Unix

Question 1

Specify the difference between absolute path and related path.

Answer 1

Absolute path refers to the exact path as defined from the root directory.

Related path refers to the path related to the current locations.

Question 2

What are the main features of UNIX?

Answer 2

Machine independent
Portability
Multi-user operations
Unix Shells
Hierarchical file system
Pipes and filters
Background processors
Utilities
Development tools.

Question 3

What is called Shell?

Answer 3

The interface between user and system called a shell. Shell accepts commands and set them to execute for user operations.

Question 4

What are the responsibilities of a shell?

Answer 4

Program Execution
Input/output redirection
Filename and variable substitution
Pipeline hookup
Environment control
Integrated programming language

Question 5

What is the UNIX command to list files/folders in alphabetical order?

Answer 5

The ‘ls –l’ command is used to list down files and folders in alphabetical order. When you use ‘ls –lt’ is list down files /folders sorted with modified time.

Question 6

Describe links and symbolic links in UNIX?

Answer 6

Links are defined as a second name which is used to assign more than one name to a file. Although links are referred to as a pointer to another file it cannot be used to link filenames on different computers.

A Symbolic link is also known as the soft link is defined as a special type of file that contains links or references to another file or directory in the form of absolute or relative path. It does not contain the data actually in the target file but the pointer to another entry in the file system. Symbolic links can also be used to create a file system.

The following command is used to create a symbolic link:

Ln –s target link_name

Here, path is ‘target’
Name of the link is represented by link_name.

Question 7

What is the FIFO?

Answer 7

FIFO (First In First Out) is also called named pipes and it is a special file for date transient. Data is read only in the written order. This is use to inter-process communications, where data write to one end and reads from another end of the pipe.

Question 8

Describe fork() system call?

Answer 8

The command use to create a new process from an existing process is called fork().The main process is called parent process and new process id called child process. The parent gets the child process id returned and the child gets 0. The returned values are used to check which process which code executed.

Question 9

‘It is not advisable to use root as the default login.’ Explain.

Answer 9

The root account is very important and it can leads to system damage easily with abusive usage. So that the securities that normally apply to user accounts are not applicable to the root account.

Question 10

What is mean by Super User?

Answer 10

The user with access to all files and commands within the system is called super user. Generally, super user login is to root and the login is secured with the root password.

Question 11

What is process group?

Answer 11

A collection of one or more processes is called process group. There is a unique process id for each process group. The function “getpgrp” returns the process group ID for the calling process. The group of processes associated with a call

Question 12

What is the behavioral difference between “cmp” and “diff” commands?

Answer 12

Ans) Both commands for file comparison.

Cmp – Compare given two files with byte by byte and display the first mismatch.

Diff – Display changes that need to done to make both file identical.

Question 13

What are the duties of following commands?chmod, chown, chgrp

Answer 13

chmod – Change the permission set of the file.
chown – Change ownership of the file.
chgrp – Change group of the file.

Question 14

How to display the last line of a file?

Answer 14

This can perform using either “tail” or “sed” commands. The easiest way is to use “tail” command.

Question 15

What are the various IDs in UNIX processes?

Answer 15

Process ID is a unique integer that UNIX uses to identify each process. The process executes to initiate other processes is called parent process and its ID is defined as PPID (Parent Process ID).

Question 16

Who can kill a process?

Answer 16

Owner or process or root.

Every process is associated with a specific owner of the process. The owner has all the privileges over the process and is the user who executed the process.
Identification for a user is User ID. The process also associated with Effective User ID which determines the access privileges to accessing resources like files.

getpid() – Retrieve process id
getuid() – Retrieve user id
geteuid() – Retrieve effective user id

Question 17

What is the command to find maximum memory taking process on the server?

Answer 17

top or htop

Question 18

What is the command to find hidden files in the current directory?

Answer 18

‘ls –lrta’ is to display hidden files in current directory.

Question 19

What is the command to find the currently running process in Unix Server?

Answer 19

“ps –ef” command is used to find current running process. Also “grep” with a pipe can use to find specific process.

Question 20

What is the command to find remaining disk space in UNIX server?

Answer 20

The command “df -kl” use to get a detail description on disk space usage.

Question 21

What is the method to see command line history?

Answer 21

The “history” command display all the command used previously within the session.

Question 22

Discuss the difference between swapping and paging?

Answer 22

Ans) Swapping – Complete process is moved to main memory for execution. To provide the memory requirement, process size must be less than the available main memory capacity. The implementation is easy but is an overhead to the system. Memory handling is not more flexible with swapping systems.

Paging – Only the required memory pages are moved to the main memory for execution. The size of the process does not a matter of execution and it no needs to be less than available memory size. Allow a number of processes to load to main memory simultaneously.

Question 23

What is the method to edit a large file without opening it in UNIX?

Answer 23

The “sed” command is available for this process ‘.sed’ stands for a team editor.

Question 24

What is called piping?

Answer 24

“piping” is used to combine two or more commands together. The output of the first command work as the input of the second command, and so on. Pipe character ( | ) is represent piping.

Question 25

What is the process to count the number of characters and line in a file?

Answer 25

“wc – c filename” command can use to retrieve the number of characters in a file and “wc –l filename” command can use to retrieve the number of lines in a file.

Question 26

What do understand by Kernel?

Answer 26

Unix operating system is basically divided into three parts, namely, the kernel, the shell and the commands and utilities. Kernel serves as the heart of the Unix operating system which does not deal directly with the user but rather act as a separate interactive program for users logged in.

It performs the following functions:

a) Interacts with the hardware
b) Perform tasks like memory management, file management and task scheduling.
c) Control computer resources
d) Help allotting resources to different tasks and users.

Question 27

Describe responsibilities of Shell in brief.

Answer 27

Apart from analyzing the input line as well as initiating the execution of the program entered by the user, Shell also serves various responsibilities.

Find below a brief description:

a) The shell is responsible for the execution of all the programs by analyzing the line and determining the steps to be performed and then initiate the execution of the selected program.
b) Shell allows you to assign values to the variables when specified on the command line. It also performs Filename substitution.
c) To take care of input and output redirection.
d) Performs pipeline hook-up by connecting the standard output from the command preceding the ‘|’ to the standard input of the one following ‘|’.
e) Provides certain commands to customize and control environment.
f) Has its own built-in integrated programming language which is typically easier to debug and modify.

Question 28

What is the role of the superuser?

Answer 28

There are basically three types of accounts in Unix operating system:

Root account
System accounts
User accounts

‘Root account’ is basically referred to as a ‘Super user’. This user has completely open access or says control on all files and commands on a system. This user can also be assumed as a system administrator and thus has the ability to run any command without any restriction. It is protected by the root password.

Question 29

Explain alias mechanism.

Answer 29

To avoid typing long commands or to improve efficiency, the alias command is used to assign another name to a command. Basically, it acts as a shortcut to the larger commands which can be typed and run instead.

For creating an alias in Unix, following command format is used:

alias name=’command you want to run’

Here, replace the ‘name’ with your shortcut command and replace ‘command you want to run’ with the larger command of which you want to create an alias of.

For example:

alias dir ‘Is –sFC’

here, in the above example ‘dir’ is the another name for the command ‘Is-sFC’. Thus user now simply is required to remember and use the specified alias name and the command will perform the same task as to be performed by the long command.

Question 30

What do you understand by terms ‘system calls’ and ‘library functions’ with respect to UNIX command?

Answer 30

System calls: As the name implies, system calls are defined as an interface which basically is used in the kernel itself. Although, they may not be fully portable but these calls request the operating system to perform tasks on behalf of user programs.

The system calls appear as a normal C function. Whenever a system call is invoked within the operating system, the application program performs context switch from user space to kernel space.

Library functions: The set of common functions that are not part of the kernel but is used by the application programs are known as ‘Library functions’. As compared to system calls, library functions are portable and can perform certain tasks only in ‘kernel mode’. Also, it takes lesser time for execution as compared to the execution of system calls.

Question 31

What do know about tee command and its usage?

Answer 31

‘tee’ command is basically used in connection with pipes and filters.

This command basically performs two tasks:

a) Get data from standard input and send it to the standard output.
b) Redirects a copy of the input data to the specified file.

Question 32

Stack vs. Heap

Answer 32

The stack and the heap are two different regions of memory your program can access. The main difference is how they’re managed.

The Stack is memory that’s managed (to some degree) for you. When you declare a variable from within a function the memory for that variable is allocated from the stack. This allows the memory to automatically be returned (deallocated) when the function returns.

The heap is memory that is NOT managed for you**. When you malloc something (allocate memory block) you are taking a chunk of memory from the heap. It will last forever until you explicitly free it.

Important differences: each thread has its own stack, while the heap is available globally. The stack is also used for temporary variables, while the heap basically doesn’t unallocate unless you specifically do so (failing to do so is what memory leaks are, basically). The stack gets created and exited with its thread, the heap is allocated at application startup, and is reclaimed by the OS when the program exits.