unix presentation 4 (21 jan 08)

8/7/2019 Unix Presentation 4 (21 Jan 08)

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Security Features of the UNIX

� Password Security

� File Security User

Group

Other

� File Encryption

Device Driver

Structure of UNIX

� Kernel

Kernel Function

� Shell

In the today¶s session we¶ll read :-



Security Features of UNIX

UNIX is case sensitive.

The goal of the computer security is to maintain the

integrity, availability and privacy of the informationentrusted to the system.

UNIX is a multi-user operating system and so it offers

protection to one user¶s information from another.

UNIX has a hierarchical file structure. This structure allows

to implement the file security system.

Conti«.



UNIX provides three levels for protection data :-

� Password Security

� File Security

� File Encryption

Password Security :- Password are one of the most

important security feature used today. The security is

provided by assigning un-guessable password andlogin name to individual users ensuring that anybody

else can not have access to the work.

Conti«.



Conti«.

File Security :- UNIX provides security at file and directory

level. It classifies access control on files and directories

according to three categories : user, group and others

� User :- The user is the owner of the file. There is always

exactly one owner who has all the permission. The owner

of the file is the one who has created the file or to whom

the ownership has been transferred.

� Group :- The group has any number of members

established by the system staff.A group is a programming

team who share the same data for testing their programs.The

members of the group have the same group-id but differentuser-id¶s.



� Other :- The other members are anyone else who is neither

the owners nor group members of the file. There are three

forms of access or permission to any file- read, write and

execute, which can access a particular file, who can modifyit and who can execute it.

File Encryption :- This utility encodes the file into an

unreadable format, so that even if someone succeeds in

opening it, the secret are safe. For reading the file it needs to

be decrypt.

Conti«.



Device Driver

The UNIX system considers all devices connected to it as

files. Every device has a file name and is accessed like a

file.The special file or routines through which the devices

are accessed are called Device Drivers.

By writing to and reading from these files all I/O activity

can be performed. The functions to open, read, write and

close a device are built into the kernel,for each and every

device of the system.

When a particular device is accessed, the kernel calls the

right device driver and passes some parameter to it to act

properly.Conti«.



Device drivers are a process to communicate with peripheral

devices such as disk, tape drives, terminals and network.

and the kernel modules that control devices.

In other words a device driver controls many physical

devices of a given type. For ex. One disk driver may control

all disk drives connected to the system, one terminal driver

may control all terminals connected to the system.

Conti«.

Conti«.



� The UNIX system has two type of devices :-

Block-special

Character-special devices.

� Block-special :- Block devices are hard disk, floppy-drive

and CD-ROM, where all the data is read

and written in blocks and use buffer cache.

� Character-special :- The terminal, tape drive and printer

are character-special where read/write

operations don¶t use the buffer and access

the device directly.

Conti«.



Structure of UNIX

Conti«.



User

User

User

User User



The UNIX operating system is made up of three parts;

The kernel, The shell and The programs.

� K ernel :- The kernel is the heart of the system ± acollection of the programs mostly written in C that

directly communicate with the hardware.

� There is only one kernel for any system.

� Its that part of the UNIX system that is loaded into

memory when the system is booted and stay there while

system is running.

Conti«.

K ernel



� It manages the system resources, allocates time between

users processes, decide process priorities and performs all

other tasks.

� Kernel forms an interface between hardware and shell.

� It isolates the user programs from there hardware, and

these programs are independent of the hardware they use,it is easy to move them across different systems.

� This makes the UNIX system to run on different

machines.

Conti«.



Conti«.

� The kernel provides the file system, CPU scheduling,

memory management and other operating system functions

through system call.

� All the other components like programs and commands call

on the kernel¶s service.(*)



K ernel Function

The UNIX system kernel provides the following function :

� File management and security

� Memory management� Process scheduling and management

� Input/output devices

� System accounting

�Interrupt and error handling

� Date and time services



� Shell :- It is actually interface between the user and kernel.

� Shell interact with kernel by invoking a well defined set of

system calls.

� When a user logs in, the login program checks the username

and password, and then starts another program called the shell.

� The shell is your interface to the operating system. It acts as

a command interpreter; it takes each command and

passes it to the operating system. It then displays the results

of this operation on your screen.

Conti«.

Shell



� It interprets the commands the user types in and arranges for

them to be carried out one at a time. The commands are

themselves programs.

� Shell provides the arrangement for the kernel to run a

command.

�No command can be executed unless it obtain the clearance

of the shell. The shell, when analyzing the command and its

associated arguments,often modifies and simplifies its input

before it forwards it to another agency (Kernel) which

actually executes the commands.

Conti«.

Conti«.



� UNIX permits the use of complex command structures that

can¶t be understood by the kernel,the shell has to take on the

role of interpreter to translate them into forms that the kernel

can understand.

� Shell has a programming capability of its own.

� The shell is sleeping beauty of UNIX.

� The shell is a command line interpreter. The user interacts withthe kernel through the shell. You can write ASCII (text) scripts

to be acted upon by a shell.

� One great thing about Unix is the fact that you can change your shell easil once ou know how.

Conti«.



hanks

unix presentation 4 (21 jan 08)

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