Interview Questions.

Question 1. What Is The Function Of Qemu?

Answer :

Qemu is a virtualization platform utility that works as an emulator that emulates an existing gadget to run multiple operating device collectively on the identical time. It has its personal configuration and it is easy to install and use. It is used to emulate many subsystems like hardware and softwares. It emulates the processors as properly like multiprocessing systems.

Question 2. What Are The Different Modes Of Operations Performed By Qemu?

Answer :

Qemu has  modes of operations and they're as follows:

User mode emulation: this allow the procedure execution from one CPU to any other CPU. It performs dynamic translation of instructions for host CPU. 
System mode emulation: this permit the emulation of the entire gadget that includes hardware in addition to peripheral related components.
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Question 3. What Is The Function Of Dynamic Translator In Context With The Qemu?

Answer :

Dynamic translator interprets the commands this is being given by using the guest system to the host gadget language. It interprets the commands at runtime to offer the emulation between the host CPU and guest CPU. To translate the commands it maps the instructions that are handed from one CPU to another CPU. In this case there remains usually the possibility that the behavior or additional commands might be required through the architecture for translations.

Question four. What Is The Function Of Qemu Accelerator?

Answer :

To obtain high overall performance and the usage of QEMU emulation surroundings there may be a demand to apply QEMU accelerator that allows the execution of emulated codes and the libraries attached to it immediately at the host CPU the usage of the kernel module. It speeds up the interpretation of commands from one CPU to another CPU with out delaying the output to the person.

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Question 5. How Can You Achieve Dynamic Translation Using Qemu?

Answer :

Dynamic translation can be achieved by way of first changing the goal into micro-operations. Micro-operations in this situation are within the form of C code that receives compiled into gadgets. A middle translator is needed that maps the target instructions into micro-operations commands. It is an effective and transportable way to achieve translation using Qemu. It gets rid of the overhead by caching the translated code. It supports self change by making the translated block invalidate in cache.

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Question 6. What Are The Supported Peripherals Used By Qemu?

Answer :

QEMU presents an extended range of peripheral help for example:

Hardware video pictures array emulator
Mouse and key-word help
Hard disk
CD-ROM interface
floppy disk emulation.
PCI network adapter
Serial ports
PCI generic Host controller Interface
Question 7. What Is The Use Of The Command Qemu-img?

Answer :

Qemu as an emulator allow the person to experience the virtualization on their device without the want to install a OS one at a time. Qemu affords qemu-img command to create the hard disk. This command is used to create pics of numerous formats like qcow (QEMU replica-on-write). This layout permits the dimensions of the disk picture is different from the file this is physically present. It creates a compact picture such that the dimensions decreases and the photograph that gets produced is compressed to make it protable. 

For instance: to create a disk picture of 128 MB the following code may be written.

Qemu-img create -f qcow disk.Img 128MB

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Question eight. How To Setup Tap Network Using Qemu?

Answer :

QEMU runs on consumer mode network this is being setup between host and visitor running structures. QEMU affords the emulation to manipulate the network interface internally and for the application as nicely. It gives a manner to manage DHCP host IPs that assigns the IP dynamically to the visitor OS. The protocols which can be was once redirected from host to visitor OS is executed by TCP and UDP. TCP and UDP are the most effective connections that are present through default. To setup TAP networking, first the connection with the visitor OS needs to be set up through the usage of Ethernet connection related to the host OS this is the use of TAP network bridge. The script this is referred to as by using qemu for community configuration is /and so forth/qemu-ifup script, this script sets up the bridge network.

Question 9. How Qemu Speeds Up The Performance Of The System?

Answer :

QEMU increases the speed and overall performance by using the dynamic translators and virtualization method that is getting used on exclusive running device. It provides excessive performance with the aid of executing the visitor code immediately at the host CPU. It gives high performance while executing under the Xen hypervisor or KVM.

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Question 10. How Qemu Uses Hardware Virtualization Extensions?

Answer :

QEMU is inside the process of making a kernel based totally digital device that makes use of modified QEMU to offer the extensions for extraordinary technologies. The  maximum processors that are used are Intel and AMD-V processors for which QEMU is creating this extensions. VT (virtualization technology) is disabled by means of BIOS by using default however it can be enabled from BIOS menu to turn on all the functionalities of QEMU.

Question eleven. Where Can I Find The Configuration If Tuntap Network Mode Is Being Set By Qemu?

Answer :

The area in which you may locate tuntap network mode configuration settings is /dev/tap0 or within the fle /dev/internet/tap0. The tuntap community mode can be seen by way of the use of the command ifconfig -a. For tuntap mode to exist QEMU should be running and whilst it shuts down then the devices which can be attached to it automatically receives close down. During close down it removes the tuntap devices as well.

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Question 12. What Is The Purpose Of Using Tun0 Instead Of Tap0 In Qemu?

Answer :

QEMU uses a faucet device handiest the tun0 call that is being given permits the user to connect within the networking. The kernel of the device create a tap tool named as tun0 and a tap device with call tap0. It just makes use of the name to differentiate its own configuration but it makes use of faucet device only for networking methods. It uses Ethernet frames for the configuration to be stored.

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Question thirteen. What Is The Process Of Setup Up Tuntap Network Mode Without Using Vde?

Answer :

To setup tuntap networking mode it calls for the implication of tap networking device on the host device. It presents right overall performance usual and can be configured to create digital community topology. At the equal time, it requires high cease configuration of the network topology in host that has a tendency to vary from one running device to some other operating gadget. 

The command that lets in it to run faucet networking mode is

netdev tap
To trade the community configuration for the person it calls for
netdev kind=person
The device alternative within the command is used to plug within the specific network device like
netdeve type=person, id=mynet0 -tool e2000, netdev= mynet0
Question 14. How To Connect Many Vlan To Tap Devices Using Qemu?

Answer :

To join VLANs to tap devices the requirement is of vlan that need to be to be had inside the host operating system. Any body that appears in this tool can be connected using the QEMU system. This procedure request is obtained by means of some other interfaces on VLAN and then frames are acquired by means of device. 

The command this is used to configure the networking mode:

qemu -net nic -net faucet,ifname=qtap0 …

QEMU needs tuntap device motive force that allow the person-space utility to gain specific record discriptors which might be linked to a network tool. The faucet gadgets can be visible through going to the listing file /dev/net/tun in any other case calling the function TUNSETIFF ioctl() this is allowed simplest to the person who're privileged.

Question 15. How To Make Bridging Possible In Qemu?

Answer :

To construct bridges in QEMU the configuration documents has to be modified and the firewall has to be set up such that it doesn't intrude in between the system. If firewall creates hassle then there's a possibility of loosing the network connection to QEMU virtual machines. So, to enable the firewall to all the site visitors to the servers configure the IP addresses via the usage of the command like:

allow incoming packets for qemu
IPTABLES -A FORWARD -d $IPADDR_FROM_CLIENT_OS -j ACCEPT
permit outgoing packets from qemu
IPTABLES -A FORWARD -s $IPADDR_FROM_CLIENT_OS -j ACCEPT
These instructions will take care of the firewall settings and will assist in permitting the visitors to flow to the digital machine's IP address. To add a range add the network address and netmask in the configuration report.

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