=encoding utf8

=head1 名前

guestfs-faq - libguestfs Frequently Asked Questions (FAQ)

=head1 ABOUT LIBGUESTFS

=head2 What is libguestfs?

libguestfs is a way to create, access and modify disk images.  You can look
inside disk images, modify the files they contain, create them from scratch,
resize them, and much more.  It's especially useful from scripts and
programs and from the command line.

libguestfs is a C library (hence "lib-"), and a set of tools built on this
library, and a set of bindings in many different programming languages.

For more information about what libguestfs can do read the introduction on
the home page (L<http://libguestfs.org>).

=head2 What are the virt tools?

Virt tools (website: L<http://virt-tools.org>) are a whole set of
virtualization management tools aimed at system administrators.  Some of
them come from libguestfs, some from libvirt and many others from other open
source projects.  So virt tools is a superset of libguestfs.  However
libguestfs comes with many important tools.  See L<http://libguestfs.org>
for a full list.

=head2 Does libguestfs need { libvirt / KVM / Red Hat / Fedora }?

No!

libvirt is not a requirement for libguestfs.

libguestfs works with any disk image, including ones created in VMware, KVM,
qemu, VirtualBox, Xen, and many other hypervisors, and ones which you have
created from scratch.

Red Hat sponsors (ie. pays for) development of libguestfs and a huge number
of other open source projects.  But you can run libguestfs and the virt
tools on many different Linux distros and Mac OS X.  Some virt tools have
been ported to Windows.

=head2 How does libguestfs compare to other tools?

=over 4

=item I<vs. kpartx>

Libguestfs takes a different approach from kpartx.  kpartx needs root, and
mounts filesystems on the host kernel (which can be insecure - see
L<guestfs(3)/SECURITY>).  Libguestfs isolates your host kernel from guests,
is more flexible, scriptable, supports LVM, doesn't require root, is
isolated from other processes, and cleans up after itself.  Libguestfs is
more than just file access because you can use it to create images from
scratch.

=item I<vs. vdfuse>

vdfuse is like kpartx but for VirtualBox images.  See the kpartx comparison
above.  You can use libguestfs on the partition files exposed by vdfuse,
although it's not necessary since libguestfs can access VirtualBox images
directly.

=item I<vs. qemu-nbd>

nbd is like kpartx but for qcow2 images.  See the kpartx comparison above.
You can use libguestfs and qemu-nbd together for access to block devices
over the network.

=item I<vs. mounting filesystems in the host>

Mounting guest filesystems in the host is insecure and should be avoided
completely for untrusted guests.  Use libguestfs to provide a layer of
protection against filesystem exploits.  See also L<guestmount(1)>.

=item I<vs. parted>

Libguestfs supports LVM.  Libguestfs uses parted and provides most parted
features through the libguestfs API.

=back

=head1 GETTING HELP AND REPORTING BUGS

=head2 How do I know what version I'm using?

The simplest method is:

 guestfish --version

Libguestfs development happens along an unstable branch and we periodically
create a stable branch which we backport stable patches to.  To find out
more, read L<guestfs(3)/LIBGUESTFS VERSION NUMBERS>.

=head2 How can I get help? What mailing lists or chat rooms are available?

If you are a Red Hat customer using Red Hat Enterprise Linux, please contact
Red Hat Support: L<http://redhat.com/support>

There is a mailing list, mainly for development, but users are also welcome
to ask questions about libguestfs and the virt tools:
L<https://www.redhat.com/mailman/listinfo/libguestfs>

You can also talk to us on IRC channel C<#libguestfs> on FreeNode.  We're
not always around, so please stay in the channel after asking your question
and someone will get back to you.

For other virt tools (not ones supplied with libguestfs) there is a general
virt tools mailing list:
L<https://www.redhat.com/mailman/listinfo/virt-tools-list>

=head2 How do I report bugs?

Please use the following link to enter a bug in Bugzilla:

 https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools

Include as much detail as you can and a way to reproduce the problem.

Include the full output of L<libguestfs-test-tool(1)>.

=head1 COMMON ERRORS

=head2 "child process died unexpectedly"

This error indicates that qemu failed or the host kernel could not boot.  To
get further information about the failure, you have to run:

 libguestfs-test-tool

If, after using this, you still don't understand the failure, contact us
(see previous section).

=head1 COMMON PROBLEMS

See also L<guestfs(3)/LIBGUESTFS GOTCHAS> for some "gotchas" with using the
libguestfs API.

=head2 Non-ASCII characters don't appear on VFAT filesystems.

Typical symptoms of this problem:

=over 4

=item *

You get an error when you create a file where the filename contains
non-ASCII characters, particularly non 8-bit characters from Asian languages
(Chinese, Japanese, etc).  The filesystem is VFAT.

=item *

When you list a directory from a VFAT filesystem, filenames appear as
question marks.

=back

This is a design flaw of the GNU/Linux system.

VFAT stores long filenames as UTF-16 characters.  When opening or returning
filenames, the Linux kernel has to translate these to some form of 8 bit
string.  UTF-8 would be the obvious choice, except for Linux users who
persist in using non-UTF-8 locales (the user's locale is not known to the
kernel because it's a function of libc).

Therefore you have to tell the kernel what translation you want done when
you mount the filesystem.  The two methods are the C<iocharset> parameter
(which is not relevant to libguestfs) and the C<utf8> flag.

So to use a VFAT filesystem you must add the C<utf8> flag when mounting.
From guestfish, use:

 ><fs> mount-options utf8 /dev/sda1 /

or on the guestfish command line:

 guestfish [...] -m /dev/sda1:/:utf8

or from the API:

 guestfs_mount_options (g, "utf8", "/dev/sda1", "/");

The kernel will then translate filenames to and from UTF-8 strings.

We considered adding this mount option transparently, but unfortunately
there are several problems with doing that:

=over 4

=item *

On some Linux systems, the C<utf8> mount option doesn't work.  We don't
precisely understand what systems or why, but this was reliably reported by
one user.

=item *

It would prevent you from using the C<iocharset> parameter because it is
incompatible with C<utf8>.  It is probably not a good idea to use this
parameter, but we don't want to prevent it.

=back

=head2 Non-ASCII characters appear as underscore (_) on ISO9660 filesystems.

The filesystem was not prepared correctly with mkisofs or genisoimage.  Make
sure the filesystem was created using Joliet and/or Rock Ridge extensions.
libguestfs does not require any special mount options to handle the
filesystem.

=head1 DOWNLOADING, INSTALLING, COMPILING LIBGUESTFS

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=head2 Where can I get the latest binaries for ...?

=over 4

=item Fedora E<ge> 11, RHEL E<ge> 5.3, EPEL 5

Use:

 yum install '*guestf*'

For the latest builds, see:
L<http://koji.fedoraproject.org/koji/packageinfo?packageID=8391>

=item Red Hat Enterprise Linux 6

It is part of the default install.  On RHEL 6 (only) you have to install
C<libguestfs-winsupport> to get Windows guest support.

=item RHEL 6.3

Preview packages are available here:
L<http://people.redhat.com/~rjones/libguestfs-RHEL-6.3-preview/>

=item Debian Squeeze (6)

Use Hilko Bengen's backport repository:
L<http://people.debian.org/~bengen/libguestfs/>

=item Debian Wheezy and later (7+)

Official Debian packages are available:
L<http://packages.debian.org/search?keywords=libguestfs> (thanks Hilko
Bengen).

=item Ubuntu

We don't have an Ubuntu maintainer, and the packages supplied by Canonical
(which are outside our control) are often broken.  Try compiling from source
(next section).

Canonical decided to change the permissions on the kernel so that it's not
readable except by root.  This is completely stupid, but they won't change
it (L<https://bugs.launchpad.net/ubuntu/+source/linux/+bug/759725>).  So
every user should do this:

 sudo chmod 0644 /boot/vmlinuz*

=item Ubuntu 10.04

See: L<http://libguestfs.org/download/binaries/ubuntu1004-packages/>

=item Ubuntu 12.04

libguestfs in this version of Ubuntu works, but you need to update
febootstrap and seabios to the latest versions.

You need febootstrap E<ge> 3.14-2 from:
L<http://packages.ubuntu.com/precise/febootstrap>

You need seabios E<ge> 0.6.2-0ubuntu2.1 or E<ge> 0.6.2-0ubuntu3 from:
L<http://packages.ubuntu.com/precise-updates/seabios> or
L<http://packages.ubuntu.com/quantal/seabios>

Also you need to do (see above):

 sudo chmod 0644 /boot/vmlinuz*

=item Other Linux distro

Compile from source (next section).

=item Other non-Linux distro

You'll have to compile from source, and port it.

=back

=head2 How can I compile and install libguestfs from source?

If your Linux distro has a working port of febootstrap (that is, Fedora, Red
Hat Enterprise Linux >= 6.3, Debian, Ubuntu and ArchLinux)  then you should
just be able to compile from source in the usual way.  Download the latest
tarball from L<http://libguestfs.org/download>, unpack it, and start by
reading the README file.

If you I<don't> have febootstrap, you will need to use the "fixed appliance
method".  See: L<http://libguestfs.org/download/binaries/appliance/>

Patches to port febootstrap to more Linux distros are welcome.

=head2 Why do I get an error when I try to rebuild from the source RPMs supplied by
Red Hat / Fedora?

Because of the complexity of building the libguestfs appliance, the source
RPMs provided cannot be rebuilt directly using C<rpmbuild> or C<mock>.

If you use Koji (which is open source software and may be installed
locally), then the SRPMs can be rebuilt in Koji.
L<https://fedoraproject.org/wiki/Koji>

If you don't have or want to use Koji, then you have to give libguestfs
access to the network so it can download the RPMs for building the
appliance.  You also need to set an RPM macro to tell libguestfs to use the
network.  Put the following line into a file called C<$HOME/.rpmmacros>:

 %libguestfs_buildnet   1

If you are using mock, do:

 mock -D '%libguestfs_buildnet 1' [etc]

=head2 Libguestfs has a really long list of dependencies!

That's because it does a lot of things.

=head2 How can I speed up libguestfs builds?

By far the most important thing you can do is to install and properly
configure Squid.  Note that the default configuration that ships with Squid
is rubbish, so configuring it is not optional.

A very good place to start with Squid configuration is here:
L<https://fedoraproject.org/wiki/Extras/MockTricks#Using_Squid_to_Speed_Up_Mock_package_downloads>

Make sure Squid is running, and that the environment variables
C<$http_proxy> and C<$ftp_proxy> are pointing to it.

With Squid running and correctly configured, appliance builds should be
reduced to a few minutes.

=head1 SPEED, DISK SPACE USED BY LIBGUESTFS

Note: Most of the information in this section has moved:
L<guestfs-performance(1)>.

=head2 Upload or write seem very slow.

In libguestfs E<lt> 1.13.16, the mount command (L<guestfs(3)/guestfs_mount>)
enabled option C<-o sync> implicitly.  This causes very poor write
performance, and was one of the main gotchas for new libguestfs users.

For libguestfs E<lt> 1.13.16, replace mount with C<mount-options>, leaving
the first parameter as an empty string.

You can also do this with more recent versions of libguestfs, but if you
know that you are using libguestfs ≥ 1.13.16 then it's safe to use plain
mount.

If the underlying disk is not fully allocated (eg. sparse raw or qcow2) then
writes can be slow because the host operating system has to do costly disk
allocations while you are writing. The solution is to use a fully allocated
format instead, ie. non-sparse raw, or qcow2 with the
C<preallocation=metadata> option.

=head2 Libguestfs uses too much disk space!

libguestfs caches a large-ish appliance in:

 /var/tmp/.guestfs-<UID>

If the environment variable C<TMPDIR> is defined, then
C<$TMPDIR/.guestfs-E<lt>UIDE<gt>> is used instead.

It is safe to delete this directory when you are not using libguestfs.

=head1 USING LIBGUESTFS IN YOUR OWN PROGRAMS

=head2 The API has hundreds of methods, where do I start?

We recommend you start by reading the API overview: L<guestfs(3)/API
OVERVIEW>.

Although the API overview covers the C API, it is still worth reading even
if you are going to use another programming language, because the API is the
same, just with simple logical changes to the names of the calls:

                  C  guestfs_ln_sf (g, target, linkname);
             Python  g.ln_sf (target, linkname);
              OCaml  g#ln_sf target linkname;
               Perl  $g->ln_sf (target, linkname);
  Shell (guestfish)  ln-sf target linkname
                PHP  guestfs_ln_sf ($g, $target, $linkname);

Once you're familiar with the API overview, you should look at this list of
starting points for other language bindings: L<guestfs(3)/USING LIBGUESTFS
WITH OTHER PROGRAMMING LANGUAGES>.

=begin HTML

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=end HTML

=head2 Can I use libguestfs in my proprietary / closed source / commercial program?

In general, yes.  However this is not legal advice.  You should read the
license that comes with libguestfs, and if you have specific questions about
your obligations when distributing libguestfs, contact a lawyer.  In the
source tree the license is in the file C<COPYING.LIB> (LGPLv2+ for the
library and bindings) and C<COPYING> (GPLv2+ for the standalone programs).

=head1 DEBUGGING LIBGUESTFS

=head2 How do I debug when using any libguestfs program or tool (eg. virt-v2v or
virt-df)?

There are two C<LIBGUESTFS_*> environment variables you can set in order to
get more information from libguestfs.

=over 4

=item C<LIBGUESTFS_TRACE>

Set this to 1 and libguestfs will print out each command / API call in a
format which is similar to guestfish commands.

=item C<LIBGUESTFS_DEBUG>

Set this to 1 in order to enable massive amounts of debug messages.  If you
think there is some problem inside the libguestfs appliance, then you should
use this option.

=back

To set these from the shell, do this before running the program:

 export LIBGUESTFS_TRACE=1
 export LIBGUESTFS_DEBUG=1

For csh/tcsh the equivalent commands would be:

 setenv LIBGUESTFS_TRACE 1
 setenv LIBGUESTFS_DEBUG 1

For further information, see: L<guestfs(3)/ENVIRONMENT VARIABLES>.

=head2 How do I debug when using guestfish?

You can use the same environment variables above.  Alternatively use the
guestfish options -x (to trace commands) or -v (to get the full debug
output), or both.

For further information, see: L<guestfish(1)>.

=head2 How do I debug when using the API?

Call L<guestfs(3)/guestfs_set_trace> to enable command traces, and/or
L<guestfs(3)/guestfs_set_verbose> to enable debug messages.

For best results, call these functions as early as possible, just after
creating the guestfs handle if you can, and definitely before calling
launch.

=head2 How do I capture debug output and put it into my logging system?

Use the event API.  For examples, see: L<guestfs(3)/SETTING CALLBACKS TO
HANDLE EVENTS>.

=head2 Digging deeper into the appliance boot process.

Enable debugging and then read this documentation on the appliance boot
process: L<guestfs(3)/INTERNALS>.

=head2 libguestfs hangs or fails during run/launch.

Enable debugging and look at the full output.  If you cannot work out what
is going on, file a bug report, including the I<complete> output of
L<libguestfs-test-tool(1)>.

=head1 DESIGN/INTERNALS OF LIBGUESTFS

=head2 Why don't you do everything through the FUSE / filesystem interface?

We offer a command called L<guestmount(1)> which lets you mount guest
filesystems on the host.  This is implemented as a FUSE module.  Why don't
we just implement the whole of libguestfs using this mechanism, instead of
having the large and rather complicated API?

The reasons are twofold.  Firstly, libguestfs offers API calls for doing
things like creating and deleting partitions and logical volumes, which
don't fit into a filesystem model very easily.  Or rather, you could fit
them in: for example, creating a partition could be mapped to C<mkdir
/fs/hda1> but then you'd have to specify some method to choose the size of
the partition (maybe C<echo 100M E<gt> /fs/hda1/.size>), and the partition
type, start and end sectors etc., but once you've done that the
filesystem-based API starts to look more complicated than the call-based API
we currently have.

The second reason is for efficiency.  FUSE itself is reasonably efficient,
but it does make lots of small, independent calls into the FUSE module.  In
guestmount these have to be translated into messages to the libguestfs
appliance which has a big overhead (in time and round trips).  For example,
reading a file in 64 KB chunks is inefficient because each chunk would turn
into a single round trip.  In the libguestfs API it is much more efficient
to download an entire file or directory through one of the streaming calls
like C<guestfs_download> or C<guestfs_tar_out>.

=head2 Why don't you do everything through GVFS?

The problems are similar to the problems with FUSE.

GVFS is a better abstraction than POSIX/FUSE.  There is an FTP backend for
GVFS, which is encouraging because FTP is conceptually similar to the
libguestfs API.  However the GVFS FTP backend makes multiple simultaneous
connections in order to keep interactivity, which we can't easily do with
libguestfs.

=head2 Can I use C<guestfish --ro> as a way to backup my virtual machines?

Usually this is not a good idea.  The question is answered in more detail in
this mailing list posting:
L<https://www.redhat.com/archives/libguestfs/2010-August/msg00024.html>

=head2 What's the difference between guestfish and virt-rescue?

A lot of people are confused by the two superficially similar tools we
provide:

 $ guestfish --ro -a guest.img
 ><fs> run
 ><fs> fsck /dev/sda1

 $ virt-rescue --ro guest.img
 ><rescue> /sbin/fsck /dev/sda1

And the related question which then arises is why you can't type in full
shell commands with all the --options in guestfish (but you can in
L<virt-rescue(1)>).

L<guestfish(1)> is a program providing structured access to the
L<guestfs(3)> API.  It happens to be a nice interactive shell too, but its
primary purpose is structured access from shell scripts.  Think of it more
like a language binding, like Python and other bindings, but for shell.  The
key differentiating factor of guestfish (and the libguestfs API in general)
is the ability to automate changes.

L<virt-rescue(1)> is a free-for-all freeform way to boot the libguestfs
appliance and make arbitrary changes to your VM. It's not structured, you
can't automate it, but for making quick ad-hoc fixes to your guests, it can
be quite useful.

But, libguestfs also has a "backdoor" into the appliance allowing you to
send arbitrary shell commands.  It's not as flexible as virt-rescue, because
you can't interact with the shell commands, but here it is anyway:

 ><fs> debug sh "cmd arg1 arg2 ..."

Note that you should B<not> rely on this.  It could be removed or changed in
future. If your program needs some operation, please add it to the
libguestfs API instead.

=head2 What's the deal with C<guestfish -i>? Why does virt-cat only work on a real
VM image, but virt-df works on any disk image? What does "no root device
found in this operating system image" mean?

These questions are all related at a fundamental level which may not be
immediately obvious.

At the L<guestfs(3)> API level, a "disk image" is just a pile of partitions
and filesystems.

In contrast, when the virtual machine boots, it mounts those filesystems
into a consistent hierarchy such as:

 /          (/dev/sda2)
 |
 +-- /boot  (/dev/sda1)
 |
 +-- /home  (/dev/vg_external/Homes)
 |
 +-- /usr   (/dev/vg_os/lv_usr)
 |
 +-- /var   (/dev/vg_os/lv_var)

(または Windows におけるドライブレター)。

The API first of all sees the disk image at the "pile of filesystems"
level.  But it also has a way to inspect the disk image to see if it
contains an operating system, and how the disks are mounted when the
operating system boots: L<guestfs(3)/INSPECTION>.

Users expect some tools (like L<virt-cat(1)>) to work with VM paths:

 virt-cat fedora.img /var/log/messages

How does virt-cat know that C</var> is a separate partition? The trick is
that virt-cat performs inspection on the disk image, and uses that to
translate the path correctly.

Some tools (including L<virt-cat(1)>, L<virt-edit(1)>, L<virt-ls(1)>)  use
inspection to map VM paths.  Other tools, such as L<virt-df(1)> and
L<virt-filesystems(1)> operate entirely at the raw "big pile of filesystems"
level of the libguestfs API, and don't use inspection.

L<guestfish(1)> is in an interesting middle ground.  If you use the I<-a>
and I<-m> command line options, then you have to tell guestfish exactly how
to add disk images and where to mount partitions. This is the raw API level.

If you use the I<-i> option, libguestfs performs inspection and mounts the
filesystems for you.

The error C<no root device found in this operating system image> is related
to this.  It means inspection was unable to locate an operating system
within the disk image you gave it.  You might see this from programs like
virt-cat if you try to run them on something which is just a disk image, not
a virtual machine disk image.

=head1 関連項目

L<guestfish(1)>, L<guestfs(3)>, L<http://libguestfs.org/>.

=head1 著者

Richard W.M. Jones (C<rjones at redhat dot com>)

=head1 COPYRIGHT

Copyright (C) 2012 Red Hat Inc. L<http://libguestfs.org/>

This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
for more details.

You should have received a copy of the GNU Lesser General Public License
along with this library; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA