libvirt/docs/uri.rst

Connection URIs

Since libvirt supports many different kinds of virtualization (often referred to as "drivers" or "hypervisors"), we need a way to be able to specify which driver a connection refers to. Additionally we may want to refer to a driver on a remote machine over the network.

To this end, libvirt uses URIs as used on the Web and as defined in RFC 2396. This page documents libvirt URIs.

Specifying URIs to libvirt

The URI is passed as the name parameter to virConnectOpen or virConnectOpenReadOnly . For example:

virConnectPtr conn = virConnectOpenReadOnly ("test:///default");

Configuring URI aliases

To simplify life for administrators, it is possible to setup URI aliases in a libvirt client configuration file. The configuration file is /etc/libvirt/libvirt.conf for the root user, or $XDG_CONFIG_HOME/libvirt/libvirt.conf for any unprivileged user. In this file, the following syntax can be used to setup aliases

uri_aliases = [
  "hail=qemu+ssh://root@hail.cloud.example.com/system",
  "sleet=qemu+ssh://root@sleet.cloud.example.com/system",
]

A URI alias should be a string made up from the characters a-Z, 0-9, _, -. Following the = can be any libvirt URI string, including arbitrary URI parameters. URI aliases will apply to any application opening a libvirt connection, unless it has explicitly passed the VIR_CONNECT_NO_ALIASES parameter to virConnectOpenAuth. If the passed in URI contains characters outside the allowed alias character set, no alias lookup will be attempted.

Default URI choice

If the URI passed to virConnectOpen* is NULL or empty string, then libvirt will use the following logic to determine what URI to use.

1. The environment variable LIBVIRT_DEFAULT_URI
2. The client configuration file uri_default parameter
3. Probe each hypervisor in turn until one that works is found

Historically an empty URI was equivalent to xen:///system.

Specifying URIs to virsh, virt-manager and virt-install

In virsh use the -c or --connect option:

virsh -c test:///default list

If virsh finds the environment variable VIRSH_DEFAULT_CONNECT_URI set, it will try this URI by default. Use of this environment variable is, however, deprecated now that libvirt supports LIBVIRT_DEFAULT_URI itself.

When using the interactive virsh shell, you can also use the connect URI command to reconnect to another hypervisor.

In virt-manager use the -c or --connect=URI option:

virt-manager -c test:///default

In virt-install use the --connect=URI option:

virt-install --connect=test:///default [other options]

Local hypervisor URIs

xen:///system URI

To access a Xen hypervisor running on the local machine use the URI xen:///system.

Historically libvirt 0.2.2 and previous versions required to use the name "xen" to refer to the Xen hypervisor.

qemu:///... QEMU and KVM URIs

To use QEMU support in libvirt you must be running the libvirtd daemon (named libvirt_qemud in releases prior to 0.3.0). The purpose of this daemon is to manage qemu instances.

The libvirtd daemon should be started by the init scripts when the machine boots. It should appear as a process libvirtd --daemon running as root in the background and will handle qemu instances on behalf of all users of the machine (among other things).

So to connect to the daemon, one of two different URIs is used:

• qemu:///system connects to a system mode daemon.
• qemu:///session connects to a session mode daemon.

(If you do libvirtd --help, the daemon will print out the paths of the Unix domain socket(s) that it listens on in the various different modes).

KVM URIs are identical. You select between qemu, qemu accelerated and KVM guests in the guest XML as described here.

test:///... Test URIs

The test driver is a dummy hypervisor for test purposes. The URIs supported are:

• test:///default connects to a default set of host definitions built into the driver.
• test:///path/to/host/definitions connects to a set of host definitions held in the named file.

Remote URIs

Remote URIs have the general form ("[...]" meaning an optional part):

driver[+transport]://[username@][hostname][:port]/[path][?extraparameters]

Either the transport or the hostname must be given in order to distinguish this from a local URI.

Some examples:

• xen+ssh://rjones@towada/system — Connect to a remote Xen hypervisor on host towada using ssh transport and ssh username rjones.
• xen://towada/system — Connect to a remote Xen hypervisor on host towada using TLS.
• xen://towada/system?no_verify=1 — Connect to a remote Xen hypervisor on host towada using TLS. Do not verify the server's certificate.
• qemu+unix:///system?socket=/opt/libvirt/run/libvirt/libvirt-sock — Connect to the local qemu instances over a non-standard Unix socket (the full path to the Unix socket is supplied explicitly in this case).
• test+tcp://localhost:5000/default — Connect to a libvirtd daemon offering unencrypted TCP/IP connections on localhost port 5000 and use the test driver with default settings.
• qemu+libssh2://user@host/system?known_hosts=/home/user/.ssh/known_hosts — Connect to a remote host using a ssh connection with the libssh2 driver and use a different known_hosts file.
• qemu+libssh://user@host/system?known_hosts=/home/user/.ssh/known_hosts — Connect to a remote host using a ssh connection with the libssh driver and use a different known_hosts file.

Transport configuration

The remote driver supports multiple transport protocols and approaches which are configurable via the URI.

Extra parameters can be added to remote URIs as part of the query string (the part following ?). Remote URIs understand the extra parameters shown below. Any others are passed unmodified through to the back end. Note that parameter values must be URI-escaped.

All transports support the following parameters:

name

The name passed to the remote virConnectOpen function. The name is normally formed by removing transport, hostname, port number, username and extra parameters from the remote URI, but in certain very complex cases it may be better to supply the name explicitly.

Example: name=qemu:///system

ssh transport

The ssh transport uses the standard SSH protocol via the system installed binary.

Supported extra parameters:

mode

See the info on the mode parameter.

proxy

See the info on the proxy parameter.

command

Path to the ssh binary to use.

Example: command=/opt/openssh/bin/ssh

socket

See the info on the socket parameter.

netcat

See the info on the netcat parameter.

keyfile

See the info on the keyfile parameter.

no_verify

If set to a non-zero value, this disables client's strict host key checking making it auto-accept new host keys. Existing host keys will still be validated.

Example: no_verify=1

no_tty

If set to a non-zero value, this stops ssh from asking for a password if it cannot log in to the remote machine automatically (eg. using ssh-agent etc.). Use this when you don't have access to a terminal - for example in graphical programs which use libvirt.

Example: no_tty=1

libssh and libssh2 transport

Same as the ssh transport but the SSH client is handled directly by using either libssh or libssh2 to handle the SSH protocol without spawning an extra process.

Supported extra parameters:

mode

See the info on the mode parameter.

proxy

See the info on the proxy parameter.

socket

See the info on the socket parameter.

netcat

See the info on the netcat parameter.

keyfile

See the info on the keyfile parameter.

known_hosts

Path to the known_hosts file to verify the host key against. LibSSH2 and libssh support OpenSSH-style known_hosts files, although LibSSH2 does not support all key types, so using files created by the OpenSSH binary may result into truncating the known_hosts file. Thus, with LibSSH2 it's recommended to use the default known_hosts file is located in libvirt's client local configuration directory e.g.: ~/.conf ig/libvirt/known_hosts.

Note: Use absolute paths.

Example: known_hosts=/root/.ssh/known_hosts

known_hosts_verify

If set to normal (default), then the user will be asked to accept new host keys. If set to auto, new host keys will be auto-accepted, but existing host keys will still be validated. If set to ignore, this disables client's strict host key checking.

Example: known_hosts_verify=ignore

sshauth

A comma separated list of authentication methods to use. Default (is "agent,privkey,password ,keyboard-interactive". The order of the methods is preserved. Some methods may require additional parameters.

Example: sshauth=privkey,agent

tls transport

This transport uses a TCP connection to the socket. The data is encrypted using TLS to ensure security. Note that TLS certificates must be setup for this to work.

Supported extra parameters:

tls_priority

A valid GNUTLS priority string.

Example: tls_priority=NORMAL:-VERS-SSL3.0

no_verify

If set to a non-zero value, this disables client checks of the server's certificate. Note that to disable server checks of the client's certificate or IP address you must change the libvirtd configuration

Example: no_verify=1

pkipath

Specifies x509 certificates path for the client. If any of the CA certificate, client certificate, or client key is missing, the connection will fail with a fatal error.

Example: pkipath=/tmp/pki/client

unix transport

This transport uses an unix domain socket is used to connect to the daemon. This is the most common case. In most cases no extra parameters are needed.

Supported extra parameters:

mode

See the info on the mode parameter.

socket

See the info on the socket parameter.

ext transport

The ext transport invokes the user specified command to transport the libvirt RPC protocol to the destination. The command must be able to handle the proper connection. Standard input/output is used for the communication.

Supported extra parameters:

command

The external command launched to tunnel the data to the destination.

tcp transport

The tcp transport uses plain unencrypted TCP connection to libvirt. This is insecure and should not be used. This transport has no additional arguments.

Common extra parameters

Certain extra parameters are shared between multiple protocols. See the list of transport protocols above for specific usage.

mode parameter

Controls whether to connect to per-driver daemons or libvirtd.

Supported values:

auto

automatically determine the daemon

direct

connect to per-driver daemons

legacy

connect to libvirtd

Default is auto. Can also be set in libvirt.conf as remote_mode.

Example: mode=direct

proxy parameter

Controls which proxy binary is used on the remote side of connection to connect to the daemon.

Supported values:

auto

try native, fallback to netcat

netcat

only use netcat

native

use the libvirt native proxy binary

Default is auto. Can also be set in libvirt.conf as remote_proxy.

Example: proxy=native

socket parameter

The path to the Unix domain socket, which overrides the compiled-in default. This may be passed to the remote proxy command (See. proxy parameter).

Example: socket=/opt/libvirt/run/libvirt/libvirt-sock

netcat parameter

The name of the netcat command on the remote machine. The default is nc. This is not permitted when using the native proxy mode.

The command used here is used on the remote side of the connection as:

netcat -U socket

Example: netcat=/opt/netcat/bin/nc

keyfile parameter

The name of the private key file to use to authentication to the remote machine. If this option is not used the default keys are used.

Example: keyfile=/root/.ssh/example_key