This document is WORK IN PROGRESS
Introduction
This article tries to summarise Linux Virtual Machine methods and is in its early stage. It does not focus on different types of hypervisors, but more on the issues and features you get with each hypervisor.
Host Kernel
Some supervisors need their own (modified Linux) kernel to operate, whereas others work with any Linux kernel. Though some of them again need some configurations to be turned on in the stock kernel.
VM Installation
Depending on the hypervisor, there are different requirements and methods for the installation:
- Installation can be done within the VM for completly isolated machines
- Installation must be done outside / on the host for systems without own kernel
Some hypervisors can boot from the network, whereas others just create a very lightweight isolation and boot an installed system only.
Guest OS changes
Some hypervisors require changes to the virtual machines, to be able to run successfully. Others allow a original OS version to be installed.
Network configuration
Whether the VM is attached to a bridge, a tun/tap device, treated as a normal process, there may be a lot of different configurations. Furthermore, firewall (masquerade/nat) configurations may be necessary.
Additionally, some of the hypervisors support dynamic allocation of mac or even ip addresses.
Templates
Some hypervisors support reusage of installations.
Management
Most hypervisors contain some minor collection of utilities to manage virtual machines. Some libraries / frameworks try to integrate those utilities, to abstract the different implementations.
Typical issues are:
- Autostart machines on startup / autostop on shutdown
- Creation of new VMs / including template handling
- Manual start/stop of VMs
- Listing of running / existing VMs
Automated usage
Especially interesting for a sysadmin is, how easy a system can be automated, which steps need to be taken to get a new image or copy of an existing one. This aspect is one focus of this document.
Hypervisors
| Name | Host Kernel | Guest OS changes | Installation |
|---|---|---|---|
| QEMU | Original | no | inside |
| KVM | Original w/KVM | no | inside |
| Lguest | Original w/Lguest | ? | ? |
| Linux Containers | Original w/Containers | yes | outside |
| Linux VServer | Own | ? | ? |
| User Mode Linux | Original | ? | outside |
| OpenVZ | Own | ? | ? |
| Virtualbox | Original+Modules | no | inside |
| VMWare | Original+Modules / Own | no | inside |
| Xen | Own | ? | ? |
lxc
Some hints on lxc:
- Helper scripts existent (lxc-debian, lxc-fedora, ...)
- adjust init. change dev. do not run udev (why?)
- Root open in the filesystem
- No network specified = all from host accessible!
Management Libraries / Frameworks
| Name | Hints |
|---|---|
| Ganetti | |
| Libvirt | |
Poor man's management
This sections describes typical vm management tasks, done with easy commands.
Creating a new (sparse) image file
dd if=/dev/zero of=<filename> bs=1 count=0 seek=<gigabytes>G