike many self-contained
commercial products, open source software tends to be built in pieces that are
meant to interact with other pieces, so you are free to mix and match
components to suit your tastes.
Another
advantage of using Linux is that help is always available on the Internet. For
the IBM PC, Linux provides a complete system with built in multi-user and
multitasking capabilities that take advantage of the entire processing power of
your 386 and higher computer systems. Linux comes with a complete
implementation of the TCP/IP networking protocol. With Linux, you can connect
to the Internet and the vast wealth of information it contains. Linux also
provides a complete email system to send message back and forth through
cyberspace. Linux also has a complete graphical user interface (GUI), Xfree86,
that’s based on the popular X Window System. Xfree86 is a complete
implementation of the X Window System that can be distributed free of charge
with Linux. Xfree86 provides the common GUI elements you find on other
commercial GUI platforms, such as Windows and OS/2. Today, all these features
are available for Linux and are basically free.
Although
using an operating system is sometimes fun in and of itself, it is not the
reason most people use a computer. Most people need to do productive work with
their computers. Linux has literally thousands of application available today,
including programs for spreadsheets, databases, word processing, and
application development in a variety of computer languages and
telecommunications packages to get you online. Linux also comes with a wide
range of games, both text and graphics-based. If you are a computer
professional, Linux provides a wealth of tools for program development. It
includes compilers for many of the top computer programming languages today,
such as C, C++ and Smalltalk. If you don’t like those languages, Linux provides
you with tools, such as Flex and Bison that you can use to build your own
computer languages. Linux also allows you to communicate with your company’s
office systems. And if you are a UNIX system administrator, Linux can help you
perform your duties from home.
Linux
is a culture that encourages interoperability. For example, if you don’t like a
window manager, you can plug in a different one because so many were built to
operate within the same framework. Linux is also beneficial to students also.
Linux provides you with editors to write your assignments and spell checkers to
proof those assignments.
At
the basic level, Linux is a system built by and for hackers. The popular
definition of hacker has a negative connotation (suggestion/shade) in today’s
society, but computer hackers are not criminals by their definition of the
world. (Hackers feel a certain depth of commitment and an enhanced level of
excitement at hacking a system). Hacking basically means learning all there is
to know about a system, becoming absorbed (deep) in the system to the point of
distraction (interruption), and being able to fix the system if it breaks.
Hardware Requirements of
Linux
To be able to install Linux successfully, you need
supported hardware. Choosing the right level of hardware for your Linux system
depends on such factors as the number of users to be supported and the types of
application to be run. Most Linux system today consist of PCs. These Linux
installations are often for only a single user, although they may also be tied
into larger Linux or UNIX systems. Linux developers typically have access only
to their personal computers. Luckily, because so many Linux developers exist,
most of the standard hardware found in the PC world is supported.
- The
System’s CPU:- A
basic system requires an IBM-compatible PC with an Intel 80386 or later
CPU in any of the various CPU types and Intel’s various Pentium
processors. Other CPU clones, such as the 80686 clone chips made by Cyrix
and Advanced Micro Devices(AMD), are also compatible with Linux. For a
text-only installation, a 200 MHz Pentium, while a 400 MHz Pentium II is
the minimum for a GUI installation. The Linux kernel has also been ported(believe)
to other processors. Among those now supported are the DEC Alpha, the
PowerPC(Macintoshes), Sun Sparcs and even embedded systems processors such
as those used in Corel’s Network PC running the Debian distribution.
- The
System’s Bus:- The
types of bus used to communicate with the peripherals is also important.
Linux works with only the ISA, EISA and PCI buses. Some newer systems use
a faster bus, called the local bus, for example, for disk access and video displays.
Linux does support the VESA Local Bus might not support a non-VESA Local
Bus architecture.
- Memory
Needs:- Linux
requires surprisingly little RAM to run, especially when compared to
comparable operating system such as OS/2 and Windows NT. Linux requires at
least 16MB of RAM, although 64MB is highly recommended. If you have less
than 32Mb of RAM, you need to use what’s called a swap file. The next
memory consideration for Linux is the use of the X Window System clone
called XFree86. XFree86 is a version of the X Window System that can be freely
distributed and is included with Linux for that reason. XFree86 is a GUI
similar to Microsoft Windows.
- Disk
Drives and Space Requirements:- Although you can run Linux from a floppy drive only system,
running Linux from your system’s floppy drive is not recommended. For
better system performance, you should install Linux on a hard drive. The
amount of disk space required depends on the software you install and the
amount of data you expect that software will generate. Linux requires less
disk space than most implementation of UNIX systems. You can run a
completely functional Linux system, without X Window System support, in
600MB. For a complete installation of everything in the distribution, more
than 1.6 GBs is recommended.
- Swap
Space:- If you have
limited RAM, you need swap space. Whereas systems such as Microsoft
Windows create a swap file that resides on your hard drive as any other
file, Linux allows the swap file to reside on a separate swap partition.
Most Linux installation use partitions rather than files. Because you can
place multiple on the same physical hard drive, you can place the swap
partition on the same drive as
Linux, but for better performance, you should place the swap partition on
a separate drive. Linux allows up to eight swap partitions that can be no
larger than 16MB. A rule of thumb is set to set the swap file size to
twice the amount of physical RAM contained on your system. Thus, if you
have 8MB of physical RAM, your swap partition should be 16MB in size.
- Monitor
Requirements:- For
text-based terminals, Linux supports all standard CGA, EGA, VGA and
SuperVGA video cards and monitors. To take advantage of the color coding
directory listings available with Linux, you need a color monitor. So for
text-based operation, any video/controller combination should work.
- CD-ROMs:-
To install the Linux
system, you must have a CD-ROM drive supported by Linux. Because most
CD-ROMs use a SCSI interface controller, any SCSI controller should work
with a CD-ROM attached to the controller. Linux also now supports many of
the new EIDE and ATAPI CD-ROMs available on the market.
- Mouse
Devices:- Using
text-based Linux does not require a mouse. However, Linux does allow you
to cut text from any area of the screen and paste it to the command line
by using a mouse. If you intend to use the X Windows system clone,
XFree86, you must like a mouse.
Various flavors of Linux
Linux is distributed by many different organizations,
each of which provides a unique collection of programs along with the core
group of files that constitute a Linux release. Today there are close to 200
Linux distribution versions. Some of the most popular distribution versions
include Caldera OpenLinux eServer, Red Hat, SuSe, TurboLinux Server,
Linux-Mandrake, Debian Linux, Connectiva and Red Flag. These versions are
available from commercial vendors who make money by selling their
implementation as well as installation, maintenance and other services. Linux
is also distributed by the non-profit Debian organization, which is developing a
free operating system and related software. The main difference among various
distribution versions includes the set of tools, library version, number and
quality of application, documentation, support and service. Different Linux distributions are suited for
different purposes. People looking for a more stable, well tested system may
want to go with Debian, CentOS(a free version of Red Hat Enterprise Linux), or
even Ubuntu LTS. There is no one right distribution for everyone has a
favorite.
Linux Standard Directories
When you log in, the system places you in your home
directory. The PATH environments variable is set to point to other directories
that contain executable programs. These other directories are part of the
standard Linux directory structure. These directories include the classic set
of directories for UNIX and what can be called the “emerging standard set of
directories”, which Linux basically follows.
Classic UNIX Directories: - Before UNIX System V Releases 4 (for example, UNIX
System V Release 3.2 and earlier), most versions of UNIX settled on a regular
system of organizing the UNIX directories that looked like this:
/
/etc
/lib
/tmp
/bin
/usr
/spool
/bin
/include
/tmp
/adm
/lib
The
/etc directory contains most of the system-specific data required to boot, or
bring the system to life. It contains such files as passwd and inittab, which
are necessary for the proper operation of the system.
The /lib directory contains a library of function
needed by the C compiler. Even if you don’t have a C compiler on your system,
this directory is important because it contains all the shared libraries that
application programs can call. A shared library is loaded into memory only when
the command calling it is run. This arrangement keeps executable programs
small. Otherwise, every running program contains duplicate code, requiring a
lot more disk space to store and a lot more memory to run.
The /tmp directory is used for temporary storage.
Programs that use /tmp generally clean up after themselves and delete any
temporary files. If you use /tmp, you should be sure to delete any files before
logging out. Because the system automatically deletes the contents of this
directory periodically, don’t keep anything you might need later in it.
The /bin directory keeps all the executable programs
needed to boot the system and is usually home for the most commonly used Linux
commands. However, note that an executable program does not have to be binary
(which the names bin implies). Several smaller programs in /bin are, in fact,
shell scripts.
The /usr directory contains everything else. Your PATH
variable contains the string /bin:/usr/bin because the /usr/bin directory
contains all the Linux commands that are not in the /bin directory. This
arrangement has a historical precedence. In the early days of Linux, hard disks
were not very big. Linux needs at least the /etc/tmp/ and /bin directories to
bootstrap itself. Because the disks of the early Linux era held only those
three directories, everything else was on a disk that could be mounted after
Linux was up and running. When Linux was still a relatively small operating
system, placing additional subdirectories in the /usr directory was not much of
a burden. It allowed a moderately sized Linux system to exist with just two
disks: a root disk and a /usr disk.*********************************
Linux Directories: - One problem with the classical structure of UNIX
is that backing up your data files is difficult with a fragmented /usr
directory. Three different levels of backup generally are required in a system:
the basic system itself, any changes to the tables that define the basic system
for a specific site, and user data.
The
basic system should be backed up only once, with changes to the controlling
tables backed up when changes are made. User data changes all the time and
should be backed up frequently. The typical Linux directory structure is shown
here, but your structure might be a little different depending on what packages
you have installed:
/
/etc
/passwd
(user database)
/rc.d
(system initialization scripts)
/sbin
/tmp
/var
/lib
/home
/
<your user name here>(user accounts)
/install
/usr
/bin
/proc
The /bin, /etc, and /tmp directories have the same
function as they do in the classic structure. System definition tables are
moved into the /var directory so that whenever the operation of the system
changes, you can back up only that directory.
What’s new is that all system programs are moved into
the /sbin directory. All the standard Linux programs are in /usr/bin, which is
linked to /bin. For compatibility, all the classic directories are maintained
with symbolic links. The /usr directory, which no longer contains user data,
has been reorganized to make sense from the chaos that once was the /usr/libdirectory.
Functions of Profile and Login Files in Linux
The /etc/profile file—It stores system-wide
environment configuration and startup programs for login setup. All
configurations that you want to apply to all system user’s environments should
be added in this file. For instance, you can set you’re the global PATH
environment variable.
Linux
is a multi-user, time sharing system, implying that more than one user can log
in and use a system. Linux also allows user’s environment to be created or maintained
in two major ways: using system-wide(global) and user-specific(personal)
configurations. Normally, the basic method of working with a linux system is
the shell, and the shell creates an environment depending on certain files it
reads during its initialization after a successful user login.
When
the shell is invoked, there are certain initialization/startup files it reads
which help to setup an environment for the shell itself and the system user:
that is predefined (and customized) functions, variables, aliases and so on.
There are two categories of initializations files read
by the shell:
- System-wide startup files – these
contain global configuration that apply to all users on the system, and
are usually located in the /etc directory. They include: /etc/profiles and
/etc/bashrc or /etc/bash.bashrc
- User-specfic startup files – these
store configurations that apply to a single user on the system and are
normally located in the users home directory as dot files. They can
override the system-wide configuarions. They include : .profiles,
.bash_profile, .bashrc and .bash_login
SHELL: - Shell is a command interpreter. There are a large number of
commands, which is provided by shell. After you log in, Linux places you in
your home directory and runs a program called a shell. A shell is really
nothing more than a program designed to accept commands from you and execute
them. Many kinds of programs can be used as shells, but several standard shells
are available with almost all versions of Linux. Before icons and windows took
over computer screens, you typed commands to run most computers. On UNIX
systems, from which Linux was derived, the program used to interpret and manage
commands was referred to as the shell. The shell provides a way to run
programs, work with the file system, compile code, and manage the computer.
Although the shell is less intuitive (perceptive) than common GUIs, most Linux
experts consider the shell to be much more powerful than GUIs. Because shells
have been around for so long, many advanced features have been built into them.
Red Hat Linux provides the following shells: sh, bash
(Bourne Again Shell), tcsh, csh, pkdsh (Public Domain Korn Shell), zsh, ash and
mc. You should try each shell and pick the one you like. Most Linux distributions
install bash as the default shell. Also, sh is available on most UNIX systems,
and you will find many shell scripts written with sh commands. Because the shell serves as the primary
interface between the operating system and the user, many users identify the
shell with Linux. They expect the shell to be programmable, but the shell is
not part of the kernel of the operating system. With enough background in
systems programming and knowledge of the Linux operating system, you can write
a program that can become a shell.
Linux Kernel
The kernel is the core of the
Linux operating system and provides the basic system services to the rest of
Linux. As you know, Linux is not a commercial product, so you might find some
problems after a new distribution is released. This happens all the time with
both commercial and free operating systems. The difference is that with Linux,
because the source code is available, you can patch any problems immediately
after they are discovered. You don’t have to wait for your commercial vendor to
release a new service pack to fix a hole in your system. In addition, a new feature in the current
releases of the Linux kernel enables you to load specific device and program
support into the kernel without precompiling the support into a large kernel.
As a result, Linux can load into memory only those parts of the kernel it
needs. Modules also provide a way for you to modify the kernel to solve a
problem or to add a new feature without recompiling the entire system.
Sometimes a problem has only one solution- a new
kernel. The Kernel is the core operating system for Linux. If you have some
programming experience and know your way around way the C Programming language,
you should be able to build and install a new kernel.
Login and Logout from Linux System
When you begin working on your system, you will need
to log in. Logging in tells the system who you are and what you have permission
to do. Likewise, when you finish, you will log out so that no one else can
access your files without permission.
To
ensure security and organization on a system with many users, Unix machines
employ a system of users accounts. The user accounting features of Unix provide
a basis for analysis and control of system resources, preventing any user from
taking up more than his or her share, and preventing unauthorized people from
accessing the system. Every user of a Unix system must get permission by some
access control mechanism.
Logging in to a Unix system requires two pieces of
information: A username and a password. When you sit down for a Unix session,
you are given a login prompt that looks like this:
Login:
Type your username at the login prompt, and press the
return key. The system will then ask you for your password. Your username is
assigned by the person who creates your account. Your username must be unique
on the system where your account exists since it is the means by which your are
identified on the system.
When
your account is created, a password is assigned. The first thing you should do
is change your password, using the password utility. To change your password,
type the command
Passwd
It is very important that you choose a good password,
so that someone else cannot guess it.
When you are ready to quit, type the command
Exit
Before you leave your terminal, make sure that you see
the login prompt, indicating that you have successfully loffed out. It is
always a good idea to clear the display before you log out, so that the next
user doesnot get a screenful of information about you, your work, or your user
account. You can type the command
Clear
Linux Commands
BC :- The calculator
called bc. Bc stands for base conversion, which is one of its function, or the
best calculator. It is invoked by typing bc at the shell prompt. Once you type
bc at the prompt, you are in the calculator mode, and the $ prompt disappears.
The input to the calculator is taken line by line. Enter an expression and
Linux supplies the result as shown here:
$bc
10/2*2
10
2.5*2.5+2
8.25
quit
Typing quit ends your tryst(meeting) with bc. While
working with floats if you want precise answers all that you need to do is set
the variable scale to a value equal to the number of digits after the decimal
point till which you want the answer to be printed.
$bc
scale=1
2.25+1
3.35
After setting the scale variable if the answer of an
expression turns out more than what scale can provide than the value in scale
is ignored and the correct answer is displayed.
Another useful features of bc is that of base
conversion. Ibase and obase, two command are used for base conversion.
$bc
ibase=2
obase=16
11010011
89275
1010
A
Quit
By setting the variable ibase to 2 and obase to 16 all
input that we supply is taken as a binary number whereas all output is
displayed in hexadecimal.
Bc also supports functions like sqrt, cosine, sine
tangent etc.
$bc
sqrt(196)
14
s(3.14)
unimplemented
sqrt() is an in-built funtion whereas s() and c()
which stand for sine and cosine respectively would work only when bc is
invoked(appeal to) with the –l option.
$bc-l
scale=2
s(3.14)
0
Note that the trigonometric functions expect their
argument in radians and not in degrees.
Bc also allows setting up of variables. The life of
these variables is until you exit bc(by typing quit). These variables can be
used in programs. Yes, bc is a programmable calculator in its truest sense.
$bc
for(I=1;I<=5;I=I+1) I
1
2
3
4
5
quit
[This C like program prints numbers from 1 to 5 using
a for loop which gives values 1 to 5 to the variable i. If you want print the
variable’s value, simply type it’s name, as justified by the I following the
closing parenthesis in the above program. ]
The scope of bc’s programming ability is vast. It can
support loops, decision, function definitions, several operators etc. [Just say
man bc and explore on your own what more bc has to offer.]
Cal:- Linux
understanding of time is superb(excellent ). You already know that date command
is displayed current date and time. But if you want to calendar, you can use
cal command. It is capable or printing calendar
for any year in the range 1 to 9999. To invoke it all that we have to do
is type cal.
$ cal
Fri Apr 26 18:21:10 1996
Mar Apr May
The output shows the current date as well as the
calendar of preceding, current and succeeding month. If you want to see only
calendar of only a specific month, say, February 1997, you will have to be more
explicit(begin) while using the cal command.
$ cal 2 1997
Here, 2 indicates February. In place of 2 you could
have used feb or just a f. However, you can not use cal j 1997 to obtain
January 1997’s calendar. This is because j might as well stand for June or
July. If you become more specific and say cal ja 1997, it works.
CAT: Cat( concatenate) command is very
frequently used in Linux. It reads data from the file and gives their content
as output. It helps us to create, view, concatenate files.
1) To view a single file command
$cat filename
2) To view multiple files command
$ cat file1 file2
3) To view contents of a file preceding with
line numbers
$cat –n filename
4) Create a file command
$cat >newfile
CD: Cd command in Linux known as change
directory command. It is used to change current working directory.
Syntax:
$cd [directory]
To move inside a subdirectory
$cd [directory_name]
Clear: Clear is a
standard Unix computer operating system command that is used to clear the
terminal screen. This command first looks for a terminal type in the
environment and after that, it figures out the terminfo database for how to
clear the screen. And this command will ognore any command line parameters that
may be present. Also, the clear command does not take any argument and it is
almost similar to cls command on a number of operating system.
Syntax:
$Clear
CMP:- You may often require to know whether two
files are identical so that one of them can be deleted. There are three
commands in the UNIX/Linux system that can tell you that. It needs two
filenames as arguments:
$ cmp chap01 chap02
chap01 chap02 differ: char 9, line 1
the two files are compared byte by byte, and the
location of the first mismatch (in the ninth character of the first line) is
echoed to the screen. The –l(list) option gives a detailed list of the byte
number and the differing bytes in octal for each character that differs in both
files:
$ cmp –l note1 note2
3 143 145
6 170 167
7 171 170
8 172 171
There are four differences in the two files. If the
two files are identical, cmp displays no message, but simply returns the $
prompt. For example,
$ cmp chap01 chap01
$
CP: The cp command is similar to the DOS copy
command. You can use this command to copy one or more files from one directory
to another directory. The syntax of cp is as follows:
Cp from-filename to-filename
You must supply both the from-filename and to-filename
parameters for the files to be copied. For example:
$ cp letter.a letter.b
This will copy the contents of letter.a into a file
letter.b. If letter.b does not exist, it will be created. However, if it
does exist, Linux will overwrite it
without warning you. Just as in DOS, in
Linux too you can copy files from or to different directories by specifying
their name along with the path. For example,
$ cp /usr/aa16/chapter1 /usr/aa16/newbook/chap1
here the file chapter1 is copied from the directory
/usr/aa16 to the directory /usr/aa16/newbook. When copied to this directory it
would have the name chap1 instead of capter1.
Also note that in the above example we have used
absolute pathname to refer to the file chapter1. the absolute pathname started
at the root directory /.
Sometimes instead of absolute pathname we may use a
relative pathname. This refers to the pathname starting from the directory in
which you are now. This command is used
to copy files or group of files or
directory. It creates an exact image of a file on a disk with different file
name. cp command require at least two filenames in its arguments.
Syntax:
Cp [option] Source Destination
Cp [option] Source Directory
MV: mv command is used to move existing file or
directory from one location to another. Is is also used to rename a single
directory or file then mv option will be better to use.
Syntax:
Mv [option] source destination
For example
$ mv a.txt geek.txt
If the destination file does not exist, it will be
created. In the above command mv simply replace the source filename in the
directory with the destination file name (new name). if the destination file
exist, then it will be overwrite and the source file will be deleted. By
default, mv does not prompt for overwriting the existing file, so be carefule.
Date- command is used to display the system date and time. date command is also
used to set date and time of the system. By default the date command displays
the date in the time zone on which unix/linux operating system is
configured.You must be the super-user (root) to change the date and time.
Syntax:
date [OPTION]... [+FORMAT]
date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]
Options with Examples
1: date (no option) : With no options, the date command
displays the current date and time, including the abbreviated day name,
abbreviated month name, day of the month, the time separated by colons, the
time zone name, and the year.
Command:
$date
Output:
Tue Oct 10 22:55:01 PDT 2017
Find Command:- If you can not find a file by looking with
the ls command, you can use the find command. The find command is an extremely
powerful tool, which makes it one of the more difficult commands to use. The
find command has three parts, each of which can consist of multiple subparts:
- Where to
look
- What to
lokk for
- What to
do when you find it
If you know the name of a file but do not know where
in the Linux file stricture it’s located, the simplest case of the find command
works like this:
Find / -name filename –print
If you know that a file is probably in the /usr or
/usr2 directory, you can use the following command instead:
Find /usr/usr2 –name filename –print
For example,
Find *.jpg
It finds all the files in the current directory with
the .jpg extension.***
Listing Files: - The basic
command to list files is ls. The way ls displays files depends on how you use
the command. If you use the ls command in a pipe, every file is displayed on a
line by itself. This is also the default for some version of UNIX, such as SCO
UNIX. Other version of UNIX list files in several columns. For most uses, the
columnar format is more convenient; systems that list files one per row often
have an alternative command, usually lc, for lists in column format. The ls
command’s behavior is modified with the use of flags that take the form –abcd.
Flags used with the ls command can be concatenated or
listed separately. This means that the following commands are effectively
identical:
Ls –l –F
Ls –lF
Several of the flags used with ls and their uses are
shown in the table: -
|
Flag |
Description |
|
-a |
Lists all entries. In the absence of this or the –A
option, entries whose names begin with a period (.) are not listed. Linux has
a way of “hiding” files; all files that begin with a period by default are
not listed because they are generally files used to customize applications. |
|
-A |
Acts the same as –a, except that. and .. are not
listed. |
|
-b |
Forces printing of nongraphic characters to be in
octal \ddd notation. –b is more useful than the –q flag because it allows you
to figure out what the characters are. |
|
-c |
Uses the time of the last edit (or last mode change)
for sorting or printing. Linux maintains three time and date stamps on every
file: the file creations date, the date of last access, and the date of last
modifications. Normally, files are listed in ASCII order (alphabetical order,
except that capitals are sorted before lowercase letters). |
|
-C |
|
|
|
|
|
|
|
|
|
|
|
|
|
PWD: pwd stands for Print Working Directory. It
prints the path of the working directory, starting from the root. Pwd is shell
built-in command (pwd) or an actual binary(/bin/pwd). $PWD is an environment
variable which stores the path of the current directory. This command has two
flags.
Pwd –L: Prints the symbolic path
Pwq –P: Prints the actual path
MKDIR:-
Because Linux’s file
system is based on directories, Linux provides the mkdir command so that users
can create new ones. Unlike DOS, which has an alias for the mkdir command
called MD, Linux requires that the full mkdir command be spelled out. You must
specify a name for each new directory, as shown in the following example:
$ mkdir backup
among the options available with mkdir is –p, which
allows you to create multiple generations of directorie, at one go. That means,
it creates all the parent directories specified in the given path too. For
example
$ mkdir –p works/bpb/linux/book
The –p option tells Linux to first create works, then
within it bpb, next its child directory linux, and lastly book, nested within
all these.
MORE:- The more command
displays a screen of a text file. You can look through a text file without
invoking an editor, printing the file, or trying to pause the terminal as it
displays the file. For example, to display the contents of your Emacs
configuration file, you can type the following:
$ more –emacs
A disadvantage of using more is that you can not
backup to see a screen of information after it passes.
RM:- To delete files under Linux, you can use
the rm command. The rm command is dangerous because as soon as a file is
deleted, you can never recover it. for safety reasons , you should use the
following form of the rm command:
$ rm –i filename
where –i is a switch, removes file interactively; i.e.
you are asked for confirmation before deleting the file. For example, the
command rm fred1 removes the file named fred1, whereas the command rm-i fred1
deletes the fred1 file after asking whether you really want to remove this
file.
In
DOS, to remove a directory, you are first required to empty the directory, and
then delete it. Linux offers a single command for the same.
$ rm –r dir1
This command recursively (-r) removes all contents of
dir1 and also dir1 itself.
Rm used with the –f option removes files forcibly,
irrespective of whether you have write permission to them or not.
RMDIR:- The rmdir command
deletes Linux directories. The command takes the name of the directory to
delete. This directory must be empty, otherwise, Linux can not remove it.
For example, if the /backup directory
has two directories within it, the command rmdir /backup fails. The command
rmdir /backup/jack/* removes all files in the /backup/jack directory, and then
rmdir /backup/jack removes the now empty /backup/jack directory.
With
the –p option, rmdir wields enough power to remove not only the specified
directory, but also its parent directories.
Chgrp- chgrp in Linux is used to
change the group ownership of a file or directory. All files in Linux belong to
an owner and a group. You can set the owner by using “chown”
command, and the group by the “chgrp” command.
Syntax:
chgrp [OPTION]… GROUP FILE…
chgrp [OPTION]… –reference=RFILE FILE…
Note: First we need to have administrator permission to
add or delete groups. We can Login as root for this purpose or using sudo. In order to
add a new group we can use:
sudo addgroup geeksforgeeks
Example 1: To change the group ownership of
a file.
Chmod- It
is used to change the access permissions of files and directories. It stands
for change mode. The file permission in Linux are the following three types:
- Read(r)
- Write(w)
- Execute(x)
Syntax:
Chmod [reference][operator][mode] file
The references are used to distinguish the users to
whom the permissions apply i.e. they are list of letters that specifies whom to
give permissions. The references are represented by one or more of the
following letters:
Reference Class Description
U Owner File’s owner
G group users who are members of the
file’s group
O others users who are neither the file’s
owner nor members of the file’s group
A all All three of the above, same
as ugo
The operator is used to specify how the modes of a
file should be adjusted. The following operators are accepted.
Operator Description
+ Adds
the specified modes to the specified classes
-- Removes the
specified modes from the specified classes
= The
modes specified are to be made the exact modes for the specified classes
Finding out Who’s on the
system with who:- The purpose of the who
command is to find out who’s logged in to the system. The who command lists the
login names, terminal lines, and login times of users currently logged in. The
who command is useful in many situations. For example, If you want to
communicate with someone on the computer by using the write command, you can
find out whether that person is on the system by using who. You can also use
who to see when certain users are logged in to the computer to keep track of
their time spent on the system. To see everyone who’s currently logged in to
the system, you can enter who. Then you see a display similar to the following:
- $ who
- root console Dec
13 08:00
- ernie tty02 Dec
13 10:37
- bkraft tty03 Dec
13 11:02
- jdurum tty05 Dec
13 09:21
- ernie tty07 Dec
11 18:49
- $
- This listing shows that root,
ernie, bkraft, and jdurum are now logged in.
- Several
option are available with who.
- -u Lists only users who are
currently logged in
- -H Displays headers above each
column
- the headers displayed with the –H
option are NAME, LINE, TIME, IDLE, PID and COMMENTS. Table explains the
terms appearing in the heading.
|
Field |
Description |
|
NAME |
Lists the
user’s login name |
|
LINE |
Lists the line
or terminal being used |
|
TIME |
Lists the time
the user logged in |
|
IDLE |
Lists the
hours and minutes since the last activity on that line. A period is displayed
if activity occurred within the last minute of system time. If more than 24
hours has elapsed sine the line was used, the word old is displayed. |
|
PID |
Lists the
process ID number of the user’s login shell |
|
COMMENTS |
Lists the
contents of the comment field if comments have been included in /etc/inittab
or if there are network connections. |
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