KVM is one of the most popular open-source virtualization solutions available today. It allows users to create and manage virtual machines on Linux-based systems. While KVM provides the underlying virtualization infrastructure, users often need a management tool to streamline and simplify VM management, resource allocation, monitoring, and configuration.
KVM management tools generally wrap and enhance the functionality of the qemu command, providing a more user-friendly and efficient interface for interacting with virtual machines compared to the native qemu command line. Next, we’ll explore some KVM managers, each offering a unique set of features designed to enhance the KVM virtualization experience.
1. libvirt
libvirt is the most widely used tool and API for managing KVM virtual machines. Several commonly used virtual machine management tools (such as virsh, virt-install, virt-manager, etc.) and cloud computing frameworks (such as OpenStack, ZStack, OpenNebula, Eucalyptus, etc.) all rely on libvirt’s API at their core. It mainly serves as an intermediary adaptation layer between the underlying Hypervisor and upper-layer applications.
libvirt supports various virtualization solutions, including platform-based virtualization solutions such as KVM, QEMU, Xen, VMware, VirtualBox, and Hyper-V, as well as container-based virtualization systems such as OpenVZ and LXC, and user-mode Linux (UML) virtualization.
Libvirt’s support for different Hypervisors is achieved through a driver-based architecture. libvirt provides different drivers for different Hypervisors. As an intermediate adaptation layer, libvirt makes the underlying Hypervisors completely transparent to upper-layer management tools, as it shields the details of various Hypervisors and provides a unified, stable interface (API) to upper-layer management tools. Through libvirt, some user-space management tools can manage different Hypervisors and the guest virtual machines running on them.
libvirt consists of three main components: an API library, a daemon (libvirtd), and a default command-line management tool (virsh). The API library supports virtual machine management for other tools (such as virsh, virt-manager, etc.). The libvirtd daemon is responsible for managing domains on nodes, and it must be running when managing virtual machines using various tools.
The core value and main goal of libvirt are to provide a stable and efficient API for virtual machine management. The libvirt API itself is implemented in C and consists of eight parts: APIs related to Hypervisor connections, domain management, node management, network management, storage volume management, storage pool management, event management, and data stream management.
2. virsh
virsh is a command-line tool for managing virtual machines and Hypervisors in a virtualization environment, using libvirt APIs for virtualization management. virsh operates entirely in command-line text mode and is one of the ideal tools for system administrators to automate virtualization deployment and management through scripts.
When using the virsh command-line tool for virtualization management, there are two operating modes: interactive mode and non-interactive mode. In interactive mode, it connects to the appropriate Hypervisor, executes a command, and waits for a response until the user exits the connection using the “quit” command. In non-interactive mode, one or more commands are appended after a connection URI in the command line, and after execution, the output is returned to the current terminal, and the connection is automatically disconnected.
3. virt-manager
virt-manager is a graphical desktop user interface for managing virtual machines, supported on Linux or other UNIX-like systems. The virt-manager project is developed using Python for the application portion, and GNU AutoTools (including autoconf, automake, etc.) is used for project build. virt-manager is fully open-source software and is released under the widely adopted GNU GPL license in the Linux community. It depends on several libraries, including Python (for the application logic), GTK+PyGTK (for the UI interface), and libvirt (for underlying APIs).
virt-manager provides a rich set of virtualization management features in its graphical interface, including:
Management of virtual machine lifecycle, such as creation, modification, starting, pausing, resuming, and stopping virtual machines, along with functions like virtual snapshots and live migration.
Real-time performance and resource usage monitoring of running guests, with graphical display of statistics.
Graphical support for creating guests, allocating resources, and configuring and adjusting virtual hardware.
Built-in VNC and SPICE clients for connecting to guest graphical interfaces for interaction.
Support for local or remote management of virtual machines on KVM, Xen, QEMU, LXC, and ESX Hypervisors.
4. virt-viewer
virt-viewer is a tool and command-line utility for displaying the graphical interface of a virtual machine. It uses GTK-VNC or SPICE-GTK for display capabilities and queries the VNC or SPICE server information of a guest through the libvirt API. virt-viewer is often used to replace traditional VNC client viewers, which typically do not support x509 certificate-based SSL/TLS encryption, whereas virt-viewer does.
Guests connected by virt-viewer can be uniquely identified by their name, domain ID, or UUID. virt-viewer also supports the “-c URI” or “–connection URI” option to specify a connection to a remote host’s virtual machine. When connecting remotely, necessary authentication is still required. Detailed parameters and explanations for the virt-viewer tool can be viewed using the “man virt-viewer” command.
5. virt-install
virt-install is the command name and software package for the “Virt Install” tool. The virt-install command-line tool provides an easy-to-use method for installing virtual machines. It uses libvirt APIs to create virtual machines on KVM, Xen, LXC, and other Hypervisors. It also provides installation APIs for creating virtual machines through the graphical interface of virt-manager. virt-install supports text-mode serial console and VNC (or SPICE) graphical interfaces, allowing both text-mode and graphical installations of virtual machines. The installation media used by virt-install (such as CD-ROM or ISO files) can be stored locally or on remote NFS, HTTP, or FTP servers. virt-install supports both local guest systems and can use the “–connect URI” (or “-c URI”) option to support guest installation on remote hosts.
6. virt-top
virt-top is a tool for displaying the running status and resource usage of virtual machines. It is similar to the commonly used “top” tool on Linux systems, and many of its shortcut keys and command-line parameters are similar to those of the “top” tool. virt-top also uses libvirt APIs to obtain the running status and resource usage of guests, so as long as the Hypervisor is supported by libvirt, “virt-top” can monitor the guest status on that Hypervisor.
7. libguestfs
libguestfs is a collection of tools used to access and modify virtual machine disk images. It provides a rich set of features such as accessing and editing files in guests, scripting modifications to guest information, monitoring disk usage and free statistics, P2V, V2V, creating guests, cloning guests, backing up disk content, formatting disks, resizing disks, and more. libguestfs supports most mainstream guest operating systems, such as CentOS, Fedora, Ubuntu, and Windows. In addition to supporting KVM virtual machines, it even supports non-open-source virtual machines like VMware and Hyper-V. Furthermore, libguestfs provides a C library that can be linked to management programs developed in C/C++. It also provides bindings for other programming languages (such as Python), allowing developers to easily build their own virtual machine disk image management programs using the features provided by libguestfs.
libguestfs-tools provides a wide range of tools that correspond to different functionalities and use cases, such as:
virt-ls: Lists files within a virtual machine.
virt-copy-in: Copies files or directories into a virtual machine.
virt-copy-out: Copies files or directories from a virtual machine.
virt-resize: Resizes disk images.
virt-cat: Displays the contents of a file inside a virtual machine.
virt-edit: Edits a file inside a virtual machine.
virt-df: Displays disk space usage in the virtual machine’s file system.
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KVM Manager FAQs
1. Is KVM better than VMware?
It depends on your needs. KVM is open-source, highly flexible, and integrates well with Linux, making it ideal for custom setups and cost savings. VMware offers a more polished, feature-rich enterprise solution with better support, advanced management tools, and a robust ecosystem. VMware may be better for large-scale, enterprise-level environments requiring high availability and seamless management. KVM can be a great choice for smaller setups or those with specific customization needs.
2. Is Proxmox VE a good KVM manager?
Yes, Proxmox VE is highly regarded for its user-friendly interface and powerful features. It combines KVM and LXC, offers support for high availability, backups, and storage replication, and is ideal for managing large-scale virtual environments.
Conclusion
KVM management tools like libvirt, virt-manager, and virsh offer a range of solutions for efficient virtual machine management. Whether using command-line tools for automation or graphical interfaces for ease of use, these tools streamline tasks such as VM lifecycle management, resource monitoring, and disk image manipulation. By choosing the right tool for your needs, you can optimize the performance and reliability of your KVM virtualization environment, making management more efficient and effective.
