1. What are
the different standard given by POSIX ? What is POSIX ?
Ans. :- The
different standard given by POSIX are:-
§ POSIX.1
§ POSIX.1B
§ POSIX.1C
§ POSIX.2
§ POSIX:2001
§ POSIX:2004
§ POSIX:2008
POSIX is the
Portable Operating System Interface, the open operating interface standard
accepted world-wide. It is produced by IEEE and recognized by ISO and ANSI.
2. On which
variable terminal setting is done ? Name any three terminal setting
keys.
Ans.:- Using
STTY
Three
terminal setting key
quit, kill,
erase, ...
The
environment variable TERM is used to identify the type of terminal (or terminal
emulator) to the curses library and programs that use the curses library to
display text. It is also associated with the TERMINFO and (in archaic systems)
TERMCAP environment variables
3. Explain
key features of UNIX.
Ans. :- The
UNIX system is supported by the file and the process. Directories and devices
are treated as files and there are many text manipulation tools to edit these
files. When a file is executed as a program, it is called a process. There are
tools to control processes like sending a processes into background or even
terminating it.
Unix is a
multitasking operating system, which allows the computer to run several
programs at the same time. By going quickly from one task to another and
performing a little bit of each task every time, the operating system gives an
impression of doing many things at the same time. Unix uses this technique of
time-sharing. Unix is also able to interact with more than one user at a time.
This feature of Unix makes it a multitasking system.
4. What is
script command, with command explain how to create script file of a
session?
Ans.-
5. What
happens if a directory permission charged?
Ans.- Every time
a file or a directory is created, default permissions are established
for it.
These default permissions are initially assigned either by the operating
system or
the program being run. Setting default permissions saves us the
trouble of
specifying permission codes explicitly every time a file or directory is
created. The
operating system assigns the default permission values of 777 for
executable
files and 666
for all
other files.
To put
further restrictions on the permissions assigned by a program when it
creates a
file or directory, a user mask is specified with the umask command.
The user
mask is a numeric value that determines the access permissions when a
file or
directory is created. Consequently, when a file or directory is created, its
permissions
are set to the permissions specified by the creating program minus
the
permission values denied by the umask value.
Example
The command
umask without arguments gives the octal value of the user mask.
$ umask
022
6. How do
you yank and paste lines?
Ans. :- The
command 'Y' or 'yy' copies (yanks) one or more lines. To copy one line, two
lines, 10 lines, and all lines to the end of the file, respectively:
Y 2Y 10Y yG
To paste the
text contained in the buffer above (uppercase P) or below the current cursor
position (lowercase p), respectively:
P p
It is also
possible to yank text within a line. The following commands yank text from the
current cursor position to the end of the word and the end of the line,
respectively:
yw y$
The same
commands paste the text within a line. Lower case p pastes after the cursor
position and upper case P pastes before.
Paste will
also work with deleted text, either lines or parts of lines. Be careful not to
execute any other commands prior to pasting as this will empty the buffer.
7. List out
the different attributes of a file.
Ans.:-
Listing File Attribute:-
-rw-r----- 1
sibnas sibgrp 4562 sep 22 10:30
-rw-r----- 1
sibnas sibgrp 8976 sep 22 10:30
-rw-r----- 1
sibnas sibgrp 10234 sep 22 10:30
-rw-r----- 1
sibnas sibgrp 4352 sep 22 9:30
-rw-r--r--r-
1 sibnas sibgrp 87632 aug 2 11:30
-rw-r--r--r-
1 sibnas sibgrp 6528 june 20 10:30
-rw-r--r--r-
1 sibnas sibgrp 9234 may 22 10:00
File type
link User id group id file size date &
Count in
bytes of modi.
8. What are
the different ways of coming out of vi after saving the file?
Ans.:- There
are three different ways to quit vi after saving the file:
a. :wq
b. :x
c. ZZ
9. Write
general syntax of CASE statements.
Ans. :- The
case statement compares word with pattern; if they match ,the shell runs the
command on the first line. Otherwise the shell checks the remaining patterns
,one by one ,until it finds one that matches the word; it then runs the command
on that online.
Syntax for
case statement:-
#!/bin/sh
Set „date‟
Case $1 in
Fri) echo
“thank goodness it‟s Friday!”;;
Sat | Sun)
echo “you should not work on week-ends”;
Echo “log
off and go home!”;;
*) echo “it
is not yet the weekend.”;
Echo “get to
work! “;;
Esac
10. What is
a process ? Name two important attributes of a process.
Ans :-
Process is born when a program starts execution and exists as long as
the program
is running. After execution the process is usually the name of the
program
being executed.
The two
important attribute of a process are:-
1) The
process-id(PID).Each process is identified by a unique number called
the
process-id which is allotted by the kernel when the process is born.
2) The
parent PID(PPID) the PID of the parent is also a process attribute.
When many
processes have the same PPID it is easier to kill the parent
process
rather than the children separately.
PART – B
1. a)
Explain layered architecture of unix operating system. With a suitable
command
explain the interaction between Shell and Kernel.
Ans.:-Unix,
like other operating systems, is a layer between the hardware and the
applications that run on the computer. it has functions that manage the
hardware functions that manage executing applications. So what‟s h difference
between UNIX and any other operating system? Basically two things: internal
implementation and the interface that is seen and used by users.
The part of
UNIX that manages the hardware and the executing processes is called the
kernel. The kernel is collection of programs written in c which directly
communicate with the hardware . Application programs communicate with the
hardware by using the services of Kernel. Along with the memory management, the
kernel also schedules processes and decides their priorities.
In the Unix
system , each hardware device is viewed as a file and is called a device file
.this allows the same simple method of reading and writing files to be used to
access each hardware device.
The user
commands are translated in to action by the shell which acts as interpreter.
The shell forms the outer part of the operating systems and forms the interface
between the user and kernel. for each user logged in, there is shell in action.
When a command is
given by the
user, it is examined by the shell and communicated to the kernel for execution.
Application
portability is the ability of a single application to be executed on various
types of computer hardware without being modified. This can be achieved if the
application uses the UNIX interface to manage its hardware needs.
b) Explain
uname command with different options.
Ans.:- uname
– displays the name of the operating system
Syntax
uname
[options]
Examples:
Displays all
the information
$uname –a
SCO_SV sco5
3.2 5.0.5 i386
Displays the
machine‟s node name in the communication network.
$uname-n
Sco-5
Displays the
operating system release.
$uname-r
3.2
Displays the
name of the operating system
$uname –s
SCO_SV
Displays the
operating system version
$uname –v
5.0.5
Displays the
information about system name, node name, operating system
release
number, kernel ID, processor type, serial number, number of users
license, OEM
number, origin number and number of CPUs.
2. a)
Explain the advantages of ispell, list out the basic commands used in ispell.
Ans.:-
b) Explain
unix file system and give the difference between relative and absolute
pathname.
Ans.:-Unix
file system can be defined as belonging to one of four possible types:-
Ordinary
files: ordinary files can contain text, data, or program information. An
ordinary file cannot contain another file, or directory. An ordinary file can
be a text file or binary file. Most of the UNIX command are binary files.
Directory
files :- Directories are containers that can hold files, and other directories.
A directory is actually implemented as a file that has one line for each item
contained within the directory. Each line in a directory file contains only the
name of the item, and a numerical reference to the location of the item.
Special
files :- Special files represent i/o devices like, a tty, a disk drive, or a
printer. Because UNIX treats such devices as files. Some of the commands used
to access ordinary files will also work with devices files. This allows more
efficient use of software.
Links:- A
link is a pointer to another file. Since a directory is alist of the names and
i-numbers of files, directory entry can be a hard link. In which the i-number
points directly to another file. A hard link to a file cannot be distinguished
from the file itself.
Difference
between ABSOULATE AND RELATIVE PATHNAMES
ABSOULATE
PATHNAMES
RELATIVE
PATHNAMES
An Absoulate
pathname specifies the location of a file .
Relative
pathname specifies a file in relation to the current directory.
An Absoulate
pathname starts at the / root directory.
A Relative
pathname starts from the current directory.
An Absoulate
pathname uses a slash (/) between each directory name in the path to indicate
different directories.
In a
Relative pathname, a single dot (.) represents the current working directory
and two dots (..) represent the parent of the current working directory.
3. a)
Explain how to split file into multiple files. Give suitable example.
Ans. :- we
used “split” command to split file into multiple files.
split –
split large files into “smaller files”
syntax –
split[options]
filename prefix
where file
name is the name of the large file to be split ,prefix is the name to be given
the small output files and options can either be excluded or can be one of the
or can be one of the following:-
-l =
linenumber
-b = bytes
If –l option
is used, linenumber will be the number of the lines to be put in each of the
smaller files (the default is 1000). If the –b option is used ,bytes will be
the number of bytes to be put in each of the smaller files.
The split
command will give each output file created the name prefix with an extension
attached to the end to indicate its order
EXAMPLE :
Assuming
that file.txt is 3000 lines long , it will output three files, xaa, xab, and
xac, and each one will be 1000 lines long.
$
splitfile.txt
This will
output six soo-line files: fileaa, fileab, fileac,filead, fileae, and fileaf.
$split-1500
file.txt file
Assuming
that file.txt has 200 kb ,this will output five 40 kb files: fileaa, fileab, fileac
,filead, fileae, and fileaf.
$ split –b
40k .txt file
b) Give the
difference between Hard Link and Symbolic Link.
Ans: - Soft
Link:
-------------
- Soft links
are links to a file but not the inode.
- Created
using
ln -s file1
file2
=> ls -il
131135 lrwxrwxrwx
1 user user 5 Jul 10 09:04 file2 -> file1
131137
-rw-r--r-- 1 user user 35 Jul 10 09:03 file1
- The inode
for file1 is 131137 and inode for file2 is 131135.
- If you see
the permission bits, there is 'l' in the front for a soft link.
- If file1 is
deleted, the link still exists. But if you try to view file2, its empty. This
means that once the main file is deleted the data is gone.
Hard Link:
--------------
- Hard links
are links to inode
- Created
using
ln file1
file2
=> ls -il
131136
-rw-r--r-- 2 user, user 48 Jul 10 09:27 file1
131136
-rw-r--r-- 2 user, user 48 Jul 10 09:27 file2
- The inode
for file1 and file2 is the same (131136).
- If you see
the output above for "ls -i", file2 does not show that it is linked
to file1. In reality it is not linked to file1 but it is linked to the inode.
- If you see
that there is number '2' before the username 'user'. This shows the number of
hard links to the inode.
- If file1
is deleted, the data is not deleted. If you view file2 the data is still there.
Deleting file1 only deletes a link. The data is gone once the last hard link is
deleted.
4. a) What
is a process? Explain the mechanism of creation in unix.
Ans :-
A process is
a collection of interrelated work tasks initiated in response to an event that
achieves a specific result for the customer of the process. Adding more
specific detail to that general definition:
· that achieves a specific result:
·
must deliver
a specific result
this result
must be individually identifiable and countable
a good
process name clearly indicates the result or end state of the process
· for the customer of the process:
·
a customer
receives the result or is the beneficiary of it
the customer
can be a person or an organization
customer can
be identified and can pass judgment on the result and process
customer
point of view helps identify and name the process accurately
· initiated in response to a specific event:
·
the process
must be initiated in response to a specific event
multiple
events can initiate a process
having an
event AND a result allows the tracing of the sequence of tasks that turns the
event into the result
· work tasks:
·
a collection
of actions, activities, steps or tasks make up a business process
a step in
the initial workflow will probably be divided into more detailed steps later
· a collection of interrelated:
·
the process
steps must relate to each other
interrelationship
is through sequence and flow...the completion of one step leads to (flows into)
the initiation of the next step
also
interrelated by dealing with the same work item
steps
related by being traceable back to the same initiation event
b) List out
the navigation keys for the cursor movement.
Ans. :- in
the command mode ,navigation keys for the movement of the cursor by characters,
words and lines are as follows:
Keys
Movement of
cursor
H
Cursor moves
left
J
Cursor moves
down
K
Cursor moves
up
L
Cursor moves
right
W
Word forward
B
Word
backward
E
End of word
^
First
character
$
End of line
0
Beginning of
line
The screen
display can be controlled by scrolling the display forward and backward using
the following keys:-
Keys
Screen
display
[ctrl-f]
Scroll
display forward
[ctrl-h]
scroll
display backward
[ctrl-d]
Scroll
half-screen forward
[ctrl-u]
Scroll
half-screen backward
5. a)
Explain grep command with at least 5 examples with different options.
Ans.- 1) A
simple Linux grep example - searching for a text string in one file
This first
grep command example searches for all occurrences of the text string 'fred'
within the "/etc/passwd" file. It will find and print (on the screen)
all of the lines in this file that contain the text string fred, including
lines that contain usernames like "fred" - and also
"alfred".
grep 'fred'
/etc/passwd
In a simple
grep example like this, the quotes around the string fred aren't necessary, but
they are needed if you're searching for a string that contains spaces, and may
be needed when you get into using regular expressions (search patterns).
2) Linux
grep command - searching for a string in multiple files
Our next
grep command example searches for all occurrences of the text string joe within
all files of the current directory:
grep 'joe' *
The '*'
wildcard matches all files in the current directory, and the grep output from
this command will show both (a) the matching filename and (b) all lines in all
files that contain the string 'joe'.
As another
example, you can also use grep to search all files in the current directory
that end in the file extension ".txt", as shown here:
grep 'joe'
*.txt
3)
Case-insensitive file searching with the Unix grep command
To perform a
case-insensitive search with the grep command, just add the -i option, like
this:
grep -i
score gettysburg-address.txt
This grep
search example matches the string "score", whether it is uppercase,
lowercase, or any mix of the two.
4) Reversing
the meaning of a grep search
You can
reverse the meaning of a Linux grep search with the -v option. For instance, to
show all the lines of my /etc/passwd file that don't contain the string fred,
I'd issue this grep command:
grep -v fred
/etc/passwd
5) Using
grep in a Unix/Linux command pipeline
The grep
command is often used in a Unix/Linux pipeline. For instance, to show all the
Apache httpd processes running on my Linux system, I can use the grep command
in a pipeline with the 'ps' command:
ps auxwww |
grep httpd
b) Explain
Uniq command.
Ans.- The
default output is to display lines that only appear once and one copy of lines
that appear more than once. It is also useful to filter out multiple blank
lines from unsorted output of other commands. For example, the dircmp command
displays its output using pr; thus the output usually scrolls off your screen
before you can read it. But if you pipe the output of the dircmp command
through the uniq command, the blank lines are reduced and the output is more
compact.
· -u Print only lines which are not repeated (unique) in
the original file
· -d Don't output lines that are not repeated in the
input.
· -c Generate an output report in default style except
that each line is preceded by a count of the number of times it occurred. If
this option is specified, the -u and -d options are ignored if either or both
are also present.
· -i Ignore case differences when comparing lines
· -f Ignore a number of fields in a line
· -s Skips a number of characters in a line
· -w Specifies the number of characters to compare in
lines, after any characters and fields have been skipped
· --help Displays a help message
· --version Displays version number on stdout and exits.
6. a)
Explain the mechanism of executing job periodically using cron.
Ans. A task
can be automatically run in the background at regular intervals by a Unix
utility called cron.
The cron
daemon takes care of running these background jobs, which are called cron jobs.
crontab or
the crontable is a file which contains the schedule of cron entries to be run
and at specified times. cron checks the crontable at regular tables to see if
there are any jobs scheduled. A user can execute crontab if the user‟s name
appears in the file /usr/lib/cron/cron.allow. If the cron.allow does not exist,
the cron.deny file in /usr/lib/cron is checked. If the user‟s name is not in
this file the user is allowed to use crontab. If only cron.deny exists and is
empty, all users can use crontab. If neither file exists, only the root user can
use crontab. The allow and deny files contain one user name per line.
b) Write a
shell script to add two numbers by using Expr utility.
Ans.:- To
use it in a shell script, you simply surround the expression with backquotes.
For
example,
let‟s write a simple script called add that adds two numbers typed as
arguments:
# /bin/sh
# Shell
Script to Add two numbers
sum=„expr $1
+ $2„
echo $sum
Here we
defined a variable sum to hold the result of the operation. (Note the spaces
around the plus
sign, but
not around the equals sign). To run this script, we might type the following
line: (assume the script
add is
executable)
$ add 4 3
The first
argument (4) is stored in $1, and the second (3) is stored in $2. The expr
utility then adds
these
quantities and stores the result in sum. Finally, the contents of sum are
echoed on the screen:
7
$
The expr
command only works on integers (i.e., whole numbers). It can perform addition
(+), subtraction
(-),
multiplication (*), integer division (/), and integer remainder (%).
7. a) What
are positional parameters? Explain the command used to set the
positional
parameters.
Ans. – These
are used by the shell to store the values of command-line
arguments.
The command
which used to set the positional parameter
#!/bin/sh
#
Demonstrate the set command
set „date„
echo “Time:
$4 $5”
echo “Day:
$1”
echo “Date:
$3 $2 $6”
Assuming
that setdate has been made executable with the chmod command, we can run the
script by
typing the
command
$ setdate
The output
will look something like this:
Time:10:56:08
EST
Day: Fri
Date: 20 Aug
2004
What
happened? Consider the command line
set „date„
The
backquotes run the date command, which produces output something like this:
Fri Aug 20
10:56:08 EST 2004
This does
not appear on the screen. Instead, the set command catches the output and
stores it in the
positional
parameters $1 through $6:
$1 contains
Fri
$2 Contains
Aug
$3 contains
20
$4 contains
10:56:08
$5 contains
EST
$6 contains
2004
b) Explain
Head Command with example.
Ans :- The
head command, as the name implies, displays the top of the file. When used
without an option, it
displays the
first ten lines of the file.
You can use
the –n option to display the first „n‟ number of lines.
$ head
emp.lst Shows first ten lines of the emp.lst file
The head
command, as the name implies, displays the top of the file. When used without
an option, it
displays the
first ten lines of the file.
You can use
the –n option to display the first „n‟ number of lines.
$ head
emp.lst Shows first ten lines of the emp.lst file
1001|T.N.Raju
|Professor |Information Science|14/06/61|30000
1004|D.S.Raghu
|Lecturer |Information Science|05/12/75|17000
1005|S.K.Anantha
|Asst.Prof. |Information Science|20/07/63|24000
1009|M.P.Rajendra
|Sr.Lecturer |Computer Science |13/03/66|20000
1002|Mallu
|Lecturer |Information Science|20/07/74|15000
8. a) What
are positional parameters? Explain the command used to set the
positional
parameters.
Positional
paremeters:-These are used by the shell to store the values of command-line
arguments.
The command
which are used to set the positional parameter
#!/bin/sh
#
Demonstrate the set command
set „date„
echo “Time:
$4 $5”
echo “Day:
$1”
echo “Date:
$3 $2 $6”
Assuming
that setdate has been made executable with the chmod command, we can run the
script by
typing the
command
$ setdate
The output
will look something like this:
Time:10:56:08
EST
Day: Fri
Date: 20 Aug
2004
What
happened? Consider the command line
set „date„
The
backquotes run the date command, which produces output something like this:
Fri Aug 20
10:56:08 EST 2004
This does
not appear on the screen. Instead, the set command catches the output and
stores it in the
positional
parameters $1 through $6:
$1 contains
Fri
$2 Contains
Aug
$3 contains
20
$4 contains
10:56:08
$5 contains
EST
b) Explain
Head Command with example.
“head command ” displays the top of the file.
Example:-
$ head
emp.1st
It displays
the first ten lines of the file.
We can use
–n option with the head command to display the first „n‟ number of lines.
$ head – n 3
emp.1st
This
displays the first 3 lines of the file.
8. Explain
the options and associated actions for ls command.
Ans :- The
Is command shows the contents of a directory , and a view of basic information
(like size ,ownership, and access permission) about files and directories.
The options
and associated actions for Is command are:
OPTION
ACTION
-1
One file
name in each line
-a
All files
including those beginning with a dot(.), current directory (.) and directory
above (..)
-A
All files
including those beginning with a dot(.).does not list current directory(.) and
directory above.
-d
If an
argument is a directory ,lists only its name (not its contents)
-F
Marks
directories with a /,executables with a * and symbolic links with a @
-I
Shows the
inode number
-l
Lists in
long format , giving mode, number of links, owner, group, size in bytes, the
time that each file was last modified.
-p
Puts a slash
(/) after each directory.
-r
Sorts the
filenames in the reverse order
-R
Recursive
list
-t
Sorts by
time modified (latest first)
-u
Sorts by
last access time
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