Unix Interview Questions and Answers
Unix is a stable and secure operating system that is capable of handling commands from multiple users at the same time. The innermost level of the Unix environment, Kernel coordinates the computer internals and allocates all the resources. Users can communicate with the kernel through a program known as a shell, which translates commands written by the user into a language that the kernel can interpret. Want to clear interviews in one shot? Read our Unix interview questions.
Advantages of Unix
- Each big task can be split into simple commands and utilities
- Can be used on a variety of machines
- Can run many programs with less physical memory consumption
- Multiple users can perform various tasks at the same time without interfering with each other’s work. Each user’s work is protected.
- Cleanly defined permissions and access for each user for each file.
Most Frequently Asked Unix Interview Questions
You can use the following commands to compare two files –
- cmp [options] file1 file2 – compare 2 files character by character
- comm [options] file1 file2 – compare sorted files
- diff [options] file1 file2 – compare two files line by line
Type the command jobs to see the processes running in the background.
Example – $ jobs give the output as –
[134]+ Running sleep 50 &
where 134 is the job number.
Use the command kill along with the process id (PID) to kill a process.
Example – kill 12323
If this does not destroy the process, add the signal number for a kill to kill the process. Unix cannot ignore the signal number.
Example – kill -9 12323
Continue reading Unix interview questions to know how you can stop an infinite loop using the same command
Shell is a program that gives us an interface between the Unix OS kernel and user. By this interfacing, the user can execute utilities and applications using the shell. Each user gets a unique shell when he logs in or opens a console. The different shells are Bourne shell (sh), C shell (csh), the Korn shell (ksh), GNU Bourne-Again Shell (bash).
| S.no | ABSOLUTE PATH | RELATIVE PATH |
|---|---|---|
| 1. | the full path starting at the root directory (/). | Path in relation to the present working directory as the reference. |
| 2. | Example - /home/math/tutorial | Access the current directory using the command ‘pwd’. Change the directory using ‘cd’. |
Some system variables set in Unix by default are HOME, USER, HOST, DISPLAY, and PATH. These can be environment variables or local variables enabled by the shell.
- Pipes – a pipe connects small commands together to execute a complete complex task. Pipe symbol is ‘|.’ The flow of data through the pipe is from left to right. Example – $ cat names.txt | grep “Sam” | tee sam.txt | wc -1
- Filter – Filters are used to modify the output of a command. Examples of filters are grep, sort, more, less, cat, cut and so on.
To find the path, use the command – echo $PATH
Use the ‘su’ command to switch between users in Unix.
Syntax – su [options] [username]
You can check logs in the file syslog located in /etc/syslog.conf
In our list of Unix interview questions, we have covered all the essential aspects of Unix. Read on to know more.
Development History
Unix was developed at AT&T Bell Labs by Ken Thompson and Dennis Ritchie in 1979. The first portable version of Unix was V7. Check out our Unix interview questions list to understand how Unix processes command written by the user.
Latest version
The latest version of Unix is 4.20.8 released on 12 February 2019.