• Remote URIs
• Other & legacy URI formats

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

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

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

To simplify life for administrators, it is possible to setup URI aliases in alibvirt client configuration file. The configuration file is /etc/libvirt/libvirt.conffor 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

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.

If the URI passed to virConnectOpen* is NULL, then libvirt will use the followinglogic to determine what URI to use.

With ssh-keygen. Ssh-keygen -t rsa -b 2048 -f dummy-ssh-keygen.pem -N ' -C 'Test Key' Converting DER to PEM. If you have an RSA key pair in DER format, you may want to convert it to PEM to allow the format conversion below: Generation: openssl genpkey -algorithm RSA -out genpkey-dummy.cer -outform DER -pkeyopt rsakeygenbits:2048 Conversion.

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

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

If virsh finds the environment variableVIRSH_DEFAULT_CONNECT_URI set, it will try this URI bydefault. Use of this environment variable is, however, deprecatednow that libvirt supports LIBVIRT_DEFAULT_URI itself.

When using the interactive virsh shell, you can also use theconnectURI command to reconnect to anotherhypervisor.

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

X509 Ssh Cisco

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

This section describes a feature which is new in libvirt >0.2.3. For libvirt ≤ 0.2.3 use 'xen'.

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

To use QEMU support in libvirt you must be running thelibvirtd daemon (named libvirt_qemudin releases prior to 0.3.0). The purpose of thisdaemon is to manage qemu instances.

The libvirtd daemon should be started by theinit scripts when the machine boots. It should appear asa process libvirtd --daemon running as rootin the background and will handle qemu instances on behalfof all users of the machine (among other things).

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

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

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

KVM URIs are identical. You select between qemu, qemu accelerated andKVM guests in the guest XML as describedhere.

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 orderto distinguish this from a local URI.

Some examples:

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

Extra parameters can be added to remote URIs as partof 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 beURI-escaped.

Name	Transports	Meaning
name	any transport	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
tls_priority	tls	A valid GNUTLS priority string
Example: tls_priority=NORMAL:-VERS-SSL3.0
mode	unix, ssh, libssh, libssh2	auto automatically determine the daemon direct connect to per-driver daemons legacy connect to libvirtd Can also be set in libvirt.conf as remote_mode
Example: mode=direct
proxy	auto, netcat, native	auto try native, fallback to netcat netcat only use netcat native only use native Can also be set in libvirt.conf as remote_proxy
Example: proxy=native
command	ssh, ext	The external command. For ext transport this is required. For ssh the default is ssh. The PATH is searched for the command.
Example: command=/opt/openssh/bin/ssh
socket	unix, ssh, libssh2, libssh	The path to the Unix domain socket, which overrides the compiled-in default. For ssh transport, this is passed to the remote netcat command (see next).
Example: socket=/opt/libvirt/run/libvirt/libvirt-sock
netcat	ssh, libssh2, libssh	The name of the netcat command on the remote machine. The default is nc. This is not permitted when using the native proxy mode. For ssh transport, libvirt constructs an ssh command which looks like: where port, username, hostname can be specified as part of the remote URI, and command, netcat and socket come from extra parameters (or sensible defaults).
Example: netcat=/opt/netcat/bin/nc
keyfile	ssh, libssh2, libssh	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
no_verify	ssh, tls	SSH: 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. TLS: 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
no_tty	ssh	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
pkipath	tls	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
known_hosts	libssh2, libssh	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.: ~/.config/libvirt/known_hosts. Note: Use absolute paths.
Example: known_hosts=/root/.ssh/known_hosts
known_hosts_verify	libssh2, libssh	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	libssh2, libssh	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

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

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

Libvirt allows you to pass a NULL pointer tovirConnectOpen*. Empty string (') acts inthe same way. Traditionally this has meantconnect to the local Xen hypervisor. However in future thismay change to mean connect to the best available hypervisor.

Ssh X509v3-sign-rsa

The theory is that if, for example, Xen is unavailable but themachine is running an OpenVZ kernel, then we should not try toconnect to the Xen hypervisor since that is obviously the wrongthing to do.

Ssh X509 Rfc

In any case applications linked to libvirt can continue to passNULL as a default choice, but should always allow theuser to override the URI, either by constructing one or by allowingthe user to type a URI in directly (if that is appropriate). If yourapplication wishes to connect specifically to a Xen hypervisor, thenfor future proofing it should choose a full xen:///system URI.

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Another legacy URI is to specify name as the string'xen'. This will continue to refer to the Xenhypervisor. However you should prefer a full xen:///system URI in all future code.