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UNIX INTERVIEW QUESTIONS
 
91What Happens When You Execute A Program
Date Posted: 07/02/2012

Ans: When you execute a program on your UNIX system, the system creates a special environment for that program. This environment contains everything needed for the system to run the program as if no other program were running on the system. Each process has process context, which is everything that is unique about the state of the program you are currently running. Every time you execute a program the UNIX system does a fork, which performs a series of operations to create a process context and then execute your program in that context. The steps include the following:
Allocate a slot in the process table, a list of currently running programs kept by UNIX.
Assign a unique process identifier (PID) to the process.
ICopy the context of the parent, the process that requested the spawning of the new process.
Return the new PID to the parent process. This enables the parent process to examine or control the process directly. After the fork is complete, UNIX runs your program.

 
 
921.What Are The Special Arrangements To Make A Terminal I/p And O/p?
Date Posted: 07/02/2012

Ans: When it is started by the shell, a program inherits three open files, with file descriptor 0, 1 and 2 called the standard i/p, the standard o/p, and the standard error. If the program reads ‘0’ and writes descriptors 1 and 2, it can do I/O without opening files.

 
 
931.What Are The Events Done By The Kernel After A Process Is Being Swapped Out From The Main Memory?
Date Posted: 07/02/2012

Ans: When Kernel swaps the process out of the primary memory, it performs the following:
1. Kernel decrements the Reference Count of each region of the process. If the reference count becomes zero, swaps the region out of the main memory,
2.  Kernel allocates the space for the swapping process in the swap device,
3. Kernel locks the other swapping process while the current swapping operation is going on,
4. The Kernel saves the swap address of the region in the region table.

 
 
94Suppose That You Are Using A Terminal In Which The Screen Size Is Bigger Than The Normal 24 Lines. If You Want To Use P And Take Full Advantage Of Your Terminal Capabilities What Choices Are Open To You
Date Posted: 07/02/2012

Ans:
You have to specify the screen size each time you use P. $P-36.
Also you could put a shell file in your bin.
$cat/usr/you/bin/p
Exec/usr/bin/p-36$*
$
another solution is to modify p to use an environment variable that defines the properties of your terminal.

 
 
95What Is The Working Set Of A Process?
Date Posted: 07/02/2012

Ans: The set of pages that are referred by the process in the last ‘n’, references, where ‘n’ is called the window of the working set of the process.

 
 
96How Do You Change File Access Permissions
Date Posted: 07/02/2012

Ans:
Every file has following attributes:
owner's user ID ( 16 bit integer )
owner's group ID ( 16 bit integer )
File access mode word
'r w x -r w x- r w x'
(user permission-group permission-others permission)
r-read, w-write, x-execute
To change the access mode, we use chmod(filename, mode).
Example 1:
To change mode of my file to 'rw-rw-r--' (i.e. read, write permission for user - read, write permission for group - only read permission for others) we give the args as:
chmod(myfile,0664) .
Each operation is represented by discrete values
'r' is 4
'w' is 2
'x' is 1
Therefore, for 'rw' the value is 6(4+2).
Example 2:
To change mode of my file to 'rwxr--r--' we give the args as:
chmod(myfile,0744).

 
 
97What Is The Principle Of Locality?
Date Posted: 07/02/2012

Ans: It’s the nature of the processes that they refer only to the small subset of the total data space of the process. I.e. the process frequently calls the same subroutines or executes the loop instructions.

 
 
98What Is Fork Swap
Date Posted: 07/02/2012

Ans: fork () is a system call to create a child process. When the parent process calls fork() system call, the child process is created and if there is short of memory then the child process is sent to the read-to-run state in the swap device, and return to the user state without swapping the parent process. When the memory will be available the child process will be swapped into the main memory.

 
 
99Which Are Typical System Directories Below The Root Directory
Date Posted: 07/02/2012

Ans:
(1)/bin: contains many programs which will be executed by users (2)/etc : files used by administrator (3)/dev: hardware devices (4)/lib: system libraries (5)/usr: application software (6)/home: home directories for different systems.

 
 
100Explain About ZAP
Date Posted: 07/02/2012

Ans: ZAP, which selectively kills processes, is another program. The main problem with that version is speed; it creates so many processes that it runs slowly, which is especially undesirable for a program that kills errant processes rewriting ZAP in C will make it faster.

 
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