- Installation
- Qemu Overview
- The Qemu VM Instance
- Qemu Resources
- Logging into a QEMU VM
- Managing a QEMU VM
KVM requires a CPU with virtualization extensions, found on most consumer CPUs. These extensions are called Intel VT or AMD-V. Command to check for CPU support:
egrep '^flags.*(vmx|svm)' /proc/cpuinfoOptional:
Install Virtualization packages; this includes Libvirt tools.
sudo dnf install @virtualizationVirtual machines created with qemu-kvm are not visible for libvirt-based tools, meaning if virt-manager was launched, the VM will not show up on this interface.
Virtualization stack simplified:
------- Vagrant
----- Libvirt e.g. virsh + virt-manager
---- Qemu e.g. qemu-kvm
--- KVM i.e. Kernel Based Virtual Machine
This is simply because Qemu cannot communicate up the virtualization stack. OpenSuse KVM Cookbook is a great resource. Communication can only go down the stack.
Run this command to get the a qemu-kvm virtual machine for Red Hat CoreOS instance running:
$ qemu-kvm -m 2048M -accel kvm -smp cores=4 -fw_cfg \
name=opt/com.coreos/config,file=key.ign -drive file=rhcos.qcow2.qemu \
-net nic,model=virtio -net user,hostfwd=tcp::2222-:22
-m Sets guest startup RAM size to megs megabytes. Default is 128 MiB. Optionally, a suffix of "M" or "G" can be used to signify a value in megabytes or gigabytes respectively. 2048M is equivalent to 2G.
-accel Enables a kvm accelerator. tcg is the default.
-smp Specifies symmetric multiprocessing of four cores.
-fw_cfg Creates a firmware configuration entry named opt/com.coreos/config with the contents from key.ign. See this qemu fw_cfg doc.
-drive Creates a new drive and is a shortcut to defining -blockdev and device options. -drive file= defines the image rhcos.qcow2.qemu which is in the qcow2 format to use with this drive. Run qemu-img info rhcos.qcow2.qemu for more information on this file.
-net nic,... Defines a paravirtualized network adapter via model=virtio. Specify -net nic,model=help for a list of available devices for the target vm.
-net user, Redirects TCP or UDP connections from host to guest, in this case with TCP hostfwd=tcp::2222-:22.
-M The machine type e.g Standard PC, ISA-only PC, or Intel-Mac was not specified in this command, so it will default to pc-0.12. Use qemu-kvm -M ? to display a list of valid parameters.
For more information on the general command structure to start a qemu vm, see page 94 titled Basic Installation with qemu-kvm
Additionally, run man qemu-system-x86_64 or man qemu-kvm and see QEMU Quickstart for a more detailed explaination of each of the qemu options/flags.
On the terminal, type qemu- and hit tab. You may notice that there's a number of qemu commands.
qemu-aarch64 qemu-io qemu-mipsel qemu-ppc64le qemu-system-alpha qemu-system-mips64 qemu-system-s390x qemu-system-xtensaeb
qemu-alpha qemu-keymap qemu-mipsn32 qemu-pr-helper qemu-system-arm qemu-system-mips64el qemu-system-sh4 qemu-x86_64
qemu-arm qemu-kvm qemu-mipsn32el qemu-s390x qemu-system-cris qemu-system-mipsel qemu-system-sh4eb
qemu-armeb qemu-m68k qemu-nbd qemu-sh4 qemu-system-i386 qemu-system-moxie qemu-system-sparc
qemu-cris qemu-microblaze qemu-nios2 qemu-sh4eb qemu-system-lm32 qemu-system-nios2 qemu-system-sparc64
qemu-ga qemu-microblazeel qemu-or1k qemu-sparc qemu-system-m68k qemu-system-or1k qemu-system-tricore
qemu-hppa qemu-mips qemu-ppc qemu-sparc32plus qemu-system-microblaze qemu-system-ppc qemu-system-unicore32
qemu-i386 qemu-mips64 qemu-ppc64 qemu-sparc64 qemu-system-microblazeel qemu-system-ppc64 qemu-system-x86_64
qemu-img qemu-mips64el qemu-ppc64abi32 qemu-system-aarch64 qemu-system-mips qemu-system-ppcemb qemu-system-xtensa
A full QEMU installation includes several binaries, each of which emulates a different CPU architecture. The binary filenames take the form
qemu-system-arch, where arch is an architecture code, such as ppc for PowerPC or x86_64 for x86-64. An exception is x86 systems, which are emulated via the qemu binary.Binaries with names of the form
qemu-archprovide user-mode emulation for their respective architectures.
If the above explaination wasn't enough:
The qemu-system-* binaries e.g. qemu-system-i386 or qemu-system-x86_64 are used depending on guest OS's architecture. [sourced from the ArchLinux Wiki KVM page]
Whereas qemu-arch is for running the specified arch under Linux without starting an actual virtual machine with that architecture. [Sourced from a GNU email thread and a ServerFault forum discussion]
Note: qemu-kvm is the equivalent to qemu-system-x86_64 --enable kvm. [sourced from a GNU email thread]
.. .. .. .. .. ..
When a VM instance is booted without the -ncurses option, enter the QEMU console by pressing esc + 2 and esc + 1 to switch back.
With the -nographic option, press ctrl + a then c to switch back and forth between the QEMU console and the VM.
If none of the above options were used, press ctrl + alt then 2 to enter the console and with ctrl + alt then 1 to go back.
Shutting down is simply clicking [x] on the tool-bar of the Qemu monitor console or doing CTRL+c on the terminal where the qemu-kvm command was initiated.
It is also possible to shutdown the VM by pressing CTRL+a and then c when focus is on the QEMU monitor console (this is if the -nographic option was used).
Cached memory on the VM will not be saved but whatever that was saved to disk is persistent since all data is saved with the rhcos.qcow2.qemu file; a raw disk image.
Starting up is by running same command again, as long as the -drive file= option was provided with the same disk image as before. If a new clean VM of the same OS is needed, download or use qemu-img create a new raw disk image of the same OS.
Then provide that file within the -drive file= option. Essentially, the raw disk image is the identity of a particular VM.
It is possible to make snapshots of a VM at a given state, see page 101 of the OpenSUSE Virtualization with KVM book. Note that the snapshots will be saved within a given raw disk image. It is not available globally.
- change image file example
- add vnc logging
- add logging details
Logging into a QEMU VM can vary from OS... I'll find a more generic way to login. 😄