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 FTP.
18 Libguestfs is a library that can be linked with C and C++ management
19 programs (or management programs written in OCaml, Perl, Python, Ruby, Java
20 or Haskell). You can also use it from shell scripts or the command line.
22 Libguestfs was written by Richard W.M. Jones (rjones@redhat.com) and
23 hacked on by lots of other people. For discussion, development,
24 patches, etc. please use the mailing list:
26 http://www.redhat.com/mailman/listinfo/libguestfs
30 ----------------------------------------------------------------------
32 http://libguestfs.org/
36 ----------------------------------------------------------------------
38 - recent QEMU >= 0.10 with vmchannel support
39 http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html
47 - XDR, rpcgen (on Linux these are provided by glibc)
49 - squashfs-tools (mksquashfs only)
51 - genisoimage / mkisofs
55 - (Optional) Augeas (http://augeas.net/)
57 - perldoc (pod2man, pod2text) to generate the manual pages and
60 - (Optional) Readline to have nicer command-line editing in guestfish.
62 - (Optional) 'reged' program from chntpw to decode Windows registry
63 entries (http://home.eunet.no/~pnordahl/ntpasswd/)
65 - (Optional) xmllint to validate virt-inspector RELAX NG schema
67 - (Optional) OCaml if you want to rebuild the generated files, and
68 also to build the OCaml bindings
70 - (Optional) OCaml xml-light, only needed if you want to rebuild the
71 virt-inspector bindings from virt-inspector.rng.
73 - (Optional) local Fedora mirror
75 - (Optional) Perl if you want to build the perl bindings
77 - (Optional) Python if you want to build the python bindings
79 - (Optional) Ruby, rake if you want to build the ruby bindings
81 - (Optional) Java, JNI, jpackage-utils if you want to build the java
84 - (Optional) GHC if you want to build the Haskell bindings
86 - (Optional) Perl XML::XPath, Sys::Virt modules (for libvirt support
89 - (Optional, but highly recommended) perl-libintl for translating perl code.
91 Running ./configure will check you have all the requirements installed
96 ----------------------------------------------------------------------
98 Then make the daemon, library and root filesystem:
100 ./configure [--with-mirror=URI]
103 Use the optional --with-mirror parameter to specify the URI of a local
104 Fedora mirror. See the discussion of the MIRROR parameter in the
105 febootstrap(8) manpage.
107 Finally run the tests:
111 If everything works, you can install the library and tools by running
112 this command as root:
118 ----------------------------------------------------------------------
120 We provide packages for Fedora >= 11 in Fedora. Use those, or build
121 from our source RPMs - it's far simpler that way.
123 You can compile libguestfs on Fedora 10 but you cannot use it with the
124 version of qemu in Fedora 10. You need to compile your own qemu, see
125 section 'qemu' below.
128 RHEL / EPEL / CentOS etc
129 ----------------------------------------------------------------------
131 We provide packages in EPEL which cover RHEL/CentOS >= 5. Use those
132 or build from our source RPMs.
136 ----------------------------------------------------------------------
138 libguestfs is now built as a package in Debian by Guido Gunther and
139 the other Debian libvirt maintainers. See:
141 http://wiki.debian.org/Teams/DebianLibvirtTeam#Packages
143 You can build for Debian in two different ways, either building a
144 Fedora-based appliance using febootstrap, yum, rpm, fakeroot,
145 fakechroot (all packaged in Debian). However the recommended way is
146 to build a Debian-based appliance using debootstrap and debirf.
148 Both ways are supported by the configure script.
152 ----------------------------------------------------------------------
154 By far the most common problem is with broken or incompatible
157 Different versions of qemu have problems booting the appliance for
158 different reasons. This varies between versions of qemu, and Linux
159 distributions which add their own patches.
161 If you find a problem, you could try using your own qemu built from
162 source (qemu is very easy to build from source), with a 'qemu
163 wrapper'. Qemu wrappers are described in the guestfs(3) manpage.
167 ----------------------------------------------------------------------
169 By default the configure script will look for qemu-kvm (KVM support).
170 You will need a reasonably recent processor for this to work. KVM is
171 much faster than using plain Qemu.
173 You may also need to enable KVM support for non-root users, by following
176 http://www.linux-kvm.org/page/FAQ#How_can_I_use_kvm_with_a_non-privileged_user.3F
178 On some systems, this will work too:
182 On some systems, the chmod will not survive a reboot, and you will
183 need to make edits to the udev configuration.
187 ----------------------------------------------------------------------
189 Previous versions of libguestfs required something called "vmchannel".
190 Vmchannel is a special device given to virtual machines which allows
191 them to communicate in some way with the host, often (but not always)
192 without using a traditional network device. In reality, there is no
193 one thing called "vmchannel". This idea has been reimplemented
194 several times under the name vmchannel, and other hypervisors have
195 their own incompatible implementation(s) too.
197 In libguestfs <= 1.0.71, we required a specific vmchannel which is
198 properly known as "guestfwd" and has been upstream in qemu since here:
200 http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html
202 In libguestfs >= 1.0.71 we don't require any vmchannel implementation,
203 as long as qemu has been compiled with support for SLIRP (user mode
204 networking, or "-net user"), which is almost always the case.
206 However we still offer the ability to use vmchannel, and in future we
207 may add support for other types of qemu, which is useful in a few
208 cases, specifically where qemu packagers decide to compile out support
209 for SLIRP (qemu packagers: please don't do this).
213 ----------------------------------------------------------------------
215 If you configure with --enable-supermin then we will build a supermin
216 appliance (supermin = super-minimized). This is a very specialized
217 appliance which is built on-the-fly at runtime (specifically, when you
218 call guestfs_launch).
220 The normal appliance is a self-contained Linux operating system, based
221 on the Fedora/RHEL/CentOS Linux distro. So it contains a complete
222 copy of all the libraries and programs needed, like kernel, libc,
223 bash, coreutils etc etc.
225 The supermin appliance removes the kernel and all the executable
226 libraries and programs from the appliance. That just leaves a
227 skeleton of config files and some data files, which is obviously
228 massively smaller than the normal appliance. At runtime we rebuild
229 the appliance on-the-fly from the libraries and programs on the host
230 (eg. pulling in the real /lib/libc.so, the real /bin/bash etc.)
232 Although this process of rebuilding the appliance each time sounds
233 slow, it turns out to be faster than using the prebuilt appliance.
234 (Most of the saving comes from not compressing the appliance - it
235 transpires that decompressing the appliance is the slowest part of the
236 whole boot sequence). On my machine, a new appliance can be built in
237 under a fifth of a second, and the boot time is several seconds
240 The big advantage of the supermin appliance for distributions like
241 Fedora is that it gets security fixes automatically from the host, so
242 there is no need to rebuild the whole of libguestfs for a security
243 update in some underlying library.
245 There are several DISADVANTAGES:
247 It won't work at all except in very narrow, controlled cases like the
248 Fedora packaging case. We control the dependencies of the libguestfs
249 RPM tightly to ensure that the required binaries are actually present
252 Furthermore there are certain unlikely changes in the packages on the
253 host which could break a supermin appliance, eg. an updated library
254 which depends on an additional data file.
256 Also supermin appliances are subjected to changes in the host kernel
257 which might break compatibility with qemu -- these are, of course,
258 real bugs in any case.
260 Lastly, supermin appliances really can't be moved between branches of
261 distributions (eg. built on Fedora 12 and moved to Fedora 10) because
262 they are not self-contained and they rely on certain libraries being
263 around. You shouldn't do this anyway.
265 Use supermin appliances with caution.
268 Notes on cross-architecture support
269 ----------------------------------------------------------------------
271 At the moment we basically don't support cross-architecture or
272 32-on-64. This limits what is possible for some guests. Filesystem
273 operations and FTP export will work fine, but running commands in
274 guests may not be possible.
276 To enable this requires work for cross-architecture and 32-on-64
277 support in febootstrap, fakeroot and fakechroot.
279 The daemon/ directory contains its own configure script. This is so
280 that in future we will be able to cross-compile the daemon.
284 ----------------------------------------------------------------------
286 On my machines I can usually rebuild the appliance in around 3
287 minutes. If it takes much longer for you, use a local Fedora mirror
290 To use squid to cache yum downloads, read this first:
291 https://lists.dulug.duke.edu/pipermail/yum/2006-August/009041.html
292 (In brief, because yum chooses random mirrors each time, squid doesn't
293 work very well with default yum configuration. To get around this,
294 choose a Fedora mirror which is close to you, set this with
295 './configure --with-mirror=[...]', and then proxy the whole lot
296 through squid by setting http_proxy environment variable).
298 You will also need to substantially increase the squid configuration
300 http://fedoraproject.org/wiki/Using_Mock_to_test_package_builds#Using_Squid_to_Speed_Up_Mock_package_downloads
303 Porting to other Linux distros / non-Linux
304 ----------------------------------------------------------------------
306 libguestfs itself should be fairly portable to other Linux
307 distributions. Non-Linux ports are trickier, but we will accept
308 patches if they aren't too invasive.
310 The main porting issues are with the dependencies needed to build the
311 appliance. You will need to find or port the following packages
317 - rpm-python http://www.rpm.org/
318 - yum http://yum.baseurl.org/
319 - febootstrap http://et.redhat.com/~rjones/febootstrap/
322 Copyright and license information
323 ----------------------------------------------------------------------
325 Copyright (C) 2009 Red Hat Inc.
327 The library is distributed under the LGPLv2+. The programs are
328 distributed under the GPLv2+. Please see the files COPYING and
329 COPYING.LIB for full license information.