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Libvirt Virtualization API

= Virsh =

'virsh' is a command line interface to libvirt.

It can be used interactively:
<pre>
$ virsh 
Welcome to virsh, the virtualization interactive terminal.

Type:  'help' for help with commands
       'quit' to quit
</pre>
or by passing a subcommand directly:
<pre>
$ virsh list --all
 Id    Name                           State
----------------------------------------------------
 -     demo                           shut off
</pre>

Note that you can run virsh locally, and let it connect to the machine hosting the guests:
<pre>
$ virsh --connect qemu+ssh://my-virtual-host/system
</pre>

== Preparation ==

Before you can instantiate a guest, you have to create an XML file describing the guest.
Fortunately virsh provides a way to convert your QEMU command line invocation into an XML file.
E.g.
<pre>
$ virsh domxml-from-native qemu-argv <(echo /usr/bin/qemu-system-aarch64 -m 1024 -cpu cortex-a57 -M virt \
        -nographic -serial pty -kernel /path/to/linux-arm64-virt/arch/arm64/boot/Image) | \
        sed -e 's/unnamed/demo/' > demo.xml
</pre>

Caveats:
* Use an absolute path when referring to the QEMU binary,
* As libvirt's console doesn't connect to QEMU's stdout, but to a pty, your QEMU command line must include '-serial pty',
* Make sure 'libvirt-qemu' has permissions to access the kernel Image (and write access to the directory containing it?).

== Virsh subcommands ==

Create (define) a guest (domain) from an existing XML file:
<pre>
$ virsh define demo.xml
Domain demo defined from demo.xml
</pre>

Start a created guest:
<pre>
$ virsh start demo
Domain demo started
</pre>

Connect to the console of a running guest:
<pre>
$ virsh console demo
Connected to domain demo
Escape character is ^]



BusyBox v1.24.2 () built-in shell (ash)

  _______                     ________        __
 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 -----------------------------------------------------
 DESIGNATED DRIVER (Bleeding Edge, 50072)
 -----------------------------------------------------
  * 2 oz. Orange Juice         Combine all juices in a
  * 2 oz. Pineapple Juice      tall glass filled with
  * 2 oz. Grapefruit Juice     ice, stir well.
  * 2 oz. Cranberry Juice
 -----------------------------------------------------
</pre>

Stop (destroy) a running guest:
<pre>
$ virsh destroy demo
Domain demo destroyed
</pre>

Delete (undefine) a created guest:
<pre>
$ virsh undefine demo
Domain demo has been undefined
</pre>

List all running guests (use '--all' for all defined guests):
<pre>
$ virsh list
 Id    Name                           State
----------------------------------------------------
 5     demo                           running
</pre>

Dump the XML describing a guest:
<pre>
$ virsh dumpxml demo
<domain type='qemu' id='4'>
  <name>demo</name>
  <uuid>ff9c71e0-53d4-4222-b0b9-70fd00a8f840</uuid>
  ...
</domain>
</pre>

= Virt-manager =

Virt-manager is a GUI for libvirt.
You can use it to manage guests created with virsh.

You can run it either on the machine hosting the guests:
<pre>
$ virt-manager
</pre>
or run it locally, and let it connect to the machine hosting the guests:
<pre>
$ virt-manager -c qemu+ssh://my-virtual-host/system
</pre>

Note that just running 'virt-manager' over ssh with X forwarding doesn't seem to work.

= References =

* https://libvirt.org/