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  1. What is Linux and also explain the basic components of Linux?

Answer: Linux is the most commonly used operating system that is open source and free. For any computer, the operating system acts as the backbone, and it is most important software that is required for any computer. From network routers, television, video games console, smartwatches, smartphones, desktops, laptops to any other electronic device, Linux is everywhere.

Linux operating system is consist of 3 components which are as below:

  • Kernel: Linux is a monolithic kernel that is free and open source software that is responsible for managing hardware resources for the users.
  • System Library: System Library plays a vital role because application programs access Kernels feature using system library.
  • System Utility: System Utility performs specific and individual level tasks.
  1. What are the differences between UNIX and Linux Operating System?

Answer: To understand the differences between UNIX and Linux Operating system, first of all, we should know that Linux is a UNIX clone, the Kernel of which is created by Linus Torvalds. There are so many differences between Linux and UNIX operating system which are as follows:

  • Open Source Operating System:

The most significant difference between UNIX and Linux operating system is Linux is an open source operating system. The open-source operating system that means Linux source code is available for use so that developers can modify it as per their requirement. But UNIX operating system doesn’t come under the broad category of an open-source operating system for which developers can edit it.

  • Free of Cost:

One of the biggest reason that it is broadly used is Linux operating system is free of cost. Linux operating system is free, but UNIX Operating system is not free. We can download it from the internet.

  • Compatibility and Flexibility:

If we compare the flexibility and compatibility of both operating system, you will find that Linux is more flexible than UNIX operating system and more compatible with different types of hardware as compared to UNIX operating System.

  1. Describe BASH.

Answer: BASH stands for Bourne Again Shell. BASH is the UNIX shell for the GNU operating system. So, BASH is the command language interpreter that helps you to enter your input, and thus you can retrieve information. In a straightforward language, we can say that it is a program that will understand the data entered by the user and execute the command and gives output.

  1. What is crontab and explain its functionality and explain the format of crontab?

Answer: Cron is a scheduler that executes the commands at a regular interval as per the specific date and time defined. We have multiple users in Linux, and all the users can have their crontab separately. The crontabs files are saved at a particular location that is /var/spool/cron/crontabs.

There are six fields in the format for the crontab that is as below:

<Minute><Hour><Day_of_the_Month><Month_of_the_Year><Day_of_the_Week><command/program to execute>

  1. What do you understand by CLI?

Answer: CLI is an acronym for Command Line Interface. We have to provide the information to the computer so that it can perform the function accordingly. In Linux, CLI is the interface that provides the user an interface so that user can type the commands and it complete the tasks. CLI is very easy to use, but it should be typed very precisely.

  1. Explain Network Bonding and also explain the different types of Network bonding?

Answer: Network Bonding as the name implies that it is the process of bonding or joining two or more than two network interfaces to create one interface. It helps in improving the network throughput, bandwidth, redundancy, load balancing as in case any of the interfaces is down; the other one will continue to work. Several types of Network Bonding are available that are based on the kind of bonding method.

Below are the different bonding types in Linux:

  • balance-rr or mode 0 –This is the default mode of network bonding that works on the round-robin policy that means from the first slave to the last, and it is used for fault tolerance and load balancing.
  • active-backup or mode 1 –This type of network bonding works on the active-backup policy that means only one slave will be active and other will work just when another slave fails. This mode is also used for fault tolerance.
  • balance-xor or mode 2 –This type of network bonding sets an exclusive or mode that means source MAC address is XOR’d with the destination address, and thus it provides fault tolerance and load balancing.
  • broadcast or mode 3 –This mode sets a broadcast mode to provide fault tolerance, and it should be used for particular purposes. In this type of network bonding, all transmissions are sent to all slave interfaces.
  • 3ad or mode 4 –This mode will create the aggregation groups, and all the groups will share the same speed. For this, mode sets an IEEE 802.3ad dynamic link aggregation mode. It is done by particular switch support that supports IEEE 802.3ad dynamic link.
  • balance-tlb or mode 5 –This mode sets a transmit load balancing mode for fault tolerance and load balancing and does not require any switch support.
  • balance-alb or mode 6 –This mode sets an active load balancing to achieve fault tolerance and load balancing.
  1. What is the similarity and difference between cron and anacron? Which one would you prefer to use?

Answer: Here we are going to discuss the similarity and the differences between cron and anacron. So, let’s start with the analogy:

Cron and Anacron are used to schedule the tasks in cron jobs. Both of these are the daemons that are used to schedule the execution of commands or tasks as per the information provided by the user.

Differences between cron and anacron:

  1. One of the main difference between cron and anacron jobs is that cron works on the system that are running continuously that means it is designed for the system that is running24*7. While anacron is used for the systems that are not running continuously.
  2. Other difference between the two is cron jobs can run every minute, but anacron jobs can be run only once a day.
  3. Any normal user can do the scheduling of cron jobs, but the scheduling of anacron jobs can be done by the superuser only.
  4. Cron should be used when you need to execute the job at a specific time as per the given time in cron, but anacron should be used in when there is no any restriction for the timing and can be executed at any time.
  5. If we think about which one is ideal for servers or desktops, then cron should be used for servers while anacron should be used for desktops or laptops.
  6. What is the issue behind getting an error “filesystem is full” while there is space available when you check it through “df” command? How will you rectify this problem?

Answer: When all the inodes are consumed then even though you have free space, you will get the error that filesystem is full. So, to check whether there is space available, we have to use the command df –i.  Sometimes, it may happen file system or storage unit contains the substantial number of small files, and each of the files takes 128 bytes of the inode structure then inode structure fills up, and we will not be able to copy any more file to the disk. So, to rectify the problem, you need to free the space in inode storage, and you will be able to save more files.

  1. Where is password file located in Linux and how can you improve the security of password file?

Answer: This is an important question that is generally asked by the interviewers. User information along with the passwords in Linux is stored in/etc/passwd that is a compatible format. But this file is used to get the user information by several tools. Here, security is at risk. So, we have to make it secured.

To improve the security of the password file, instead of using a compatible format we can use shadow password format. So, in shadow password format, the password will be stored as single “x” character which is not the same file (/etc/passwd). This information is stored in another file instead with a file name /etc/shadow. So, to enhance the security, the file is made word readable and also, this file is readable only by the root user. Thus security risks are overcome to a great extent by using the shadow password format.

  1. What is Key-based authentication? Explain.

Answer: There are various methods to enter into the servers. One of the ways to log in is using password-based authentication, but that is not secure. So, we need a method that is secured.

One of the ways to achieve the security is to use Key-based authentication. To use this type of authentication, we have to disable the password-based authentication.