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Link into the examples of the qemu driver. Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>
406 lines
13 KiB
ReStructuredText
406 lines
13 KiB
ReStructuredText
===============
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Connection URIs
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===============
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.. contents::
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Since libvirt supports many different kinds of virtualization (often referred to
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as "drivers" or "hypervisors"), we need a way to be able to specify which driver
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a connection refers to. Additionally we may want to refer to a driver on a
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remote machine over the network.
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To this end, libvirt uses URIs as used on the Web and as defined in `RFC
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2396 <https://www.ietf.org/rfc/rfc2396.txt>`__. This page documents libvirt
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URIs.
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Specifying URIs to libvirt
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--------------------------
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The URI is passed as the ``name`` parameter to
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`virConnectOpen <html/libvirt-libvirt-host.html#virConnectOpen>`__ or
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`virConnectOpenReadOnly <html/libvirt-libvirt-host.html#virConnectOpenReadOnly>`__
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. For example:
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::
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virConnectPtr conn = virConnectOpenReadOnly ("test:///default");
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Configuring URI aliases
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-----------------------
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To simplify life for administrators, it is possible to setup URI aliases in a
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libvirt client configuration file. The configuration file is
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``/etc/libvirt/libvirt.conf`` for the root user, or
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``$XDG_CONFIG_HOME/libvirt/libvirt.conf`` for any unprivileged user. In this
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file, the following syntax can be used to setup aliases
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::
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uri_aliases = [
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"hail=qemu+ssh://root@hail.cloud.example.com/system",
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"sleet=qemu+ssh://root@sleet.cloud.example.com/system",
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]
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A URI alias should be a string made up from the characters ``a-Z, 0-9, _, -``.
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Following the ``=`` can be any libvirt URI string, including arbitrary URI
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parameters. URI aliases will apply to any application opening a libvirt
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connection, unless it has explicitly passed the ``VIR_CONNECT_NO_ALIASES``
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parameter to ``virConnectOpenAuth``. If the passed in URI contains characters
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outside the allowed alias character set, no alias lookup will be attempted.
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Default URI choice
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------------------
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If the URI passed to ``virConnectOpen*`` is NULL or empty string, then libvirt
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will use the following logic to determine what URI to use.
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#. The environment variable ``LIBVIRT_DEFAULT_URI``
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#. The client configuration file ``uri_default`` parameter
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#. Probe each hypervisor in turn until one that works is found
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Historically an empty URI was equivalent to ``xen:///system``.
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Specifying URIs to virsh, virt-manager and virt-install
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-------------------------------------------------------
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In virsh use the ``-c`` or ``--connect`` option:
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::
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virsh -c test:///default list
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If virsh finds the environment variable ``VIRSH_DEFAULT_CONNECT_URI`` set, it
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will try this URI by default. Use of this environment variable is, however,
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deprecated now that libvirt supports ``LIBVIRT_DEFAULT_URI`` itself.
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When using the interactive virsh shell, you can also use the ``connect`` *URI*
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command to reconnect to another hypervisor.
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In virt-manager use the ``-c`` or ``--connect=``\ *URI* option:
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::
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virt-manager -c test:///default
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In virt-install use the ``--connect=``\ *URI* option:
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::
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virt-install --connect=test:///default [other options]
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Local hypervisor URIs
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---------------------
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xen:///system URI
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~~~~~~~~~~~~~~~~~
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To access a Xen hypervisor running on the local machine use the URI
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``xen:///system``.
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Historically libvirt 0.2.2 and previous versions required to use the name
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``"xen"`` to refer to the Xen hypervisor.
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qemu:///... QEMU and KVM URIs
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To use QEMU support in libvirt you must be running the ``libvirtd`` daemon
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(named ``libvirt_qemud`` in releases prior to 0.3.0). The purpose of this daemon
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is to manage qemu instances.
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The ``libvirtd`` daemon should be started by the init scripts when the machine
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boots. It should appear as a process ``libvirtd --daemon`` running as root in
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the background and will handle qemu instances on behalf of all users of the
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machine (among other things).
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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.
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- ``qemu:///session`` connects to a session mode daemon.
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(If you do ``libvirtd --help``, the daemon will print out the paths of the Unix
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domain socket(s) that it listens on in the various different modes).
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KVM URIs are identical. You select between qemu, qemu accelerated and KVM guests
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in the `guest XML as described here <drvqemu.html#example-domain-xml-config>`__.
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test:///... Test URIs
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~~~~~~~~~~~~~~~~~~~~~
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The test driver is a dummy hypervisor for test purposes. The URIs supported are:
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- ``test:///default`` connects to a default set of host definitions built into
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the driver.
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- ``test:///path/to/host/definitions`` connects to a set of host definitions
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held in the named file.
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Remote URIs
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-----------
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Remote URIs have the general form ("[...]" meaning an optional part):
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::
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driver[+transport]://[username@][hostname][:port]/[path][?extraparameters]
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Either the transport or the hostname must be given in order to distinguish this
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from a local URI.
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Some examples:
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- ``xen+ssh://rjones@towada/system``
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— Connect to a remote Xen hypervisor on host ``towada`` using ssh transport
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and ssh username ``rjones``.
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- ``xen://towada/system``
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— Connect to a remote Xen hypervisor on host ``towada`` using TLS.
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- ``xen://towada/system?no_verify=1``
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— Connect to a remote Xen hypervisor on host ``towada`` using TLS. Do not
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verify the server's certificate.
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- ``qemu+unix:///system?socket=/opt/libvirt/run/libvirt/libvirt-sock``
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— Connect to the local qemu instances over a non-standard Unix socket (the
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full path to the Unix socket is supplied explicitly in this case).
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- ``test+tcp://localhost:5000/default``
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— Connect to a libvirtd daemon offering unencrypted TCP/IP connections on
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localhost port 5000 and use the test driver with default settings.
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- ``qemu+libssh2://user@host/system?known_hosts=/home/user/.ssh/known_hosts``
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— Connect to a remote host using a ssh connection with the libssh2 driver and
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use a different known_hosts file.
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- ``qemu+libssh://user@host/system?known_hosts=/home/user/.ssh/known_hosts``
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— Connect to a remote host using a ssh connection with the libssh driver and
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use a different known_hosts file.
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Transport configuration
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~~~~~~~~~~~~~~~~~~~~~~~
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The remote driver supports multiple transport protocols and approaches which are
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configurable via the URI.
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Extra parameters can be added to remote URIs as part of the query string (the
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part following ``?``). Remote URIs understand the extra parameters shown
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below. Any others are passed unmodified through to the back end. Note that
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parameter values must be
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`URI-escaped <https://gnome.pages.gitlab.gnome.org/libxml2/devhelp/libxml2-uri.html#xmlURIEscapeStr>`__.
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All transports support the following parameters:
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``name``
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The name passed to the remote ``virConnectOpen`` function. The name is
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normally formed by removing transport, hostname, port number, username and
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extra parameters from the remote URI, but in certain very complex cases it
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may be better to supply the name explicitly.
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**Example:** ``name=qemu:///system``
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``ssh`` transport
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^^^^^^^^^^^^^^^^^
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The ``ssh`` transport uses the standard SSH protocol via the system installed
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binary.
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Supported extra parameters:
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``mode``
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See the info on the `mode parameter`_.
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``proxy``
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See the info on the `proxy parameter`_.
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``command``
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Path to the ``ssh`` binary to use.
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**Example:** ``command=/opt/openssh/bin/ssh``
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``socket``
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See the info on the `socket parameter`_.
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``netcat``
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See the info on the `netcat parameter`_.
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``keyfile``
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See the info on the `keyfile parameter`_.
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``no_verify``
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If set to a non-zero value, this disables client's strict host key checking
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making it auto-accept new host keys. Existing host keys will still be
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validated.
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**Example:** ``no_verify=1``
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``no_tty``
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If set to a non-zero value, this stops ssh from asking for a password if it
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cannot log in to the remote machine automatically (eg. using ssh-agent
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etc.). Use this when you don't have access to a terminal - for example in
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graphical programs which use libvirt.
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**Example:** ``no_tty=1``
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``libssh`` and ``libssh2`` transport
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Same as the ``ssh`` transport but the SSH client is handled directly by using
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either ``libssh`` or ``libssh2`` to handle the SSH protocol without spawning an
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extra process.
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Supported extra parameters:
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``mode``
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See the info on the `mode parameter`_.
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``proxy``
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See the info on the `proxy parameter`_.
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``socket``
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See the info on the `socket parameter`_.
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``netcat``
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See the info on the `netcat parameter`_.
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``keyfile``
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See the info on the `keyfile parameter`_.
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``known_hosts``
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Path to the known_hosts file to verify the host key against. LibSSH2 and
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libssh support OpenSSH-style known_hosts files, although LibSSH2 does not
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support all key types, so using files created by the OpenSSH binary may
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result into truncating the known_hosts file. Thus, with LibSSH2 it's
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recommended to use the default known_hosts file is located in libvirt's
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client local configuration directory e.g.: ~/.conf ig/libvirt/known_hosts.
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*Note:* Use absolute paths.
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**Example:** ``known_hosts=/root/.ssh/known_hosts``
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``known_hosts_verify``
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If set to ``normal`` (default), then the user will be asked to accept new
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host keys. If set to ``auto``, new host keys will be auto-accepted, but
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existing host keys will still be validated. If set to ``ignore``, this
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disables client's strict host key checking.
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**Example:** ``known_hosts_verify=ignore``
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``sshauth``
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A comma separated list of authentication methods to use. Default (is
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"agent,privkey,password ,keyboard-interactive". The order of the methods
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is preserved. Some methods may require additional parameters.
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**Example:** ``sshauth=privkey,agent``
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``tls`` transport
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^^^^^^^^^^^^^^^^^
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This transport uses a TCP connection to the socket. The data is encrypted using
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TLS to ensure security. Note that TLS certificates must be setup for this to
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work.
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Supported extra parameters:
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``tls_priority``
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A valid GNUTLS priority string.
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**Example:** ``tls_priority=NORMAL:-VERS-SSL3.0``
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``no_verify``
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If set to a non-zero value, this disables client checks of the server's
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certificate. Note that to disable server checks of the client's certificate
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or IP address you must `change the libvirtd configuration
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<remote.html#libvirtd-configuration-file>`__
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**Example:** ``no_verify=1``
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``pkipath``
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Specifies x509 certificates path for the client. If any of the CA
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certificate, client certificate, or client key is missing, the connection
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will fail with a fatal error.
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**Example:** ``pkipath=/tmp/pki/client``
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``unix`` transport
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^^^^^^^^^^^^^^^^^^
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This transport uses an unix domain socket is used to connect to the daemon.
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This is the most common case. In most cases no extra parameters are needed.
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Supported extra parameters:
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``mode``
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See the info on the `mode parameter`_.
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``socket``
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See the info on the `socket parameter`_.
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``ext`` transport
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^^^^^^^^^^^^^^^^^
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The ``ext`` transport invokes the user specified command to transport the
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libvirt RPC protocol to the destination. The command must be able to handle
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the proper connection. Standard input/output is used for the communication.
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Supported extra parameters:
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``command``
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The external command launched to tunnel the data to the destination.
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``tcp`` transport
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^^^^^^^^^^^^^^^^^
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The ``tcp`` transport uses plain unencrypted TCP connection to libvirt. This
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is insecure and should not be used. This transport has no additional arguments.
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Common extra parameters
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~~~~~~~~~~~~~~~~~~~~~~~
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Certain extra parameters are shared between multiple protocols. See the list of
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transport protocols above for specific usage.
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``mode`` parameter
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^^^^^^^^^^^^^^^^^^
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Controls whether to connect to per-driver daemons or libvirtd.
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Supported values:
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``auto``
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automatically determine the daemon
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``direct``
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connect to per-driver daemons
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``legacy``
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connect to libvirtd
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Default is ``auto``. Can also be set in ``libvirt.conf`` as ``remote_mode``.
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**Example:** ``mode=direct``
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``proxy`` parameter
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^^^^^^^^^^^^^^^^^^^
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Controls which proxy binary is used on the remote side of connection to connect
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to the daemon.
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Supported values:
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``auto``
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try native, fallback to netcat
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``netcat``
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only use netcat
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``native``
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use the libvirt native proxy binary
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Default is ``auto``. Can also be set in ``libvirt.conf`` as ``remote_proxy``.
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**Example:** ``proxy=native``
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``socket`` parameter
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^^^^^^^^^^^^^^^^^^^^
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The path to the Unix domain socket, which overrides the compiled-in default.
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This may be passed to the remote proxy command (See. `proxy parameter`).
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**Example:** ``socket=/opt/libvirt/run/libvirt/libvirt-sock``
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``netcat`` parameter
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^^^^^^^^^^^^^^^^^^^^
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The name of the netcat command on the remote machine. The default is ``nc``.
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This is not permitted when using the ``native`` proxy mode.
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The command used here is used on the remote side of the connection as:
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``netcat -U socket``
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**Example:** ``netcat=/opt/netcat/bin/nc``
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``keyfile`` parameter
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^^^^^^^^^^^^^^^^^^^^^
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The name of the private key file to use to authentication to the remote
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machine. If this option is not used the default keys are used.
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**Example:** ``keyfile=/root/.ssh/example_key``
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