KVM Interview Questions & Answers

Question 1. What Is The Use Of Kvm Switch?

Answer :

KVM switch allows user to take control of two or more computers using the resources that are shared like mouse, keyboard, monitor, etc. This allows the administrator to access multiple servers from a single place. Administrator can access fileserver or internal server or proxy server and can separate out these servers from each other. This gives the freedom to administrator to use the components anywhere and make it efficient.

Question 2. How Does Kvm Fit In With Cloud?

Answer :

• Virtualization is overwhelmingly used for cloud computing, and open virtualization enables open clouds. KVM is an open proven, enterprise-ready virtualization technology that helps enable interoperability and portability so customers can avoid vendor lock-in.
• But, as cloud computing becomes more accepted, the focus is also shifting to cost containment, making KVM a desirable addition to data center environments. For cloud service providers in particular, cost efficiency is important so that they can provide services at reasonable prices. Important advances have also been made in management solutions that enable KVM to be controlled alongside other virtualization technologies like VMware. For example, IBM Systems Director VMControl enables the management of virtual environments across multiple virtualization technologies and hardware platforms.

Question 3. Why Kvm And Not Xen ?

Answer :

• Xen is an external hypervisor; it assumes control of the machine and divides resources among guests. On the other hand, KVM is part of Linux and uses the regular Linux scheduler and memory management. This means that KVM is much smaller and simpler to use; it is also more featureful; for example KVM can swap guests to disk in order to free RAM.
• KVM only run on processors that supports x86 hvm (vt/svm instructions set) whereas Xen also allows running modified operating systems on non-hvm x86 processors using a technique called paravirtualization. KVM does not support paravirtualization for CPU but may support paravirtualization for device drivers to improve I/O performance.

Question 4. What Is The Requirement Of Kvm Switch?

Answer :

KVM switch is required to access more than one server from one place. The requirements of different switches differ from one institute to another. There are switches that give no protection but provide higher efficiency. Some switch offer the password to protect the switch. The password helps in locking the switch so that more security can be given. The switches provide protection to the user so that the data can be kept safe.

Question 5. What Is The Difference Between Passive And Active Switches?

Answer :

• Passive switch doesn't have any active components and it is a hard wired connection whereas, active switches are used to retain the actions performed by hardware devices that are connected during switching process.
• Passive switches are wired internally between Input/Output ports whereas, active switches uses the computers connection for their connections they don't rely on external or internal wires.
• Passive switches are simple and cheap whereas, active switches are a bit expensive in terms of its application and it requires separate power supplies.

Question 6. What Are The Various Uses Of Kvm?

Answer :

KVM acts as a virtualization platform that is required by machines to run other operating system in synchronization with host operating system. It is an inbuilt virtualization platform that comes with Linux kernel. It is used for non-graphic servers and supports wide range of operating system to run with. It runs along with QEMU to provide strong virtualization platform.

Question 7. What Are The Different Formats Supported By Kvm?

Answer :

KVM supports various formats in synchronization with QEMU as it supports many raw images, native QEMU format of qcow2, VMWare format like .vmx, .vmdk, etc. VirtualBox format like .vbx, etc. and many more. QEMU and KVM together give the advanced functionality to run virtualized servers and platforms.

• Manual Testing
• SAP ABAP
• SAP HANA
• SAP HANA
• Mantis Bug Tracker
• QlikView
• Hadoop
• SQL
• Linux Administration
• Tableau.

Question 8. How Can I Use Kvm With A Non-privileged User?

Answer :

To use KVM as a non-privileged user firs the creation of a group has to take place in which addition of the users takes places and then making their group. The file that has to be modified for the groups and by which the permissions can be set resides in /dev/kvm that has to be changed to give permissions to non-privileged users. To set the permission the following line has to be added or replaced in the file mentioned above.

KERNEL=="kvm", GROUP= "kvm"

Question 9. How To Check The Hardware Acceleration Provided By Kvm?

Answer :

KVM module provides hardware acceleration for better performance and to provide better efficiency in between the virtual machines.

To check the hardware acceleration checks the system configuration settings by using the following commands:

1 qemu-system-x86_64 -hda myvm.qcow2

If it gives any error message or module not find message then the modules are not loaded correctly.

Question 10. What Is The Procedure To Set Up Network For Guest To Make It Accessible From Host Machine?

Answer :

KVM known as kernel virtual machine uses QEMU for device emulation. In this there are two networking modes that are defined. First mode is root networking mode and another mode is network bridge mode. If the IP address to the virtual machines has to be assigned then the kvm need to be up and running.

To setup the network interface across the host machine the command that is required to be followed is as follows:

/sbin/ip

/usr/sbin/brctl

/usr/sbin/tunctl

Question 11. What Is The Difference Between Kvm And Xen?

Answer :

• KVM is an internal part of the linux kernel module and uses regular memory and scheduler like linux, whereas Xen is an external hypervisor that takes the control and divides the resources between the guest machines.
• KVM is easy to use and provide more features, whereas Xen is powerful but it requires good amount of knowledge to operate.
• KVM runs on processors that support hvm, whereas Xen runs non-hvm compatible processors.
• KVM doesn't have any support for para-virtualization, whereas Xen supports para-virtualization that is used for device drivers to improve the performance of input/output.

Question 12. How To Identify The Kvm Version ?

Answer :

To find the KVM version use the command ‘virsh version’

Question 13. Which Command Is Used To List All Virtual Machine Running On The Kvm Hypervisor ?

Answer :

Using the command ‘virsh list –all’ we can list all virtual machines irrespective of their states.

Question 14. How Kvm Does Support Dynamic Memory Management?

Answer :

KVM allows the resources to be shared to the guest operating systems. KVM allocates the memory dynamically between many processes. KVM allows the host to allocate the memory for the guest and beyond it guest can't use memory. The guest system that has a balloon driver keeps the guest from taking full memory. This ballooning is controlled by balloon monitor. KVM allows the pages that are similar to be grouped or collapse together in one to save the space this way the dynamic memory management can be performed by KVM.

• Manual Testing
• SAP ABAP
• SAP HANA
• SAP HANA
• Mantis Bug Tracker
• QlikView
• Hadoop
• SQL
• Linux Administration
• Tableau

Question 15. How To Forcefully Shutdown The Kvm Based Virtual Machine From The Command Line ?

Answer :

We can forcefully shutdown the VM using the command ‘virsh destroy machine_name’.This command should only be used in a case where VM is in Hung state because forcefully shutdowm may cause filesystem corruption.

Question 16. What Is Libvirt And Why It's Useful ?

Answer :

• Libvirt is collection of software that provides a convenient way to manage virtual machines and other virtualization functionality, such as storage and network interface management. These software pieces include an API library, a daemon (libvirtd), and a command line utility (virsh).
• A primary goal of libvirt is to provide a single way to manage multiple different virtualization providers/hypervisors. For example, the command 'virsh list --all' can be used to list the existing virtual machines for any supported hypervisor (KVM, Xen, VMWare ESX, etc.) No need to learn the hypervisor specific tools.

Question 17. Explain Libvert Features?

Answer :

VM management: Various domain lifecycle operations such as start, stop, pause, save, restore, and migrate. Hotplug operations for many device types including disk and network interfaces, memory, and cpus.

Remote machine support: All libvirt functionality is accessible on any machine running the libvirt daemon, including remote machines. A variety of network transports are supported for connecting remotely, with the simplest being SSH, which requires no extra explicit configuration. If example.com is running libvirtd and SSH access is allowed, the following command will provide access to all virsh commands on the remote host for qemu/kvm:

1 [root@host]# virsh --connect qemu+ssh://root@example.com/system

Storage management: Any host running the libvirt daemon can be used to manage various types of storage: create file images of various formats (qcow2, vmdk, raw, ...), mount NFS shares, enumerate existing LVM volume groups, create new LVM volume groups and logical volumes, partition raw disk devices, mount iSCSI shares, and much more. Since libvirt works remotely as well, all these options are available for remote hosts as well.

Network interface management: Any host running the libvirt daemon can be used to manage physical and logical network interfaces. Enumerate existing interfaces, as well as configure (and create) interfaces, bridges, vlans, and bond devices. This is with the help of netcf.

Virtual NAT and Route based networking: Any host running the libvirt daemon can manage and create virtual networks. Libvirt virtual networks use firewall rules to act as a router, providing VMs transparent access to the host machines network.

Question 18. What Are The Basic Requirements Of Vm Live Migration In Kvm ?

Answer :

Some of the basic requirements are listed below :

• The guest image or virtual machine image must be located on a shared storage and it must be accessible using iSCSI, NFS, GFS2 or Fibre Channel.
• The shared storage must be mounted on the same path on both the hypervisors / hosts.
• Both hypervisors / hosts must run the same version of KVM.
• Both guests or VMs must have the same network configuration & bridging configuration (their IPs must be different)

Question 19. How Can We Do The Live Kvm Migration?

Answer :

A guest can be migrated to another host with the virsh command.

First make sure that the gust is running by running:

1 [root@host]# virsh list

To migrate the host execute:

[root@host]# virsh migrate --live testbox 

    qemu+ssh://remotelinuxbox/system

This will keep all the connections to the migrated host alive after the migration with no perceived outage.

Question 20. How To Get Hardware Information Of Kvm Guest Machine ?

Answer :

Use the command ‘virsh dominfo ’

Question 21. What Are Kvm Switches?

Answer :

Depending on the variants applied, you can use KVM switches – KVM is short for keyboard, video, mouse – to operate up to 64 computers from your workstation. This workstation, sometimes also called console, consists of keyboard, monitor and mouse that are directly connected to the KVM switch. So far, so good.

Question 22. How Do Kvm Switches Work?

Answer :

KVM switches establish a connection between the signals of keyboard, monitor and mouse and the selected computer. Whenever you use the switch to switch to another computer, keyboard and mouse are provided at said computer.

There are different ways of accessing computers:

• Buttons on the device
• Definable hotkeys
• Middle mouse key
• OSD menus (on-screen display)

Most KVM switches support any of these ways of switching between computers.

Question 23. Which Signals Do Kvm Switches Switch?

Answer :

KVM switches switch one or several of the following signals:

• Single- and dual-link DVI/VGA (some KVM switches support mixed operation)
• PS/2 and USB keyboard/mouse
• transparent USB 2.0
• Audio
• RS232

Question 24. What Are The Differences Between Kvm Switches?

Answer :

• At some KVM switches like G&D’s TradeSwitch, video signals don’t run through the switch. The console monitors are directly connected to the computers and display their images permanently. With the switch and CrossDisplay-Switching, you can access the connected computers by mouse. By moving the cursor from one monitor to another, keyboard and mouse automatically switch to the computer connected to the selected monitor.
•  Multichannel variants of KVM switches let you switch up to 4 × DVI/VGA, keyboard/mouse, USB 2.0 and audio per computer. The MC4 variant of miniMUX KVM switches provides ports for four computers with four graphics outputs each. Meaning that instead of 16 monitors that would be required to show the screen contents without employing a switch, the data of all computers is shown on four monitors. This doesn’t only save hardware but energy costs as well.
• Multichannel KVM switches are often used to monitor many processes at the same time. When employing the devices at the stock exchange, for example, three monitors can display the courses from different markets while the fourth is used to show the e-mail program or any other application.
• In short:
• Workstations without KVM switch: many devices, high energy costs, high hardware costs, cluttered
• Workstations with KVM switch: fewer devices, less costs, clearly arranged.

Question 25. What Advantages Does Employing Kvm Switches Have?

Answer :

As shortly mentioned before, employing KVM switches has many advantages. Its not only the reduced costs for hardware that play an important role. Even the environment benefits from employing fewer devices.

And here are even more advantages:

• Easy, central administration of computers in the server room
• More space in the server room through less additional hardware (mouse, keyboard, monitor)
• Reduced energy costs thanks to fewer monitors
• Clearly arranged server racks provide better overview of computers
• No additional software required
• Protection against unauthorized access when computers are placed in access-protected server rooms.