Linux Interview Questions and Answers

An open-source operating system, Linux is currently one of the best OSs. It can be considered as software that sits underneath and communicates with the other software on a computer and passes on requests from those software programs to the hardware.

Linux is used because it is –

• Highly stable and secure
• Can be maintained easily
• Can run on any hardware system
• Open source and free to use
• Extensive documentation and support

If a Linux server runs out of memory, the kernel moves some inactive processes from Linux server to a disk that acts as the virtual memory. This disk space is called a Swap.

• Multi-tasking is possible without slowing down CPU.
• Offers high security compared to other OSs like Windows, iOS, etc.
• Can be converted from the command line to GUI by installing required packages.
• Open source code with great community and support.
• Can run on different hardware types.
• Hierarchical file system.

Read details about the security features of Linux in the next question of our Linux Interview questions list.

There are multiple reasons for this –

• Linux gives very low access to its users. If there is a virus attack, only a few files will be corrupted not the whole system.
• It is less vulnerable because a user needs complete execution rights for opening even an email attachment.
• The working environment in Linux is segmented in different environments like Ubuntu, Arch, Linux Mint, etc. This division gives much protection from the virus.
• Linux uses Iptables which requires advanced privileges to function.

Linux has a layered structure –

• Hardware - the CPU, RAM, mouse, the keyboard is the hardware
• Kernel - contains device drivers and handles resource allocation, acts as an interface between the hardware and the operating system.
• The standard library of procedures – termed as libc, allows the user to communicate with the kernel.
• User applications and standard utilities – the commands for various tasks like computing, modifying files or taking backups, etc.

The core components of Linux are boot loader, kernel, shell, Daemons, window manager and X window server.

Virtual desktop provides secure access to Linux VDI even from non-Linux devices like Windows. This helps admins manage Windows and Linux applications using one console.

You can use the key combination Ctrl+Alt+T to open a command prompt in Linux.

• Open the command prompt using Ctrl+Alt+T
• If your file does not have to execute permission, add the same chmod +x /root/home/your file.sh
• Run the script by typing /root/home/your file.sh and press enter.

Use df [options] [devices] to check hard drive space.

Example –

df -h /test/tmp gives output as

It is an environment variable that contains a list of paths that are used to resolve the library dependencies at run-time (dynamic libraries). This path is checked before the standard paths /lib or /usr/lib.

Idconfig is a command that creates the required links and cache to the most recently shared libraries that are present in the directories specified in the

• command line,
• the file /etc/ld.so.conf,
• the trusted directories /lib and /usr/lib

Graphical User Interface or GUI makes it easier for a Linux user to execute programs via a desktop, similar to Windows. The desktops in Linux are KDE, Java, GNOME.

Puppet is a Configuration Management tool. It is used to

• Deploy, configure and manage servers,
• Define and monitor unique configurations for each host
• Scale-up and scale-down machines dynamically
• Provide control over configured devices to propagate changes in a centralized manner

For enhanced security, a shadow copy of the password file is made, which stores hashed passwords of all the users. The hashed password is a long string of characters, generated based on the hashing method used.

Read further for more questions on security in our list of Linux interview questions.

Symbolic link :-

• links the libraries
• ensures that the files are in their place without the original being copied or moved.

A program that gets executed in the background because of the occurrence of a specific event, process or condition. Daemon processes are managed by the Kernel. The operations are given unique PIDs.

• Ifconfig – configure interface parameters of the network.
• dig – performs DNS lookups to display a result obtained from name servers.
• traceroute – prints the route that the packets take to the network host.
• nslookup – queries internet domain name servers.
• telnet – connect destination port if the connection between hosts is working fine
• netstat – reviews each network connection and the open sockets.
• w – writes (prints) current activities and processes by each user.
• scp – secure copy the files from and to another host in the network.
• ifup/ifdown – enable or disable the network interface respectively.
• nmap – checks for the opened port on the server

Use chmod 777 to give full permission to reading, write and execute.

There are three modes – command mode, insert mode and last line or escape mode.

Use the command apt-get as –

        apt-get --purge remove [filename]

There are 80 system calls in Unix that are used to control processes, manage filesystem and for inter-process communication. System calls occur in the kernel.

For this access the individual command’s manual page. For instance, to know the description of

     cat command, type

man cat

This will display a description of the said command.

There are 7 types of network bond in Linux – mode=0 (balance-rr), mode-1 (active-backup),

       mode=2 (balance-xor), mode=3 (broadcast), mode=4 (802.3ad), mode=5 (balance-tlb),

       mode=6 (balance-alb)

You can kill the process using –

• kill PID – It is used to kill a particular process.
• killall – It is also used to kill all the running processes.