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Linux OS Interview Questions

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Linux supports to work with sending mails using a set of commands called as mail commands. The command to send email is ‘mail’. The ‘mail’ command is used to send and receive emails.

mail [options] [users]
Options are: -s,-c,-b
Where –s for subject, -c for copy and –b for blind carbon copy

Ex: mail username –s “Reports are needed”

It prompts displays the subject as “Reports are needed”.
Similarly if –c and –b is given the mail will be sent to the corresponding recipients.

RPM is a powerful software management tool for installing, uninstalling, verifying, querying and updating software packages. RPM is a straight forward program to perform the above software management tasks. It is available with Fedora, Suse, CentOS, Mandriva Linux and other version of Linux.

Kernel is used in UNIX like systems and is considered to be the heart of the operating system. It is responsible for communication between hardware and software components. It is primarily used for managing the systems resources as well.

Kernel Activities:

The Kernel task manager allows tasks to run concurrently.
Managing the computer resources: Kernel allows the other programs to run and use the resources. Resources include i/o devices, CPU, memory.
Kernel is responsible for Process management. It allows multiple processes to run simultaneously allowing user to multitask.
Kernel has an access to the systems memory and allows the processes to access the memory when required.
Processes may also need to access the devices attached to the system. Kernel assists the processes in doing so.
For the processes to access and make use of these services, system calls are used. 


Linux shell is a user interface used for executing the commands. Shell is a program the user uses for executing the commands. In UNIX, any program can be the users shell. Shell categories in Linux are:

Bourne shell compatible, C shell compatible, nontraditional, and historical.

A shell script, as the name suggests, is a script written for the shell. Script here means a programming language used to control the application. The shell script allows different commands entered in the shell to be executed. Shell script is easy to debug, quicker as compared to writing big programs. However the execution speed is slow because it launches a new process for every shell command executed. Examples of commands are cp, cn, cd. 


Linux shell is the user interface to communicate with Linux operating system. Shell interprets the user requests, executes them. Shell may use kernel to execute certain programs. Shell Script: A shell script is a program file in which certain Linux commands are placed to execute one after another. A shell script is a flat text file. Shell scripts are useful to accept inputs and provide output to the user. Everyday automation process can be simplified by a shell script.

A pipe is a chain of processes so that output of one process (stdout) is fed an input (stdin) to another. UNIX shell has a special syntax for creation of pipelines. The commands are written in sequence separated by |. Different filters are used for Pipes like AWK, GREP.

e.g. sort file | lpr ( sort the file and send it to printer)

Uses of Pipe

  • Several powerful functions can be in a single statement
  • Streams of processes can be redirected to user specified locations using 

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