1 Libguestfs is a library for accessing and modifying guest disk images.
2 Amongst the things this is good for: making batch configuration
3 changes to guests, getting disk used/free statistics (see also:
4 virt-df), migrating between virtualization systems (see also:
5 virt-p2v), performing partial backups, performing partial guest
6 clones, cloning guests and changing registry/UUID/hostname info, and
9 Libguestfs uses Linux kernel and qemu code, and can access any type of
10 guest filesystem that Linux and qemu can, including but not limited
11 to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
12 schemes, qcow, qcow2, vmdk.
14 Libguestfs provides ways to enumerate guest storage (eg. partitions,
15 LVs, what filesystem is in each LV, etc.). It can also run commands
16 in the context of the guest. Also you can access filesystems over
19 Libguestfs is a library that can be linked with C and C++ management
20 programs (or management programs written in OCaml, Perl, Python, Ruby,
21 Java, Haskell or C#). You can also use it from shell scripts or the
24 Libguestfs was written by Richard W.M. Jones (rjones@redhat.com) and
25 hacked on by lots of other people. For discussion, development,
26 patches, etc. please use the mailing list:
28 http://www.redhat.com/mailman/listinfo/libguestfs
32 ----------------------------------------------------------------------
34 http://libguestfs.org/
38 ----------------------------------------------------------------------
40 - recent QEMU >= 0.10 with vmchannel support
41 http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html
49 - XDR, rpcgen (on Linux these are provided by glibc)
51 - pcre (Perl Compatible Regular Expressions C library)
53 - libmagic (the library that corresponds to the 'file' command)
59 - squashfs-tools (mksquashfs only)
61 - genisoimage / mkisofs
63 - (Optional) hivex >= 1.2.1 to build Windows Registry support
65 - (Optional) FUSE to build the FUSE module
67 - (Optional) Augeas (http://augeas.net/)
69 - perldoc (pod2man, pod2text) to generate the manual pages and
72 - (Optional) Readline to have nicer command-line editing in guestfish.
74 - (Optional) xmllint to validate virt-inspector RELAX NG schema
76 - (Optional) OCaml + OCaml library xml-light if you want to rebuild
77 the generated files, and also to build the OCaml bindings
78 (http://tech.motion-twin.com/xmllight.html)
80 - (Optional) local Fedora mirror
82 - (Optional) Perl if you want to build the perl bindings
84 - (Optional) Python if you want to build the python bindings
86 - (Optional) Ruby, rake if you want to build the ruby bindings
88 - (Optional) Java, JNI, jpackage-utils if you want to build the java
91 - (Optional) GHC if you want to build the Haskell bindings
93 - (Optional) Perl XML::XPath, Sys::Virt modules (for libvirt support
96 - (Optional, but highly recommended) perl-libintl for translating perl code.
98 Running ./configure will check you have all the requirements installed
103 ----------------------------------------------------------------------
105 Then make the daemon, library and root filesystem:
107 ./configure [--with-mirror=URI]
110 Use the optional --with-mirror parameter to specify the URI of a local
111 Fedora mirror. See the discussion of the MIRROR parameter in the
112 febootstrap(8) manpage.
114 Finally run the tests:
118 If everything works, you can install the library and tools by running
119 this command as root:
125 ----------------------------------------------------------------------
127 We provide packages for Fedora >= 11 in Fedora. Use those, or build
128 from our source RPMs - it's far simpler that way.
130 You can compile libguestfs on Fedora 10 but you cannot use it with the
131 version of qemu in Fedora 10. You need to compile your own qemu, see
132 section 'qemu' below.
135 RHEL / EPEL / CentOS etc
136 ----------------------------------------------------------------------
138 We provide packages in EPEL which cover RHEL/CentOS >= 5. Use those
139 or build from our source RPMs.
143 ----------------------------------------------------------------------
145 libguestfs is now built as a package in Debian by Guido Gunther and
146 the other Debian libvirt maintainers. See:
148 http://wiki.debian.org/Teams/DebianLibvirtTeam#Packages
150 You can build for Debian in two different ways, either building a
151 Fedora-based appliance using febootstrap, yum, rpm, fakeroot,
152 fakechroot (all packaged in Debian). However the recommended way is
153 to build a Debian-based appliance using debootstrap and debirf.
155 Both ways are supported by the configure script.
159 ----------------------------------------------------------------------
161 By far the most common problem is with broken or incompatible
164 Different versions of qemu have problems booting the appliance for
165 different reasons. This varies between versions of qemu, and Linux
166 distributions which add their own patches.
168 If you find a problem, you could try using your own qemu built from
169 source (qemu is very easy to build from source), with a 'qemu
170 wrapper'. Qemu wrappers are described in the guestfs(3) manpage.
174 ----------------------------------------------------------------------
176 By default the configure script will look for qemu-kvm (KVM support).
177 You will need a reasonably recent processor for this to work. KVM is
178 much faster than using plain Qemu.
180 You may also need to enable KVM support for non-root users, by following
183 http://www.linux-kvm.org/page/FAQ#How_can_I_use_kvm_with_a_non-privileged_user.3F
185 On some systems, this will work too:
189 On some systems, the chmod will not survive a reboot, and you will
190 need to make edits to the udev configuration.
194 ----------------------------------------------------------------------
196 Previous versions of libguestfs required something called "vmchannel".
197 Vmchannel is a special device given to virtual machines which allows
198 them to communicate in some way with the host, often (but not always)
199 without using a traditional network device. In reality, there is no
200 one thing called "vmchannel". This idea has been reimplemented
201 several times under the name vmchannel, and other hypervisors have
202 their own incompatible implementation(s) too.
204 In libguestfs <= 1.0.71, we required a specific vmchannel which is
205 properly known as "guestfwd" and has been upstream in qemu since here:
207 http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html
209 In libguestfs >= 1.0.71 we don't require any vmchannel implementation,
210 as long as qemu has been compiled with support for SLIRP (user mode
211 networking, or "-net user"), which is almost always the case.
213 However we still offer the ability to use vmchannel, and in future we
214 may add support for other types of qemu, which is useful in a few
215 cases, specifically where qemu packagers decide to compile out support
216 for SLIRP (qemu packagers: please don't do this).
220 ----------------------------------------------------------------------
222 If you configure with --enable-supermin then we will build a supermin
223 appliance (supermin = super-minimized). This is a very specialized
224 appliance which is built on-the-fly at runtime (specifically, when you
225 call guestfs_launch).
227 The normal appliance is a self-contained Linux operating system, based
228 on the Fedora/RHEL/CentOS Linux distro. So it contains a complete
229 copy of all the libraries and programs needed, like kernel, libc,
230 bash, coreutils etc etc.
232 The supermin appliance removes the kernel and all the executable
233 libraries and programs from the appliance. That just leaves a
234 skeleton of config files and some data files, which is obviously
235 massively smaller than the normal appliance. At runtime we rebuild
236 the appliance on-the-fly from the libraries and programs on the host
237 (eg. pulling in the real /lib/libc.so, the real /bin/bash etc.)
239 Although this process of rebuilding the appliance each time sounds
240 slow, it turns out to be faster than using the prebuilt appliance.
241 (Most of the saving comes from not compressing the appliance - it
242 transpires that decompressing the appliance is the slowest part of the
243 whole boot sequence). On my machine, a new appliance can be built in
244 under a fifth of a second, and the boot time is several seconds
247 The big advantage of the supermin appliance for distributions like
248 Fedora is that it gets security fixes automatically from the host, so
249 there is no need to rebuild the whole of libguestfs for a security
250 update in some underlying library.
252 There are several DISADVANTAGES:
254 It won't work at all except in very narrow, controlled cases like the
255 Fedora packaging case. We control the dependencies of the libguestfs
256 RPM tightly to ensure that the required binaries are actually present
259 Furthermore there are certain unlikely changes in the packages on the
260 host which could break a supermin appliance, eg. an updated library
261 which depends on an additional data file.
263 Also supermin appliances are subjected to changes in the host kernel
264 which might break compatibility with qemu -- these are, of course,
265 real bugs in any case.
267 Lastly, supermin appliances really can't be moved between branches of
268 distributions (eg. built on Fedora 12 and moved to Fedora 10) because
269 they are not self-contained and they rely on certain libraries being
270 around. You shouldn't do this anyway.
272 Use supermin appliances with caution.
275 Notes on cross-architecture support
276 ----------------------------------------------------------------------
278 At the moment we basically don't support cross-architecture or
279 32-on-64. This limits what is possible for some guests. Filesystem
280 operations and FUSE will work fine, but running commands in guests may
283 To enable this requires work for cross-architecture and 32-on-64
284 support in febootstrap, fakeroot and fakechroot.
286 The daemon/ directory contains its own configure script. This is so
287 that in future we will be able to cross-compile the daemon.
291 ----------------------------------------------------------------------
293 On my machines I can usually rebuild the appliance in around 3
294 minutes. If it takes much longer for you, use a local Fedora mirror
297 To use squid to cache yum downloads, read this first:
298 https://lists.dulug.duke.edu/pipermail/yum/2006-August/009041.html
299 (In brief, because yum chooses random mirrors each time, squid doesn't
300 work very well with default yum configuration. To get around this,
301 choose a Fedora mirror which is close to you, set this with
302 './configure --with-mirror=[...]', and then proxy the whole lot
303 through squid by setting http_proxy environment variable).
305 You will also need to substantially increase the squid configuration
307 http://fedoraproject.org/wiki/Using_Mock_to_test_package_builds#Using_Squid_to_Speed_Up_Mock_package_downloads
310 Porting to other Linux distros / non-Linux
311 ----------------------------------------------------------------------
313 libguestfs itself should be fairly portable to other Linux
314 distributions. Non-Linux ports are trickier, but we will accept
315 patches if they aren't too invasive.
317 The main porting issues are with the dependencies needed to build the
318 appliance. You will need to find or port the following packages
324 - rpm-python http://www.rpm.org/
325 - yum http://yum.baseurl.org/
326 - febootstrap http://people.redhat.com/~rjones/febootstrap/
329 Copyright and license information
330 ----------------------------------------------------------------------
332 Copyright (C) 2009-2010 Red Hat Inc.
334 The library is distributed under the LGPLv2+. The programs are
335 distributed under the GPLv2+. Please see the files COPYING and
336 COPYING.LIB for full license information.