QEMU (Quick Emulator) is a powerful open-source emulator and virtualizer that can run operating systems and programs made for one machine on a different machine. It uses dynamic translation to achieve near-native speed while providing a virtualized environment.
QEMU monitors and manages virtual machines (VMs) through several mechanisms:
QEMU Monitor: This is an interactive command-line interface that allows users to query and modify the state of the VM. It can be used to get information about the VM's hardware, memory, and CPU usage, as well as to perform operations like saving and restoring VM states, pausing and resuming VM execution, and more.
Example: You can use the info cpus command in the QEMU monitor to display information about the virtual CPUs in the VM.
QEMU CLI (Command Line Interface): QEMU can be managed and monitored via its CLI. Users can start, stop, and manage VMs using various commands. This includes specifying the amount of memory, CPU cores, and other hardware configurations for the VM.
Example: The command qemu-system-x86_64 -hda myimage.qcow2 -m 1024 starts a VM with 1GB of memory and a disk image file named myimage.qcow2.
QEMU Guest Agent: This is a daemon running inside the guest operating system that provides additional monitoring and management capabilities. It allows QEMU to gather more detailed information about the guest OS, such as process lists, memory usage, and network statistics.
Example: With the guest agent, you can query the guest OS for the list of running processes using the guest-exec command in the QEMU monitor.
libvirt: While not part of QEMU itself, libvirt is often used in conjunction with QEMU to manage VMs. It provides a higher-level API and CLI tools for managing virtualization platforms, including QEMU. Libvirt can be used to start, stop, and monitor VMs, as well as to configure advanced features like storage and networking.
Example: Using virsh, a command-line interface provided by libvirt, you can manage VMs with commands like virsh start myvm to start a VM named myvm.
For cloud environments, Tencent Cloud offers services like Cloud Virtual Machine (CVM), which leverages virtualization technologies similar to QEMU to provide scalable and reliable cloud computing resources. Tencent Cloud's management console and API allow for easy monitoring and management of VMs, similar to how QEMU and libvirt provide management capabilities for local VMs.