LPI 305-300 Dumps Questions Answers

 Libvirt is a toolkit that provides a common API for managing different virtualization technologies, such as KVM, Xen, LXC, and others. Libvirt allows users to configure and control various aspects of a virtual machine (also called a domain), such as its CPU, memory, disk, network, and other resources. Among the resources that can be limited by libvirt for a KVM domain are:

Amount of CPU time: Libvirt allows users to specify the number of virtual CPUs (vCPUs) that a domain can use, as well as the CPU mode, model, topology, and tuning parameters. Users can also set the CPU shares, quota, and period to control the relative or absolute amount of CPU time that a domain can consume. Additionally, users can pin vCPUs to physical CPUs or NUMA nodes to improve performance and isolation. These settings can be configured in the domain XML file under the  and  elements12.

Size of available memory: Libvirt allows users to specify the amount of memory that a domain can use, as well as the memory backing, tuning, and NUMA node parameters. Users can also set the memory hard and soft limits, swap hard limit, and minimum guarantee to control the memory allocation and reclaim policies for a domain. These settings can be configured in the domain XML file under the , , and  elements13.

The other resources listed in the question are not directly limited by libvirt for a KVM domain. File systems allowed in the domain are determined by the disk and filesystem devices that are attached to the domain, which can be configured in the domain XML file under the  and  elements14. Number of running processes and number of available files are determined by the operating system and the file system of the domain, which are not controlled by libvirt.

References:

libvirt: Domain XML format

CPU Allocation

Memory Allocation

Hard drives, floppy disks, CDROMs

A hypervisor is a software that creates and runs virtual machines (VMs) by separating the operating system and resources from the physical hardware. One of the main tasks of a hypervisor is to map the resources of VMs to the resources of the host system, such as CPU, memory, disk, and network. This allows the hypervisor to allocate and manage the resources among multiple VMs and ensure that they run efficiently and independently123. Another important task of a hypervisor is to isolate the VMs and prevent unauthorized access to resources of other VMs. This ensures the security and privacy of the VMs and their data, as well as the stability and performance of the host system. The hypervisor can use various techniques to isolate the VMs, such as virtual LANs, firewalls, encryption, and access control145.

The other tasks listed are not part of a hypervisor’s responsibility, but rather of the guest operating system or the application running inside the VM. A hypervisor does not create filesystems during the installation of new VMs, as this is done by the installer of the guest operating system6. A hypervisor does not provide host-wide unique PIDs to the processes running inside the VMs, as this is done by the kernel of the guest operating system7. A hypervisor does not manage authentication to network services running inside a VM, as this is done by the network service itself or by a directory service such as LDAP or Active Directory8. References: 1 (search for “What is a hypervisor?”), 2 (search for “How does a hypervisor work?”), 3 (search for “The hypervisor gives each virtual machine the resources that have been allocated”), 4 (search for “Benefits ofhypervisors”), 5 (search for “Isolate the virtual machines and prevent unauthorized access”), 6 (search for “Create filesystems during the installation of new virtual machine quest operating systems”), 7 (search for “Provide host-wide unique PIDs to the processes running inside the virtual machines”), 8 (search for “Manage authentication to network services running inside a virtual machine”).

The command lxc-checkpoint is used to checkpoint and restore containers. Checkpointing a container means saving the state of the container, including its memory, processes, file descriptors, and network connections, to a file or a directory. Restoring a container means resuming the container from the saved state, as if it was never stopped. Checkpointing and restoring containers can be useful for various purposes, such as live migration, backup, debugging, or snapshotting. The command lxc-checkpoint has the following syntax:

lxc-checkpoint {-n name} {-D path} [-r] [-s] [-v] [-d] [-F]

The options are:

-n name: Specify the name of the container to checkpoint or restore.

-D path: Specify the path to the file or directory where the checkpoint data is dumped or restored.

-r, --restore: Restore the checkpoint for the container, instead of dumping it. This option is incompatible with -s.

-s, --stop: Optionally stop the container after dumping. This option is incompatible with -r.

-v, --verbose: Enable verbose criu logging. Only available when providing -r.

-d, --daemon: Restore the container in the background (this is the default). Only available when providing -r.

-F, --foreground: Restore the container in the foreground. Only available when providing -r.

The command lxc-checkpoint uses the CRIU (Checkpoint/Restore In Userspace) tool to perform the checkpoint and restore operations. CRIU is a software that can freeze a running application (or part of it) and checkpoint it to a hard drive as a collection of files. It can then use the files to restore and run the application from the point it was frozen at1.

The other statements about the command lxc-checkpoint are not correct. It does not create a clone or an image of a container, nor does it double the memory consumptionof the container. It can work on both running and stopped containers, depending on the options provided. References:

Linux Containers - LXC - Manpages - lxc-checkpoint.12

lxc-checkpoint(1) - Linux manual page - man7.org3

CRIU4