Unix-T1 Solution
1 a.With a neat diagram, explain the architecture of Unix operating system.
(4 marks)
Ans: The unix architecture mainly consists of of 3 divisions:
 Division of labor:Kernel and Shell
Division of labor between two agencies the kernel and shell.The kernel interacts with the
machine's hardware, and the shell with the user.The kernel is core of operating system-a collection
of routines mostly written in C.It is loaded into memory when the system is booted and
communicates directly with the hardwarte.User programs-To use the hardware through a set of
functions called the system calls.Kernel manages the system's memory,schedules processes,decides
their priorities and performs other tasks.This is called the operating system-a program's gateway to
the computer's resources.Command interpreter is actually the interface between the user and kernel.
User
User
User
Shell
Kernel
Hardware
Kernel-Shell relationship diagram
 The file and process
Two simple entities support the Unix system-the file and process where files have places and
processes have life.A file is just an array of bytes and can contain virtually anything.It contains
directories and dominant file type is text.The secondary entity is the process,which is the name
given to a file when it is executed as a program.Processes have parents,chidren and
grandchildren,and are born and die.
 The system calls
These are handful of functions used to communicate with the kernel.All UNIX flavours use the
same system calls.These system calls are built into the kernel,and interaction through them
represents an efficient means of communication with the system.
(3 points and diagram each 1 mark)
b.Discuss the salient features of Unix operating system.
(6 marks)
Ans: The following are major features of the unix operating system.
 A multiuser system
 A multitasking system
 The building block approach
 The unix toolkit



Pattern matching
Programming facility
Documentation
(Each 1 mark with explanation of 2-3 lines)
2 a.Explain absolute pathname and relative pathname with example.
(4 marks)
Ans:Absolute pathname: (2 marks)
If the first character of the pathname is /,the file's location must be determined with respect to
root(the first /).Such a pathname is called as absolute pathname.(Eg:/home/kumar/login.sql).When
we have more than one / in a pathname,for each such /,you have to descend one level in the file
system.No two files in a UNIX system can have identical absolute pathnames.
Using absolute pathname for a command:
Eg;
$ /bin/date
Relative pathname: (2 marks)
If the first character of the pathname is not /,.Such a pathname is called as relative
pathname.Relative pathnamkes can be distinguished using . and . . in the pathname.
 . (a single dot) --This represents the current directory
 . . (two dots) – This represents the parent directory
cd .. ---Moves one level up
cd../.. ---Moves two levels up
cd..
A filename can begin with a dot
cp ../sharma/.profile
b.With the help of diagram explain the parent child relationship.Explain the unix file system.
(6 marks) (2+4)
Ans:The unix file system can be grouped into two categories:
The files available at installation:
 /bin and /usr/bin
 /sbin and /usr/sbin
 /etc
 /dev
 /lib and /usr/lib
 /usr/include
 /usr/share/man
The temporary files:
 /tmp
 /var
 /home
All files in unix are related to one another.The file system in unix is a collection of all of these
related files (ordinary,directory and device files)organized in a hierarchical structure.The implicit
feature of file system is it consists of the top which is a reference point for all files.this top is called
root and is represented as /(frontslash).Root is actually a directory and it has a number of sub
directories under it as seen in the diagram.It is obvious that,in these parent-child relationships,the
parent is always a directory and child an ordinary file.
Root(/)
bin
cat date
dev
etc
who
home
lib
sbin
stand
kumar sharma
unix
tmp
usr
var
bin include sbin
login.sql progs safe
The unix file system tree diagram
3 a. Explain the different modes of operation in vi editor.
(5 marks)
Ans:vi editor mainly consists of 3 modes:
 Command mode:The default mode of the editor where every key pressed is interpreted as a
command to run on text.This mode is used to copy and delete the text.
 Input mode:Every key pressed after switching to this mode actually shows up as text.This
mode is invoked by pressing any one of the following keys:-(i,a,IA,o,O,R,S,s,rch)
 ex mode(Last Line mode):This mode is used to handle the files and perform
substitution.pressing a : in the command mode invokes this mode.This is carried out by
pressing any one of the following keys:-(:w,:x,:wq,:q)
Input
mode
ex mode
Command
mode
Shell
The three modes of vi editor diagram
b.List and explain the attributes of ls-l option.
Ans:File attributes of ls-l
 File type and permissions
 Links
 Ownership
 Group ownership
 File size
 Last modification time
 File name
(5 marks)
4 a.ELAIN THE USE OF CHM9OD COMMAND TO CHANGE THE FILE PERMISSIONS
WITH SUITABLE EXAMPLES (6 marks)
Ans:The chmod(change mode) command is used to set the permissions of one or more files for all
three categories of users(user,group and others).It can be run only by the user (the owner) and the
superuser.The command can be used in two ways:
 In a relative manner by specifying the changes to the current permissions.
◦ (u-user,g-group,o-others,a-All ugo)
◦ (r-read,w-Write,x-Execute permission)
◦ +assigns permissions
◦ -removes permission
◦ Examples:chmod o +wx filename ;chmod ug-x,o+rw filename
 In a absolute manner by specifying the final permissions.
◦ (0 to 7)
◦ File permissions in the form of numbers(read-4,write-2,execute-1))
◦ Examples:chmod 555 filename; chmod 776 filename
b.Give commands for the following in vi editor with examples.(4 marks)
1) To replace text from cursor to right--R
2) To execute a shell command while in editor --:sh
3) To move forward to the beginning of next word--w
4)To move to the 10th line---10k
5 a.Explain the three standard files with respect to UNIX operating system. (6 marks)
Ans:The shell associates three files with the terminal-two for the display and one for the
keyboard.These special files are actually streams of characters which many commads see as input
and output.A stream is simply a sequence of bytes.Each stream is associated with a default device,
and generically this device is a terminal.
 Standard Input
 Standard Output
 Stansard Error
b.With suitable examples,discuss how wild cards can be used for pattern matching in UNIX.
(6 marks)
Ans:The metacharacters that are used to construct the generalized pattern for matching filenames
belong to a category called wild cards.This pattern is framed with ordinary characters and a
metacharacter using well defined rules.The pattern can then be used as an argument to the
command,and the shell will expand it suitably before the command is executed.
Explanation of the following wild cards with examples.
 *
 ?
 [ijk]
 [x-z]
 [!ijk]
 [!x-z]