# Libvirt the virtualization API

# Note: this is the flat content of the web site

# libvirt

### what is libvirt?

Libvirt is a C toolkit to interact with the virtualization capabilities of recent versions of Linux (and other OSes). It is free software available under the GNU Lesser General Public License. Virtualization of the Linux Operating System means the ability to run multiple instances of Operating Systems concurently on a single hardware system where the basic resources are driven by a Linux (or Solaris) instance. The library aims at providing a long term stable C API initially for Xen paravirtualization but it can also integrate with other virtualization mechanisms. It currently also supports QEMU, KVM and OpenVZ.

## Releases

Here is the list of official releases, however since it is early on in the development of libvirt, it is preferable when possible to just use the CVS version or snapshot, contact the mailing list and check the ChangeLog to gauge progress.

### 0.4.0: Sep 30 2007

- New features: Compilation on Windows cygwin/mingw (Richard Jones), Ruby bindings (David Lutterkort), SASL based authentication for libvirt remote support (Daniel Berrange), PolicyKit authentication (Daniel Berrange)
- Documentation: example files for QEMU and libvirtd configuations (Daniel Berrange), english cleanups (Jim Paris), CIM and OpenVZ references, document <shareable/>, daemon startup when using QEMU/KVM, document HV support for new NUMA calls (Richard Jones), various english fixes (Bruce Montague), OCaml docs links (Richard Jones), describe the various bindings add Ruby link, Windows support page (Richard Jones), authentication documentation updates (Daniel Berrange)
- Bug fixes: NUMA topology error handling (Beth Kon), NUMA topology cells without CPU (Beth Kon), XML to/from XM bridge config (Daniel Berrange), XM processing of vnc parameters (Daniel Berrange), Reset migration source after failure (Jim Paris), negative integer in config (Tatsuro Enokura), zero terminating string buffer, detect integer overflow (Jim Meyering), QEmu command line ending fixes (Daniel Berrange), recursion problem in the daemon (Daniel Berrange), HVM domain with CDRom (Masayuki Sunou), off by one error in NUMA cpu count (Beth Kon), avoid xend errors when adding disks (Masayuki Sunou), compile error (Chris Lalancette), transposed fwrite args (Jim Meyering), compile without xen and on solaris (Jim Paris), parsing of interface names (Richard Jones), overflow for starts on 32bits (Daniel Berrange), fix problems in error reporting (Saori Fukuta), wrong call to brSetForwardDelay changed to brSetEnableSTP (Richard Jones), allow shareable disk in old Xen, fix wrong certificate file (Jim Meyering), avoid some startup error when non-root, off-by-1 buffer NULL termination (Daniel Berrange), various string allocation fixes (Daniel Berrange), avoid problems with vnetXXX interfaces in domain dumps (Daniel Berrange), build fixes for RHEL (Daniel Berrange), virsh prompt should not depend on uid (Richard Jones), fix scaping of '<' (Richard Jones), fix detach-disk on Xen tap devices (Saori Fukuta), CPU parameter setting in XM config (Saori Fukuta), credential handling fixes (Daniel Berrange), fix compatibility with Xen 3.2.0 (Daniel Berrange)
- Improvements: /etc/libvirt/qemu.conf configuration for QEMU driver (Daniel Berrange), NUMA cpu pinning in config files (DV and Saori Fukuta), CDRom media change in KVM/QEMU (Daniel Berrange), tests for <shareable/> in configs, pinning inactive domains for Xen 3.0.3 (Saori Fukuta), use gnulib for portability enhancement (Jim Meyering), --without-libvirtd config option (Richard Jones), Python bindings for NUMA, add extra utility functions to buffer (Richard Jones), separate qparams module for handling query parameters (Richard Jones)
- Code cleanups: remove virDomainRestart from API as it was never used (Richard Jones), constify params for attach/detach APIs (Daniel Berrange), gcc printf attribute checkings (Jim Meyering), refactoring of device parsing code and shell escaping (Daniel Berrange), virsh schedinfo parameters validation (Masayuki Sunou), Avoid risk of format string abuse (Jim Meyering), integer parsing cleanups (Jim Meyering), build out of the source tree (Jim Meyering), URI parsing refactoring (Richard Jones), failed strdup/malloc handling (Jim Meyering), Make "make distcheck" work (Jim Meyering), improve xen internall error reports (Richard Jones), cleanup of the daemon remote code (Daniel Berrange), rename error VIR_FROM_LINUX to VIR_FROM_STATS_LINUX (Richard Jones), don't compile the proxy if without Xen (Richard Jones), fix paths when configuring for /usr prefix, improve error reporting code (Jim Meyering), detect heap allocation failure (Jim Meyering), disable xen sexpr parsing code if Xen is disabled (Daniel Berrange), cleanup of the GetType entry point for Xen drivers, move some QEmu path handling to generic module (Daniel Berrange), many code cleanups related to the Windows port (Richard Jones), disable the proxy if using PolicyKit, readline availability detection, test libvirtd's config-processing code (Jim Meyering), use a variable name as sizeof argument (Jim Meyering)

### 0.3.3: Sep 30 2007

- New features: Avahi mDNS daemon export (Daniel Berrange), NUMA support (Beth Kan)
- Documentation: cleanups (Toth Istvan), typos (Eduardo Pereira),
- Bug fixes: memory corruption on large dumps (Masayuki Sunou), fix virsh vncdisplay command exit (Masayuki Sunou), Fix network stats TX/RX result (Richard Jones), warning on Xen 3.0.3 (Richard Jones), missing buffer check in virDomainXMLDevID (Hugh Brock), avoid zombies when using remote (Daniel Berrange), xend connection error message (Richard Jones), avoid ssh tty prompt (Daniel Berrange), username handling for remote URIs (Fabian Deutsch), fix potential crash on multiple input XML tags (Daniel Berrange), Solaris Xen hypercalls fixup (Mark Johnson)
- Improvements: OpenVZ support (Shuveb Hussain and Anoop Cyriac), CD-Rom reload on XEn (Hugh Brock), PXE boot got QEmu/KVM (Daniel Berrange), QEmu socket permissions customization (Daniel Berrange), more QEmu support (Richard Jones), better path detection for qemu and dnsmasq (Richard Jones), QEmu flags are per-Domain (Daniel Berrange), virsh freecell command, Solaris portability fixes (Mark Johnson), default bootloader support (Daniel Berrange), new virNodeGetFreeMemory API, vncpasswd extraction in configuration files if secure (Mark Johnson and Daniel Berrange), Python bindings for block and interface statistics
- Code cleanups: virDrvOpenRemoteFlags definition (Richard Jones), configure tests and output (Daniel Berrange)

### 0.3.2: Aug 21 2007

- New features: KVM migration and save/restore (Jim Paris), added API for migration (Richard Jones), added APIs for block device and interface statistic (Richard Jones).
- Documentation: examples for XML network APIs, fix typo and schedinfo synopsis in man page (Atsushi SAKAI), hypervisor support page update (Richard Jones).
- Bug fixes: remove a couple of leaks in QEmu/KVM backend(Daniel berrange), fix GnuTLS 1.0 compatibility (Richard Jones), --config/-f option mistake for libvirtd (Richard Jones), remove leak in QEmu backend (Jim Paris), fix some QEmu communication bugs (Jim Paris), UUID lookup though proxy fix, setvcpus checking bugs (with Atsushi SAKAI), int checking in virsh parameters (with Masayuki Sunou), deny devices attach/detach for < Xen 3.0.4 (Masayuki Sunou), XenStore query memory leak (Masayuki Sunou), virsh schedinfo cleanup (Saori Fukuta).
- Improvement: virsh new ttyconsole command, networking API implementation for test driver (Daniel berrange), qemu/kvm feature reporting of ACPI/APIC (David Lutterkort), checking of QEmu architectures (Daniel berrange), improve devices XML errors reporting (Masayuki Sunou), speedup of domain queries on Xen (Daniel berrange), augment XML dumps with interface devices names (Richard Jones), internal API to query drivers for features (Richard Jones).
- Cleanups: Improve virNodeGetInfo implentation (Daniel berrange), general UUID code cleanup (Daniel berrange), fix API generator file selection.

### 0.3.1: Jul 24 2007

- Documentation: index to remote page, script to test certificates, IPv6 remote support docs (Daniel Berrange), document VIRSH_DEFAULT_CONNECT_URI in virsh man page (David Lutterkort), Relax-NG early grammar for the network XML (David Lutterkort)
- Bug fixes: leaks in disk XML parsing (Masayuki Sunou), hypervisor alignment call problems on PPC64 (Christian Ehrhardt), dead client registration in daemon event loop (Daniel Berrange), double free in error handling (Daniel Berrange), close on exec for log file descriptors in the daemon (Daniel Berrange), avoid caching problem in remote daemon (Daniel Berrange), avoid crash after QEmu domain failure (Daniel Berrange)
- Improvements: checks of x509 certificates and keys (Daniel Berrange), error reports in the daemon (Daniel Berrange), checking of Ethernet MAC addresses in XML configs (Masayuki Sunou), support for a new clock switch between UTC and localtime (Daniel Berrange), early version of OpenVZ support (Shuveb Hussain), support for input devices on PS/2 and USB buses (Daniel Berrange), more tests especially the QEmu support (Daniel Berrange), range check in credit scheduler (with Saori Fukuta and Atsushi Sakai), add support for listen VNC parameter un QEmu and fix command line arg (Daniel Berrange)
- Cleanups: debug tracing (Richard Jones), removal of --with-qemud-pid-file (Richard Jones), remove unused virDeviceMode, new util module for code shared between drivers (Shuveb Hussain), xen header location detection (Richard Jones)

### 0.3.0: Jul 9 2007

- Secure Remote support (Richard Jones). See the remote page of the documentation
- Documentation: remote support (Richard Jones), description of the URI connection strings (Richard Jones), update of virsh man page, matrix of libvirt API/hypervisor support with version informations (Richard Jones)
- Bug fixes: examples Makefile.am generation (Richard Jones), SetMem fix (Mark Johnson), URI handling and ordering of drivers (Daniel Berrange), fix virsh help without hypervisor (Richard Jones), id marshalling fix (Daniel Berrange), fix virConnectGetMaxVcpus on remote (Richard Jones), avoid a realloc leak (Jim Meyering), scheduler parameters handling for Xen (Richard Jones), various early remote bug fixes (Richard Jones), remove virsh leaks of domains references (Masayuki Sunou), configCache refill bug (Richard Jones), fix XML serialization bugs
- Improvements: QEmu switch to XDR-based protocol (Dan Berrange), device attach/detach commands (Masayuki Sunou), OCaml bindings (Richard Jones), new entry points virDomainGetConnect and virNetworkGetConnect useful for bindings (Richard Jones), reunitifaction of remote and qemu daemon under a single libvirtd with a config file (Daniel Berrange)
- Cleanups: parsing of connection URIs (Richard Jones), messages from virsh (Saori Fukuta), Coverage files (Daniel Berrange), Solaris fixes (Mark Johnson), avoid [r]index calls (Richard Jones), release information in Xen backend, virsh cpupin command cleanups (Masayuki Sunou), xen:/// suppport as standard Xen URI (Richard Jones and Daniel Berrange), improve driver selection/decline mechanism (Richard Jones), error reporting on XML dump (Richard Jones), Remove unused virDomainKernel structure (Richard Jones), daemon event loop event handling (Daniel Berrange), various unifications cleanup in the daemon merging (Daniel Berrange), internal file and timer monitoring API (Daniel Berrange), remove libsysfs dependancy, call brctl program directly (Daniel Berrange), virBuffer functions cleanups (Richard Jones), make init script LSB compliant, error handling on lookup functions (Richard Jones), remove internal virGetDomainByID (Richard Jones), revamp of xen subdrivers interfaces (Richard Jones)
- Localization updates

### 0.2.3: Jun 8 2007

- Documentation: documentation for upcoming remote access (Richard Jones), virConnectNumOfDefinedDomains doc (Jan Michael), virsh help messages for dumpxml and net-dumpxml (Chris Wright),
- Bug fixes: RelaxNG schemas regexp fix (Robin Green), RelaxNG arch bug (Mark McLoughlin), large buffers bug fixes (Shigeki Sakamoto), error on out of memory condition (Shigeki Sakamoto), virshStrdup fix, non-root driver when using Xen bug (Richard Jones), use --strict-order when running dnsmasq (Daniel Berrange), virbr0 weirdness on restart (Mark McLoughlin), keep connection error messages (Richard Jones), increase QEmu read buffer on help (Daniel Berrange), rpm dependance on dnsmasq (Daniel Berrange), fix XML boot device syntax (Daniel Berrange), QEmu memory bug (Daniel Berrange), memory leak fix (Masayuki Sunou), fix compiler flags (Richard Jones), remove type ioemu on recent Xen HVM for paravirt drivers (Saori Fukuta), uninitialized string bug (Masayuki Sunou), allow init even if the daemon is not running, XML to config fix (Daniel Berrange)
- Improvements: add a special error class for the test module (Richard Jones), virConnectGetCapabilities on proxy (Richard Jones), allow network driver to decline usage (Richard Jones), extend error messages for upcoming remote access (Richard Jones), on_reboot support for QEmu (Daniel Berrange), save daemon output in a log file (Daniel Berrange), xenXMDomainDefineXML can override guest config (Hugh Brock), add attach-device and detach-device commands to virsh (Masayuki Sunou and Mark McLoughlin and Richard Jones), make virGetVersion case insensitive and Python bindings (Richard Jones), new scheduler API (Atsushi SAKAI), localizations updates, add logging option for virsh (Nobuhiro Itou), allow arguments to be passed to bootloader (Hugh Brock), increase the test suite (Daniel Berrange and Hugh Brock)
- Cleanups: Remove VIR_DRV_OPEN_QUIET (Richard Jones), disable xm_internal.c for Xen > 3.0.3 (Daniel Berrange), unused fields in _virDomain (Richard Jones), export __virGetDomain and __virGetNetwork for libvirtd only (Richard Jones), ignore old VNC config for HVM on recent Xen (Daniel Berrange), various code cleanups, -Werror cleanup (Hugh Brock)

### 0.2.2: Apr 17 2007

- Documentation: fix errors due to Amaya (with Simon Hernandez), virsh uses kB not bytes (Atsushi SAKAI), add command line help to qemud (Richard Jones), xenUnifiedRegister docs (Atsushi SAKAI), strings typos (Nikolay Sivov), ilocalization probalem raised by Thomas Canniot
- Bug fixes: virsh memory values test (Masayuki Sunou), operations without libvirt_qemud (Atsushi SAKAI), fix spec file (Florian La Roche, Jeremy Katz, Michael Schwendt), direct hypervisor call (Atsushi SAKAI), buffer overflow on qemu networking command (Daniel Berrange), buffer overflow in quemud (Daniel Berrange), virsh vcpupin bug (Masayuki Sunou), host PAE detections and strcuctures size (Richard Jones), Xen PAE flag handling (Daniel Berrange), bridged config configuration (Daniel Berrange), erroneous XEN_V2_OP_SETMAXMEM value (Masayuki Sunou), memory free error (Mark McLoughlin), set VIR_CONNECT_RO on read-only connections (S.Sakamoto), avoid memory explosion bug (Daniel Berrange), integer overflow for qemu CPU time (Daniel Berrange), QEMU binary path check (Daniel Berrange)
- Cleanups: remove some global variables (Jim Meyering), printf-style functions checks (Jim Meyering), better virsh error messages, increase compiler checkings and security (Daniel Berrange), virBufferGrow usage and docs, use calloc instead of malloc/memset, replace all sprintf by snprintf, avoid configure clobbering user's CTAGS (Jim Meyering), signal handler error cleanup (Richard Jones), iptables internal code claenup (Mark McLoughlin), unified Xen driver (Richard Jones), cleanup XPath libxml2 calls, IPTables rules tightening (Daniel Berrange),
- Improvements: more regression tests on XML (Daniel Berrange), Python bindings now generate exception in error cases (Richard Jones), Python bindings for vir*GetAutoStart (Daniel Berrange), handling of CD-Rom device without device name (Nobuhiro Itou), fix hypervisor call to work with Xen 3.0.5 (Daniel Berrange), DomainGetOSType for inactive domains (Daniel Berrange), multiple boot devices for HVM (Daniel Berrange),

### 0.2.1: Mar 16 2007

- Various internal cleanups (Richard Jones,Daniel Berrange,Mark McLoughlin)
- Bug fixes: libvirt_qemud daemon path (Daniel Berrange), libvirt config directory (Daniel Berrange and Mark McLoughlin), memory leak in qemud (Mark), various fixes on network support (Mark), avoid Xen domain zombies on device hotplug errors (Daniel Berrange), various fixes on qemud (Mark), args parsing (Richard Jones), virsh -t argument (Saori Fukuta), avoid virsh crash on TAB key (Daniel Berrange), detect xend operation failures (Kazuki Mizushima), don't listen on null socket (Rich Jones), read-only socket cleanup (Rich Jones), use of vnc port 5900 (Nobuhiro Itou), assorted networking fixes (Daniel Berrange), shutoff and shutdown mismatches (Kazuki Mizushima), unlimited memory handling (Atsushi SAKAI), python binding fixes (Tatsuro Enokura)
- Build and portability fixes: IA64 fixes (Atsushi SAKAI), dependancies and build (Daniel Berrange), fix xend port detection (Daniel Berrange), icompile time warnings (Mark), avoid const related compiler warnings (Daniel Berrange), automated builds (Daniel Berrange), pointer/int mismatch (Richard Jones), configure time selection of drivers, libvirt spec hacking (Daniel Berrange)
- Add support for network autostart and init scripts (Mark McLoughlin)
- New API virConnectGetCapabilities() to detect the virtualization capabilities of a host (Richard Jones)
- Minor improvements: qemud signal handling (Mark), don't shutdown or reboot domain0 (Kazuki Mizushima), QEmu version autodetection (Daniel Berrange), network UUIDs (Mark), speed up UUID domain lookups (Tatsuro Enokura and Daniel Berrange), support for paused QEmu CPU (Daniel Berrange), keymap VNC attribute support (Takahashi Tomohiro and Daniel Berrange), maximum number of virtual CPU (Masayuki Sunou), virtsh --readonly option (Rich Jones), python bindings for new functions (Daniel Berrange)
- Documentation updates especially on the XML formats

### 0.2.0: Feb 14 2007

- Various internal cleanups (Mark McLoughlin, Richard Jones, Daniel Berrange, Karel Zak)
- Bug fixes: avoid a crash in connect (Daniel Berrange), virsh args parsing (Richard Jones)
- Add support for QEmu and KVM virtualization (Daniel Berrange)
- Add support for network configuration (Mark McLoughlin)
- Minor improvements: regression testing (Daniel Berrange), localization string updates

### 0.1.11: Jan 22 2007

- Finish XML <-> XM config files support
- Remove memory leak when freeing virConf objects
- Finishing inactive domain support (Daniel Berrange)
- Added a Relax-NG schemas to check XML instances

### 0.1.10: Dec 20 2006

- more localizations
- bug fixes: VCPU info breakages on xen 3.0.3, xenDaemonListDomains buffer overflow (Daniel Berrange), reference count bug when creating Xen domains (Daniel Berrange).
- improvements: support graphic framebuffer for Xen paravirt (Daniel Berrange), VNC listen IP range support (Daniel Berrange), support for default Xen config files and inactive domains of 3.0.4 (Daniel Berrange).

### 0.1.9: Nov 29 2006

- python bindings: release interpeter lock when calling C (Daniel Berrange)
- don't raise HTTP error when looking informations for a domain
- some refactoring to use the driver for all entry points
- better error reporting (Daniel Berrange)
- fix OS reporting when running as non-root
- provide XML parsing errors
- extension of the test framework (Daniel Berrange)
- fix the reconnect regression test
- python bindings: Domain instances now link to the Connect to avoid garbage collection and disconnect
- separate the notion of maximum memory and current use at the XML level
- Fix a memory leak (Daniel Berrange)
- add support for shareable drives
- add support for non-bridge style networking configs for guests(Daniel Berrange)
- python bindings: fix unsigned long marshalling (Daniel Berrange)
- new config APIs virConfNew() and virConfSetValue() to build configs from scratch
- hot plug device support based on Michel Ponceau patch
- added support for inactive domains, new APIs, various associated cleanup (Daniel Berrange)
- special device model for HVM guests (Daniel Berrange)
- add API to dump core of domains (but requires a patched xend)
- pygrub bootloader informations take over <os> informations
- updated the localization strings

### 0.1.8: Oct 16 2006

- Bug for system with page size != 4k
- vcpu number initialization (Philippe Berthault)
- don't label crashed domains as shut off (Peter Vetere)
- fix virsh man page (Noriko Mizumoto)
- blktapdd support for alternate drivers like blktap (Daniel Berrange)
- memory leak fixes (xend interface and XML parsing) (Daniel Berrange)
- compile fix
- mlock/munlock size fixes (Daniel Berrange)
- improve error reporting

### 0.1.7: Sep 29 2006

- fix a memory bug on getting vcpu informations from xend (Daniel Berrange)
- fix another problem in the hypercalls change in Xen changeset 86d26e6ec89b when getting domain informations (Daniel Berrange)

### 0.1.6: Sep 22 2006

- Support for localization of strings using gettext (Daniel Berrange)
- Support for new Xen-3.0.3 cdrom and disk configuration (Daniel Berrange)
- Support for setting VNC port when creating domains with new xend config files (Daniel Berrange)
- Fix bug when running against xen-3.0.2 hypercalls (Jim Fehlig)
- Fix reconnection problem when talking directly to http xend

### 0.1.5: Sep 5 2006

- Support for new hypercalls change in Xen changeset 86d26e6ec89b
- bug fixes: virParseUUID() was wrong, netwoking for paravirt guestsi (Daniel Berrange), virsh on non-existent domains (Daniel Berrange), string cast bug when handling error in python (Pete Vetere), HTTP 500 xend error code handling (Pete Vetere and Daniel Berrange)
- improvements: test suite for SEXPR <-> XML format conversions (Daniel Berrange), virsh output regression suite (Daniel Berrange), new environ variable VIRSH_DEFAULT_CONNECT_URI for the default URI when connecting (Daniel Berrange), graphical console support for paravirt guests (Jeremy Katz), parsing of simple Xen config files (with Daniel Berrange), early work on defined (not running) domains (Daniel Berrange), virsh output improvement (Daniel Berrange

### 0.1.4: Aug 16 2006

- bug fixes: spec file fix (Mark McLoughlin), error report problem (with Hugh Brock), long integer in Python bindings (with Daniel Berrange), XML generation bug for CDRom (Daniel Berrange), bug whem using number() XPath function (Mark McLoughlin), fix python detection code, remove duplicate initialization errors (Daniel Berrange)
- improvements: UUID in XML description (Peter Vetere), proxy code cleanup, virtual CPU and affinity support + virsh support (Michel Ponceau, Philippe Berthault, Daniel Berrange), port and tty informations for console in XML (Daniel Berrange), added XML dump to driver and proxy support (Daniel Berrange), extention of boot options with support for floppy and cdrom (Daniel Berrange), features block in XML to report/ask PAE, ACPI, APIC for HVM domains (Daniel Berrange), fail saide-effect operations when using read-only connection, large improvements to test driver (Daniel Berrange)
- documentation: spelling (Daniel Berrange), test driver examples.

### 0.1.3: Jul 11 2006

- bugfixes: build as non-root, fix xend access when root, handling of empty XML elements (Mark McLoughlin), XML serialization and parsing fixes (Mark McLoughlin), allow to create domains without disk (Mark McLoughlin),
- improvement: xenDaemonLookupByID from O(n^2) to O(n) (Daniel Berrange), support for fully virtualized guest (Jim Fehlig, DV, Mark McLoughlin)
- documentation: augmented to cover hvm domains

### 0.1.2: Jul 3 2006

- headers include paths fixup
- proxy mechanism for unpriviledged read-only access by httpu

### 0.1.1: Jun 21 2006

- building fixes: ncurses fallback (Jim Fehlig), VPATH builds (Daniel P. Berrange)
- driver cleanups: new entry points, cleanup of libvirt.c (with Daniel P. Berrange)
- Cope with API change introduced in Xen changeset 10277
- new test driver for regression checks (Daniel P. Berrange)
- improvements: added UUID to XML serialization, buffer usage (Karel Zak), --connect argument to virsh (Daniel P. Berrange),
- bug fixes: uninitialized memory access in error reporting, S-Expr parsing (Jim Fehlig, Jeremy Katz), virConnectOpen bug, remove a TODO in xs_internal.c
- documentation: Python examples (David Lutterkort), new Perl binding URL, man page update (Karel Zak)

### 0.1.0: Apr 10 2006

- building fixes: --with-xen-distdir option (Ronald Aigner), out of tree build and pkginfo cflag fix (Daniel Berrange)
- enhancement and fixes of the XML description format (David Lutterkort and Jim Fehlig)
- new APIs: for Node information and Reboot
- internal code cleanup: refactoring internals into a driver model, more error handling, structure sharing, thread safety and ref counting
- bug fixes: error message (Jim Meyering), error allocation in virsh (Jim Meyering), virDomainLookupByID (Jim Fehlig),
- documentation: updates on architecture, and format, typo fix (Jim Meyering)
- bindings: exception handling in examples (Jim Meyering), perl ones out of tree (Daniel Berrange)
- virsh: more options, create, nodeinfo (Karel Zak), renaming of some options (Karel Zak), use stderr only for errors (Karel Zak), man page (Andrew Puch)

### 0.0.6: Feb 28 2006

- add UUID lookup and extract API
- add error handling APIs both synchronous and asynchronous
- added minimal hook for error handling at the python level, improved the python bindings
- augment the documentation and tests to cover error handling

### 0.0.5: Feb 23 2006

- Added XML description parsing, dependance to libxml2, implemented the creation API virDomainCreateLinux()
- new APIs to lookup and name domain by UUID
- fixed the XML dump when using the Xend access
- Fixed a few more problem related to the name change
- Adding regression tests in python and examples in C
- web site improvement, extended the documentation to cover the XML format and Python API
- Added devhelp help for Gnome/Gtk programmers

### 0.0.4: Feb 10 2006

- Fix various bugs introduced in the name change

### 0.0.3: Feb 9 2006

- Switch name from from 'libvir' to libvirt
- Starting infrastructure to add code examples
- Update of python bindings for completeness

### 0.0.2: Jan 29 2006

- Update of the documentation, web site redesign (Diana Fong)
- integration of HTTP xend RPC based on libxend by Anthony Liquori for most operations
- Adding Save and Restore APIs
- extended the virsh command line tool (Karel Zak)
- remove xenstore transactions (Anthony Liguori)
- fix the Python bindings bug when domain and connections where freed

### 0.0.1: Dec 19 2005

- First release
- Basic management of existing Xen domains
- Minimal autogenerated Python bindings

## Introduction

Libvirt is a C toolkit to interact with the virtualization capabilities of recent versions of Linux (and other OSes), but libvirt won't try to provide all possible interfaces for interacting with the virtualization features.

To avoid ambiguity about the terms used here here are the definitions for some of the specific concepts used in libvirt documentation:

- a node is a single physical machine
- an hypervisor is a layer of software allowing to virtualize a node in a set of virtual machines with possibly different configurations than the node itself
- a domain is an instance of an operating system running on a virtualized machine provided by the hypervisor

Now we can define the goal of libvirt: to provide the lowest possible generic and stable layer to manage domains on a node.

This implies the following:

- the API should not be targetted to a single virtualization environment though Xen is the current default, which also means that some very specific capabilities which are not generic enough may not be provided as libvirt APIs
- the API should allow to do efficiently and cleanly all the operations needed to manage domains on a node
- the API will not try to provide hight level multi-nodes management features like load balancing, though they could be implemented on top of libvirt
- stability of the API is a big concern, libvirt should isolate applications from the frequent changes expected at the lower level of the virtualization framework

So libvirt should be a building block for higher level management tools and for applications focusing on virtualization of a single node (the only exception being domain migration between node capabilities which may need to be added at the libvirt level). Where possible libvirt should be extendable to be able to provide the same API for remote nodes, however this is not the case at the moment, the code currently handle only local node accesses (extension for remote access support is being worked on, see the mailing list discussions about it).

## libvirt architecture

Currently libvirt supports 2 kind of virtualization, and its internal structure is based on a driver model which simplifies adding new engines:

- Xen hypervisor
- QEmu and KVM based virtualization
- the driver architecture

### Libvirt Xen support

When running in a Xen environment, programs using libvirt have to execute in "Domain 0", which is the primary Linux OS loaded on the machine. That OS kernel provides most if not all of the actual drivers used by the set of domains. It also runs the Xen Store, a database of informations shared by the hypervisor, the kernels, the drivers and the xen daemon. Xend. The xen daemon supervise the control and execution of the sets of domains. The hypervisor, drivers, kernels and daemons communicate though a shared system bus implemented in the hypervisor. The figure below tries to provide a view of this environment:

The library can be initialized in 2 ways depending on the level of priviledge of the embedding program. If it runs with root access, virConnectOpen() can be used, it will use three different ways to connect to the Xen infrastructure:

- a connection to the Xen Daemon though an HTTP RPC layer
- a read/write connection to the Xen Store
- use Xen Hypervisor calls
- when used as non-root libvirt connect to a proxy daemon running as root and providing read-only support

The library will usually interact with the Xen daemon for any operation changing the state of the system, but for performance and accuracy reasons may talk directly to the hypervisor when gathering state informations at least when possible (i.e. when the running program using libvirt has root priviledge access).

If it runs without root access virConnectOpenReadOnly() should be used to connect to initialize the library. It will then fork a libvirt_proxy program running as root and providing read_only access to the API, this is then only useful for reporting and monitoring.

### Libvirt QEmu and KVM support

The model for QEmu and KVM is completely similar, basically KVM is based on QEmu for the process controlling a new domain, only small details differs between the two. In both case the libvirt API is provided by a controlling process forked by libvirt in the background and which launch and control the QEmu or KVM process. That program called libvirt_qemud talks though a specific protocol to the library, and connects to the console of the QEmu process in order to control and report on its status. Libvirt tries to expose all the emulations models of QEmu, the selection is done when creating the new domain, by specifying the architecture and machine type targetted.

The code controlling the QEmu process is available in the `qemud/` directory.

### the driver based architecture

As the previous section explains, libvirt can communicate using different channels with the current hypervisor, and should also be able to use different kind of hypervisor. To simplify the internal design, code, ease maintainance and simplify the support of other virtualization engine the internals have been structured as one core component, the libvirt.c module acting as a front-end for the library API and a set of hypvisor drivers defining a common set of routines. That way the Xen Daemon accces, the Xen Store one, the Hypervisor hypercall are all isolated in separate C modules implementing at least a subset of the common operations defined by the drivers present in driver.h:

- xend_internal: implements the driver functions though the Xen Daemon
- xs_internal: implements the subset of the driver available though the Xen Store
- xen_internal: provide the implementation of the functions possible via direct hypervisor access
- proxy_internal: provide read-only Xen access via a proxy, the proxy code is in the `proxy/`directory.
- xm_internal: provide support for Xen defined but not running domains.
- qemu_internal: implement the driver functions for QEmu and KVM virtualization engines. It also uses a qemud/ specific daemon which interacts with the QEmu process to implement libvirt API.
- test: this is a test driver useful for regression tests of the front-end part of libvirt.

Note that a given driver may only implement a subset of those functions, (for example saving a Xen domain state to disk and restoring it is only possible though the Xen Daemon), in that case the driver entry points for unsupported functions are initialized to NULL.

## Downloads

The latest versions of libvirt can be found on the libvirt.org server ( HTTP, FTP). You will find there the released versions as well as snapshot tarballs updated from CVS head every hour

Anonymous CVS is also available, first register onto the server:

`cvs -d :pserver:anoncvs@libvirt.org:2401/data/cvs login`

it will request a password, enter anoncvs. Then you can checkout the development tree with:

`cvs -d :pserver:anoncvs@libvirt.org:2401/data/cvs co libvirt`

Use ./autogen.sh to configure the local checkout, then `make` and `make install`, as usual. All normal cvs commands are now available except commiting to the base.

## XML Format

This section describes the XML format used to represent domains, there are variations on the format based on the kind of domains run and the options used to launch them:

- Normal paravirtualized Xen domains
- Fully virtualized Xen domains
- KVM domains
- Networking options for QEmu and KVM
- QEmu domains
- Discovering virtualization capabilities

The formats try as much as possible to follow the same structure and reuse elements and attributes where it makes sense.

### Normal paravirtualized Xen guests:

The library use an XML format to describe domains, as input to virDomainCreateLinux() and as the output of virDomainGetXMLDesc(), the following is an example of the format as returned by the shell command `virsh xmldump fc4` , where fc4 was one of the running domains:

    <domain type='xen' id='18'>
      <name>fc4</name>
      <os>
        <type>linux</type>
        <kernel>/boot/vmlinuz-2.6.15-1.43_FC5guest</kernel>
        <initrd>/boot/initrd-2.6.15-1.43_FC5guest.img</initrd>
        <root>/dev/sda1</root>
        <cmdline> ro selinux=0 3</cmdline>
      </os>
      <memory>131072</memory>
      <vcpu>1</vcpu>
      <devices>
        <disk type='file'>
          <source file='/u/fc4.img'/>
          <target dev='sda1'/>
        </disk>
        <interface type='bridge'>
          <source bridge='xenbr0'/>
          <mac address='aa:00:00:00:00:11'/>
          <script path='/etc/xen/scripts/vif-bridge'/>
        </interface>
        <console tty='/dev/pts/5'/>
      </devices>
    </domain>

The root element must be called `domain` with no namespace, the `type` attribute indicates the kind of hypervisor used, 'xen' is the default value. The `id` attribute gives the domain id at runtime (not however that this may change, for example if the domain is saved to disk and restored). The domain has a few children whose order is not significant:

- name: the domain name, preferably ASCII based
- memory: the maximum memory allocated to the domain in kilobytes
- vcpu: the number of virtual cpu configured for the domain
- os: a block describing the Operating System, its content will be dependant on the OS type
  - type: indicate the OS type, always linux at this point
  - kernel: path to the kernel on the Domain 0 filesystem
  - initrd: an optional path for the init ramdisk on the Domain 0 filesystem
  - cmdline: optional command line to the kernel
  - root: the root filesystem from the guest viewpoint, it may be passed as part of the cmdline content too
- devices: a list of `disk`, `interface` and `console` descriptions in no special order

The format of the devices and their type may grow over time, but the following should be sufficient for basic use:

A `disk` device indicates a block device, it can have two values for the type attribute either 'file' or 'block' corresponding to the 2 options available at the Xen layer. It has two mandatory children, and one optional one in no specific order:

- source with a file attribute containing the path in Domain 0 to the file or a dev attribute if using a block device, containing the device name ('hda5' or '/dev/hda5')
- target indicates in a dev attribute the device where it is mapped in the guest
- readonly an optional empty element indicating the device is read-only
- shareable an optional empty element indicating the device can be used read/write with other domains

An `interface` element describes a network device mapped on the guest, it also has a type whose value is currently 'bridge', it also have a number of children in no specific order:

- source: indicating the bridge name
- mac: the optional mac address provided in the address attribute
- ip: the optional IP address provided in the address attribute
- script: the script used to bridge the interface in the Domain 0
- target: and optional target indicating the device name.

A `console` element describes a serial console connection to the guest. It has no children, and a single attribute `tty` which provides the path to the Pseudo TTY on which the guest console can be accessed

Life cycle actions for the domain can also be expressed in the XML format, they drive what should be happening if the domain crashes, is rebooted or is poweroff. There is various actions possible when this happen:

- destroy: The domain is cleaned up (that's the default normal processing in Xen)
- restart: A new domain is started in place of the old one with the same configuration parameters
- preserve: The domain will remain in memory until it is destroyed manually, it won't be running but allows for post-mortem debugging
- rename-restart: a variant of the previous one but where the old domain is renamed before being saved to allow a restart

The following could be used for a Xen production system:

    <domain>
      ...
      <on_reboot>restart</on_reboot>
      <on_poweroff>destroy</on_poweroff>
      <on_crash>rename-restart</on_crash>
      ...
    </domain>

While the format may be extended in various ways as support for more hypervisor types and features are added, it is expected that this core subset will remain functional in spite of the evolution of the library.

### Fully virtualized guests (added in 0.1.3):

Here is an example of a domain description used to start a fully virtualized (a.k.a. HVM) Xen domain. This requires hardware virtualization support at the processor level but allows to run unmodified operating systems:

    <domain type='xen' id='3'>
      <name>fv0</name>
      <uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
      <os>
        <type>hvm</type>
        <loader>/usr/lib/xen/boot/hvmloader</loader>
        <boot dev='hd'/>
      </os>
      <memory>524288</memory>
      <vcpu>1</vcpu>
      <on_poweroff>destroy</on_poweroff>
      <on_reboot>restart</on_reboot>
      <on_crash>restart</on_crash>
      <features>
         <pae/>
         <acpi/>
         <apic/>
      </features>
      <clock sync="localtime"/>
      <devices>
        <emulator>/usr/lib/xen/bin/qemu-dm</emulator>
        <interface type='bridge'>
          <source bridge='xenbr0'/>
          <mac address='00:16:3e:5d:c7:9e'/>
          <script path='vif-bridge'/>
        </interface>
        <disk type='file'>
          <source file='/root/fv0'/>
          <target dev='hda'/>
        </disk>
        <disk type='file' device='cdrom'>
          <source file='/root/fc5-x86_64-boot.iso'/>
          <target dev='hdc'/>
          <readonly/>
        </disk>
        <disk type='file' device='floppy'>
          <source file='/root/fd.img'/>
          <target dev='fda'/>
        </disk>
        <graphics type='vnc' port='5904'/>
      </devices>
    </domain>

There is a few things to notice specifically for HVM domains:

- the optional `<features>` block is used to enable certain guest CPU / system features. For HVM guests the following features are defined:
  - `pae` - enable PAE memory addressing
  - `apic` - enable IO APIC
  - `acpi` - enable ACPI bios
- the optional `<clock>` element is used to specify whether the emulated BIOS clock in the guest is synced to either `localtime` or `utc`. In general Windows will want `localtime` while all other operating systems will want `utc`. The default is thus `utc`
- the `<os>` block description is very different, first it indicates that the type is 'hvm' for hardware virtualization, then instead of a kernel, boot and command line arguments, it points to an os boot loader which will extract the boot informations from the boot device specified in a separate boot element. The `dev` attribute on the `boot` tag can be one of:
  - `fd` - boot from first floppy device
  - `hd` - boot from first harddisk device
  - `cdrom` - boot from first cdrom device
- the `<devices>` section includes an emulator entry pointing to an additional program in charge of emulating the devices
- the disk entry indicates in the dev target section that the emulation for the drive is the first IDE disk device hda. The list of device names supported is dependant on the Hypervisor, but for Xen it can be any IDE device `hda`-`hdd`, or a floppy device `fda`, `fdb`. The `<disk>` element also supports a 'device' attribute to indicate what kinda of hardware to emulate. The following values are supported:
  - `floppy` - a floppy disk controller
  - `disk` - a generic hard drive (the default it omitted)
  - `cdrom` - a CDROM device
  For Xen 3.0.2 and earlier a CDROM device can only be emulated on the `hdc` channel, while for 3.0.3 and later, it can be emulated on any IDE channel.
- the `<devices>` section also include at least one entry for the graphic device used to render the os. Currently there is just 2 types possible 'vnc' or 'sdl'. If the type is 'vnc', then an additional `port` attribute will be present indicating the TCP port on which the VNC server is accepting client connections.

It is likely that the HVM description gets additional optional elements and attributes as the support for fully virtualized domain expands, especially for the variety of devices emulated and the graphic support options offered.

### KVM domain (added in 0.2.0)

Support for the KVM virtualization is provided in recent Linux kernels (2.6.20 and onward). This requires specific hardware with acceleration support and the availability of the special version of the QEmu binary. Since this relies on QEmu for the machine emulation like fully virtualized guests the XML description is quite similar, here is a simple example:

    <domain type='kvm'>
      <name>demo2</name>
      <uuid>4dea24b3-1d52-d8f3-2516-782e98a23fa0</uuid>
      <memory>131072</memory>
      <vcpu>1</vcpu>
      <os>
        <type>hvm</type>
      </os>
      <clock sync="localtime"/>
      <devices>
        <emulator>/home/user/usr/kvm-devel/bin/qemu-system-x86_64</emulator>
        <disk type='file' device='disk'>
          <source file='/home/user/fedora/diskboot.img'/>
          <target dev='hda'/>
        </disk>
        <interface type='user'>
          <mac address='24:42:53:21:52:45'/>
        </interface>
        <graphics type='vnc' port='-1'/>
      </devices>
    </domain>

The specific points to note if using KVM are:

- the top level domain element carries a type of 'kvm'
- the <clock> optional is supported as with Xen HVM
- the <devices> emulator points to the special qemu binary required for KVM
- networking interface definitions definitions are somewhat different due to a different model from Xen see below

except those points the options should be quite similar to Xen HVM ones.

### Networking options for QEmu and KVM (added in 0.2.0)

The networking support in the QEmu and KVM case is more flexible, and support a variety of options:

1. Userspace SLIRP stack

   Provides a virtual LAN with NAT to the outside world. The virtual network has DHCP & DNS services and will give the guest VM addresses starting from `10.0.2.15`. The default router will be `10.0.2.2` and the DNS server will be `10.0.2.3`. This networking is the only option for unprivileged users who need their VMs to have outgoing access. Example configs are:

       <interface type='user'/>

       <interface type='user'>
         <mac address="11:22:33:44:55:66"/>
       </interface>

2. Virtual network

   Provides a virtual network using a bridge device in the host. Depending on the virtual network configuration, the network may be totally isolated, NAT'ing to an explicit network device, or NAT'ing to the default route. DHCP and DNS are provided on the virtual network in all cases and the IP range can be determined by examining the virtual network config with '`virsh net-dumpxml <network name>`'. There is one virtual network called 'default' setup out of the box which does NAT'ing to the default route and has an IP range of `192.168.22.0/255.255.255.0`. Each guest will have an associated tun device created with a name of vnetN, which can also be overriden with the <target> element. Example configs are:

       <interface type='network'>
         <source network='default'/>
       </interface>

       <interface type='network'>
         <source network='default'/>
         <target dev='vnet7'/>
         <mac address="11:22:33:44:55:66"/>
       </interface>

3. Bridge to to LAN

   Provides a bridge from the VM directly onto the LAN. This assumes there is a bridge device on the host which has one or more of the hosts physical NICs enslaved. The guest VM will have an associated tun device created with a name of vnetN, which can also be overriden with the <target> element. The tun device will be enslaved to the bridge. The IP range / network configuration is whatever is used on the LAN. This provides the guest VM full incoming & outgoing net access just like a physical machine. Examples include:

       <interface type='bridge'>
        <source dev='br0'/>
       </interface>

       <interface type='bridge'>
         <source dev='br0'/>
         <target dev='vnet7'/>
         <mac address="11:22:33:44:55:66"/>
       </interface>

4. Generic connection to LAN

   Provides a means for the administrator to execute an arbitrary script to connect the guest's network to the LAN. The guest will have a tun device created with a name of vnetN, which can also be overriden with the <target> element. After creating the tun device a shell script will be run which is expected to do whatever host network integration is required. By default this script is called /etc/qemu-ifup but can be overriden.

       <interface type='ethernet'/>

       <interface type='ethernet'>
         <target dev='vnet7'/>
         <script path='/etc/qemu-ifup-mynet'/>
       </interface>

5. Multicast tunnel

   A multicast group is setup to represent a virtual network. Any VMs whose network devices are in the same multicast group can talk to each other even across hosts. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing. The multicast protocol is compatible with that used by user mode linux guests too. The source address used must be from the multicast address block.

       <interface type='mcast'>
         <source address='230.0.0.1' port='5558'/>
       </interface>

6. TCP tunnel

   A TCP client/server architecture provides a virtual network. One VM provides the server end of the network, all other VMS are configured as clients. All network traffic is routed between the VMs via the server. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing.

   Example server config:

       <interface type='server'>
         <source address='192.168.0.1' port='5558'/>
       </interface>

   Example client config:

       <interface type='client'>
         <source address='192.168.0.1' port='5558'/>
       </interface>

To be noted, options 2, 3, 4 are also supported by Xen VMs, so it is possible to use these configs to have networking with both Xen & QEMU/KVMs connected to each other.

### QEmu domain (added in 0.2.0)

Libvirt support for KVM and QEmu is the same code base with only minor changes. The configuration is as a result nearly identical, the only changes are related to QEmu ability to emulate various CPU type and hardware platforms, and kqemu support (QEmu own kernel accelerator when the emulated CPU is i686 as well as the target machine):

    <domain type='qemu'>
      <name>QEmu-fedora-i686</name>
      <uuid>c7a5fdbd-cdaf-9455-926a-d65c16db1809</uuid>
      <memory>219200</memory>
      <currentMemory>219200</currentMemory>
      <vcpu>2</vcpu>
      <os>
        <type arch='i686' machine='pc'>hvm</type>
        <boot dev='cdrom'/>
      </os>
      <devices>
        <emulator>/usr/bin/qemu</emulator>
        <disk type='file' device='cdrom'>
          <source file='/home/user/boot.iso'/>
          <target dev='hdc'/>
          <readonly/>
        </disk>
        <disk type='file' device='disk'>
          <source file='/home/user/fedora.img'/>
          <target dev='hda'/>
        </disk>
        <interface type='network'>
          <source name='default'/>
        </interface>
        <graphics type='vnc' port='-1'/>
      </devices>
    </domain>

The difference here are:

- the value of type on top-level domain, it's 'qemu' or kqemu if asking for kernel assisted acceleration
- the os type block defines the architecture to be emulated, and optionally the machine type, see the discovery API below
- the emulator string must point to the right emulator for that architecture

### Discovering virtualization capabilities (Added in 0.2.1)

As new virtualization engine support gets added to libvirt, and to handle cases like QEmu supporting a variety of emulations, a query interface has been added in 0.2.1 allowing to list the set of supported virtualization capabilities on the host:

        char * virConnectGetCapabilities (virConnectPtr conn);

The value returned is an XML document listing the virtualization capabilities of the host and virtualization engine to which `@conn` is connected. One can test it using `virsh` command line tool command '`capabilities`', it dumps the XML associated to the current connection. For example in the case of a 64 bits machine with hardware virtualization capabilities enabled in the chip and BIOS you will see

    <capabilities>
      <host>
        <cpu>
          <arch>x86_64</arch>
          <features>
            <vmx/>
          </features>
        </cpu>
      </host>

      <!-- xen-3.0-x86_64 -->
      <guest>
        <os_type>xen</os_type>
        <arch name="x86_64">
          <wordsize>64</wordsize>
          <domain type="xen"></domain>
          <emulator>/usr/lib64/xen/bin/qemu-dm</emulator>
        </arch>
        <features>
        </features>
      </guest>

      <!-- hvm-3.0-x86_32 -->
      <guest>
        <os_type>hvm</os_type>
        <arch name="i686">
          <wordsize>32</wordsize>
          <domain type="xen"></domain>
          <emulator>/usr/lib/xen/bin/qemu-dm</emulator>
          <machine>pc</machine>
          <machine>isapc</machine>
          <loader>/usr/lib/xen/boot/hvmloader</loader>
        </arch>
        <features>
        </features>
      </guest>
      ...
    </capabilities>

The first block (in red) indicates the host hardware capbilities, currently it is limited to the CPU properties but other information may be available, it shows the CPU architecture, and the features of the chip (the feature block is similar to what you will find in a Xen fully virtualized domain description).

The second block (in blue) indicates the paravirtualization support of the Xen support, you will see the os_type of xen to indicate a paravirtual kernel, then architecture informations and potential features.

The third block (in green) gives similar informations but when running a 32 bit OS fully virtualized with Xen using the hvm support.

This section is likely to be updated and augmented in the future, see the discussion which led to the capabilities format in the mailing-list archives.

## Bindings for other languages

Libvirt comes with bindings to support other languages than pure C. First the headers embeds the necessary declarations to allow direct acces from C++ code, but also we have bindings for higher level kind of languages:

- Python: Libvirt comes with direct support for the Python language (just make sure you installed the libvirt-python package if not compiling from sources). See below for more informations about using libvirt with python
- Perl: Daniel Berrange provides bindings for Perl.
- OCaml: Richard Jones supplies bindings for OCaml.
- Ruby: David Lutterkork provides bindings for Ruby.

Support, requests or help for libvirt bindings are welcome on the mailing list, as usual try to provide enough background informations and make sure you use recent version, see the help page.

The remaining of this page focuses on the Python bindings.

The Python binding should be complete and are mostly automatically generated from the formal description of the API in xml. The bindings are articulated around 2 classes `virConnect` and virDomain mapping to the C types. Functions in the C API taking either type as argument then becomes methods for the classes, their name is just stripped from the virConnect or virDomain(Get) prefix and the first letter gets converted to lower case, for example the C functions:

`int virConnectNumOfDomains (virConnectPtr conn);`

`int virDomainSetMaxMemory (virDomainPtr domain, unsigned long memory);`

become

`virConn::numOfDomains(self)`

`virDomain::setMaxMemory(self, memory)`

This process is fully automated, you can get a summary of the conversion in the file libvirtclass.txt present in the python dir or in the docs.There is a couple of function who don't map directly to their C counterparts due to specificities in their argument conversions:

- `virConnectListDomains` is replaced by `virDomain::listDomainsID(self)` which returns a list of the integer ID for the currently running domains
- `virDomainGetInfo` is replaced by `virDomain::info()` which returns a list of
  1. state: one of the state values (virDomainState)
  2. maxMemory: the maximum memory used by the domain
  3. memory: the current amount of memory used by the domain
  4. nbVirtCPU: the number of virtual CPU
  5. cpuTime: the time used by the domain in nanoseconds

So let's look at a simple example inspired from the `basic.py` test found in `python/tests/` in the source tree:

    import libvirt
    import sys

    conn = libvirt.openReadOnly(None)
    if conn == None:
        print 'Failed to open connection to the hypervisor'
        sys.exit(1)

    try:
        dom0 = conn.lookupByName("Domain-0")
    except:
        print 'Failed to find the main domain'
        sys.exit(1)

    print "Domain 0: id %d running %s" % (dom0.ID(), dom0.OSType())
    print dom0.info()

There is not much to comment about it, it really is a straight mapping from the C API, the only points to notice are:

- the import of the module called `libvirt`
- getting a connection to the hypervisor, in that case using the openReadOnly function allows the code to execute as a normal user.
- getting an object representing the Domain 0 using lookupByName
- if the domain is not found a libvirtError exception will be raised
- extracting and printing some informations about the domain using various methods associated to the virDomain class.

## Handling of errors

The main goals of libvirt when it comes to error handling are:

- provide as much detail as possible
- provide the informations as soon as possible
- dont force the library user into one style of error handling

As result the library provide both synchronous, callback based and asynchronous error reporting. When an error happens in the library code the error is logged, allowing to retrieve it later and if the user registered an error callback it will be called synchronously. Once the call to libvirt ends the error can be detected by the return value and the full information for the last logged error can be retrieved.

To avoid as much as prossible troubles with a global variable in a multithreaded environment, libvirt will associate when possible the errors to the current connection they are related to, that way the error is stored in a dynamic structure which can be made thread specific. Error callback can be set specifically to a connection with

So error handling in the code is the following:

1. if the error can be associated to a connection for example when failing to look up a domain
   1. if there is a callback associated to the connection set with virConnSetErrorFunc, call it with the error informations
   2. otherwise if there is a global callback set with virSetErrorFunc, call it with the error information
   3. otherwise call virDefaultErrorFunc which is the default error function of the library issuing the error on stderr
   4. save the error in the connection for later retrieval with virConnGetLastError
2. otherwise like when failing to create an hypervisor connection:
   1. if there is a global callback set with virSetErrorFunc, call it with the error information
   2. otherwise call virDefaultErrorFunc which is the default error function of the library issuing the error on stderr
   3. save the error in the connection for later retrieval with virGetLastError

In all cases the error informations are provided as a virErrorPtr pointer to read-only structure virError containing the following fields:

- code: an error number from the virErrorNumber enum
- domain: an enum indicating which part of libvirt raised the error see virErrorDomain
- level: the error level, usually VIR_ERR_ERROR, though there is room for warnings like VIR_ERR_WARNING
- message: the full human-readable formatted string of the error
- conn: if available a pointer to the virConnectPtr connection to the hypervisor where this happened
- dom: if available a pointer to the virDomainPtr domain targetted in the operation

and then extra raw informations about the error which may be initialized to 0 or NULL if unused

- str1, str2, str3: string informations, usually str1 is the error message format
- int1, int2: integer informations

So usually, setting up specific error handling with libvirt consist of registering an handler with with virSetErrorFunc or with virConnSetErrorFunc, chech the value of the code value, take appropriate action, if needed let libvirt print the error on stderr by calling virDefaultErrorFunc. For asynchronous error handing, set such a function doing nothing to avoid the error being reported on stderr, and call virConnGetLastError or virGetLastError when an API call returned an error value. It can be a good idea to use virResetError or virConnResetLastError once an error has been processed fully.

At the python level, there only a global reporting callback function at this point, see the error.py example about it:

    def handler(ctxt, err):
        global errno

        #print "handler(%s, %s)" % (ctxt, err)
        errno = err

    libvirt.registerErrorHandler(handler, 'context')

the second argument to the registerErrorHandler function is passed as the first argument of the callback like in the C version. The error is a tuple containing the same field as a virError in C, but cast to Python.

## FAQ

Table of Contents:

- License(s)
- Installation
- Compilation
- Developer corner

### License(s)

1. Licensing Terms for libvirt

   libvirt is released under the GNU Lesser General Public License, see the file COPYING.LIB in the distribution for the precise wording. The only library that libvirt depends upon is the Xen store access library which is also licenced under the LGPL.

2. Can I embed libvirt in a proprietary application ?

   Yes. The LGPL allows you to embed libvirt into a proprietary application. It would be graceful to send-back bug fixes and improvements as patches for possible incorporation in the main development tree. It will decrease your maintainance costs anyway if you do so.

### Installation

1. Where can I get libvirt ?

   The original distribution comes from ftp://libvirt.org/libvirt/.

2. I can't install the libvirt/libvirt-devel RPM packages due to failed dependencies

   The most generic solution is to re-fetch the latest src.rpm , and rebuild it locally with

   `rpm --rebuild libvirt-xxx.src.rpm`.

   If everything goes well it will generate two binary rpm packages (one providing the shared libs and virsh, and the other one, the -devel package, providing includes, static libraries and scripts needed to build applications with libvirt that you can install locally.

   One can also rebuild the RPMs from a tarball:

   `rpmbuild -ta libdir-xxx.tar.gz`

   Or from a configured tree with:

   `make rpm`

3. Failure to use the API for non-root users

   Large parts of the API may only be accessible with root priviledges, however the read only access to the xenstore data doesnot have to be forbidden to user, at least for monitoring purposes. If "virsh dominfo" fails to run as an user, change the mode of the xenstore read-only socket with:

   `chmod 666 /var/run/xenstored/socket_ro`

   and also make sure that the Xen Daemon is running correctly with local HTTP server enabled, this is defined in `/etc/xen/xend-config.sxp` which need the following line to be enabled:

   `(xend-http-server yes)`

   If needed restart the xend daemon after making the change with the following command run as root:

   `service xend restart`

### Compilation

1. What is the process to compile libvirt ?

   As most UNIX libraries libvirt follows the "standard":

   `gunzip -c libvirt-xxx.tar.gz | tar xvf -`

   `cd libvirt-xxxx`

   `./configure --help`

   to see the options, then the compilation/installation proper

   `./configure [possible options]`

   `make`

   `make install`

   At that point you may have to rerun ldconfig or a similar utility to update your list of installed shared libs.

2. What other libraries are needed to compile/install libvirt ?

   Libvirt requires libxenstore, which is usually provided by the xen packages as well as the public headers to compile against libxenstore.

3. I use the CVS version and there is no configure script

   The configure script (and other Makefiles) are generated. Use the autogen.sh script to regenerate the configure script and Makefiles, like:

   `./autogen.sh --prefix=/usr --disable-shared`

### Developer corner

1. Troubles compiling or linking programs using libvirt

   To simplify the process of reusing the library, libvirt comes with pkgconfig support, which can be used directly from autoconf support or via the pkg-config command line tool, like:

   `pkg-config libvirt --libs`

## Reporting bugs and getting help

There is a mailing-list libvir-list@redhat.com for libvirt, with an on-line archive. Please subscribe to this list before posting by visiting the associated Web page and follow the instructions. Patches with explanations and provided as attachments are really appreciated and will be discussed on the mailing list. If possible generate the patches by using cvs diff -u in a CVS checkout.

We use Red Hat Bugzilla to track bugs and new feature requests to libvirt. If you want to report a bug or ask for a feature, please check the existing open bugs, then if yours isn't a duplicate of an existing bug, log a new bug and attach any patch or extra data that you may have available. It is always a good idea to also to post to the mailing-list too, so that everybody working on the project can see it, thanks !

Some of the libvirt developpers may be found on IRC on the OFTC network. Use the settings:

- server: irc.oftc.net
- port: 6667 (the usual IRC port)
- channel: #virt

But there is no guarantee that someone will be watching or able to reply, use the mailing-list if you don't get an answer there.

## Windows support

Instructions for compiling and installing libvirt on Windows.

- Binaries
- Compiling from source

### Binaries

Binaries will be available from the download area (but we don't have binaries at the moment).

### Compiling from source

These are the steps to compile libvirt and the other tools from source on Windows.

You will need:

1. MS Windows. Microsoft makes free (as beer) versions of some of its operating systems available to MSDN subscribers. We used Windows 2008 Server for testing, virtualized under Linux using KVM-53 (earlier versions of KVM and QEMU won't run recent versions of Windows because of lack of full ACPI support, so make sure you have the latest KVM).
2. Cygwin's setup.exe.
3. A large amount of free disk space to install Cygwin. Make sure you have 10 GB free to install most Cygwin packages, although if you pare down the list of dependencies you may get away with much less.
4. A network connection for Windows, since Cygwin downloads packages from the net as it installs.
5. Libvirt latest version from CVS
6. The latest source patch from the download area.
7. A version of Cygwin sunrpc, patched to support building `librpc.dll`. A patch and a binary package are available from the download area.

These are the steps to take to compile libvirt from source on Windows:

1. Run Cygwin setup.exe. When it starts up it will show a dialog like this:

2. Step through the setup program accepting defaults or making choices as appropriate, until you get to the screen for selecting packages:

   The user interface here is very confusing. You have to click the "recycling icon" as shown by the arrow:

   which takes the package (and all packages in the subtree) through several states such as "Install", "Reinstall", "Keep", "Skip", "Uninstall", etc.

3. You can install "All" (everything) or better select just the groups and packages needed. Select the following groups and packages for installation:

   Groups | Archive Base Devel Editors Mingw Perl Python Shells
   Packages | openssh sunrpc ≥ 4.0-4 (see below)

4. Once Cygwin has finished installing, start a Cygwin bash shell (either click on the desktop icon or look for Cygwin bash shell in the Start menu).

   The very first time you start the Cygwin bash shell, you may find you need to run the `mkpasswd` and `mkgroup` commands in order to create `/etc/passwd` and `/etc/group` files from Windows users. If this is needed then a message is printed in the shell. Note that you need to do this as Windows Administrator.

5. Install Cygwin sunrpc ≥ 4.0-4 package, patched to include `librpc.dll`. To do this, first check to see whether `/usr/lib/librpc.dll` exists. If it does, you're good to go and can skip to the next step.

   If you don't have this file, either install the binary package sunrpc-4.0-4.tar.bz2 (just unpack it, as Administrator, in the Cygwin root directory). Or you can download the source patch and apply it by hand to the Cygwin sunrpc package (eg. using cygport).

6. Check out Libvirt from CVS and apply the latest Windows patch to the source.

7. Configure libvirt by doing:

       autoreconf
       ./configure --without-xen --without-qemu

   (The autoreconf step is probably optional).

   The configure step will tell you if you have all the required parts installed. If something is missing you will need to go back through Cygwin setup and install it.

8. Rebuild the XDR structures:

       rm qemud/remote_protocol.[ch] qemud/remote_dispatch_*.h
       make -C qemud remote_protocol.c

9. Build:

       make

   If this step is not successful, you should post a full report including complete messages to the libvirt mailing list.

10. Test it. If you have access to a remote machine running Xen or QEMU/KVM, and the libvirt daemon (`libvirtd`) then you should be able to connect to it and display domains using, eg:

        src/virsh.exe -c qemu://remote/system list --all

    Please read more about remote support before sending bug reports, to make sure that any problems are really Windows and not just with remote configuration / security.

11. You may want to install the library and programs by doing:

        make install

12. The above steps should also build and install Python modules. However for reasons which I don't fully understand, Python won't look in the non-standard `/usr/local/lib/python*/site-packages/` directory by default so you may need to set the environment variable PYTHONPATH:

        export PYTHONPATH=/usr/local/lib/python2.5/site-packages

    (Change the version number to your version of Python). You can test Python support from the command line:

        python
        >>> import libvirt
        >>> conn = libvirt.open ("test:///default")
        >>> conn.listDomainsID ()
        [1]
        >>> dom = conn.lookupByID (1)
        >>> dom.XMLDesc (0)
        "<domain type='test' id='1'> ..."

    The most common failure will be with `import libvirt` which usually indicates that either `PYTHONPATH` is wrong or a DLL cannot be loaded.

## Remote support

Libvirt allows you to access hypervisors running on remote machines through authenticated and encrypted connections.

- Basic usage
- Transports
- Remote URIs
  - Extra parameters
- Generating TLS certificates
  - Public Key Infrastructure set up
  - Background to TLS certificates
  - Setting up a Certificate Authority (CA)
  - Issuing server certificates
  - Issuing client certificates
  - Troubleshooting TLS certificate problems
- libvirtd configuration file
- IPv6 support
- Limitations
- Implementation notes

### Basic usage

On the remote machine, `libvirtd` should be running. See the section on configuring libvirtd for more information.

To tell libvirt that you want to access a remote resource, you should supply a hostname in the normal URI that is passed to `virConnectOpen` (or `virsh -c ...`). For example, if you normally use `qemu:///system` to access the system-wide QEMU daemon, then to access the system-wide QEMU daemon on a remote machine called `oirase` you would use `qemu://oirase/system`.

The section on remote URIs describes in more detail these remote URIs.

From an API point of view, apart from the change in URI, the API should behave the same. For example, ordinary calls are routed over the remote connection transparently, and values or errors from the remote side are returned to you as if they happened locally. Some differences you may notice:

- Additional errors can be generated, specifically ones relating to failures in the remote transport itself.
- Remote calls are handled synchronously, so they will be much slower than, say, direct hypervisor calls.

### Transports

Remote libvirt supports a range of transports:

tls
  TLS 1.0 (SSL 3.1) authenticated and encrypted TCP/IP socket, usually listening on a public port number. To use this you will need to generate client and server certificates. The standard port is 16514.
unix
  Unix domain socket. Since this is only accessible on the local machine, it is not encrypted, and uses Unix permissions or SELinux for authentication. The standard socket names are `/var/run/libvirt/libvirt-sock` and `/var/run/libvirt/libvirt-sock-ro` (the latter for read-only connections).
ssh
  Transported over an ordinary ssh (secure shell) connection. Requires Netcat (nc) installed and libvirtd should be running on the remote machine. You should use some sort of ssh key management (eg. ssh-agent) otherwise programs which use this transport will stop to ask for a password.
ext
  Any external program which can make a connection to the remote machine by means outside the scope of libvirt.
tcp
  Unencrypted TCP/IP socket. Not recommended for production use, this is normally disabled, but an administrator can enable it for testing or use over a trusted network. The standard port is 16509.

The default transport, if no other is specified, is `tls`.

### Remote URIs

See also: documentation on ordinary ("local") 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/`
  — Connect to a remote Xen hypervisor on host `towada` using ssh transport and ssh username `rjones`.
- `xen://towada/`
  — Connect to a remote Xen hypervisor on host `towada` using TLS.
- `xen://towada/?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.

#### Extra parameters

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.

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`
`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 | 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

The name of the netcat command on the remote machine. The default is `nc`. For ssh transport, libvirt constructs an ssh command which looks like:

    command -p port [-l username] hostname netcat -U socket

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`
`no_verify` | 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`

### Generating TLS certificates

#### Public Key Infrastructure set up

If you are unsure how to create TLS certificates, skip to the next section.

Location | Machine | Description | Required fields
--- | --- | --- | ---
`/etc/pki/CA/cacert.pem` | Installed on all clients and servers | CA's certificate (more info) | n/a
`/etc/pki/libvirt/ private/serverkey.pem` | Installed on the server | Server's private key (more info) | n/a
`/etc/pki/libvirt/ servercert.pem` | Installed on the server | Server's certificate signed by the CA. (more info) | CommonName (CN) must be the hostname of the server as it is seen by clients.
`/etc/pki/libvirt/ private/clientkey.pem` | Installed on the client | Client's private key. (more info) | n/a
`/etc/pki/libvirt/ clientcert.pem` | Installed on the client | Client's certificate signed by the CA (more info) | Distinguished Name (DN) can be checked against an access control list (`tls_allowed_dn_list`).

#### Background to TLS certificates

Libvirt supports TLS certificates for verifying the identity of the server and clients. There are two distinct checks involved:

- The client should know that it is connecting to the right server. Checking done by client by matching the certificate that the server sends to the server's hostname. May be disabled by adding `?no_verify=1` to the remote URI.
- The server should know that only permitted clients are connecting. This can be done based on client's IP address, or on client's IP address and client's certificate. Checking done by the server. May be enabled and disabled in the libvirtd.conf file.

For full certificate checking you will need to have certificates issued by a recognised Certificate Authority (CA) for your server(s) and all clients. To avoid the expense of getting certificates from a commercial CA, you can set up your own CA and tell your server(s) and clients to trust certificates issues by your own CA. Follow the instructions in the next section.

Be aware that the default configuration for libvirtd allows any client to connect provided they have a valid certificate issued by the CA for their own IP address. You may want to change this to make it less (or more) permissive, depending on your needs.

#### Setting up a Certificate Authority (CA)

You will need the GnuTLS certtool program documented here. In Fedora, it is in the `gnutls-utils` package.

Create a private key for your CA:

    certtool --generate-privkey > cakey.pem

and self-sign it by creating a file with the signature details called `ca.info` containing:

    cn = Name of your organization
    ca
    cert_signing_key

and sign:

    certtool --generate-self-signed --load-privkey cakey.pem \
      --template ca.info --outfile cacert.pem

(You can delete `ca.info` file now if you want).

Now you have two files which matter:

- `cakey.pem` - Your CA's private key (keep this very secret!)
- `cacert.pem` - Your CA's certificate (this is public).

`cacert.pem` has to be installed on clients and server(s) to let them know that they can trust certificates issued by your CA.

The normal installation directory for `cacert.pem` is `/etc/pki/CA/cacert.pem` on all clients and servers.

To see the contents of this file, do:

    certtool -i --infile cacert.pem

    X.509 certificate info:

    Version: 3
    Serial Number (hex): 00
    Subject: CN=Red Hat Emerging Technologies
    Issuer: CN=Red Hat Emerging Technologies
    Signature Algorithm: RSA-SHA
    Validity:
            Not Before: Mon Jun 18 16:22:18 2007
            Not After: Tue Jun 17 16:22:18 2008
    [etc]

This is all that is required to set up your CA. Keep the CA's private key carefully as you will need it when you come to issue certificates for your clients and servers.

#### Issuing server certificates

For each server (libvirtd) you need to issue a certificate with the X.509 CommonName (CN) field set to the hostname of the server. The CN must match the hostname which clients will be using to connect to the server.

In the example below, clients will be connecting to the server using a URI of `xen://oirase/`, so the CN must be "`oirase`".

Make a private key for the server:

    certtool --generate-privkey > serverkey.pem

and sign that key with the CA's private key by first creating a template file called `server.info` (only the CN field matters, which as explained above must be the server's hostname):

    organization = Name of your organization
    cn = oirase
    tls_www_server
    encryption_key
    signing_key

and sign:

    certtool --generate-certificate --load-privkey serverkey.pem \
      --load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \
      --template server.info --outfile servercert.pem

This gives two files:

- `serverkey.pem` - The server's private key.
- `servercert.pem` - The server's public key.

We can examine this certificate and its signature:

    certtool -i --infile servercert.pem
    X.509 certificate info:

    Version: 3
    Serial Number (hex): 00
    Subject: O=Red Hat Emerging Technologies,CN=oirase
    Issuer: CN=Red Hat Emerging Technologies
    Signature Algorithm: RSA-SHA
    Validity:
            Not Before: Mon Jun 18 16:34:49 2007
            Not After: Tue Jun 17 16:34:49 2008

Note the "Issuer" CN is "Red Hat Emerging Technologies" (the CA) and the "Subject" CN is "oirase" (the server).

Finally we have two files to install:

- `serverkey.pem` is the server's private key which should be copied to the server only as `/etc/pki/libvirt/private/serverkey.pem`.
- `servercert.pem` is the server's certificate which can be installed on the server as `/etc/pki/libvirt/servercert.pem`.

#### Issuing client certificates

For each client (ie. any program linked with libvirt, such as virt-manager) you need to issue a certificate with the X.509 Distinguished Name (DN) set to a suitable name. You can decide this on a company / organisation policy. For example, I use:

    C=GB,ST=London,L=London,O=Red Hat,CN=name_of_client

The process is the same as for setting up the server certificate so here we just briefly cover the steps.

1. Make a private key:

       certtool --generate-privkey > clientkey.pem

2. Act as CA and sign the certificate. Create client.info containing:

       country = GB
       state = London
       locality = London
       organization = Red Hat
       cn = client1
       tls_www_client
       encryption_key
       signing_key

   and sign by doing:

       certtool --generate-certificate --load-privkey clientkey.pem \
         --load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \
         --template client.info --outfile clientcert.pem

3. Install the certificates on the client machine:

       cp clientkey.pem /etc/pki/libvirt/private/clientkey.pem
       cp clientcert.pem /etc/pki/libvirt/clientcert.pem

#### Troubleshooting TLS certificate problems

failed to verify client's certificate

  On the server side, run the libvirtd server with the '--listen' and '--verbose' options while the client is connecting. The verbose log messages should tell you enough to diagnose the problem.

You can use the pki_check.sh shell script to analyze the setup on the client or server machines, preferably as root. It will try to point out the possible problems and provide solutions to fix the set up up to a point where you have secure remote access.

### libvirtd configuration file

Libvirtd (the remote daemon) is configured from a file called `/etc/libvirt/libvirtd.conf`, or specified on the command line using `-f filename` or `--config filename`.

This file should contain lines of the form below. Blank lines and comments beginning with `#` are ignored.

    setting = value

The following settings, values and default are:

Line | Default | Meaning
--- | --- | ---
listen_tls [0|1] | 1 (on) | Listen for secure TLS connections on the public TCP/IP port.
listen_tcp [0|1] | 0 (off) | Listen for unencrypted TCP connections on the public TCP/IP port.
tls_port "service" | "16514" | The port number or service name to listen on for secure TLS connections.
tcp_port "service" | "16509" | The port number or service name to listen on for unencrypted TCP connections.
mdns_adv [0|1] | 1 (advertise with mDNS) | If set to 1 then the virtualization service will be advertised over mDNS to hosts on the local LAN segment.
mdns_name "name" | "Virtualization Host HOSTNAME" | The name to advertise for this host with Avahi mDNS. The default includes the machine's short hostname. This must be unique to the local LAN segment.
unix_sock_group "groupname" | "root" | The UNIX group to own the UNIX domain socket. If the socket permissions allow group access, then applications running under matching group can access the socket. Only valid if running as root
unix_sock_ro_perms "octal-perms" | "0777" | The permissions for the UNIX domain socket for read-only client connections. The default allows any user to monitor domains.
unix_sock_rw_perms "octal-perms" | "0700" | The permissions for the UNIX domain socket for read-write client connections. The default allows only root to manage domains.
tls_no_verify_certificate [0|1] | 0 (certificates are verified) | If set to 1 then if a client certificate check fails, it is not an error.
tls_no_verify_address [0|1] | 0 (addresses are verified) | If set to 1 then if a client IP address check fails, it is not an error.
key_file "filename" | "/etc/pki/libvirt/ private/serverkey.pem" | Change the path used to find the server's private key. If you set this to an empty string, then no private key is loaded.
cert_file "filename" | "/etc/pki/libvirt/ servercert.pem" | Change the path used to find the server's certificate. If you set this to an empty string, then no certificate is loaded.
ca_file "filename" | "/etc/pki/CA/cacert.pem" | Change the path used to find the trusted CA certificate. If you set this to an empty string, then no trusted CA certificate is loaded.
crl_file "filename" | (no CRL file is used) | Change the path used to find the CA certificate revocation list (CRL) file. If you set this to an empty string, then no CRL is loaded.

tls_allowed_dn_list ["DN1", "DN2"]

(none - DNs are not checked)

Enable an access control list of client certificate Distinguished Names (DNs) which can connect to the TLS port on this server.

The default is that DNs are not checked.

This list may contain wildcards such as `"C=GB,ST=London,L=London,O=Red Hat,CN=*"` See the POSIX `fnmatch` function for the format of the wildcards.

Note that if this is an empty list, no client can connect.

Note also that GnuTLS returns DNs without spaces after commas between the fields (and this is what we check against), but the `openssl x509` tool shows spaces.

tls_allowed_ip_list ["ip1", "ip2", "ip3"]

(none - clients can connect from anywhere)

Enable an access control list of the IP addresses of clients who can connect to the TLS or TCP ports on this server.

The default is that clients can connect from any IP address.

This list may contain wildcards such as `192.168.*` See the POSIX `fnmatch` function for the format of the wildcards.

Note that if this is an empty list, no client can connect.

### IPv6 support

The libvirtd service and libvirt remote client driver both use the `getaddrinfo()` functions for name resolution and are thus fully IPv6 enabled. ie, if a server has IPv6 address configured the daemon will listen for incoming connections on both IPv4 and IPv6 protocols. If a client has an IPv6 address configured and the DNS address resolved for a service is reachable over IPv6, then an IPv6 connection will be made, otherwise IPv4 will be used. In summary it should just 'do the right thing(tm)'.

### Limitations

- Remote storage: To be fully useful, particularly for creating new domains, it should be possible to enumerate and provision storage on the remote machine. This is currently in the design phase.
- Migration: We expect libvirt will support migration, and obviously remote support is what makes migration worthwhile. This is also in the design phase. Issues to discuss include which path the migration data should follow (eg. client to client direct, or client to server to client) and security.
- Fine-grained authentication: libvirt in general, but in particular the remote case should support more fine-grained authentication for operations, rather than just read-write/read-only as at present.

Please come and discuss these issues and more on the mailing list.

### Implementation notes

The current implementation uses XDR-encoded packets with a simple remote procedure call implementation which also supports asynchronous messaging and asynchronous and out-of-order replies, although these latter features are not used at the moment.

The implementation should be considered strictly internal to libvirt and subject to change at any time without notice. If you wish to talk to libvirtd, link to libvirt. If there is a problem that means you think you need to use the protocol directly, please first discuss this on the mailing list.

The messaging protocol is described in `qemud/remote_protocol.x`.

Authentication and encryption (for TLS) is done using GnuTLS and the RPC protocol is unaware of this layer.

Protocol messages are sent using a simple 32 bit length word (encoded XDR int) followed by the message header (XDR `remote_message_header`) followed by the message body. The length count includes the length word itself, and is measured in bytes. Maximum message size is `REMOTE_MESSAGE_MAX` and to avoid denial of services attacks on the XDR decoders strings are individually limited to `REMOTE_STRING_MAX` bytes. In the TLS case, messages may be split over TLS records, but a TLS record cannot contain parts of more than one message. In the common RPC case a single `REMOTE_CALL` message is sent from client to server, and the server then replies synchronously with a single `REMOTE_REPLY` message, but other forms of messaging are also possible.

The protocol contains support for multiple program types and protocol versioning, modelled after SunRPC.

## Access control

When connecting to libvirt, some connections may require client authentication before allowing use of the APIs. The set of possible authentication mechanisms is administrator controlled, independant of applications using libvirt.

- Server configuration
- UNIX socket permissions/group
- UNIX socket PolicyKit auth
- Username/password auth
- Kerberos auth

### Server configuration

The libvirt daemon allows the adminstrator to choose the authentication mechanisms used for client connections on each network socket independantly. This is primarily controlled via the libvirt daemon master config file in `/etc/libvirt/libvirtd.conf`. Each of the libvirt sockets can have its authentication mechanism configured independantly. There is currently a choice of `none`, `polkit`, and `sasl`. The SASL scheme can be further configured to choose between a large number of different mechanisms.

### UNIX socket permissions/group

If libvirt does not contain support for PolicyKit, then access control for the UNIX domain socket is done using traditional file user/group ownership and permissions. There are 2 sockets, one for full read-write access, the other for read-only access. The RW socket will be restricted (mode 0700) to only allow the `root` user to connect. The read-only socket will be open access (mode 0777) to allow any user to connect.

To allow non-root users greater access, the `libvirtd.conf` file can be edited to change the permissions via the `unix_sock_rw_perms`, config parameter and to set a user group via the `unix_sock_group` parameter. For example, setting the former to mode `0770` and the latter `wheel` would let any user in the wheel group connect to the libvirt daemon.

### UNIX socket PolicyKit auth

If libvirt contains support for PolicyKit, then access control options are more advanced. The `unix_sock_auth` parameter will default to `polkit`, and the file permissions will default to `0777` even on the RW socket. Upon connecting to the socket, the client application will be required to identify itself with PolicyKit. The default policy for the RW daemon socket will require any application running in the current desktop session to authenticate using the user's password. This is akin to `sudo` auth, but does not require that the client application ultimately run as root. Default policy will still allow any application to connect to the RO socket.

The default policy can be overriden by the adminstrator using the PolicyKit master configuration file in `/etc/PolicyKit/PolicyKit.conf`. The `PolicyKit.conf(5)` manual page provides details on the syntax available. The two libvirt daemon actions available are named `org.libvirt.unix.monitor` for the RO socket, and `org.libvirt.unix.manage` for the RW socket.

As an example, to allow a user `fred`full access to the RW socket, while requiring `joe` to authenticate with the admin password, would require adding the following snippet to `PolicyKit.conf`.

      <match action="org.libvirt.unix.manage" user="fred">
        <return result="yes"/>
      </match>
      <match action="org.libvirt.unix.manage" user="joe">
        <return result="auth_admin"/>
      </match>

### Username/password auth

The plain TCP socket of the libvirt daemon defaults to using SASL for authentication. The SASL mechanism configured by default is DIGEST-MD5, which provides a basic username+password style authentication. It also provides for encryption of the data stream, so the security of the plain TCP socket is on a par with that of the TLS socket. If desired the UNIX socket and TLS socket can also have SASL enabled by setting the `auth_unix_ro`, `auth_unix_rw`, `auth_tls` config params in `libvirt.conf`.

Out of the box, no user accounts are defined, so no clients will be able to authenticate on the TCP socket. Adding users and setting their passwords is done with the `saslpasswd2` command. When running this command it is important to tell it that the appname is `libvirt`. As an example, to add a user `fred`, run

    # saslpasswd2 -a libvirt fred
    Password: xxxxxx
    Again (for verification): xxxxxx

To see a list of all accounts the `sasldblistusers2` command can be used. This command expects to be given the path to the libvirt user database, which is kept in `/etc/libvirt/passwd.db`

    # sasldblistusers2 -f /etc/libvirt/passwd.db
    fred@t60wlan.home.berrange.com: userPassword

Finally, to disable a user's access, the `saslpasswd2` command can be used again:

    # saslpasswd2 -a libvirt -d fred

### Kerberos auth

The plain TCP socket of the libvirt daemon defaults to using SASL for authentication. The SASL mechanism configured by default is DIGEST-MD5, which provides a basic username+password style authentication. To enable Kerberos single-sign-on instead, the libvirt SASL configuration file must be changed. This is `/etc/sasl2/libvirt.conf`. The `mech_list` parameter must first be changed to `gssapi` instead of the default `digest-md5`. If SASL is enabled on the UNIX and/or TLS sockets, Kerberos will also be used for them. Like DIGEST-MD5, the Kerberos mechanism provides data encryption of the session.

Some operating systems do not install the SASL kerberos plugin by default. It may be neccessary to install a sub-package such as `cyrus-sasl-gssapi`. To check whether the Kerberos plugin is installed run the `pluginviewer` program and verify that `gssapi` is listed,eg:

    # pluginviewer
    ...snip...
    Plugin "gssapiv2" [loaded],     API version: 4
            SASL mechanism: GSSAPI, best SSF: 56
            security flags: NO_ANONYMOUS|NO_PLAINTEXT|NO_ACTIVE|PASS_CREDENTIALS|MUTUAL_AUTH
            features: WANT_CLIENT_FIRST|PROXY_AUTHENTICATION|NEED_SERVER_FQDN

Next is is neccessary for the adminsitrator of the Kerberos realm to issue a principle for the libvirt server. There needs to be one principle per host running the libvirt daemon. The principle should be named `libvirt/full.hostname@KERBEROS.REALM`. This is typically done by running the `kadmin.local` command on the Kerberos server, though some Kerberos servers have alternate ways of setting up service principles. Once created, the principle should be exported to a keytab, copied to the host running the libvirt daemon and placed in `/etc/libvirt/krb5.tab`

    # kadmin.local
    kadmin.local: add_principal libvirt/foo.example.com
    Enter password for principal "libvirt/foo.example.com@EXAMPLE.COM":
    Re-enter password for principal "libvirt/foo.example.com@EXAMPLE.COM":
    Principal "libvirt/foo.example.com@EXAMPLE.COM" created.

    kadmin.local:  ktadd -k /root/libvirt-foo-example.tab libvirt/foo.example.com@EXAMPLE.COM
    Entry for principal libvirt/foo.example.com@EXAMPLE.COM with kvno 4, encryption type Triple DES cbc mode with HMAC/sha1 added to keytab WRFILE:/root/libvirt-foo-example.tab.
    Entry for principal libvirt/foo.example.com@EXAMPLE.COM with kvno 4, encryption type ArcFour with HMAC/md5 added to keytab WRFILE:/root/libvirt-foo-example.tab.
    Entry for principal libvirt/foo.example.com@EXAMPLE.COM with kvno 4, encryption type DES with HMAC/sha1 added to keytab WRFILE:/root/libvirt-foo-example.tab.
    Entry for principal libvirt/foo.example.com@EXAMPLE.COM with kvno 4, encryption type DES cbc mode with RSA-MD5 added to keytab WRFILE:/root/libvirt-foo-example.tab.

    kadmin.local: quit

    # scp /root/libvirt-foo-example.tab root@foo.example.com:/etc/libvirt/krb5.tab
    # rm /root/libvirt-foo-example.tab

Any client application wishing to connect to a Kerberos enabled libvirt server merely needs to run `kinit` to gain a user principle. This may well be done automatically when a user logs into a desktop session, if PAM is setup to authenticate against Kerberos.

## 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
- Specifying URIs to virsh, virt-manager and virt-install
- xen:/// URI
- qemu:///... QEMU and KVM URIs
- Remote URIs
- test:///... Test URIs
- Other & legacy URI formats

### Specifying URIs to libvirt

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

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

### 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.

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]

### xen:/// URI

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 machine use the URI `xen:///`.

### 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.

### Remote URIs

Remote URIs are formed by taking ordinary local URIs and adding a hostname and/or transport name. For example:

Local URI | Remote URI | Meaning
--- | --- | ---
`xen:///` | `xen://oirase/` | Connect to the Xen hypervisor running on host `oirase` using TLS.
`xen:///` | `xen+ssh://oirase/` | Connect to the Xen hypervisor running on host `oirase` by going over an `ssh` connection.
`test:///default` | `test+tcp://oirase/default` | Connect to the test driver on host `oirase` using an unsecured TCP connection.

Remote URIs in libvirt offer a rich syntax and many features. We refer you to the libvirt remote URI reference and full documentation for libvirt remote support.

### 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.

### Other & legacy URI formats

#### NULL and empty string URIs

Libvirt allows you to pass a `NULL` pointer to `virConnectOpen*`. Empty string (`""`) acts in the same way. Traditionally this has meant connect to the local Xen hypervisor. However in future this may change to mean connect to the best available hypervisor.

The theory is that if, for example, Xen is unavailable but the machine is running an OpenVZ kernel, then we should not try to connect to the Xen hypervisor since that is obviously the wrong thing to do.

In any case applications linked to libvirt can continue to pass `NULL` as a default choice, but should always allow the user to override the URI, either by constructing one or by allowing the user to type a URI in directly (if that is appropriate). If your application wishes to connect specifically to a Xen hypervisor, then for future proofing it should choose a full `xen:///` URI.

#### File paths (xend-unix-server)

If XenD is running and configured in `/etc/xen/xend-config.sxp`:

    (xend-unix-server yes)

then it listens on a Unix domain socket, usually at `/var/lib/xend/xend-socket`. You may pass a different path using a file URI such as:

    virsh -c ///var/run/xend/xend-socket

#### Legacy: `http://...` (xend-http-server)

If XenD is running and configured in `/etc/xen/xend-config.sxp`:

    (xend-http-server yes)

then it listens on TCP port 8000. libvirt allows you to try to connect to xend running on remote machines by passing `http://hostname[:port]/`, for example:

    virsh -c http://oirase/ list

This method is unencrypted and insecure and is definitely not recommended for production use. Instead use libvirt's remote support.

Notes:

1. The HTTP client does not fully support IPv6.
2. Many features do not work as expected across HTTP connections, in particular, virConnectGetCapabilities. The remote support however does work correctly.
3. XenD's new-style XMLRPC interface is not supported by libvirt, only the old-style sexpr interface known in the Xen documentation as "unix server" or "http server".

#### Legacy: `"xen"`

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

#### Legacy: Xen proxy

Libvirt continues to support connections to a separately running Xen proxy daemon. This provides a way to allow non-root users to make a safe (read-only) subset of queries to the hypervisor.

There is no specific "Xen proxy" URI. However if a Xen URI of any of the ordinary or legacy forms is used (eg. `NULL`, `""`, `"xen"`, ...) which fails, and the user is not root, and the Xen proxy socket can be connected to (`/tmp/libvirt_proxy_conn`), then libvirt will use a proxy connection.

You should consider using libvirt remote support in future.

## Hypervisor support

This page documents which libvirt calls work on which hypervisors.

This information changes frequently. This page was last checked or updated on 2007-08-20.

### Domain functions

x = not supported; empty cell means no information

Function | Since | Xen | QEMU | KVM | Remote
--- | --- | --- | --- | --- | ---
virConnectClose | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectGetCapabilities | 0.2.1 | ≥ 0.2.1 | ≥ 0.2.1 | ≥ 0.2.1 | ≥ 0.3.0
virConnectGetHostname | 0.3.0 | ≥ 0.3.0 | ≥ 0.3.3 | ≥ 0.3.3 | ≥ 0.3.0
virConnectGetMaxVcpus | 0.2.1 | ≥ 0.2.1 | x | x | ≥ 0.3.0
virConnectGetType | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectGetURI | 0.3.0 | ≥ 0.3.0 | ≥ 0.3.0 | ≥ 0.3.0 | ≥ 0.3.0
virConnectGetVersion | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectListDefinedDomains | 0.1.5 | ≥ 0.1.9 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectListDomains | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectNumOfDefinedDomains | 0.1.5 | ≥ 0.1.9 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectNumOfDomains | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectOpen | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virConnectOpenReadOnly | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainAttachDevice | 0.1.9 | ≥ 0.1.9 | x | x | ≥ 0.3.0
virDomainBlockStats | 0.3.2 | ≥ 0.3.2 | x | x | ≥ 0.3.2
virDomainCoreDump | 0.1.9 | ≥ 0.1.9 | x | x | ≥ 0.3.0
virDomainCreate | 0.1.5 | ≥ 0.1.9 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainCreateLinux | All | ≥ 0.0.5 | x | x | ≥ 0.3.0
virDomainDefineXML | 0.1.5 | ≥ 0.1.9 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainDestroy | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainDetachDevice | 0.1.9 | ≥ 0.1.9 | x | x | ≥ 0.3.0
virDomainFree | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainGetAutostart | 0.2.1 | x | ≥ 0.2.1 | ≥ 0.2.1 | ≥ 0.3.0
virDomainGetConnect | 0.3.0 | not a HV function
virDomainGetID | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainGetInfo | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainGetMaxMemory | All | All | x | x | ≥ 0.3.0
virDomainGetMaxVcpus | 0.2.1 | ≥ 0.2.1 | x | x | ≥ 0.3.0
virDomainGetName | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainGetOSType | All | All | x | x | ≥ 0.3.0
virDomainGetSchedulerParameters | 0.2.3 | ≥ 0.2.3 | x | x | ≥ 0.3.0
virDomainGetSchedulerType | 0.2.3 | ≥ 0.2.3 | x | x | ≥ 0.3.0
virDomainGetUUID | 0.1.10 | ≥ 0.1.10 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainGetUUIDString | 0.1.10 | ≥ 0.1.10 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainGetVcpus | 0.1.4 | ≥ 0.1.4 | x | x | ≥ 0.3.0
virDomainInterfaceStats | 0.3.2 | ≥ 0.3.2 | x | x | ≥ 0.3.2
virDomainGetXMLDesc | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainLookupByID | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainLookupByName | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainLookupByUUID | 0.1.10 | ≥ 0.1.10 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainLookupByUUIDString | 0.1.10 | ≥ 0.1.10 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainMigrate | 0.3.2 | ≥ 0.3.2 | x | x | 0.3.2
virDomainPinVcpu | 0.1.4 | ≥ 0.1.4 | x | x | ≥ 0.3.0
virDomainReboot | 0.1.0 | ≥ 0.1.0 | x | x | ≥ 0.3.0
virDomainRestore | All | All | x | ≥ 0.3.2 | ≥ 0.3.0
virDomainResume | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainSave | All | All | x | ≥ 0.3.2 | ≥ 0.3.0
virDomainSetAutostart | 0.2.1 | x | ≥ 0.2.1 | ≥ 0.2.1 | ≥ 0.3.0
virDomainSetMaxMemory | All | All | x | x | ≥ 0.3.0
virDomainSetMemory | 0.1.1 | ≥ 0.1.1 | x | x | ≥ 0.3.0
virDomainSetSchedulerParameters | 0.2.3 | ≥ 0.2.3 | x | x | ≥ 0.3.0
virDomainSetVcpus | 0.1.4 | ≥ 0.1.4 | x | x | ≥ 0.3.0
virDomainShutdown | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainSuspend | All | All | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virDomainUndefine | 0.1.5 | ≥ 0.1.9 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virGetVersion | All | All | Returns -1 if HV unsupported.
virInitialize | 0.1.0 | not a HV function
virNodeGetInfo | 0.1.0 | ≥ 0.1.0 | ≥ 0.2.0 | ≥ 0.2.0 | ≥ 0.3.0
virNodeGetFreeMemory | 0.3.3 | ≥ 0.3.3 | x | x | x
virNodeGetCellsFreeMemory | 0.3.3 | ≥ 0.3.3 | x | x | x

### Network functions

Network functions are not hypervisor-specific. For historical reasons they require the QEMU daemon to be running (this restriction may be lifted in future). Most network functions first appeared in libvirt 0.2.0.

Function | Since
--- | ---
virConnectNumOfNetworks | 0.2.0
virConnectListNetworks | 0.2.0
virConnectNumOfDefinedNetworks | 0.2.0
virConnectListDefinedNetworks | 0.2.0
virNetworkCreate | 0.2.0
virNetworkCreateXML | 0.2.0
virNetworkDefineXML | 0.2.0
virNetworkDestroy | 0.2.0
virNetworkFree | 0.2.0
virNetworkGetAutostart | 0.2.1
virNetworkGetConnect | 0.3.0
virNetworkGetBridgeName | 0.2.0
virNetworkGetName | 0.2.0
virNetworkGetUUID | 0.2.0
virNetworkGetUUIDString | 0.2.0
virNetworkGetXMLDesc | 0.2.0
virNetworkLookupByName | 0.2.0
virNetworkLookupByUUID | 0.2.0
virNetworkLookupByUUIDString | 0.2.0
virNetworkSetAutostart | 0.2.1
virNetworkUndefine | 0.2.0