Linux System Administrator Interview Questions and Answers

This Article Focus On Interview Questions You Will Be Asked When You apply For the Job Post of Linux System Administrator. Basic To Advance Questions Will be Included, So This will be helpful for Both Freshers and Experienced Administrators.
These Question and Answers Focus on Following Sections.

  • Basic Commands.
  • Advance Commands.
  • Networking.
  • Mail,FTP and Web Servers.
  • Server Monitoring.
  • Software Installation.
  • Update and Maintaining Linux Environment.

What is pwd command?

pwd command in Linux use to print current working when working on Command Line Interface. pwd stands for print working directory.

What command is used to monitor status of a Linux server in real time?

Top Command is the most frequently use Linux monitoring tool and available on every Linux distributions. Alternatively, you can also use htop which is an enhanced version of the top command. But HTOP is not installed by default in most Linux distributions.

View This tutorial to learn how to install htop on Centos7.

How to list Open Ports on a Linux Computer?

netstat command uses to list open ports in Linux. Following Command line Options mostly use with the netstat command.

t – List TCP Ports

u – List UDP Ports

l – Show only listening sockets

n – Numeric

p – Display Process ID

You Can use netstat command as follows

netstat -tulnp

How many Runlevels are available in Linux Operating System?

There is Seven Runlevels, 0 to 6. Following is the list of Runlevels

0 - Halt

1 - Single user mode

2 - Multiuser, without Networking

3 - Full multiuser mode with Networking

4 - Unused

5 - Graphical User Mode

6 - Reboot

Which Linux Runlevel Provides Graphical Desktop?

Graphical User Interface or the Desktop Available in Runlevel 5. This is a Standard for Every Distributions.

Which Command use to Change between Runlevels in Real Time?

telinit command uses to switch between different Runlevels while the Computer is still running. but telinit command does not change the default runlevel.

How to Connect To a Linux Server From a Remote Computer?

SSH Protocol uses to connect to a Linux Server From a another computer. If You are Trying to Connect From a Windows PC You Can use an SSH Client like Putty or Xshell. Linux Desktop Users Can use the ssh command in the Terminal.

What is the default SSH Port Number?

SSH Protocol Use Default Port Number 22 . This Can Be Changed By Editing the value of the Port parameter in the main ssh configuration file.

What is the default FTP Port Number?

FTP Protocol Use TCP Port 21 By default.

How to Configure Linux Computer as a FTP Server.

By Installing FTP server like vsftpd and pure-ftpd, we can configure linux machine as a ftp server. Following are the most Common FTP Demons used in Linux

  • VsFTPD
  • Pure-FTPD
  • ProFTPD

What is POP3?

POP3 is a TCP Protocol used to retrieve(Download) mails from a mail server. By Default POP3 Protocol Download email to the client computer and mails will be deleted from the server.

What is IMAP?

IMAP Stands for Internet Message Access Protocol. Just like POP3 IMAP also use to Download Mail From Server To Client. But IMAP Keeps the Original Message On The server, while keeping a cache on the Client Computer.