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 - squashfs-tools (mksquashfs only)
53 - genisoimage / mkisofs
55 - (Optional) hivex to build Windows Registry support
57 - (Optional) FUSE to build the FUSE module
59 - (Optional) Augeas (http://augeas.net/)
61 - perldoc (pod2man, pod2text) to generate the manual pages and
64 - (Optional) Readline to have nicer command-line editing in guestfish.
66 - (Optional) 'reged' program from chntpw to decode Windows registry
67 entries (http://home.eunet.no/~pnordahl/ntpasswd/)
69 - (Optional) xmllint to validate virt-inspector RELAX NG schema
71 - (Optional) OCaml + OCaml library xml-light if you want to rebuild
72 the generated files, and also to build the OCaml bindings
73 (http://tech.motion-twin.com/xmllight.html)
75 - (Optional) local Fedora mirror
77 - (Optional) Perl if you want to build the perl bindings
79 - (Optional) Python if you want to build the python bindings
81 - (Optional) Ruby, rake if you want to build the ruby bindings
83 - (Optional) Java, JNI, jpackage-utils if you want to build the java
86 - (Optional) GHC if you want to build the Haskell bindings
88 - (Optional) Perl XML::XPath, Sys::Virt modules (for libvirt support
91 - (Optional, but highly recommended) perl-libintl for translating perl code.
93 Running ./configure will check you have all the requirements installed
98 ----------------------------------------------------------------------
100 Then make the daemon, library and root filesystem:
102 ./configure [--with-mirror=URI]
105 Use the optional --with-mirror parameter to specify the URI of a local
106 Fedora mirror. See the discussion of the MIRROR parameter in the
107 febootstrap(8) manpage.
109 Finally run the tests:
113 If everything works, you can install the library and tools by running
114 this command as root:
120 ----------------------------------------------------------------------
122 We provide packages for Fedora >= 11 in Fedora. Use those, or build
123 from our source RPMs - it's far simpler that way.
125 You can compile libguestfs on Fedora 10 but you cannot use it with the
126 version of qemu in Fedora 10. You need to compile your own qemu, see
127 section 'qemu' below.
130 RHEL / EPEL / CentOS etc
131 ----------------------------------------------------------------------
133 We provide packages in EPEL which cover RHEL/CentOS >= 5. Use those
134 or build from our source RPMs.
138 ----------------------------------------------------------------------
140 libguestfs is now built as a package in Debian by Guido Gunther and
141 the other Debian libvirt maintainers. See:
143 http://wiki.debian.org/Teams/DebianLibvirtTeam#Packages
145 You can build for Debian in two different ways, either building a
146 Fedora-based appliance using febootstrap, yum, rpm, fakeroot,
147 fakechroot (all packaged in Debian). However the recommended way is
148 to build a Debian-based appliance using debootstrap and debirf.
150 Both ways are supported by the configure script.
154 ----------------------------------------------------------------------
156 By far the most common problem is with broken or incompatible
159 Different versions of qemu have problems booting the appliance for
160 different reasons. This varies between versions of qemu, and Linux
161 distributions which add their own patches.
163 If you find a problem, you could try using your own qemu built from
164 source (qemu is very easy to build from source), with a 'qemu
165 wrapper'. Qemu wrappers are described in the guestfs(3) manpage.
169 ----------------------------------------------------------------------
171 By default the configure script will look for qemu-kvm (KVM support).
172 You will need a reasonably recent processor for this to work. KVM is
173 much faster than using plain Qemu.
175 You may also need to enable KVM support for non-root users, by following
178 http://www.linux-kvm.org/page/FAQ#How_can_I_use_kvm_with_a_non-privileged_user.3F
180 On some systems, this will work too:
184 On some systems, the chmod will not survive a reboot, and you will
185 need to make edits to the udev configuration.
189 ----------------------------------------------------------------------
191 Previous versions of libguestfs required something called "vmchannel".
192 Vmchannel is a special device given to virtual machines which allows
193 them to communicate in some way with the host, often (but not always)
194 without using a traditional network device. In reality, there is no
195 one thing called "vmchannel". This idea has been reimplemented
196 several times under the name vmchannel, and other hypervisors have
197 their own incompatible implementation(s) too.
199 In libguestfs <= 1.0.71, we required a specific vmchannel which is
200 properly known as "guestfwd" and has been upstream in qemu since here:
202 http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html
204 In libguestfs >= 1.0.71 we don't require any vmchannel implementation,
205 as long as qemu has been compiled with support for SLIRP (user mode
206 networking, or "-net user"), which is almost always the case.
208 However we still offer the ability to use vmchannel, and in future we
209 may add support for other types of qemu, which is useful in a few
210 cases, specifically where qemu packagers decide to compile out support
211 for SLIRP (qemu packagers: please don't do this).
215 ----------------------------------------------------------------------
217 If you configure with --enable-supermin then we will build a supermin
218 appliance (supermin = super-minimized). This is a very specialized
219 appliance which is built on-the-fly at runtime (specifically, when you
220 call guestfs_launch).
222 The normal appliance is a self-contained Linux operating system, based
223 on the Fedora/RHEL/CentOS Linux distro. So it contains a complete
224 copy of all the libraries and programs needed, like kernel, libc,
225 bash, coreutils etc etc.
227 The supermin appliance removes the kernel and all the executable
228 libraries and programs from the appliance. That just leaves a
229 skeleton of config files and some data files, which is obviously
230 massively smaller than the normal appliance. At runtime we rebuild
231 the appliance on-the-fly from the libraries and programs on the host
232 (eg. pulling in the real /lib/libc.so, the real /bin/bash etc.)
234 Although this process of rebuilding the appliance each time sounds
235 slow, it turns out to be faster than using the prebuilt appliance.
236 (Most of the saving comes from not compressing the appliance - it
237 transpires that decompressing the appliance is the slowest part of the
238 whole boot sequence). On my machine, a new appliance can be built in
239 under a fifth of a second, and the boot time is several seconds
242 The big advantage of the supermin appliance for distributions like
243 Fedora is that it gets security fixes automatically from the host, so
244 there is no need to rebuild the whole of libguestfs for a security
245 update in some underlying library.
247 There are several DISADVANTAGES:
249 It won't work at all except in very narrow, controlled cases like the
250 Fedora packaging case. We control the dependencies of the libguestfs
251 RPM tightly to ensure that the required binaries are actually present
254 Furthermore there are certain unlikely changes in the packages on the
255 host which could break a supermin appliance, eg. an updated library
256 which depends on an additional data file.
258 Also supermin appliances are subjected to changes in the host kernel
259 which might break compatibility with qemu -- these are, of course,
260 real bugs in any case.
262 Lastly, supermin appliances really can't be moved between branches of
263 distributions (eg. built on Fedora 12 and moved to Fedora 10) because
264 they are not self-contained and they rely on certain libraries being
265 around. You shouldn't do this anyway.
267 Use supermin appliances with caution.
270 Notes on cross-architecture support
271 ----------------------------------------------------------------------
273 At the moment we basically don't support cross-architecture or
274 32-on-64. This limits what is possible for some guests. Filesystem
275 operations and FUSE will work fine, but running commands in guests may
278 To enable this requires work for cross-architecture and 32-on-64
279 support in febootstrap, fakeroot and fakechroot.
281 The daemon/ directory contains its own configure script. This is so
282 that in future we will be able to cross-compile the daemon.
286 ----------------------------------------------------------------------
288 On my machines I can usually rebuild the appliance in around 3
289 minutes. If it takes much longer for you, use a local Fedora mirror
292 To use squid to cache yum downloads, read this first:
293 https://lists.dulug.duke.edu/pipermail/yum/2006-August/009041.html
294 (In brief, because yum chooses random mirrors each time, squid doesn't
295 work very well with default yum configuration. To get around this,
296 choose a Fedora mirror which is close to you, set this with
297 './configure --with-mirror=[...]', and then proxy the whole lot
298 through squid by setting http_proxy environment variable).
300 You will also need to substantially increase the squid configuration
302 http://fedoraproject.org/wiki/Using_Mock_to_test_package_builds#Using_Squid_to_Speed_Up_Mock_package_downloads
305 Porting to other Linux distros / non-Linux
306 ----------------------------------------------------------------------
308 libguestfs itself should be fairly portable to other Linux
309 distributions. Non-Linux ports are trickier, but we will accept
310 patches if they aren't too invasive.
312 The main porting issues are with the dependencies needed to build the
313 appliance. You will need to find or port the following packages
319 - rpm-python http://www.rpm.org/
320 - yum http://yum.baseurl.org/
321 - febootstrap http://et.redhat.com/~rjones/febootstrap/
324 Copyright and license information
325 ----------------------------------------------------------------------
327 Copyright (C) 2009 Red Hat Inc.
329 The library is distributed under the LGPLv2+. The programs are
330 distributed under the GPLv2+. Please see the files COPYING and
331 COPYING.LIB for full license information.