Ubuntu Manpage: uvt-kvm - Ubuntu virtualisation front-end for libvirt and KVM

Provided by: uvtool-libvirt_0~git183-0ubuntu1.24.04.1_all

NAME

       uvt-kvm - Ubuntu virtualisation front-end for libvirt and KVM

SYNOPSIS

       uvt-kvm list

       uvt-kvm create [options] name [filter ...]

       uvt-kvm wait [options] name

       uvt-kvm ip name

       uvt-kvm ssh [options] ®.RI [ command ...]

       uvt-kvm destroy name

DESCRIPTION

       uvtool  provides  a  unified  and  integrated  VM front-end to Ubuntu cloud image downloads, libvirt, and
       cloud-init.

       uvt-kvm uses the volume storage pool maintained by uvt-simplestreams-libvirt(1) as  a  basis  to  provide
       quick start and management of Ubuntu VMs by wrapping libvirt and cloud-init.

       uvt-kvm  is  not intended to wrap all possible use cases. Where possible, it provides access to some more
       advanced cases using options to override entire sections of default operation, such  as  the  ability  to
       directly  override  the backing volume image used, the libvirt domain definition, cloud-init metadata and
       userdata, and directly provide a network-config file.  For yet more complex cases, it  is  expected  that
       the user will call libvirt directly (for example by using virsh(1)), and use uvt-kvm for only the simpler
       operations required on affected VMs. See ADVANCED OVERRIDE OPTIONS and ADVANCED USAGE for details.

SUBCOMMANDS

uvt-kvm's interface is designed around subcommands. The subcommand to be used must be specified as the
first positional argument. Each subcommand has its own set of available options.

Where a subcommand requires a VM to be specified, the VM name must be provided as a second positional
argument. When using uvt-kvm create to create VMs, the VM name is specified by the user at this time.
Where users have manipulated libvirt directly, VM names are expected to match libvirt domain names.

list
uvt-kvm list

Print a list of existing VMs to stdout. This list currently includes libvirt domains that are defined but
were not created by uvt-kvm, but in future this is expected to change to VMs created by uvt-kvm only.

create
uvt-kvm create [options] name [filter ...]

Create a new VM based on a backing volume specified by the provided simplestreams filters. This VM will
be called name, and the same name must be used when referring to the VM from the other subcommands.

Each filter operates on the images downloaded and managed by uvt-simplestreams-libvirt(1), and when
combined together must uniquely specify a single image. See uvt-simplestreams-libvirt(1) for details on
image selection.

Since backing volume images are downloaded and maintained by uvt-simplestreams-libvirt(1), it is
necessary to first run uvt-simplestreams-libvirt(1) to download images before this subcommand will
succeed. See EXAMPLES, below.

If no filters are specified, a filter of release=release is assumed, where release corresponds to the
current LTS release as returned by distro-info(1).

Alternatively, see --backing-image-file under ADVANCED OVERRIDE OPTIONS below to supply a backing image
directly yourself.

This subcommand supports an extensive set of options to modify the definition and behavior of the VM. See
LIBVIRT DOMAIN DEFINTION OPTIONS, CLOUD-INIT CONFIGURATION OPTIONS and ADVANCED OVERRIDE OPTIONS below.
Other general behavioural options:

--no-start Do not start the VM after creation. This is useful to make further customisations to the
VM before using it. To start the VM when done, use virsh start name.

wait
uvt-kvm wait [options] name

Wait for a VM to become ready. This includes: waiting for the VM to request an IP address, waiting for
ssh to become available on this IP, and an ssh(1) operation into the VM to wait for two things:

First the system to fully initialize.
This is checked via the runlevel to reach 2 (upstart) or 5 (systemd). Since 25.04 Plucky
runlevel stopped to be supported and instead systemctl is-system-running --wait has to
complete.

Then it checks if cloud-init finished.
This is done by checking for the existence of /var/lib/cloud/instance/boot-finished

By using the wait command, scripts can create, operate on and destroy VMs synchronously and reliably.

--timeout timeout
Give up waiting after timeout seconds. Default: 120 seconds.

--interval interval
For wait operations that must poll, poll every interval seconds. Default: 8 seconds.

--remote-wait-script remote_wait_script
Run remote_wait_script through sh(1) on the guest system, which must block and exit with a zero
status when the system is ready. Default: /usr/share/uvtool/remote-wait.sh, which assumes that
upstart and cloud-init are being used on the guest, waits for upstart to enter runlevel 2 and then
waits for cloud-init to signal that it has finished booting the system.

When remote_wait_script is run on the guest system, its environment will define the variables
UVTOOL_WAIT_INTERVAL and UVTOOL_WAIT_TIMEOUT which contain the poll interval and wait timeout as
specified by the --interval and --timeout options, respectively.

--remote-wait-user user
Run the remote wait script as user user. It must be possible to ssh(1) into the guest system as
this user for the remote wait mechanism to work.

--insecure
Permit potentially insecure operations. See COMMON OPTIONS, below.

--ssh-private-key-file ssh_private_key_file
Use ssh_private_key_file to authenticate to the guest machine when performing the ssh(1) operation

--without-ssh
Skip the ssh(1) operation. This will cause the command to exit with success as soon as the ssh
port is available, but without logging to the guest to wait until it is ready internally.

ip
uvt-kvm ip name

Guess the IP address of a VM and print it to stdout. Currently, this assumes a default (Ubuntu)
installation of libvirt and dnsmasq on the host, and default networking behaviour on the VM. IP address
guessing is currently implemented via libvirt-python.

This subcommand assumes that the VM has successfully acquired an IP address, and will fail otherwise.
Callers can use uvt-kvm wait after creating or rebooting a VM to wait for this to become the case.

In future, this subcommand may incorporate multiple IP address detection mechanisms.

ssh
uvt-kvm ssh [options] ®.RI [ command ...]

Run ssh(1) against the VM. This is a limited wrapper around ssh(1) and the ip subcommand, designed for
ease-of-use in the common case. For full functionality, use the ip subcommand to obtain the VM's IP
address, and then call ssh(1) directly instead.

--insecure Permit potentially insecure operations. See COMMON OPTIONS, below.

--login-name user
-l user

Specify the username to pass to ssh(1). This is the recommended method for use in scripts.
This option overrides the username provided by the @ notation in the first positional
argument, and thus allows the VM name to include an @ symbol. Default: ubuntu, to match the
default on Ubuntu cloud images.

destroy
uvt-kvm destroy name

Stop and completely destroy an existing VM. This stops the libvirt domain if it is running, undefines it,
and deletes all volumes that had been part of the domain's definition. It does not, however, delete any
backing volumes, thus keeping intact pristine Ubuntu cloud images as maintained by uvt-simplestreams-
libvirt(8).

COMMON OPTIONS

       --insecure
              Valid for: uvt-kvm wait, uvt-kvm ssh.

              Permit connections which  may  not  be  secure.  For  ssh(1)  connections,  this  skips  host  key
              validation.  This  is  no longer be required in the default case, since uvtool creates the guest's
              host keys, supplies them to the guest via cloud-init, and thus knows and sets  the  expected  host
              public  key  automatically.  In  the common non-default case, --insecure may be required but still
              should not be a problem since the guest system is located on the same system and this network path
              can be trusted. However, uvt-kvm will refuse to make a connection (for uvt-kvm ssh) or skip  steps
              (for  uvt-kvm wait)  without  this  option,  in order to make absolutely sure that the user cannot
              compromise his path to the guest system without being aware of this caveat.

       -d
       --developer
              Valid for: uvt-kvm create only.

              Turn on a set of options deemed most useful for developers but not  suitable  for  turning  on  by
              default.  Currently  this  is the same as specifying --unsafe-caching and --log-console-output but
              this may change between releases.

              Scripts should never use this option. To protect against future changes to the definition of  this
              option, they should instead use the expansion defined above.

LIBVIRT DOMAIN DEFINITION OPTIONS

Valid for: uvt-kvm create only.

These options modify the definition of the guest VM, and its connection to the host.

uvt-kvm create takes the default or user-supplied libvirt domain XML template definition and modifies it
according to the following parameters. Each of these parameters has a sensible default which may change
between releases.

--memory size
Amount of system RAM in megabytes. Default: 512 (MiB).

--disk size
Size of the OS disk in gigabytes. Default: 8 (GiB).

--ephemeral-disk size
Add an ephemeral disk of Size gigabytes.

--unsafe-caching
Do not flush guest syncs to the host on the OS disk. This can improve guest I/O performance at the
cost of losing data on host power failure. This option is useful for ephemeral guest machines
that do not need to be persistent beyond a host power cycle.

--cpu cores
Number of CPU cores. Default: 1.

--bridge bridge
Replace the first defined NIC with one that connects to the given host bridge. Default: unaltered
from the libvirt domain template.

--mac mac
Use this MAC address for the first defined NIC. Can be used in conjunction with --bridge. Default
unspecified.

--log-console-output
Log output to a disk file on the host instead of to a pty. With libvirt's default configuration on
Ubuntu, this log can be found in /var/log/libvirt/qemu/<name>.log. This options enables
retrospective examination of VM console output, but breaks virsh console for interactive use. On
s390x this option is currently not supported due to incompatibilties with the sclp console used.

--host-passthrough
Instead of the default CPU model - which is host-model this will use host-passthrough which will
try to make all of the host's CPU features (not migration safe) available in the guest. This
option is deprecated and will later be removed. Please use --model instead.

--cpu-model
Set the CPU model that shall be used. The default generally is host-model, except on arm64 where
host-model won't work - there the default is host-passthrough. If set to host-model or host-
passthrough this will set the CPU mode. If set to any other string it will be handled as a named
CPU passed to libvirt. Allowed values are all CPUs listed on your host as usable=yes in `virsh
domcapabilities`. This option has no effect if the target is emulated, in this case the safe
defaults of libvirt will be used.

--machine-type type
Set the machine type to the specified string before instantiating the guest. See kvm -M ? for a
list of types supported by your current system. If not set this section of the template is not
altered before the guest is defined. If set this modifies the internal temporary libvirt domain
template at the element domain->os->type and sets the attribute machine to the given value before
defining the guest. This implies that libvirt will add the type-dependent default devices when
defining the guest.

If --machine-type is not specified, the current host is an x86_64 system and the requested guest
is arch=amd64 then the machine type will by default be set to the latest available q35 based type
to overcome the ancient compatibility oriented defaults of libvirt on x86.

CLOUD-INIT CONFIGURATION OPTIONS

Valid for: uvt-kvm create only.

These options modify operation within the guest VM itself.

Unless --user-data is used to override this behaviour, uvt-kvm generates cloud-init userdata with some
sensible defaults when a VM is created. These defaults can be altered using the following options:

--password password

Permit login to the VM to the default user ubuntu and password password. This is useful for
debugging purposes, since it also enables a VT login. Using this command line option leaks the
password used to other users on the same system, so should never be used in production for
security reasons.

Default: no password login.

--run-script-once script_file
Run script_file as root on the VM the first time it is booted, but never again. This option can be
used multiple times to run multiple scripts. If the script exits with a non-zero status, it will
be left on the VM in /tmp for debugging purposes.

script_file will be copied to the guest, marked as executable, and executed directly, so it must
be an appropriate binary, start with a shebang, or otherwise be directly executable by the guest
kernel.

Default: no scripts.

--ssh-public-key-file ssh_public_key_file

Permit login to the VM to the default user ubuntu and the ssh keys specified in
ssh_public_key_file.

Default: use the output of ssh-add -L if available; otherwise use ~/.ssh/id_rsa.pub. If no source
is found at all, then a warning will be printed to stderr, and VM creation will continue with no
arrangement for access to the guest.

--packages package_list

Install the comma-separated packages specified in package_list on first boot. This option can be
used multiple times; each additional option adds to the final package list.

Default: no packages.

ADVANCED OVERRIDE OPTIONS

Valid for: uvt-kvm create only.

--template template_file
The base libvirt domain definition XML template to use when constructing a new VM's definition.
This is dynamically altered before domain creation; see LIBVIRT DOMAIN DEFINITION OPTIONS.

Default: /usr/share/uvtool/libvirt/template.xml.

--guest-arch architecture
Specify the architecture of the guest template file that will be selected. If an explicit
--template is given then --guest-arch has no effect. If neither --template nor --guest-arch are
set the host's architecture will be used to determine the default xml template.

If you set an architecture that requires emulation on the current host the guest will be set up
for that. See EMULATION OF FOREIGN ARCHITECTURES for more details on using an architecture that is
different to the current system.

Default: Current Host architecture

--user-data user_data_file
Override cloud-init userdata, instead using the file supplied. This overrides all options in the
section CLOUD-INIT CONFIGURATION OPTIONS.

Default: as described in CLOUD-INIT CONFIGURATION OPTIONS.

--meta-data meta_data_file
Override default cloud-init metadata, instead using the file supplied. This does not override any
other options, since cloud-init metadata is not otherwise tunable.

Default: minimal file with automatically generated instance-id.

--network-config network_config_file
Provide cloud-init network-config using the file supplied.

Default: no network-config file.

--backing-image-file image_file
Specify the name of a local file that will be used to create the VM instead of relying on the
volume storage pool. It must point to a qcow2 formatted file. This option overrides any
simplestreams filters provided.

ADVANCED USAGE

uvt-kvm is carefully constructed to avoid impeding the ability of the user to directly use virsh(1) or
other libvirt tooling at any time, and provides override options to supply backing image volumes and
cloud-init userdata and metadata where possible. VMs created by uvt-kvm are not "special" in libvirt.
What uvt-kvm does with VMs is well-defined, so that advanced users can manipulate a VM using libvirt
directly without necessarily losing the ability for uvt-kvm to continue to manipulate that VM for common
use cases.

TERMINOLOGY AND LIFECYCLE
For simplicity, uvt-kvm uses create to mean the definition, allocation and running of a VM, and destroy
to mean the stopping and removing of all persistent state associated with a VM, including VM-specific
disk image files and the VM definition itself. This matches the commonly expected lifecycle of VMs
created with uvt-kvm.

This works well for the common use case, but if VMs created with uvt-kvm need to be manipulated with
virsh(1) or libvirt directly, then it becomes necessary to understand how this matches up to the more
complex libvirt terminology.

In libvirt, a VM is called a domain. A domain is first defined, and then independently started. In
libvirt terminology, destroy means a VM stop; after a destroy, the domain still exists and can be
restarted. undefine finally removes the domain definition. Resources associated with a VM (such as disk
image files, which in libvirt are called volumes) must be created and destroyed separately.

When uvt-kvm creates a VM, libvirt volumes are defined and populated, a libvirt domain is defined, marked
as autostarted, and the domain started. When uvt-kvm destroys a VM, the corresponding libvirt domain is
stopped, domain-specific volumes deleted and the libvirt domain itself is undefined.

EMULATION OF FOREIGN ARCHITECTURES
emulation of foreign architectures can be done with uvt-kvm. Currently armhf being the only supported
target architecture. Please be aware that defining filters to use a different architecture image will not
be enough. To let uvtool know that you want to run as a specific architecture you need to set --guest-
arch If that is set to armhf (just like your simplestreams filters for the image would be) then uvt-kvm
will use qemu-system-arm

Since in these modes bootloaders often struggle uvt-kvm will provide externel kernel and initrd to boot
the guest. To be able to extract those from the guest image it needs root permission when syncing the non
native architecture image.

EXAMPLES

       # Update uvtool's libvirt volume storage pool with the
       # latest Precise image
       uvt-simplestreams-libvirt sync release=precise arch=amd64

       # Create an ssh key for the local user (if you don't have
       # one already)
       ssh-keygen
       # (...)

       # Create an amd64 VM running Precise
       uvt-kvm create myvm release=precise arch=amd64

       # Wait for the VM to become ready
       uvt-kvm wait --insecure myvm

       # Shell into the VM to do some testing there
       uvt-kvm ssh --insecure myvm
       # (...)

       # Destroy the VM
       uvt-kvm destroy myvm

TROUBLESHOOTING

Common Errors
Failed to connect socket to '/var/run/libvirt/libvirt-sock': Permission denied

Do you have permission to connect to libvirt? On Ubuntu, you must belong to the libvirt group (this group
was named libvirtd on 16.04 and earlier). Users with sudo(8) access are added to this group by default,
but users only get group membership on the next login after the libvirt-bin package has been installed.
To temporarily add yourself to this group in advance of your next login, try newgrp libvirt (or
newgrp libvirtd if on Ubuntu 16.04 or earlier).

no supported architecture for os type 'hvm'

libvirt did not find KVM support on your system. Try sudo kvm-ok for diagnostics, and service libvirt-
bin restart to pick up any changes before retrying.

Interactive console access
If you cannot access the VM from the host system, try using --password to set a password for the default
ubuntu user inside the VM, and then logging in to the VM over the console in order to examine it from the
inside.

To access the console interactively, use virsh console name. However, note that interactive access is
disabled if you are using --log-console-output or -d, so for interactive access you will have to drop
these options if you are using them.

If you are using --user-data, then --password will be overridden by it and you will need to modify your
cloud-init userdata manually to achieve the same effect.

NAME

SYNOPSIS

DESCRIPTION

SUBCOMMANDS

COMMON OPTIONS

LIBVIRT DOMAIN DEFINITION OPTIONS

CLOUD-INIT CONFIGURATION OPTIONS

ADVANCED OVERRIDE OPTIONS

ADVANCED USAGE

EXAMPLES

TROUBLESHOOTING

SEE ALSO