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 >= 0.12 with virtio-serial support
48 - XDR, rpcgen (on Linux these are provided by glibc)
50 - pcre (Perl Compatible Regular Expressions C library)
52 - libmagic (the library that corresponds to the 'file' command)
58 - squashfs-tools (mksquashfs only)
60 - genisoimage / mkisofs
62 - (Optional) hivex >= 1.2.1 to build Windows Registry support
64 - (Optional) FUSE to build the FUSE module
66 - (Optional) Augeas (http://augeas.net/)
68 - perldoc (pod2man, pod2text) to generate the manual pages and
71 - (Optional) Readline to have nicer command-line editing in guestfish.
73 - (Optional) xmllint to validate virt-inspector RELAX NG schema
75 - (Optional) OCaml + OCaml library xml-light if you want to rebuild
76 the generated files, and also to build the OCaml bindings
77 (http://tech.motion-twin.com/xmllight.html)
79 - (Optional) local Fedora mirror
81 - (Optional) Perl if you want to build the perl bindings
83 - (Optional) Python if you want to build the python bindings
85 - (Optional) Ruby, rake if you want to build the ruby bindings
87 - (Optional) Java, JNI, jpackage-utils if you want to build the java
90 - (Optional) GHC if you want to build the Haskell bindings
92 - (Optional) Perl XML::XPath, Sys::Virt modules (for libvirt support
95 - (Optional, but highly recommended) perl-libintl for translating perl code.
97 Running ./configure will check you have all the requirements installed
102 ----------------------------------------------------------------------
104 Then make the daemon, library and root filesystem:
106 ./configure [--with-mirror=URI]
109 Use the optional --with-mirror parameter to specify the URI of a local
110 Fedora mirror. See the discussion of the MIRROR parameter in the
111 febootstrap(8) manpage.
113 Finally run the tests:
117 If everything works, you can install the library and tools by running
118 this command as root:
124 ----------------------------------------------------------------------
126 We provide packages for Fedora >= 11 in Fedora. Use those, or build
127 from our source RPMs - it's far simpler that way.
129 You can compile libguestfs on Fedora 10 but you cannot use it with the
130 version of qemu in Fedora 10. You need to compile your own qemu, see
131 section 'qemu' below.
134 RHEL / EPEL / CentOS etc
135 ----------------------------------------------------------------------
137 We provide packages in EPEL which cover RHEL/CentOS >= 5. Use those
138 or build from our source RPMs.
142 ----------------------------------------------------------------------
144 libguestfs is now built as a package in Debian by Guido Gunther and
145 the other Debian libvirt maintainers. See:
147 http://wiki.debian.org/Teams/DebianLibvirtTeam#Packages
149 You can build for Debian in two different ways, either building a
150 Fedora-based appliance using febootstrap, yum, rpm, fakeroot,
151 fakechroot (all packaged in Debian). However the recommended way is
152 to build a Debian-based appliance using debootstrap and debirf.
154 Both ways are supported by the configure script.
158 ----------------------------------------------------------------------
160 By far the most common problem is with broken or incompatible
163 Different versions of qemu have problems booting the appliance for
164 different reasons. This varies between versions of qemu, and Linux
165 distributions which add their own patches.
167 If you find a problem, you could try using your own qemu built from
168 source (qemu is very easy to build from source), with a 'qemu
169 wrapper'. Qemu wrappers are described in the guestfs(3) manpage.
173 ----------------------------------------------------------------------
175 By default the configure script will look for qemu-kvm (KVM support).
176 You will need a reasonably recent processor for this to work. KVM is
177 much faster than using plain Qemu.
179 You may also need to enable KVM support for non-root users, by following
182 http://www.linux-kvm.org/page/FAQ#How_can_I_use_kvm_with_a_non-privileged_user.3F
184 On some systems, this will work too:
188 On some systems, the chmod will not survive a reboot, and you will
189 need to make edits to the udev configuration.
193 ----------------------------------------------------------------------
195 Previous versions of libguestfs required something called "vmchannel".
196 Vmchannel is a special device given to virtual machines which allows
197 them to communicate in some way with the host, often (but not always)
198 without using a traditional network device. In reality, there is no
199 one thing called "vmchannel". This idea has been reimplemented
200 several times under the name vmchannel, and other hypervisors have
201 their own incompatible implementation(s) too.
203 In libguestfs <= 1.0.71, we required a specific vmchannel which is
204 properly known as "guestfwd" and has been upstream in qemu since here:
206 http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html
208 In libguestfs >= 1.0.71 we don't require any vmchannel implementation,
209 as long as qemu has been compiled with support for SLIRP (user mode
210 networking, or "-net user"), which is almost always the case.
212 However we still offer the ability to use vmchannel, and in future we
213 may add support for other types of qemu, which is useful in a few
214 cases, specifically where qemu packagers decide to compile out support
215 for SLIRP (qemu packagers: please don't do this).
219 ----------------------------------------------------------------------
221 If you configure with --enable-supermin then we will build a supermin
222 appliance (supermin = super-minimized). This is a very specialized
223 appliance which is built on-the-fly at runtime (specifically, when you
224 call guestfs_launch).
226 The normal appliance is a self-contained Linux operating system, based
227 on the Fedora/RHEL/CentOS Linux distro. So it contains a complete
228 copy of all the libraries and programs needed, like kernel, libc,
229 bash, coreutils etc etc.
231 The supermin appliance removes the kernel and all the executable
232 libraries and programs from the appliance. That just leaves a
233 skeleton of config files and some data files, which is obviously
234 massively smaller than the normal appliance. At runtime we rebuild
235 the appliance on-the-fly from the libraries and programs on the host
236 (eg. pulling in the real /lib/libc.so, the real /bin/bash etc.)
238 Although this process of rebuilding the appliance each time sounds
239 slow, it turns out to be faster than using the prebuilt appliance.
240 (Most of the saving comes from not compressing the appliance - it
241 transpires that decompressing the appliance is the slowest part of the
242 whole boot sequence). On my machine, a new appliance can be built in
243 under a fifth of a second, and the boot time is several seconds
246 The big advantage of the supermin appliance for distributions like
247 Fedora is that it gets security fixes automatically from the host, so
248 there is no need to rebuild the whole of libguestfs for a security
249 update in some underlying library.
251 There are several DISADVANTAGES:
253 It won't work at all except in very narrow, controlled cases like the
254 Fedora packaging case. We control the dependencies of the libguestfs
255 RPM tightly to ensure that the required binaries are actually present
258 Furthermore there are certain unlikely changes in the packages on the
259 host which could break a supermin appliance, eg. an updated library
260 which depends on an additional data file.
262 Also supermin appliances are subjected to changes in the host kernel
263 which might break compatibility with qemu -- these are, of course,
264 real bugs in any case.
266 Lastly, supermin appliances really can't be moved between branches of
267 distributions (eg. built on Fedora 12 and moved to Fedora 10) because
268 they are not self-contained and they rely on certain libraries being
269 around. You shouldn't do this anyway.
271 Use supermin appliances with caution.
274 Notes on cross-architecture support
275 ----------------------------------------------------------------------
277 At the moment we basically don't support cross-architecture or
278 32-on-64. This limits what is possible for some guests. Filesystem
279 operations and FUSE will work fine, but running commands in guests may
282 To enable this requires work for cross-architecture and 32-on-64
283 support in febootstrap, fakeroot and fakechroot.
285 The daemon/ directory contains its own configure script. This is so
286 that in future we will be able to cross-compile the daemon.
290 ----------------------------------------------------------------------
292 On my machines I can usually rebuild the appliance in around 3
293 minutes. If it takes much longer for you, use a local Fedora mirror
296 To use squid to cache yum downloads, read this first:
297 https://lists.dulug.duke.edu/pipermail/yum/2006-August/009041.html
298 (In brief, because yum chooses random mirrors each time, squid doesn't
299 work very well with default yum configuration. To get around this,
300 choose a Fedora mirror which is close to you, set this with
301 './configure --with-mirror=[...]', and then proxy the whole lot
302 through squid by setting http_proxy environment variable).
304 You will also need to substantially increase the squid configuration
306 http://fedoraproject.org/wiki/Using_Mock_to_test_package_builds#Using_Squid_to_Speed_Up_Mock_package_downloads
309 Porting to other Linux distros / non-Linux
310 ----------------------------------------------------------------------
312 libguestfs itself should be fairly portable to other Linux
313 distributions. Non-Linux ports are trickier, but we will accept
314 patches if they aren't too invasive.
316 The main porting issues are with the dependencies needed to build the
317 appliance. You will need to find or port the following packages
323 - rpm-python http://www.rpm.org/
324 - yum http://yum.baseurl.org/
325 - febootstrap http://people.redhat.com/~rjones/febootstrap/
328 Copyright and license information
329 ----------------------------------------------------------------------
331 Copyright (C) 2009-2010 Red Hat Inc.
333 The library is distributed under the LGPLv2+. The programs are
334 distributed under the GPLv2+. Please see the files COPYING and
335 COPYING.LIB for full license information.