Ans. 5.(c)
A pointing device is an input interface (specifically a human interface device) that allows a user to input spatial (ie, continuous and multi-dimensional) data to a computer. CAD systems and graphical user interfaces (GUI) allow the user to control and provide data to the computer using physical gestures – point, click, and drag – for exaple, by moving a hand-held mouse across the surface of the physical desktop and activating switches on the mouse, Movements of the pointing device are echoed on the screen by movements of the pointer (or cursor) and other visual changes.
While the most common pointing device by far is the mouse, many more devices have been developed. However, mouse is commonly used as a metaphor for devices that move the cursor.
Examples: Mouse, Light pen, Stylus etc.
Ans. 5(c)
(0.111)2 = 1 x 2-1 + 1 x 2-2 + 0 x 2-3
= ½ + ¼ + 1/8
= 0.5 + 0.25 + 0.125
= (0.875)10
(0.111
(ii) (11011.101)2
(11011.101)2 = 1 x 24 + 1 x 23 + 0 x 22
+ 1 x 21 + 1 x 20 + 1
X 2-1 + 0 x 2-2 + 1 x 2-3
= 16 + 8 + 2 + 1 + ½ + 1/8
= 27 + ½ + 1/8
= (27.265)10
Ans. 6(a)
Linux Security Permissions: Linux is often used as a Multi-user system and it is not desirable that all users have access to all files and directories.
For eg. : On a multi-user environment is a corporate office using a central server running linux , it might be required the accounts documents be shared between employees of the accounts department . At the same time, it might be undesirable and indeed dangerous if anyone having access to the server is able to read/edit them.
It is for such situations that Linux has a 3X3 permission system.
There are 3 levels of security for a file:
Read Permission : Permission to read a file (r)
Write Permission : Permission to edit a file (w)
Execute Permission : Permission to execute a file is it is executable (x)
And 3 different levels for a directory :
Enter Permission : Permission to Enter into the Directory
Show Entry : Permission to see the contents of the Directory
Write Entry : Permission to make a new file or subdirectory in the Directory
For granting the above permissions, users are divided into 3 different sets
User : The owner of the file/directory – mostly the person who created the file/directory
Group : Linux users can be divided in groups and one user can be a member of more than one group.
A Group denotes all users who are members of group(s) to which the owner of a file/directory belongs
Others : All users not in the group(s) of the owner.
For eg : A user level r/w/x permission means only the owner can read, write and execute the file
A group level r/w/x permission means only the members of group(s) to which the owner belongs can read, write and execute the file An other level r/w/x permission means Everyone can read/write/execute the file.
The chmod Command: The chmod command is used to change the permissions of files/directories in linux. It\\\’s syntax is as follows :
Chmod –R/c/f/v [u / g / 0 / a] [+ / – / =][rwxXstugo..]
For eg. If u want to give all users in the group of the owner just read permission to a file called foo.txt, the command is chod g+r /home/aarjav/foo.txt
Here g stands for group, + stands for giving permission (as against – for taking permission away), r stands for read permission.
So g+r means ?give group read permission?.
All users for the owners group now have rad permission to foo.txt Now if they misbehave and u want to take their read permission away, The command is the same as above, just substituting the + sign with a mins sign chod g-r /home/aarjav/foo.txt
As shown the general format of the command is
Chmod –R/c/f/v [u / g / o / a] [+ / – / =] [rwxXstugo]
Here
U : user
G : group
O : Others
A : all
+ : give permission
– take permission away
= : cause the permissions given to be the only permissions of the file
R : read permission
W : write permission
X : execute permission
X : execute only if it is a directory or already has execute permission for some user
S : set user or group ID on execution
T : save program text on swap device
U : the permissions that the user who owns the file has for it
G : the permissions that the owner?s group has for a file
O : the permissions that users not in the owner?s group have for it
(X, s, t, u, g and o are not required for common tasks)
The initial options –R/c/f/v are explained as follows :
-c : Displays names of only those files whose permissions are being changed
( –changes can also be used instead of -c)
-f : Suppresses display of error messages when a file?s permissions cannot be changed
( -silent of –quiet can also be used instead of –f)
-R : Recursively changes the permission of all files in all subdirectories of the directory whose permissions are being changed
( -recursive can also be used)
-v : Displays results of all permission changes
( -verbose can also be used)
