5 guestfs - Library for accessing and modifying virtual machine images
11 guestfs_h *g = guestfs_create ();
12 guestfs_add_drive (g, "guest.img");
14 guestfs_mount (g, "/dev/sda1", "/");
15 guestfs_touch (g, "/hello");
16 guestfs_umount (g, "/");
19 cc prog.c -o prog -lguestfs
21 cc prog.c -o prog `pkg-config libguestfs --cflags --libs`
25 Libguestfs is a library for accessing and modifying guest disk images.
26 Amongst the things this is good for: making batch configuration
27 changes to guests, getting disk used/free statistics (see also:
28 virt-df), migrating between virtualization systems (see also:
29 virt-p2v), performing partial backups, performing partial guest
30 clones, cloning guests and changing registry/UUID/hostname info, and
33 Libguestfs uses Linux kernel and qemu code, and can access any type of
34 guest filesystem that Linux and qemu can, including but not limited
35 to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
36 schemes, qcow, qcow2, vmdk.
38 Libguestfs provides ways to enumerate guest storage (eg. partitions,
39 LVs, what filesystem is in each LV, etc.). It can also run commands
40 in the context of the guest. Also you can access filesystems over
43 Libguestfs is a library that can be linked with C and C++ management
44 programs (or management programs written in OCaml, Perl, Python, Ruby,
45 Java, PHP, Haskell or C#). You can also use it from shell scripts or the
48 You don't need to be root to use libguestfs, although obviously you do
49 need enough permissions to access the disk images.
51 Libguestfs is a large API because it can do many things. For a gentle
52 introduction, please read the L</API OVERVIEW> section next.
54 There are also some example programs in the L<guestfs-examples(3)>
59 This section provides a gentler overview of the libguestfs API. We
60 also try to group API calls together, where that may not be obvious
61 from reading about the individual calls in the main section of this
66 Before you can use libguestfs calls, you have to create a handle.
67 Then you must add at least one disk image to the handle, followed by
68 launching the handle, then performing whatever operations you want,
69 and finally closing the handle. By convention we use the single
70 letter C<g> for the name of the handle variable, although of course
71 you can use any name you want.
73 The general structure of all libguestfs-using programs looks like
76 guestfs_h *g = guestfs_create ();
78 /* Call guestfs_add_drive additional times if there are
79 * multiple disk images.
81 guestfs_add_drive (g, "guest.img");
83 /* Most manipulation calls won't work until you've launched
84 * the handle 'g'. You have to do this _after_ adding drives
85 * and _before_ other commands.
89 /* Now you can examine what partitions, LVs etc are available.
91 char **partitions = guestfs_list_partitions (g);
92 char **logvols = guestfs_lvs (g);
94 /* To access a filesystem in the image, you must mount it.
96 guestfs_mount (g, "/dev/sda1", "/");
98 /* Now you can perform filesystem actions on the guest
101 guestfs_touch (g, "/hello");
103 /* This is only needed for libguestfs < 1.5.24. Since then
104 * it is done automatically when you close the handle. See
105 * discussion of autosync in this page.
109 /* Close the handle 'g'. */
112 The code above doesn't include any error checking. In real code you
113 should check return values carefully for errors. In general all
114 functions that return integers return C<-1> on error, and all
115 functions that return pointers return C<NULL> on error. See section
116 L</ERROR HANDLING> below for how to handle errors, and consult the
117 documentation for each function call below to see precisely how they
118 return error indications. See L<guestfs-examples(3)> for fully worked
123 The image filename (C<"guest.img"> in the example above) could be a
124 disk image from a virtual machine, a L<dd(1)> copy of a physical hard
125 disk, an actual block device, or simply an empty file of zeroes that
126 you have created through L<posix_fallocate(3)>. Libguestfs lets you
127 do useful things to all of these.
129 The call you should use in modern code for adding drives is
130 L</guestfs_add_drive_opts>. To add a disk image, allowing writes, and
131 specifying that the format is raw, do:
133 guestfs_add_drive_opts (g, filename,
134 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
137 You can add a disk read-only using:
139 guestfs_add_drive_opts (g, filename,
140 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
141 GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
144 or by calling the older function L</guestfs_add_drive_ro>. In either
145 case libguestfs won't modify the file.
147 Be extremely cautious if the disk image is in use, eg. if it is being
148 used by a virtual machine. Adding it read-write will almost certainly
149 cause disk corruption, but adding it read-only is safe.
151 You must add at least one disk image, and you may add multiple disk
152 images. In the API, the disk images are usually referred to as
153 C</dev/sda> (for the first one you added), C</dev/sdb> (for the second
156 Once L</guestfs_launch> has been called you cannot add any more images.
157 You can call L</guestfs_list_devices> to get a list of the device
158 names, in the order that you added them. See also L</BLOCK DEVICE
163 Before you can read or write files, create directories and so on in a
164 disk image that contains filesystems, you have to mount those
165 filesystems using L</guestfs_mount_options> or L</guestfs_mount_ro>.
166 If you already know that a disk image contains (for example) one
167 partition with a filesystem on that partition, then you can mount it
170 guestfs_mount_options (g, "", "/dev/sda1", "/");
172 where C</dev/sda1> means literally the first partition (C<1>) of the
173 first disk image that we added (C</dev/sda>). If the disk contains
174 Linux LVM2 logical volumes you could refer to those instead
175 (eg. C</dev/VG/LV>). Note that these are libguestfs virtual devices,
176 and are nothing to do with host devices.
178 If you are given a disk image and you don't know what it contains then
179 you have to find out. Libguestfs can do that too: use
180 L</guestfs_list_partitions> and L</guestfs_lvs> to list possible
181 partitions and LVs, and either try mounting each to see what is
182 mountable, or else examine them with L</guestfs_vfs_type> or
183 L</guestfs_file>. To list just filesystems, use
184 L</guestfs_list_filesystems>.
186 Libguestfs also has a set of APIs for inspection of unknown disk
187 images (see L</INSPECTION> below). But you might find it easier to
188 look at higher level programs built on top of libguestfs, in
189 particular L<virt-inspector(1)>.
191 To mount a filesystem read-only, use L</guestfs_mount_ro>. There are
192 several other variations of the C<guestfs_mount_*> call.
194 =head2 FILESYSTEM ACCESS AND MODIFICATION
196 The majority of the libguestfs API consists of fairly low-level calls
197 for accessing and modifying the files, directories, symlinks etc on
198 mounted filesystems. There are over a hundred such calls which you
199 can find listed in detail below in this man page, and we don't even
200 pretend to cover them all in this overview.
202 Specify filenames as full paths, starting with C<"/"> and including
205 For example, if you mounted a filesystem at C<"/"> and you want to
206 read the file called C<"etc/passwd"> then you could do:
208 char *data = guestfs_cat (g, "/etc/passwd");
210 This would return C<data> as a newly allocated buffer containing the
211 full content of that file (with some conditions: see also
212 L</DOWNLOADING> below), or C<NULL> if there was an error.
214 As another example, to create a top-level directory on that filesystem
215 called C<"var"> you would do:
217 guestfs_mkdir (g, "/var");
219 To create a symlink you could do:
221 guestfs_ln_s (g, "/etc/init.d/portmap",
222 "/etc/rc3.d/S30portmap");
224 Libguestfs will reject attempts to use relative paths and there is no
225 concept of a current working directory.
227 Libguestfs can return errors in many situations: for example if the
228 filesystem isn't writable, or if a file or directory that you
229 requested doesn't exist. If you are using the C API (documented here)
230 you have to check for those error conditions after each call. (Other
231 language bindings turn these errors into exceptions).
233 File writes are affected by the per-handle umask, set by calling
234 L</guestfs_umask> and defaulting to 022. See L</UMASK>.
238 Libguestfs contains API calls to read, create and modify partition
239 tables on disk images.
241 In the common case where you want to create a single partition
242 covering the whole disk, you should use the L</guestfs_part_disk>
245 const char *parttype = "mbr";
246 if (disk_is_larger_than_2TB)
248 guestfs_part_disk (g, "/dev/sda", parttype);
250 Obviously this effectively wipes anything that was on that disk image
255 Libguestfs provides access to a large part of the LVM2 API, such as
256 L</guestfs_lvcreate> and L</guestfs_vgremove>. It won't make much sense
257 unless you familiarize yourself with the concepts of physical volumes,
258 volume groups and logical volumes.
260 This author strongly recommends reading the LVM HOWTO, online at
261 L<http://tldp.org/HOWTO/LVM-HOWTO/>.
265 Use L</guestfs_cat> to download small, text only files. This call is
266 limited to files which are less than 2 MB and which cannot contain any
267 ASCII NUL (C<\0>) characters. However the API is very simple to use.
269 L</guestfs_read_file> can be used to read files which contain
270 arbitrary 8 bit data, since it returns a (pointer, size) pair.
271 However it is still limited to "small" files, less than 2 MB.
273 L</guestfs_download> can be used to download any file, with no
274 limits on content or size (even files larger than 4 GB).
276 To download multiple files, see L</guestfs_tar_out> and
281 It's often the case that you want to write a file or files to the disk
284 To write a small file with fixed content, use L</guestfs_write>. To
285 create a file of all zeroes, use L</guestfs_truncate_size> (sparse) or
286 L</guestfs_fallocate64> (with all disk blocks allocated). There are a
287 variety of other functions for creating test files, for example
288 L</guestfs_fill> and L</guestfs_fill_pattern>.
290 To upload a single file, use L</guestfs_upload>. This call has no
291 limits on file content or size (even files larger than 4 GB).
293 To upload multiple files, see L</guestfs_tar_in> and L</guestfs_tgz_in>.
295 However the fastest way to upload I<large numbers of arbitrary files>
296 is to turn them into a squashfs or CD ISO (see L<mksquashfs(8)> and
297 L<mkisofs(8)>), then attach this using L</guestfs_add_drive_ro>. If
298 you add the drive in a predictable way (eg. adding it last after all
299 other drives) then you can get the device name from
300 L</guestfs_list_devices> and mount it directly using
301 L</guestfs_mount_ro>. Note that squashfs images are sometimes
302 non-portable between kernel versions, and they don't support labels or
303 UUIDs. If you want to pre-build an image or you need to mount it
304 using a label or UUID, use an ISO image instead.
308 There are various different commands for copying between files and
309 devices and in and out of the guest filesystem. These are summarised
314 =item B<file> to B<file>
316 Use L</guestfs_cp> to copy a single file, or
317 L</guestfs_cp_a> to copy directories recursively.
319 =item B<file or device> to B<file or device>
321 Use L</guestfs_dd> which efficiently uses L<dd(1)>
322 to copy between files and devices in the guest.
324 Example: duplicate the contents of an LV:
326 guestfs_dd (g, "/dev/VG/Original", "/dev/VG/Copy");
328 The destination (C</dev/VG/Copy>) must be at least as large as the
329 source (C</dev/VG/Original>). To copy less than the whole
330 source device, use L</guestfs_copy_size>.
332 =item B<file on the host> to B<file or device>
334 Use L</guestfs_upload>. See L</UPLOADING> above.
336 =item B<file or device> to B<file on the host>
338 Use L</guestfs_download>. See L</DOWNLOADING> above.
342 =head2 UPLOADING AND DOWNLOADING TO PIPES AND FILE DESCRIPTORS
344 Calls like L</guestfs_upload>, L</guestfs_download>,
345 L</guestfs_tar_in>, L</guestfs_tar_out> etc appear to only take
346 filenames as arguments, so it appears you can only upload and download
347 to files. However many Un*x-like hosts let you use the special device
348 files C</dev/stdin>, C</dev/stdout>, C</dev/stderr> and C</dev/fd/N>
349 to read and write from stdin, stdout, stderr, and arbitrary file
352 For example, L<virt-cat(1)> writes its output to stdout by
355 guestfs_download (g, filename, "/dev/stdout");
357 and you can write tar output to a file descriptor C<fd> by doing:
360 snprintf (devfd, sizeof devfd, "/dev/fd/%d", fd);
361 guestfs_tar_out (g, "/", devfd);
365 L</guestfs_ll> is just designed for humans to read (mainly when using
366 the L<guestfish(1)>-equivalent command C<ll>).
368 L</guestfs_ls> is a quick way to get a list of files in a directory
369 from programs, as a flat list of strings.
371 L</guestfs_readdir> is a programmatic way to get a list of files in a
372 directory, plus additional information about each one. It is more
373 equivalent to using the L<readdir(3)> call on a local filesystem.
375 L</guestfs_find> and L</guestfs_find0> can be used to recursively list
378 =head2 RUNNING COMMANDS
380 Although libguestfs is primarily an API for manipulating files
381 inside guest images, we also provide some limited facilities for
382 running commands inside guests.
384 There are many limitations to this:
390 The kernel version that the command runs under will be different
391 from what it expects.
395 If the command needs to communicate with daemons, then most likely
396 they won't be running.
400 The command will be running in limited memory.
404 The network may not be available unless you enable it
405 (see L</guestfs_set_network>).
409 Only supports Linux guests (not Windows, BSD, etc).
413 Architecture limitations (eg. won't work for a PPC guest on
418 For SELinux guests, you may need to enable SELinux and load policy
419 first. See L</SELINUX> in this manpage.
423 I<Security:> It is not safe to run commands from untrusted, possibly
424 malicious guests. These commands may attempt to exploit your program
425 by sending unexpected output. They could also try to exploit the
426 Linux kernel or qemu provided by the libguestfs appliance. They could
427 use the network provided by the libguestfs appliance to bypass
428 ordinary network partitions and firewalls. They could use the
429 elevated privileges or different SELinux context of your program
432 A secure alternative is to use libguestfs to install a "firstboot"
433 script (a script which runs when the guest next boots normally), and
434 to have this script run the commands you want in the normal context of
435 the running guest, network security and so on. For information about
436 other security issues, see L</SECURITY>.
440 The two main API calls to run commands are L</guestfs_command> and
441 L</guestfs_sh> (there are also variations).
443 The difference is that L</guestfs_sh> runs commands using the shell, so
444 any shell globs, redirections, etc will work.
446 =head2 CONFIGURATION FILES
448 To read and write configuration files in Linux guest filesystems, we
449 strongly recommend using Augeas. For example, Augeas understands how
450 to read and write, say, a Linux shadow password file or X.org
451 configuration file, and so avoids you having to write that code.
453 The main Augeas calls are bound through the C<guestfs_aug_*> APIs. We
454 don't document Augeas itself here because there is excellent
455 documentation on the L<http://augeas.net/> website.
457 If you don't want to use Augeas (you fool!) then try calling
458 L</guestfs_read_lines> to get the file as a list of lines which
459 you can iterate over.
463 We support SELinux guests. To ensure that labeling happens correctly
464 in SELinux guests, you need to enable SELinux and load the guest's
471 Before launching, do:
473 guestfs_set_selinux (g, 1);
477 After mounting the guest's filesystem(s), load the policy. This
478 is best done by running the L<load_policy(8)> command in the
481 guestfs_sh (g, "/usr/sbin/load_policy");
483 (Older versions of C<load_policy> require you to specify the
484 name of the policy file).
488 Optionally, set the security context for the API. The correct
489 security context to use can only be known by inspecting the
490 guest. As an example:
492 guestfs_setcon (g, "unconfined_u:unconfined_r:unconfined_t:s0");
496 This will work for running commands and editing existing files.
498 When new files are created, you may need to label them explicitly,
499 for example by running the external command
500 C<restorecon pathname>.
504 Certain calls are affected by the current file mode creation mask (the
505 "umask"). In particular ones which create files or directories, such
506 as L</guestfs_touch>, L</guestfs_mknod> or L</guestfs_mkdir>. This
507 affects either the default mode that the file is created with or
508 modifies the mode that you supply.
510 The default umask is C<022>, so files are created with modes such as
511 C<0644> and directories with C<0755>.
513 There are two ways to avoid being affected by umask. Either set umask
514 to 0 (call C<guestfs_umask (g, 0)> early after launching). Or call
515 L</guestfs_chmod> after creating each file or directory.
517 For more information about umask, see L<umask(2)>.
519 =head2 ENCRYPTED DISKS
521 Libguestfs allows you to access Linux guests which have been
522 encrypted using whole disk encryption that conforms to the
523 Linux Unified Key Setup (LUKS) standard. This includes
524 nearly all whole disk encryption systems used by modern
527 Use L</guestfs_vfs_type> to identify LUKS-encrypted block
528 devices (it returns the string C<crypto_LUKS>).
530 Then open these devices by calling L</guestfs_luks_open>.
531 Obviously you will require the passphrase!
533 Opening a LUKS device creates a new device mapper device
534 called C</dev/mapper/mapname> (where C<mapname> is the
535 string you supply to L</guestfs_luks_open>).
536 Reads and writes to this mapper device are decrypted from and
537 encrypted to the underlying block device respectively.
539 LVM volume groups on the device can be made visible by calling
540 L</guestfs_vgscan> followed by L</guestfs_vg_activate_all>.
541 The logical volume(s) can now be mounted in the usual way.
543 Use the reverse process to close a LUKS device. Unmount
544 any logical volumes on it, deactivate the volume groups
545 by caling C<guestfs_vg_activate (g, 0, ["/dev/VG"])>.
546 Then close the mapper device by calling
547 L</guestfs_luks_close> on the C</dev/mapper/mapname>
548 device (I<not> the underlying encrypted block device).
552 Libguestfs has APIs for inspecting an unknown disk image to find out
553 if it contains operating systems, an install CD or a live CD. (These
554 APIs used to be in a separate Perl-only library called
555 L<Sys::Guestfs::Lib(3)> but since version 1.5.3 the most frequently
556 used part of this library has been rewritten in C and moved into the
559 Add all disks belonging to the unknown virtual machine and call
560 L</guestfs_launch> in the usual way.
562 Then call L</guestfs_inspect_os>. This function uses other libguestfs
563 calls and certain heuristics, and returns a list of operating systems
564 that were found. An empty list means none were found. A single
565 element is the root filesystem of the operating system. For dual- or
566 multi-boot guests, multiple roots can be returned, each one
567 corresponding to a separate operating system. (Multi-boot virtual
568 machines are extremely rare in the world of virtualization, but since
569 this scenario can happen, we have built libguestfs to deal with it.)
571 For each root, you can then call various C<guestfs_inspect_get_*>
572 functions to get additional details about that operating system. For
573 example, call L</guestfs_inspect_get_type> to return the string
574 C<windows> or C<linux> for Windows and Linux-based operating systems
577 Un*x-like and Linux-based operating systems usually consist of several
578 filesystems which are mounted at boot time (for example, a separate
579 boot partition mounted on C</boot>). The inspection rules are able to
580 detect how filesystems correspond to mount points. Call
581 C<guestfs_inspect_get_mountpoints> to get this mapping. It might
582 return a hash table like this example:
585 / => /dev/vg_guest/lv_root
586 /usr => /dev/vg_guest/lv_usr
588 The caller can then make calls to L</guestfs_mount_options> to
589 mount the filesystems as suggested.
591 Be careful to mount filesystems in the right order (eg. C</> before
592 C</usr>). Sorting the keys of the hash by length, shortest first,
595 Inspection currently only works for some common operating systems.
596 Contributors are welcome to send patches for other operating systems
597 that we currently cannot detect.
599 Encrypted disks must be opened before inspection. See
600 L</ENCRYPTED DISKS> for more details. The L</guestfs_inspect_os>
601 function just ignores any encrypted devices.
603 A note on the implementation: The call L</guestfs_inspect_os> performs
604 inspection and caches the results in the guest handle. Subsequent
605 calls to C<guestfs_inspect_get_*> return this cached information, but
606 I<do not> re-read the disks. If you change the content of the guest
607 disks, you can redo inspection by calling L</guestfs_inspect_os>
608 again. (L</guestfs_inspect_list_applications> works a little
609 differently from the other calls and does read the disks. See
610 documentation for that function for details).
612 =head3 INSPECTING INSTALL DISKS
614 Libguestfs (since 1.9.4) can detect some install disks, install
615 CDs, live CDs and more.
617 Call L</guestfs_inspect_get_format> to return the format of the
618 operating system, which currently can be C<installed> (a regular
619 operating system) or C<installer> (some sort of install disk).
621 Further information is available about the operating system that can
622 be installed using the regular inspection APIs like
623 L</guestfs_inspect_get_product_name>,
624 L</guestfs_inspect_get_major_version> etc.
626 Some additional information specific to installer disks is also
627 available from the L</guestfs_inspect_is_live>,
628 L</guestfs_inspect_is_netinst> and L</guestfs_inspect_is_multipart>
631 =head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
633 Libguestfs can mount NTFS partitions. It does this using the
634 L<http://www.ntfs-3g.org/> driver.
636 =head3 DRIVE LETTERS AND PATHS
638 DOS and Windows still use drive letters, and the filesystems are
639 always treated as case insensitive by Windows itself, and therefore
640 you might find a Windows configuration file referring to a path like
641 C<c:\windows\system32>. When the filesystem is mounted in libguestfs,
642 that directory might be referred to as C</WINDOWS/System32>.
644 Drive letter mappings can be found using inspection
645 (see L</INSPECTION> and L</guestfs_inspect_get_drive_mappings>)
647 Dealing with separator characters (backslash vs forward slash) is
648 outside the scope of libguestfs, but usually a simple character
649 replacement will work.
651 To resolve the case insensitivity of paths, call
652 L</guestfs_case_sensitive_path>.
654 =head3 ACCESSING THE WINDOWS REGISTRY
656 Libguestfs also provides some help for decoding Windows Registry
657 "hive" files, through the library C<hivex> which is part of the
658 libguestfs project although ships as a separate tarball. You have to
659 locate and download the hive file(s) yourself, and then pass them to
660 C<hivex> functions. See also the programs L<hivexml(1)>,
661 L<hivexsh(1)>, L<hivexregedit(1)> and L<virt-win-reg(1)> for more help
664 =head3 SYMLINKS ON NTFS-3G FILESYSTEMS
666 Ntfs-3g tries to rewrite "Junction Points" and NTFS "symbolic links"
667 to provide something which looks like a Linux symlink. The way it
668 tries to do the rewriting is described here:
670 L<http://www.tuxera.com/community/ntfs-3g-advanced/junction-points-and-symbolic-links/>
672 The essential problem is that ntfs-3g simply does not have enough
673 information to do a correct job. NTFS links can contain drive letters
674 and references to external device GUIDs that ntfs-3g has no way of
675 resolving. It is almost certainly the case that libguestfs callers
676 should ignore what ntfs-3g does (ie. don't use L</guestfs_readlink> on
679 Instead if you encounter a symbolic link on an ntfs-3g filesystem, use
680 L</guestfs_lgetxattr> to read the C<system.ntfs_reparse_data> extended
681 attribute, and read the raw reparse data from that (you can find the
682 format documented in various places around the web).
684 =head3 EXTENDED ATTRIBUTES ON NTFS-3G FILESYSTEMS
686 There are other useful extended attributes that can be read from
687 ntfs-3g filesystems (using L</guestfs_getxattr>). See:
689 L<http://www.tuxera.com/community/ntfs-3g-advanced/extended-attributes/>
691 =head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES
693 Although we don't want to discourage you from using the C API, we will
694 mention here that the same API is also available in other languages.
696 The API is broadly identical in all supported languages. This means
697 that the C call C<guestfs_add_drive_ro(g,file)> is
698 C<$g-E<gt>add_drive_ro($file)> in Perl, C<g.add_drive_ro(file)> in Python,
699 and C<g#add_drive_ro file> in OCaml. In other words, a
700 straightforward, predictable isomorphism between each language.
702 Error messages are automatically transformed
703 into exceptions if the language supports it.
705 We don't try to "object orientify" parts of the API in OO languages,
706 although contributors are welcome to write higher level APIs above
707 what we provide in their favourite languages if they wish.
713 You can use the I<guestfs.h> header file from C++ programs. The C++
714 API is identical to the C API. C++ classes and exceptions are not
719 The C# bindings are highly experimental. Please read the warnings
720 at the top of C<csharp/Libguestfs.cs>.
724 This is the only language binding that is working but incomplete.
725 Only calls which return simple integers have been bound in Haskell,
726 and we are looking for help to complete this binding.
730 Full documentation is contained in the Javadoc which is distributed
731 with libguestfs. For examples, see L<guestfs-java(3)>.
735 See L<guestfs-ocaml(3)>.
739 See L<guestfs-perl(3)> and L<Sys::Guestfs(3)>.
743 For documentation see C<README-PHP> supplied with libguestfs
744 sources or in the php-libguestfs package for your distribution.
746 The PHP binding only works correctly on 64 bit machines.
750 See L<guestfs-python(3)>.
754 See L<guestfs-ruby(3)>.
756 =item B<shell scripts>
762 =head2 LIBGUESTFS GOTCHAS
764 L<http://en.wikipedia.org/wiki/Gotcha_(programming)>: "A feature of a
765 system [...] that works in the way it is documented but is
766 counterintuitive and almost invites mistakes."
768 Since we developed libguestfs and the associated tools, there are
769 several things we would have designed differently, but are now stuck
770 with for backwards compatibility or other reasons. If there is ever a
771 libguestfs 2.0 release, you can expect these to change. Beware of
776 =item Autosync / forgetting to sync.
778 I<Update:> Autosync is enabled by default for all API users starting
779 from libguestfs 1.5.24. This section only applies to older versions.
781 When modifying a filesystem from C or another language, you B<must>
782 unmount all filesystems and call L</guestfs_sync> explicitly before
783 you close the libguestfs handle. You can also call:
785 guestfs_set_autosync (g, 1);
787 to have the unmount/sync done automatically for you when the handle 'g'
788 is closed. (This feature is called "autosync", L</guestfs_set_autosync>
791 If you forget to do this, then it is entirely possible that your
792 changes won't be written out, or will be partially written, or (very
793 rarely) that you'll get disk corruption.
795 Note that in L<guestfish(3)> autosync is the default. So quick and
796 dirty guestfish scripts that forget to sync will work just fine, which
797 can make this very puzzling if you are trying to debug a problem.
799 =item Mount option C<-o sync> should not be the default.
801 If you use L</guestfs_mount>, then C<-o sync,noatime> are added
802 implicitly. However C<-o sync> does not add any reliability benefit,
803 but does have a very large performance impact.
805 The work around is to use L</guestfs_mount_options> and set the mount
806 options that you actually want to use.
808 =item Read-only should be the default.
810 In L<guestfish(3)>, I<--ro> should be the default, and you should
811 have to specify I<--rw> if you want to make changes to the image.
813 This would reduce the potential to corrupt live VM images.
815 Note that many filesystems change the disk when you just mount and
816 unmount, even if you didn't perform any writes. You need to use
817 L</guestfs_add_drive_ro> to guarantee that the disk is not changed.
819 =item guestfish command line is hard to use.
821 C<guestfish disk.img> doesn't do what people expect (open C<disk.img>
822 for examination). It tries to run a guestfish command C<disk.img>
823 which doesn't exist, so it fails. In earlier versions of guestfish
824 the error message was also unintuitive, but we have corrected this
825 since. Like the Bourne shell, we should have used C<guestfish -c
826 command> to run commands.
828 =item guestfish megabyte modifiers don't work right on all commands
830 In recent guestfish you can use C<1M> to mean 1 megabyte (and
831 similarly for other modifiers). What guestfish actually does is to
832 multiply the number part by the modifier part and pass the result to
833 the C API. However this doesn't work for a few APIs which aren't
834 expecting bytes, but are already expecting some other unit
837 The most common is L</guestfs_lvcreate>. The guestfish command:
841 does not do what you might expect. Instead because
842 L</guestfs_lvcreate> is already expecting megabytes, this tries to
843 create a 100 I<terabyte> (100 megabytes * megabytes) logical volume.
844 The error message you get from this is also a little obscure.
846 This could be fixed in the generator by specially marking parameters
847 and return values which take bytes or other units.
849 =item Ambiguity between devices and paths
851 There is a subtle ambiguity in the API between a device name
852 (eg. C</dev/sdb2>) and a similar pathname. A file might just happen
853 to be called C<sdb2> in the directory C</dev> (consider some non-Unix
856 In the current API we usually resolve this ambiguity by having two
857 separate calls, for example L</guestfs_checksum> and
858 L</guestfs_checksum_device>. Some API calls are ambiguous and
859 (incorrectly) resolve the problem by detecting if the path supplied
860 begins with C</dev/>.
862 To avoid both the ambiguity and the need to duplicate some calls, we
863 could make paths/devices into structured names. One way to do this
864 would be to use a notation like grub (C<hd(0,0)>), although nobody
865 really likes this aspect of grub. Another way would be to use a
866 structured type, equivalent to this OCaml type:
868 type path = Path of string | Device of int | Partition of int * int
870 which would allow you to pass arguments like:
873 Device 1 (* /dev/sdb, or perhaps /dev/sda *)
874 Partition (1, 2) (* /dev/sdb2 (or is it /dev/sda2 or /dev/sdb3?) *)
875 Path "/dev/sdb2" (* not a device *)
877 As you can see there are still problems to resolve even with this
878 representation. Also consider how it might work in guestfish.
882 =head2 KEYS AND PASSPHRASES
884 Certain libguestfs calls take a parameter that contains sensitive key
885 material, passed in as a C string.
887 In the future we would hope to change the libguestfs implementation so
888 that keys are L<mlock(2)>-ed into physical RAM, and thus can never end
889 up in swap. However this is I<not> done at the moment, because of the
890 complexity of such an implementation.
892 Therefore you should be aware that any key parameter you pass to
893 libguestfs might end up being written out to the swap partition. If
894 this is a concern, scrub the swap partition or don't use libguestfs on
897 =head2 MULTIPLE HANDLES AND MULTIPLE THREADS
899 All high-level libguestfs actions are synchronous. If you want
900 to use libguestfs asynchronously then you must create a thread.
902 Only use the handle from a single thread. Either use the handle
903 exclusively from one thread, or provide your own mutex so that two
904 threads cannot issue calls on the same handle at the same time.
906 See the graphical program guestfs-browser for one possible
907 architecture for multithreaded programs using libvirt and libguestfs.
911 Libguestfs needs a supermin appliance, which it finds by looking along
914 By default it looks for these in the directory C<$libdir/guestfs>
915 (eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
917 Use L</guestfs_set_path> or set the environment variable
918 L</LIBGUESTFS_PATH> to change the directories that libguestfs will
919 search in. The value is a colon-separated list of paths. The current
920 directory is I<not> searched unless the path contains an empty element
921 or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
922 search the current directory and then C</usr/lib/guestfs>.
926 If you want to compile your own qemu, run qemu from a non-standard
927 location, or pass extra arguments to qemu, then you can write a
928 shell-script wrapper around qemu.
930 There is one important rule to remember: you I<must C<exec qemu>> as
931 the last command in the shell script (so that qemu replaces the shell
932 and becomes the direct child of the libguestfs-using program). If you
933 don't do this, then the qemu process won't be cleaned up correctly.
935 Here is an example of a wrapper, where I have built my own copy of
939 qemudir=/home/rjones/d/qemu
940 exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
942 Save this script as C</tmp/qemu.wrapper> (or wherever), C<chmod +x>,
943 and then use it by setting the LIBGUESTFS_QEMU environment variable.
946 LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
948 Note that libguestfs also calls qemu with the -help and -version
949 options in order to determine features.
951 Wrappers can also be used to edit the options passed to qemu. In the
952 following example, the C<-machine ...> option (C<-machine> and the
953 following argument) are removed from the command line and replaced
954 with C<-machine pc,accel=tcg>. The while loop iterates over the
955 options until it finds the right one to remove, putting the remaining
956 options into the C<args> array.
961 while [ $# -gt 0 ]; do
972 exec qemu-kvm -machine pc,accel=tcg "${args[@]}"
974 =head2 ATTACHING TO RUNNING DAEMONS
976 I<Note (1):> This is B<highly experimental> and has a tendency to eat
977 babies. Use with caution.
979 I<Note (2):> This section explains how to attach to a running daemon
980 from a low level perspective. For most users, simply using virt tools
981 such as L<guestfish(1)> with the I<--live> option will "just work".
983 =head3 Using guestfs_set_attach_method
985 By calling L</guestfs_set_attach_method> you can change how the
986 library connects to the C<guestfsd> daemon in L</guestfs_launch>
987 (read L</ARCHITECTURE> for some background).
989 The normal attach method is C<appliance>, where a small appliance is
990 created containing the daemon, and then the library connects to this.
992 Setting attach method to C<unix:I<path>> (where I<path> is the path of
993 a Unix domain socket) causes L</guestfs_launch> to connect to an
994 existing daemon over the Unix domain socket.
996 The normal use for this is to connect to a running virtual machine
997 that contains a C<guestfsd> daemon, and send commands so you can read
998 and write files inside the live virtual machine.
1000 =head3 Using guestfs_add_domain with live flag
1002 L</guestfs_add_domain> provides some help for getting the
1003 correct attach method. If you pass the C<live> option to this
1004 function, then (if the virtual machine is running) it will
1005 examine the libvirt XML looking for a virtio-serial channel
1012 <channel type='unix'>
1013 <source mode='bind' path='/path/to/socket'/>
1014 <target type='virtio' name='org.libguestfs.channel.0'/>
1020 L</guestfs_add_domain> extracts C</path/to/socket> and sets the attach
1021 method to C<unix:/path/to/socket>.
1023 Some of the libguestfs tools (including guestfish) support a I<--live>
1024 option which is passed through to L</guestfs_add_domain> thus allowing
1025 you to attach to and modify live virtual machines.
1027 The virtual machine needs to have been set up beforehand so that it
1028 has the virtio-serial channel and so that guestfsd is running inside
1031 =head2 ABI GUARANTEE
1033 We guarantee the libguestfs ABI (binary interface), for public,
1034 high-level actions as outlined in this section. Although we will
1035 deprecate some actions, for example if they get replaced by newer
1036 calls, we will keep the old actions forever. This allows you the
1037 developer to program in confidence against the libguestfs API.
1039 =head2 BLOCK DEVICE NAMING
1041 In the kernel there is now quite a profusion of schemata for naming
1042 block devices (in this context, by I<block device> I mean a physical
1043 or virtual hard drive). The original Linux IDE driver used names
1044 starting with C</dev/hd*>. SCSI devices have historically used a
1045 different naming scheme, C</dev/sd*>. When the Linux kernel I<libata>
1046 driver became a popular replacement for the old IDE driver
1047 (particularly for SATA devices) those devices also used the
1048 C</dev/sd*> scheme. Additionally we now have virtual machines with
1049 paravirtualized drivers. This has created several different naming
1050 systems, such as C</dev/vd*> for virtio disks and C</dev/xvd*> for Xen
1053 As discussed above, libguestfs uses a qemu appliance running an
1054 embedded Linux kernel to access block devices. We can run a variety
1055 of appliances based on a variety of Linux kernels.
1057 This causes a problem for libguestfs because many API calls use device
1058 or partition names. Working scripts and the recipe (example) scripts
1059 that we make available over the internet could fail if the naming
1062 Therefore libguestfs defines C</dev/sd*> as the I<standard naming
1063 scheme>. Internally C</dev/sd*> names are translated, if necessary,
1064 to other names as required. For example, under RHEL 5 which uses the
1065 C</dev/hd*> scheme, any device parameter C</dev/sda2> is translated to
1066 C</dev/hda2> transparently.
1068 Note that this I<only> applies to parameters. The
1069 L</guestfs_list_devices>, L</guestfs_list_partitions> and similar calls
1070 return the true names of the devices and partitions as known to the
1073 =head3 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
1075 Usually this translation is transparent. However in some (very rare)
1076 cases you may need to know the exact algorithm. Such cases include
1077 where you use L</guestfs_config> to add a mixture of virtio and IDE
1078 devices to the qemu-based appliance, so have a mixture of C</dev/sd*>
1079 and C</dev/vd*> devices.
1081 The algorithm is applied only to I<parameters> which are known to be
1082 either device or partition names. Return values from functions such
1083 as L</guestfs_list_devices> are never changed.
1089 Is the string a parameter which is a device or partition name?
1093 Does the string begin with C</dev/sd>?
1097 Does the named device exist? If so, we use that device.
1098 However if I<not> then we continue with this algorithm.
1102 Replace initial C</dev/sd> string with C</dev/hd>.
1104 For example, change C</dev/sda2> to C</dev/hda2>.
1106 If that named device exists, use it. If not, continue.
1110 Replace initial C</dev/sd> string with C</dev/vd>.
1112 If that named device exists, use it. If not, return an error.
1116 =head3 PORTABILITY CONCERNS WITH BLOCK DEVICE NAMING
1118 Although the standard naming scheme and automatic translation is
1119 useful for simple programs and guestfish scripts, for larger programs
1120 it is best not to rely on this mechanism.
1122 Where possible for maximum future portability programs using
1123 libguestfs should use these future-proof techniques:
1129 Use L</guestfs_list_devices> or L</guestfs_list_partitions> to list
1130 actual device names, and then use those names directly.
1132 Since those device names exist by definition, they will never be
1137 Use higher level ways to identify filesystems, such as LVM names,
1138 UUIDs and filesystem labels.
1144 This section discusses security implications of using libguestfs,
1145 particularly with untrusted or malicious guests or disk images.
1147 =head2 GENERAL SECURITY CONSIDERATIONS
1149 Be careful with any files or data that you download from a guest (by
1150 "download" we mean not just the L</guestfs_download> command but any
1151 command that reads files, filenames, directories or anything else from
1152 a disk image). An attacker could manipulate the data to fool your
1153 program into doing the wrong thing. Consider cases such as:
1159 the data (file etc) not being present
1163 being present but empty
1167 being much larger than normal
1171 containing arbitrary 8 bit data
1175 being in an unexpected character encoding
1179 containing homoglyphs.
1183 =head2 SECURITY OF MOUNTING FILESYSTEMS
1185 When you mount a filesystem under Linux, mistakes in the kernel
1186 filesystem (VFS) module can sometimes be escalated into exploits by
1187 deliberately creating a malicious, malformed filesystem. These
1188 exploits are very severe for two reasons. Firstly there are very many
1189 filesystem drivers in the kernel, and many of them are infrequently
1190 used and not much developer attention has been paid to the code.
1191 Linux userspace helps potential crackers by detecting the filesystem
1192 type and automatically choosing the right VFS driver, even if that
1193 filesystem type is obscure or unexpected for the administrator.
1194 Secondly, a kernel-level exploit is like a local root exploit (worse
1195 in some ways), giving immediate and total access to the system right
1196 down to the hardware level.
1198 That explains why you should never mount a filesystem from an
1199 untrusted guest on your host kernel. How about libguestfs? We run a
1200 Linux kernel inside a qemu virtual machine, usually running as a
1201 non-root user. The attacker would need to write a filesystem which
1202 first exploited the kernel, and then exploited either qemu
1203 virtualization (eg. a faulty qemu driver) or the libguestfs protocol,
1204 and finally to be as serious as the host kernel exploit it would need
1205 to escalate its privileges to root. This multi-step escalation,
1206 performed by a static piece of data, is thought to be extremely hard
1207 to do, although we never say 'never' about security issues.
1209 In any case callers can reduce the attack surface by forcing the
1210 filesystem type when mounting (use L</guestfs_mount_vfs>).
1212 =head2 PROTOCOL SECURITY
1214 The protocol is designed to be secure, being based on RFC 4506 (XDR)
1215 with a defined upper message size. However a program that uses
1216 libguestfs must also take care - for example you can write a program
1217 that downloads a binary from a disk image and executes it locally, and
1218 no amount of protocol security will save you from the consequences.
1220 =head2 INSPECTION SECURITY
1222 Parts of the inspection API (see L</INSPECTION>) return untrusted
1223 strings directly from the guest, and these could contain any 8 bit
1224 data. Callers should be careful to escape these before printing them
1225 to a structured file (for example, use HTML escaping if creating a web
1228 Guest configuration may be altered in unusual ways by the
1229 administrator of the virtual machine, and may not reflect reality
1230 (particularly for untrusted or actively malicious guests). For
1231 example we parse the hostname from configuration files like
1232 C</etc/sysconfig/network> that we find in the guest, but the guest
1233 administrator can easily manipulate these files to provide the wrong
1236 The inspection API parses guest configuration using two external
1237 libraries: Augeas (Linux configuration) and hivex (Windows Registry).
1238 Both are designed to be robust in the face of malicious data, although
1239 denial of service attacks are still possible, for example with
1240 oversized configuration files.
1242 =head2 RUNNING UNTRUSTED GUEST COMMANDS
1244 Be very cautious about running commands from the guest. By running a
1245 command in the guest, you are giving CPU time to a binary that you do
1246 not control, under the same user account as the library, albeit
1247 wrapped in qemu virtualization. More information and alternatives can
1248 be found in the section L</RUNNING COMMANDS>.
1250 =head2 CVE-2010-3851
1252 https://bugzilla.redhat.com/642934
1254 This security bug concerns the automatic disk format detection that
1255 qemu does on disk images.
1257 A raw disk image is just the raw bytes, there is no header. Other
1258 disk images like qcow2 contain a special header. Qemu deals with this
1259 by looking for one of the known headers, and if none is found then
1260 assuming the disk image must be raw.
1262 This allows a guest which has been given a raw disk image to write
1263 some other header. At next boot (or when the disk image is accessed
1264 by libguestfs) qemu would do autodetection and think the disk image
1265 format was, say, qcow2 based on the header written by the guest.
1267 This in itself would not be a problem, but qcow2 offers many features,
1268 one of which is to allow a disk image to refer to another image
1269 (called the "backing disk"). It does this by placing the path to the
1270 backing disk into the qcow2 header. This path is not validated and
1271 could point to any host file (eg. "/etc/passwd"). The backing disk is
1272 then exposed through "holes" in the qcow2 disk image, which of course
1273 is completely under the control of the attacker.
1275 In libguestfs this is rather hard to exploit except under two
1282 You have enabled the network or have opened the disk in write mode.
1286 You are also running untrusted code from the guest (see
1287 L</RUNNING COMMANDS>).
1291 The way to avoid this is to specify the expected disk format when
1292 adding disks (the optional C<format> option to
1293 L</guestfs_add_drive_opts>). You should always do this if the disk is
1294 raw format, and it's a good idea for other cases too.
1296 For disks added from libvirt using calls like L</guestfs_add_domain>,
1297 the format is fetched from libvirt and passed through.
1299 For libguestfs tools, use the I<--format> command line parameter as
1302 =head1 CONNECTION MANAGEMENT
1306 C<guestfs_h> is the opaque type representing a connection handle.
1307 Create a handle by calling L</guestfs_create>. Call L</guestfs_close>
1308 to free the handle and release all resources used.
1310 For information on using multiple handles and threads, see the section
1311 L</MULTIPLE HANDLES AND MULTIPLE THREADS> above.
1313 =head2 guestfs_create
1315 guestfs_h *guestfs_create (void);
1317 Create a connection handle.
1319 On success this returns a non-NULL pointer to a handle. On error it
1322 You have to "configure" the handle after creating it. This includes
1323 calling L</guestfs_add_drive_opts> (or one of the equivalent calls) on
1324 the handle at least once.
1326 After configuring the handle, you have to call L</guestfs_launch>.
1328 You may also want to configure error handling for the handle. See the
1329 L</ERROR HANDLING> section below.
1331 =head2 guestfs_close
1333 void guestfs_close (guestfs_h *g);
1335 This closes the connection handle and frees up all resources used.
1337 If autosync was set on the handle and the handle was launched, then
1338 this implicitly calls various functions to unmount filesystems and
1339 sync the disk. See L</guestfs_set_autosync> for more details.
1341 If a close callback was set on the handle, then it is called.
1343 =head1 ERROR HANDLING
1345 API functions can return errors. For example, almost all functions
1346 that return C<int> will return C<-1> to indicate an error.
1348 Additional information is available for errors: an error message
1349 string and optionally an error number (errno) if the thing that failed
1352 You can get at the additional information about the last error on the
1353 handle by calling L</guestfs_last_error>, L</guestfs_last_errno>,
1354 and/or by setting up an error handler with
1355 L</guestfs_set_error_handler>.
1357 When the handle is created, a default error handler is installed which
1358 prints the error message string to C<stderr>. For small short-running
1359 command line programs it is sufficient to do:
1361 if (guestfs_launch (g) == -1)
1362 exit (EXIT_FAILURE);
1364 since the default error handler will ensure that an error message has
1365 been printed to C<stderr> before the program exits.
1367 For other programs the caller will almost certainly want to install an
1368 alternate error handler or do error handling in-line like this:
1370 g = guestfs_create ();
1372 /* This disables the default behaviour of printing errors
1374 guestfs_set_error_handler (g, NULL, NULL);
1376 if (guestfs_launch (g) == -1) {
1377 /* Examine the error message and print it etc. */
1378 char *msg = guestfs_last_error (g);
1379 int errnum = guestfs_last_errno (g);
1380 fprintf (stderr, "%s\n", msg);
1384 Out of memory errors are handled differently. The default action is
1385 to call L<abort(3)>. If this is undesirable, then you can set a
1386 handler using L</guestfs_set_out_of_memory_handler>.
1388 L</guestfs_create> returns C<NULL> if the handle cannot be created,
1389 and because there is no handle if this happens there is no way to get
1390 additional error information. However L</guestfs_create> is supposed
1391 to be a lightweight operation which can only fail because of
1392 insufficient memory (it returns NULL in this case).
1394 =head2 guestfs_last_error
1396 const char *guestfs_last_error (guestfs_h *g);
1398 This returns the last error message that happened on C<g>. If
1399 there has not been an error since the handle was created, then this
1402 The lifetime of the returned string is until the next error occurs, or
1403 L</guestfs_close> is called.
1405 =head2 guestfs_last_errno
1407 int guestfs_last_errno (guestfs_h *g);
1409 This returns the last error number (errno) that happened on C<g>.
1411 If successful, an errno integer not equal to zero is returned.
1413 If no error, this returns 0. This call can return 0 in three
1420 There has not been any error on the handle.
1424 There has been an error but the errno was meaningless. This
1425 corresponds to the case where the error did not come from a
1426 failed system call, but for some other reason.
1430 There was an error from a failed system call, but for some
1431 reason the errno was not captured and returned. This usually
1432 indicates a bug in libguestfs.
1436 Libguestfs tries to convert the errno from inside the applicance into
1437 a corresponding errno for the caller (not entirely trivial: the
1438 appliance might be running a completely different operating system
1439 from the library and error numbers are not standardized across
1440 Un*xen). If this could not be done, then the error is translated to
1441 C<EINVAL>. In practice this should only happen in very rare
1444 =head2 guestfs_set_error_handler
1446 typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
1449 void guestfs_set_error_handler (guestfs_h *g,
1450 guestfs_error_handler_cb cb,
1453 The callback C<cb> will be called if there is an error. The
1454 parameters passed to the callback are an opaque data pointer and the
1455 error message string.
1457 C<errno> is not passed to the callback. To get that the callback must
1458 call L</guestfs_last_errno>.
1460 Note that the message string C<msg> is freed as soon as the callback
1461 function returns, so if you want to stash it somewhere you must make
1464 The default handler prints messages on C<stderr>.
1466 If you set C<cb> to C<NULL> then I<no> handler is called.
1468 =head2 guestfs_get_error_handler
1470 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
1473 Returns the current error handler callback.
1475 =head2 guestfs_set_out_of_memory_handler
1477 typedef void (*guestfs_abort_cb) (void);
1478 void guestfs_set_out_of_memory_handler (guestfs_h *g,
1481 The callback C<cb> will be called if there is an out of memory
1482 situation. I<Note this callback must not return>.
1484 The default is to call L<abort(3)>.
1486 You cannot set C<cb> to C<NULL>. You can't ignore out of memory
1489 =head2 guestfs_get_out_of_memory_handler
1491 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *g);
1493 This returns the current out of memory handler.
1505 =head2 GROUPS OF FUNCTIONALITY IN THE APPLIANCE
1507 Using L</guestfs_available> you can test availability of
1508 the following groups of functions. This test queries the
1509 appliance to see if the appliance you are currently using
1510 supports the functionality.
1514 =head2 GUESTFISH supported COMMAND
1516 In L<guestfish(3)> there is a handy interactive command
1517 C<supported> which prints out the available groups and
1518 whether they are supported by this build of libguestfs.
1519 Note however that you have to do C<run> first.
1521 =head2 SINGLE CALLS AT COMPILE TIME
1523 Since version 1.5.8, C<E<lt>guestfs.hE<gt>> defines symbols
1524 for each C API function, such as:
1526 #define LIBGUESTFS_HAVE_DD 1
1528 if L</guestfs_dd> is available.
1530 Before version 1.5.8, if you needed to test whether a single
1531 libguestfs function is available at compile time, we recommended using
1532 build tools such as autoconf or cmake. For example in autotools you
1535 AC_CHECK_LIB([guestfs],[guestfs_create])
1536 AC_CHECK_FUNCS([guestfs_dd])
1538 which would result in C<HAVE_GUESTFS_DD> being either defined
1539 or not defined in your program.
1541 =head2 SINGLE CALLS AT RUN TIME
1543 Testing at compile time doesn't guarantee that a function really
1544 exists in the library. The reason is that you might be dynamically
1545 linked against a previous I<libguestfs.so> (dynamic library)
1546 which doesn't have the call. This situation unfortunately results
1547 in a segmentation fault, which is a shortcoming of the C dynamic
1548 linking system itself.
1550 You can use L<dlopen(3)> to test if a function is available
1551 at run time, as in this example program (note that you still
1552 need the compile time check as well):
1558 #include <guestfs.h>
1562 #ifdef LIBGUESTFS_HAVE_DD
1566 /* Test if the function guestfs_dd is really available. */
1567 dl = dlopen (NULL, RTLD_LAZY);
1569 fprintf (stderr, "dlopen: %s\n", dlerror ());
1570 exit (EXIT_FAILURE);
1572 has_function = dlsym (dl, "guestfs_dd") != NULL;
1576 printf ("this libguestfs.so does NOT have guestfs_dd function\n");
1578 printf ("this libguestfs.so has guestfs_dd function\n");
1579 /* Now it's safe to call
1580 guestfs_dd (g, "foo", "bar");
1584 printf ("guestfs_dd function was not found at compile time\n");
1588 You may think the above is an awful lot of hassle, and it is.
1589 There are other ways outside of the C linking system to ensure
1590 that this kind of incompatibility never arises, such as using
1593 Requires: libguestfs >= 1.0.80
1595 =head1 CALLS WITH OPTIONAL ARGUMENTS
1597 A recent feature of the API is the introduction of calls which take
1598 optional arguments. In C these are declared 3 ways. The main way is
1599 as a call which takes variable arguments (ie. C<...>), as in this
1602 int guestfs_add_drive_opts (guestfs_h *g, const char *filename, ...);
1604 Call this with a list of optional arguments, terminated by C<-1>.
1605 So to call with no optional arguments specified:
1607 guestfs_add_drive_opts (g, filename, -1);
1609 With a single optional argument:
1611 guestfs_add_drive_opts (g, filename,
1612 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
1617 guestfs_add_drive_opts (g, filename,
1618 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
1619 GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
1622 and so forth. Don't forget the terminating C<-1> otherwise
1623 Bad Things will happen!
1625 =head2 USING va_list FOR OPTIONAL ARGUMENTS
1627 The second variant has the same name with the suffix C<_va>, which
1628 works the same way but takes a C<va_list>. See the C manual for
1629 details. For the example function, this is declared:
1631 int guestfs_add_drive_opts_va (guestfs_h *g, const char *filename,
1634 =head2 CONSTRUCTING OPTIONAL ARGUMENTS
1636 The third variant is useful where you need to construct these
1637 calls. You pass in a structure where you fill in the optional
1638 fields. The structure has a bitmask as the first element which
1639 you must set to indicate which fields you have filled in. For
1640 our example function the structure and call are declared:
1642 struct guestfs_add_drive_opts_argv {
1648 int guestfs_add_drive_opts_argv (guestfs_h *g, const char *filename,
1649 const struct guestfs_add_drive_opts_argv *optargs);
1651 You could call it like this:
1653 struct guestfs_add_drive_opts_argv optargs = {
1654 .bitmask = GUESTFS_ADD_DRIVE_OPTS_READONLY_BITMASK |
1655 GUESTFS_ADD_DRIVE_OPTS_FORMAT_BITMASK,
1660 guestfs_add_drive_opts_argv (g, filename, &optargs);
1668 The C<_BITMASK> suffix on each option name when specifying the
1673 You do not need to fill in all fields of the structure.
1677 There must be a one-to-one correspondence between fields of the
1678 structure that are filled in, and bits set in the bitmask.
1682 =head2 OPTIONAL ARGUMENTS IN OTHER LANGUAGES
1684 In other languages, optional arguments are expressed in the
1685 way that is natural for that language. We refer you to the
1686 language-specific documentation for more details on that.
1688 For guestfish, see L<guestfish(1)/OPTIONAL ARGUMENTS>.
1690 =head2 SETTING CALLBACKS TO HANDLE EVENTS
1692 B<Note:> This section documents the generic event mechanism introduced
1693 in libguestfs 1.10, which you should use in new code if possible. The
1694 old functions C<guestfs_set_log_message_callback>,
1695 C<guestfs_set_subprocess_quit_callback>,
1696 C<guestfs_set_launch_done_callback>, C<guestfs_set_close_callback> and
1697 C<guestfs_set_progress_callback> are no longer documented in this
1698 manual page. Because of the ABI guarantee, the old functions continue
1701 Handles generate events when certain things happen, such as log
1702 messages being generated, progress messages during long-running
1703 operations, or the handle being closed. The API calls described below
1704 let you register a callback to be called when events happen. You can
1705 register multiple callbacks (for the same, different or overlapping
1706 sets of events), and individually remove callbacks. If callbacks are
1707 not removed, then they remain in force until the handle is closed.
1709 In the current implementation, events are only generated
1710 synchronously: that means that events (and hence callbacks) can only
1711 happen while you are in the middle of making another libguestfs call.
1712 The callback is called in the same thread.
1714 Events may contain a payload, usually nothing (void), an array of 64
1715 bit unsigned integers, or a message buffer. Payloads are discussed
1718 =head3 CLASSES OF EVENTS
1722 =item GUESTFS_EVENT_CLOSE
1723 (payload type: void)
1725 The callback function will be called while the handle is being closed
1726 (synchronously from L</guestfs_close>).
1728 Note that libguestfs installs an L<atexit(3)> handler to try to clean
1729 up handles that are open when the program exits. This means that this
1730 callback might be called indirectly from L<exit(3)>, which can cause
1731 unexpected problems in higher-level languages (eg. if your HLL
1732 interpreter has already been cleaned up by the time this is called,
1733 and if your callback then jumps into some HLL function).
1735 If no callback is registered: the handle is closed without any
1736 callback being invoked.
1738 =item GUESTFS_EVENT_SUBPROCESS_QUIT
1739 (payload type: void)
1741 The callback function will be called when the child process quits,
1742 either asynchronously or if killed by L</guestfs_kill_subprocess>.
1743 (This corresponds to a transition from any state to the CONFIG state).
1745 If no callback is registered: the event is ignored.
1747 =item GUESTFS_EVENT_LAUNCH_DONE
1748 (payload type: void)
1750 The callback function will be called when the child process becomes
1751 ready first time after it has been launched. (This corresponds to a
1752 transition from LAUNCHING to the READY state).
1754 If no callback is registered: the event is ignored.
1756 =item GUESTFS_EVENT_PROGRESS
1757 (payload type: array of 4 x uint64_t)
1759 Some long-running operations can generate progress messages. If
1760 this callback is registered, then it will be called each time a
1761 progress message is generated (usually two seconds after the
1762 operation started, and three times per second thereafter until
1763 it completes, although the frequency may change in future versions).
1765 The callback receives in the payload four unsigned 64 bit numbers
1766 which are (in order): C<proc_nr>, C<serial>, C<position>, C<total>.
1768 The units of C<total> are not defined, although for some
1769 operations C<total> may relate in some way to the amount of
1770 data to be transferred (eg. in bytes or megabytes), and
1771 C<position> may be the portion which has been transferred.
1773 The only defined and stable parts of the API are:
1779 The callback can display to the user some type of progress bar or
1780 indicator which shows the ratio of C<position>:C<total>.
1784 0 E<lt>= C<position> E<lt>= C<total>
1788 If any progress notification is sent during a call, then a final
1789 progress notification is always sent when C<position> = C<total>
1790 (I<unless> the call fails with an error).
1792 This is to simplify caller code, so callers can easily set the
1793 progress indicator to "100%" at the end of the operation, without
1794 requiring special code to detect this case.
1798 For some calls we are unable to estimate the progress of the call, but
1799 we can still generate progress messages to indicate activity. This is
1800 known as "pulse mode", and is directly supported by certain progress
1801 bar implementations (eg. GtkProgressBar).
1803 For these calls, zero or more progress messages are generated with
1804 C<position = 0> and C<total = 1>, followed by a final message with
1805 C<position = total = 1>.
1807 As noted above, if the call fails with an error then the final message
1808 may not be generated.
1812 The callback also receives the procedure number (C<proc_nr>) and
1813 serial number (C<serial>) of the call. These are only useful for
1814 debugging protocol issues, and the callback can normally ignore them.
1815 The callback may want to print these numbers in error messages or
1818 If no callback is registered: progress messages are discarded.
1820 =item GUESTFS_EVENT_APPLIANCE
1821 (payload type: message buffer)
1823 The callback function is called whenever a log message is generated by
1824 qemu, the appliance kernel, guestfsd (daemon), or utility programs.
1826 If the verbose flag (L</guestfs_set_verbose>) is set before launch
1827 (L</guestfs_launch>) then additional debug messages are generated.
1829 If no callback is registered: the messages are discarded unless the
1830 verbose flag is set in which case they are sent to stderr. You can
1831 override the printing of verbose messages to stderr by setting up a
1834 =item GUESTFS_EVENT_LIBRARY
1835 (payload type: message buffer)
1837 The callback function is called whenever a log message is generated by
1838 the library part of libguestfs.
1840 If the verbose flag (L</guestfs_set_verbose>) is set then additional
1841 debug messages are generated.
1843 If no callback is registered: the messages are discarded unless the
1844 verbose flag is set in which case they are sent to stderr. You can
1845 override the printing of verbose messages to stderr by setting up a
1848 =item GUESTFS_EVENT_TRACE
1849 (payload type: message buffer)
1851 The callback function is called whenever a trace message is generated.
1852 This only applies if the trace flag (L</guestfs_set_trace>) is set.
1854 If no callback is registered: the messages are sent to stderr. You
1855 can override the printing of trace messages to stderr by setting up a
1860 =head3 guestfs_set_event_callback
1862 int guestfs_set_event_callback (guestfs_h *g,
1863 guestfs_event_callback cb,
1864 uint64_t event_bitmask,
1868 This function registers a callback (C<cb>) for all event classes
1869 in the C<event_bitmask>.
1871 For example, to register for all log message events, you could call
1872 this function with the bitmask
1873 C<GUESTFS_EVENT_APPLIANCE|GUESTFS_EVENT_LIBRARY>. To register a
1874 single callback for all possible classes of events, use
1875 C<GUESTFS_EVENT_ALL>.
1877 C<flags> should always be passed as 0.
1879 C<opaque> is an opaque pointer which is passed to the callback. You
1880 can use it for any purpose.
1882 The return value is the event handle (an integer) which you can use to
1883 delete the callback (see below).
1885 If there is an error, this function returns C<-1>, and sets the error
1886 in the handle in the usual way (see L</guestfs_last_error> etc.)
1888 Callbacks remain in effect until they are deleted, or until the handle
1891 In the case where multiple callbacks are registered for a particular
1892 event class, all of the callbacks are called. The order in which
1893 multiple callbacks are called is not defined.
1895 =head3 guestfs_delete_event_callback
1897 void guestfs_delete_event_callback (guestfs_h *g, int event_handle);
1899 Delete a callback that was previously registered. C<event_handle>
1900 should be the integer that was returned by a previous call to
1901 C<guestfs_set_event_callback> on the same handle.
1903 =head3 guestfs_event_callback
1905 typedef void (*guestfs_event_callback) (
1911 const char *buf, size_t buf_len,
1912 const uint64_t *array, size_t array_len);
1914 This is the type of the event callback function that you have to
1917 The basic parameters are: the handle (C<g>), the opaque user pointer
1918 (C<opaque>), the event class (eg. C<GUESTFS_EVENT_PROGRESS>), the
1919 event handle, and C<flags> which in the current API you should ignore.
1921 The remaining parameters contain the event payload (if any). Each
1922 event may contain a payload, which usually relates to the event class,
1923 but for future proofing your code should be written to handle any
1924 payload for any event class.
1926 C<buf> and C<buf_len> contain a message buffer (if C<buf_len == 0>,
1927 then there is no message buffer). Note that this message buffer can
1928 contain arbitrary 8 bit data, including NUL bytes.
1930 C<array> and C<array_len> is an array of 64 bit unsigned integers. At
1931 the moment this is only used for progress messages.
1933 =head3 EXAMPLE: CAPTURING LOG MESSAGES
1935 One motivation for the generic event API was to allow GUI programs to
1936 capture debug and other messages. In libguestfs E<le> 1.8 these were
1937 sent unconditionally to C<stderr>.
1939 Events associated with log messages are: C<GUESTFS_EVENT_LIBRARY>,
1940 C<GUESTFS_EVENT_APPLIANCE> and C<GUESTFS_EVENT_TRACE>. (Note that
1941 error messages are not events; you must capture error messages
1944 Programs have to set up a callback to capture the classes of events of
1948 guestfs_set_event_callback
1949 (g, message_callback,
1950 GUESTFS_EVENT_LIBRARY|GUESTFS_EVENT_APPLIANCE|
1951 GUESTFS_EVENT_TRACE,
1954 // handle error in the usual way
1957 The callback can then direct messages to the appropriate place. In
1958 this example, messages are directed to syslog:
1967 const char *buf, size_t buf_len,
1968 const uint64_t *array, size_t array_len)
1970 const int priority = LOG_USER|LOG_INFO;
1972 syslog (priority, "event 0x%lx: %s", event, buf);
1975 =head1 CANCELLING LONG TRANSFERS
1977 Some operations can be cancelled by the caller while they are in
1978 progress. Currently only operations that involve uploading or
1979 downloading data can be cancelled (technically: operations that have
1980 C<FileIn> or C<FileOut> parameters in the generator).
1982 =head2 guestfs_user_cancel
1984 void guestfs_user_cancel (guestfs_h *g);
1986 C<guestfs_user_cancel> cancels the current upload or download
1989 Unlike most other libguestfs calls, this function is signal safe and
1990 thread safe. You can call it from a signal handler or from another
1991 thread, without needing to do any locking.
1993 The transfer that was in progress (if there is one) will stop shortly
1994 afterwards, and will return an error. The errno (see
1995 L</guestfs_last_errno>) is set to C<EINTR>, so you can test for this
1996 to find out if the operation was cancelled or failed because of
1999 No cleanup is performed: for example, if a file was being uploaded
2000 then after cancellation there may be a partially uploaded file. It is
2001 the caller's responsibility to clean up if necessary.
2003 There are two common places that you might call C<guestfs_user_cancel>.
2005 In an interactive text-based program, you might call it from a
2006 C<SIGINT> signal handler so that pressing C<^C> cancels the current
2007 operation. (You also need to call L</guestfs_set_pgroup> so that
2008 child processes don't receive the C<^C> signal).
2010 In a graphical program, when the main thread is displaying a progress
2011 bar with a cancel button, wire up the cancel button to call this
2014 =head1 PRIVATE DATA AREA
2016 You can attach named pieces of private data to the libguestfs handle,
2017 fetch them by name, and walk over them, for the lifetime of the
2018 handle. This is called the private data area and is only available
2021 To attach a named piece of data, use the following call:
2023 void guestfs_set_private (guestfs_h *g, const char *key, void *data);
2025 C<key> is the name to associate with this data, and C<data> is an
2026 arbitrary pointer (which can be C<NULL>). Any previous item with the
2027 same key is overwritten.
2029 You can use any C<key> you want, but your key should I<not> start with
2030 an underscore character. Keys beginning with an underscore character
2031 are reserved for internal libguestfs purposes (eg. for implementing
2032 language bindings). It is recommended that you prefix the key with
2033 some unique string to avoid collisions with other users.
2035 To retrieve the pointer, use:
2037 void *guestfs_get_private (guestfs_h *g, const char *key);
2039 This function returns C<NULL> if either no data is found associated
2040 with C<key>, or if the user previously set the C<key>'s C<data>
2043 Libguestfs does not try to look at or interpret the C<data> pointer in
2044 any way. As far as libguestfs is concerned, it need not be a valid
2045 pointer at all. In particular, libguestfs does I<not> try to free the
2046 data when the handle is closed. If the data must be freed, then the
2047 caller must either free it before calling L</guestfs_close> or must
2048 set up a close callback to do it (see L</GUESTFS_EVENT_CLOSE>).
2050 To walk over all entries, use these two functions:
2052 void *guestfs_first_private (guestfs_h *g, const char **key_rtn);
2054 void *guestfs_next_private (guestfs_h *g, const char **key_rtn);
2056 C<guestfs_first_private> returns the first key, pointer pair ("first"
2057 does not have any particular meaning -- keys are not returned in any
2058 defined order). A pointer to the key is returned in C<*key_rtn> and
2059 the corresponding data pointer is returned from the function. C<NULL>
2060 is returned if there are no keys stored in the handle.
2062 C<guestfs_next_private> returns the next key, pointer pair. The
2063 return value of this function is also C<NULL> is there are no further
2066 Notes about walking over entries:
2072 You must not call C<guestfs_set_private> while walking over the
2077 The handle maintains an internal iterator which is reset when you call
2078 C<guestfs_first_private>. This internal iterator is invalidated when
2079 you call C<guestfs_set_private>.
2083 If you have set the data pointer associated with a key to C<NULL>, ie:
2085 guestfs_set_private (g, key, NULL);
2087 then that C<key> is not returned when walking.
2091 C<*key_rtn> is only valid until the next call to
2092 C<guestfs_first_private>, C<guestfs_next_private> or
2093 C<guestfs_set_private>.
2097 The following example code shows how to print all keys and data
2098 pointers that are associated with the handle C<g>:
2101 void *data = guestfs_first_private (g, &key);
2102 while (data != NULL)
2104 printf ("key = %s, data = %p\n", key, data);
2105 data = guestfs_next_private (g, &key);
2108 More commonly you are only interested in keys that begin with an
2109 application-specific prefix C<foo_>. Modify the loop like so:
2112 void *data = guestfs_first_private (g, &key);
2113 while (data != NULL)
2115 if (strncmp (key, "foo_", strlen ("foo_")) == 0)
2116 printf ("key = %s, data = %p\n", key, data);
2117 data = guestfs_next_private (g, &key);
2120 If you need to modify keys while walking, then you have to jump back
2121 to the beginning of the loop. For example, to delete all keys
2122 prefixed with C<foo_>:
2127 data = guestfs_first_private (g, &key);
2128 while (data != NULL)
2130 if (strncmp (key, "foo_", strlen ("foo_")) == 0)
2132 guestfs_set_private (g, key, NULL);
2133 /* note that 'key' pointer is now invalid, and so is
2134 the internal iterator */
2137 data = guestfs_next_private (g, &key);
2140 Note that the above loop is guaranteed to terminate because the keys
2141 are being deleted, but other manipulations of keys within the loop
2142 might not terminate unless you also maintain an indication of which
2143 keys have been visited.
2147 <!-- old anchor for the next section -->
2148 <a name="state_machine_and_low_level_event_api"/>
2154 Internally, libguestfs is implemented by running an appliance (a
2155 special type of small virtual machine) using L<qemu(1)>. Qemu runs as
2156 a child process of the main program.
2162 | | child process / appliance
2163 | | __________________________
2165 +-------------------+ RPC | +-----------------+ |
2166 | libguestfs <--------------------> guestfsd | |
2167 | | | +-----------------+ |
2168 \___________________/ | | Linux kernel | |
2169 | +--^--------------+ |
2170 \_________|________________/
2178 The library, linked to the main program, creates the child process and
2179 hence the appliance in the L</guestfs_launch> function.
2181 Inside the appliance is a Linux kernel and a complete stack of
2182 userspace tools (such as LVM and ext2 programs) and a small
2183 controlling daemon called L</guestfsd>. The library talks to
2184 L</guestfsd> using remote procedure calls (RPC). There is a mostly
2185 one-to-one correspondence between libguestfs API calls and RPC calls
2186 to the daemon. Lastly the disk image(s) are attached to the qemu
2187 process which translates device access by the appliance's Linux kernel
2188 into accesses to the image.
2190 A common misunderstanding is that the appliance "is" the virtual
2191 machine. Although the disk image you are attached to might also be
2192 used by some virtual machine, libguestfs doesn't know or care about
2193 this. (But you will care if both libguestfs's qemu process and your
2194 virtual machine are trying to update the disk image at the same time,
2195 since these usually results in massive disk corruption).
2197 =head1 STATE MACHINE
2199 libguestfs uses a state machine to model the child process:
2210 / | \ \ guestfs_launch
2221 \______/ <------ \________/
2223 The normal transitions are (1) CONFIG (when the handle is created, but
2224 there is no child process), (2) LAUNCHING (when the child process is
2225 booting up), (3) alternating between READY and BUSY as commands are
2226 issued to, and carried out by, the child process.
2228 The guest may be killed by L</guestfs_kill_subprocess>, or may die
2229 asynchronously at any time (eg. due to some internal error), and that
2230 causes the state to transition back to CONFIG.
2232 Configuration commands for qemu such as L</guestfs_add_drive> can only
2233 be issued when in the CONFIG state.
2235 The API offers one call that goes from CONFIG through LAUNCHING to
2236 READY. L</guestfs_launch> blocks until the child process is READY to
2237 accept commands (or until some failure or timeout).
2238 L</guestfs_launch> internally moves the state from CONFIG to LAUNCHING
2239 while it is running.
2241 API actions such as L</guestfs_mount> can only be issued when in the
2242 READY state. These API calls block waiting for the command to be
2243 carried out (ie. the state to transition to BUSY and then back to
2244 READY). There are no non-blocking versions, and no way to issue more
2245 than one command per handle at the same time.
2247 Finally, the child process sends asynchronous messages back to the
2248 main program, such as kernel log messages. You can register a
2249 callback to receive these messages.
2253 =head2 APPLIANCE BOOT PROCESS
2255 This process has evolved and continues to evolve. The description
2256 here corresponds only to the current version of libguestfs and is
2257 provided for information only.
2259 In order to follow the stages involved below, enable libguestfs
2260 debugging (set the environment variable C<LIBGUESTFS_DEBUG=1>).
2264 =item Create the appliance
2266 C<febootstrap-supermin-helper> is invoked to create the kernel, a
2267 small initrd and the appliance.
2269 The appliance is cached in C</var/tmp/.guestfs-E<lt>UIDE<gt>> (or in
2270 another directory if C<TMPDIR> is set).
2272 For a complete description of how the appliance is created and cached,
2273 read the L<febootstrap(8)> and L<febootstrap-supermin-helper(8)> man
2276 =item Start qemu and boot the kernel
2278 qemu is invoked to boot the kernel.
2280 =item Run the initrd
2282 C<febootstrap-supermin-helper> builds a small initrd. The initrd is
2283 not the appliance. The purpose of the initrd is to load enough kernel
2284 modules in order that the appliance itself can be mounted and started.
2286 The initrd is a cpio archive called
2287 C</var/tmp/.guestfs-E<lt>UIDE<gt>/initrd>.
2289 When the initrd has started you will see messages showing that kernel
2290 modules are being loaded, similar to this:
2292 febootstrap: ext2 mini initrd starting up
2293 febootstrap: mounting /sys
2294 febootstrap: internal insmod libcrc32c.ko
2295 febootstrap: internal insmod crc32c-intel.ko
2297 =item Find and mount the appliance device
2299 The appliance is a sparse file containing an ext2 filesystem which
2300 contains a familiar (although reduced in size) Linux operating system.
2301 It would normally be called C</var/tmp/.guestfs-E<lt>UIDE<gt>/root>.
2303 The regular disks being inspected by libguestfs are the first
2304 devices exposed by qemu (eg. as C</dev/vda>).
2306 The last disk added to qemu is the appliance itself (eg. C</dev/vdb>
2307 if there was only one regular disk).
2309 Thus the final job of the initrd is to locate the appliance disk,
2310 mount it, and switch root into the appliance, and run C</init> from
2313 If this works successfully you will see messages such as:
2315 febootstrap: picked /sys/block/vdb/dev as root device
2316 febootstrap: creating /dev/root as block special 252:16
2317 febootstrap: mounting new root on /root
2319 Starting /init script ...
2321 Note that C<Starting /init script ...> indicates that the appliance's
2322 init script is now running.
2324 =item Initialize the appliance
2326 The appliance itself now initializes itself. This involves starting
2327 certain processes like C<udev>, possibly printing some debug
2328 information, and finally running the daemon (C<guestfsd>).
2332 Finally the daemon (C<guestfsd>) runs inside the appliance. If it
2333 runs you should see:
2335 verbose daemon enabled
2337 The daemon expects to see a named virtio-serial port exposed by qemu
2338 and connected on the other end to the library.
2340 The daemon connects to this port (and hence to the library) and sends
2341 a four byte message C<GUESTFS_LAUNCH_FLAG>, which initiates the
2342 communication protocol (see below).
2346 =head2 COMMUNICATION PROTOCOL
2348 Don't rely on using this protocol directly. This section documents
2349 how it currently works, but it may change at any time.
2351 The protocol used to talk between the library and the daemon running
2352 inside the qemu virtual machine is a simple RPC mechanism built on top
2353 of XDR (RFC 1014, RFC 1832, RFC 4506).
2355 The detailed format of structures is in C<src/guestfs_protocol.x>
2356 (note: this file is automatically generated).
2358 There are two broad cases, ordinary functions that don't have any
2359 C<FileIn> and C<FileOut> parameters, which are handled with very
2360 simple request/reply messages. Then there are functions that have any
2361 C<FileIn> or C<FileOut> parameters, which use the same request and
2362 reply messages, but they may also be followed by files sent using a
2365 =head3 ORDINARY FUNCTIONS (NO FILEIN/FILEOUT PARAMS)
2367 For ordinary functions, the request message is:
2369 total length (header + arguments,
2370 but not including the length word itself)
2371 struct guestfs_message_header (encoded as XDR)
2372 struct guestfs_<foo>_args (encoded as XDR)
2374 The total length field allows the daemon to allocate a fixed size
2375 buffer into which it slurps the rest of the message. As a result, the
2376 total length is limited to C<GUESTFS_MESSAGE_MAX> bytes (currently
2377 4MB), which means the effective size of any request is limited to
2378 somewhere under this size.
2380 Note also that many functions don't take any arguments, in which case
2381 the C<guestfs_I<foo>_args> is completely omitted.
2383 The header contains the procedure number (C<guestfs_proc>) which is
2384 how the receiver knows what type of args structure to expect, or none
2387 For functions that take optional arguments, the optional arguments are
2388 encoded in the C<guestfs_I<foo>_args> structure in the same way as
2389 ordinary arguments. A bitmask in the header indicates which optional
2390 arguments are meaningful. The bitmask is also checked to see if it
2391 contains bits set which the daemon does not know about (eg. if more
2392 optional arguments were added in a later version of the library), and
2393 this causes the call to be rejected.
2395 The reply message for ordinary functions is:
2397 total length (header + ret,
2398 but not including the length word itself)
2399 struct guestfs_message_header (encoded as XDR)
2400 struct guestfs_<foo>_ret (encoded as XDR)
2402 As above the C<guestfs_I<foo>_ret> structure may be completely omitted
2403 for functions that return no formal return values.
2405 As above the total length of the reply is limited to
2406 C<GUESTFS_MESSAGE_MAX>.
2408 In the case of an error, a flag is set in the header, and the reply
2409 message is slightly changed:
2411 total length (header + error,
2412 but not including the length word itself)
2413 struct guestfs_message_header (encoded as XDR)
2414 struct guestfs_message_error (encoded as XDR)
2416 The C<guestfs_message_error> structure contains the error message as a
2419 =head3 FUNCTIONS THAT HAVE FILEIN PARAMETERS
2421 A C<FileIn> parameter indicates that we transfer a file I<into> the
2422 guest. The normal request message is sent (see above). However this
2423 is followed by a sequence of file chunks.
2425 total length (header + arguments,
2426 but not including the length word itself,
2427 and not including the chunks)
2428 struct guestfs_message_header (encoded as XDR)
2429 struct guestfs_<foo>_args (encoded as XDR)
2430 sequence of chunks for FileIn param #0
2431 sequence of chunks for FileIn param #1 etc.
2433 The "sequence of chunks" is:
2435 length of chunk (not including length word itself)
2436 struct guestfs_chunk (encoded as XDR)
2438 struct guestfs_chunk (encoded as XDR)
2441 struct guestfs_chunk (with data.data_len == 0)
2443 The final chunk has the C<data_len> field set to zero. Additionally a
2444 flag is set in the final chunk to indicate either successful
2445 completion or early cancellation.
2447 At time of writing there are no functions that have more than one
2448 FileIn parameter. However this is (theoretically) supported, by
2449 sending the sequence of chunks for each FileIn parameter one after
2450 another (from left to right).
2452 Both the library (sender) I<and> the daemon (receiver) may cancel the
2453 transfer. The library does this by sending a chunk with a special
2454 flag set to indicate cancellation. When the daemon sees this, it
2455 cancels the whole RPC, does I<not> send any reply, and goes back to
2456 reading the next request.
2458 The daemon may also cancel. It does this by writing a special word
2459 C<GUESTFS_CANCEL_FLAG> to the socket. The library listens for this
2460 during the transfer, and if it gets it, it will cancel the transfer
2461 (it sends a cancel chunk). The special word is chosen so that even if
2462 cancellation happens right at the end of the transfer (after the
2463 library has finished writing and has started listening for the reply),
2464 the "spurious" cancel flag will not be confused with the reply
2467 This protocol allows the transfer of arbitrary sized files (no 32 bit
2468 limit), and also files where the size is not known in advance
2469 (eg. from pipes or sockets). However the chunks are rather small
2470 (C<GUESTFS_MAX_CHUNK_SIZE>), so that neither the library nor the
2471 daemon need to keep much in memory.
2473 =head3 FUNCTIONS THAT HAVE FILEOUT PARAMETERS
2475 The protocol for FileOut parameters is exactly the same as for FileIn
2476 parameters, but with the roles of daemon and library reversed.
2478 total length (header + ret,
2479 but not including the length word itself,
2480 and not including the chunks)
2481 struct guestfs_message_header (encoded as XDR)
2482 struct guestfs_<foo>_ret (encoded as XDR)
2483 sequence of chunks for FileOut param #0
2484 sequence of chunks for FileOut param #1 etc.
2486 =head3 INITIAL MESSAGE
2488 When the daemon launches it sends an initial word
2489 (C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest and daemon is
2490 alive. This is what L</guestfs_launch> waits for.
2492 =head3 PROGRESS NOTIFICATION MESSAGES
2494 The daemon may send progress notification messages at any time. These
2495 are distinguished by the normal length word being replaced by
2496 C<GUESTFS_PROGRESS_FLAG>, followed by a fixed size progress message.
2498 The library turns them into progress callbacks (see
2499 L</GUESTFS_EVENT_PROGRESS>) if there is a callback registered, or
2500 discards them if not.
2502 The daemon self-limits the frequency of progress messages it sends
2503 (see C<daemon/proto.c:notify_progress>). Not all calls generate
2506 =head1 LIBGUESTFS VERSION NUMBERS
2508 Since April 2010, libguestfs has started to make separate development
2509 and stable releases, along with corresponding branches in our git
2510 repository. These separate releases can be identified by version
2513 even numbers for stable: 1.2.x, 1.4.x, ...
2514 .-------- odd numbers for development: 1.3.x, 1.5.x, ...
2520 | `-------- sub-version
2522 `------ always '1' because we don't change the ABI
2524 Thus "1.3.5" is the 5th update to the development branch "1.3".
2526 As time passes we cherry pick fixes from the development branch and
2527 backport those into the stable branch, the effect being that the
2528 stable branch should get more stable and less buggy over time. So the
2529 stable releases are ideal for people who don't need new features but
2530 would just like the software to work.
2532 Our criteria for backporting changes are:
2538 Documentation changes which don't affect any code are
2539 backported unless the documentation refers to a future feature
2540 which is not in stable.
2544 Bug fixes which are not controversial, fix obvious problems, and
2545 have been well tested are backported.
2549 Simple rearrangements of code which shouldn't affect how it works get
2550 backported. This is so that the code in the two branches doesn't get
2551 too far out of step, allowing us to backport future fixes more easily.
2555 We I<don't> backport new features, new APIs, new tools etc, except in
2556 one exceptional case: the new feature is required in order to
2557 implement an important bug fix.
2561 A new stable branch starts when we think the new features in
2562 development are substantial and compelling enough over the current
2563 stable branch to warrant it. When that happens we create new stable
2564 and development versions 1.N.0 and 1.(N+1).0 [N is even]. The new
2565 dot-oh release won't necessarily be so stable at this point, but by
2566 backporting fixes from development, that branch will stabilize over
2569 =head1 EXTENDING LIBGUESTFS
2571 =head2 ADDING A NEW API ACTION
2573 Large amounts of boilerplate code in libguestfs (RPC, bindings,
2574 documentation) are generated, and this makes it easy to extend the
2577 To add a new API action there are two changes:
2583 You need to add a description of the call (name, parameters, return
2584 type, tests, documentation) to C<generator/generator_actions.ml>.
2586 There are two sorts of API action, depending on whether the call goes
2587 through to the daemon in the appliance, or is serviced entirely by the
2588 library (see L</ARCHITECTURE> above). L</guestfs_sync> is an example
2589 of the former, since the sync is done in the appliance.
2590 L</guestfs_set_trace> is an example of the latter, since a trace flag
2591 is maintained in the handle and all tracing is done on the library
2594 Most new actions are of the first type, and get added to the
2595 C<daemon_functions> list. Each function has a unique procedure number
2596 used in the RPC protocol which is assigned to that action when we
2597 publish libguestfs and cannot be reused. Take the latest procedure
2598 number and increment it.
2600 For library-only actions of the second type, add to the
2601 C<non_daemon_functions> list. Since these functions are serviced by
2602 the library and do not travel over the RPC mechanism to the daemon,
2603 these functions do not need a procedure number, and so the procedure
2604 number is set to C<-1>.
2608 Implement the action (in C):
2610 For daemon actions, implement the function C<do_E<lt>nameE<gt>> in the
2611 C<daemon/> directory.
2613 For library actions, implement the function C<guestfs__E<lt>nameE<gt>>
2614 (note: double underscore) in the C<src/> directory.
2616 In either case, use another function as an example of what to do.
2620 After making these changes, use C<make> to compile.
2622 Note that you don't need to implement the RPC, language bindings,
2623 manual pages or anything else. It's all automatically generated from
2624 the OCaml description.
2626 =head2 ADDING TESTS FOR AN API ACTION
2628 You can supply zero or as many tests as you want per API call. The
2629 tests can either be added as part of the API description
2630 (C<generator/generator_actions.ml>), or in some rarer cases you may
2631 want to drop a script into C<regressions/>. Note that adding a script
2632 to C<regressions/> is slower, so if possible use the first method.
2634 The following describes the test environment used when you add an API
2635 test in C<generator_actions.ml>.
2637 The test environment has 4 block devices:
2641 =item C</dev/sda> 500MB
2643 General block device for testing.
2645 =item C</dev/sdb> 50MB
2647 C</dev/sdb1> is an ext2 filesystem used for testing
2648 filesystem write operations.
2650 =item C</dev/sdc> 10MB
2652 Used in a few tests where two block devices are needed.
2656 ISO with fixed content (see C<images/test.iso>).
2660 To be able to run the tests in a reasonable amount of time, the
2661 libguestfs appliance and block devices are reused between tests. So
2662 don't try testing L</guestfs_kill_subprocess> :-x
2664 Each test starts with an initial scenario, selected using one of the
2665 C<Init*> expressions, described in C<generator/generator_types.ml>.
2666 These initialize the disks mentioned above in a particular way as
2667 documented in C<generator_types.ml>. You should not assume anything
2668 about the previous contents of other disks that are not initialized.
2670 You can add a prerequisite clause to any individual test. This is a
2671 run-time check, which, if it fails, causes the test to be skipped.
2672 Useful if testing a command which might not work on all variations of
2673 libguestfs builds. A test that has prerequisite of C<Always> means to
2674 run unconditionally.
2676 In addition, packagers can skip individual tests by setting
2677 environment variables before running C<make check>.
2679 SKIP_TEST_<CMD>_<NUM>=1
2681 eg: C<SKIP_TEST_COMMAND_3=1> skips test #3 of L</guestfs_command>.
2687 eg: C<SKIP_TEST_ZEROFREE=1> skips all L</guestfs_zerofree> tests.
2689 Packagers can run only certain tests by setting for example:
2691 TEST_ONLY="vfs_type zerofree"
2693 See C<capitests/tests.c> for more details of how these environment
2696 =head2 DEBUGGING NEW API ACTIONS
2698 Test new actions work before submitting them.
2700 You can use guestfish to try out new commands.
2702 Debugging the daemon is a problem because it runs inside a minimal
2703 environment. However you can fprintf messages in the daemon to
2704 stderr, and they will show up if you use C<guestfish -v>.
2706 =head2 FORMATTING CODE AND OTHER CONVENTIONS
2708 Our C source code generally adheres to some basic code-formatting
2709 conventions. The existing code base is not totally consistent on this
2710 front, but we do prefer that contributed code be formatted similarly.
2711 In short, use spaces-not-TABs for indentation, use 2 spaces for each
2712 indentation level, and other than that, follow the K&R style.
2714 If you use Emacs, add the following to one of one of your start-up files
2715 (e.g., ~/.emacs), to help ensure that you get indentation right:
2717 ;;; In libguestfs, indent with spaces everywhere (not TABs).
2718 ;;; Exceptions: Makefile and ChangeLog modes.
2719 (add-hook 'find-file-hook
2720 '(lambda () (if (and buffer-file-name
2721 (string-match "/libguestfs\\>"
2723 (not (string-equal mode-name "Change Log"))
2724 (not (string-equal mode-name "Makefile")))
2725 (setq indent-tabs-mode nil))))
2727 ;;; When editing C sources in libguestfs, use this style.
2728 (defun libguestfs-c-mode ()
2729 "C mode with adjusted defaults for use with libguestfs."
2732 (setq c-indent-level 2)
2733 (setq c-basic-offset 2))
2734 (add-hook 'c-mode-hook
2735 '(lambda () (if (string-match "/libguestfs\\>"
2737 (libguestfs-c-mode))))
2739 Enable warnings when compiling (and fix any problems this
2742 ./configure --enable-gcc-warnings
2746 make syntax-check # checks the syntax of the C code
2747 make check # runs the test suite
2749 =head2 DAEMON CUSTOM PRINTF FORMATTERS
2751 In the daemon code we have created custom printf formatters C<%Q> and
2752 C<%R>, which are used to do shell quoting.
2758 Simple shell quoted string. Any spaces or other shell characters are
2763 Same as C<%Q> except the string is treated as a path which is prefixed
2770 asprintf (&cmd, "cat %R", path);
2772 would produce C<cat /sysroot/some\ path\ with\ spaces>
2774 I<Note:> Do I<not> use these when you are passing parameters to the
2775 C<command{,r,v,rv}()> functions. These parameters do NOT need to be
2776 quoted because they are not passed via the shell (instead, straight to
2777 exec). You probably want to use the C<sysroot_path()> function
2780 =head2 SUBMITTING YOUR NEW API ACTIONS
2782 Submit patches to the mailing list:
2783 L<http://www.redhat.com/mailman/listinfo/libguestfs>
2784 and CC to L<rjones@redhat.com>.
2786 =head2 INTERNATIONALIZATION (I18N) SUPPORT
2788 We support i18n (gettext anyhow) in the library.
2790 However many messages come from the daemon, and we don't translate
2791 those at the moment. One reason is that the appliance generally has
2792 all locale files removed from it, because they take up a lot of space.
2793 So we'd have to readd some of those, as well as copying our PO files
2796 Debugging messages are never translated, since they are intended for
2799 =head2 SOURCE CODE SUBDIRECTORIES
2805 The libguestfs appliance, build scripts and so on.
2809 Automated tests of the C API.
2813 The L<virt-cat(1)>, L<virt-filesystems(1)> and L<virt-ls(1)> commands
2818 Safety and liveness tests of components that libguestfs depends upon
2819 (not of libguestfs itself). Mainly this is for qemu and the kernel.
2823 Outside contributions, experimental parts.
2827 The daemon that runs inside the libguestfs appliance and carries out
2832 L<virt-df(1)> command and documentation.
2836 L<virt-edit(1)> command and documentation.
2844 L<guestfish(1)>, the command-line shell, and various shell scripts
2845 built on top such as L<virt-copy-in(1)>, L<virt-copy-out(1)>,
2846 L<virt-tar-in(1)>, L<virt-tar-out(1)>.
2850 L<guestmount(1)>, FUSE (userspace filesystem) built on top of libguestfs.
2854 The crucially important generator, used to automatically generate
2855 large amounts of boilerplate C code for things like RPC and bindings.
2859 Files used by the test suite.
2861 Some "phony" guest images which we test against.
2865 L<virt-inspector(1)>, the virtual machine image inspector.
2869 Logo used on the website. The fish is called Arthur by the way.
2873 M4 macros used by autoconf.
2877 Translations of simple gettext strings.
2881 The build infrastructure and PO files for translations of manpages and
2882 POD files. Eventually this will be combined with the C<po> directory,
2883 but that is rather complicated.
2885 =item C<regressions>
2891 L<virt-rescue(1)> command and documentation.
2895 Source code to the C library.
2899 Command line tools written in Perl (L<virt-win-reg(1)> and many others).
2903 Test tool for end users to test if their qemu/kernel combination
2904 will work with libguestfs.
2926 =head2 MAKING A STABLE RELEASE
2928 When we make a stable release, there are several steps documented
2929 here. See L</LIBGUESTFS VERSION NUMBERS> for general information
2930 about the stable branch policy.
2936 Check C<make && make check> works on at least Fedora, Debian and
2941 Finalize RELEASE-NOTES.
2949 Run C<src/api-support/update-from-tarballs.sh>.
2953 Push and pull from Transifex.
2959 to push the latest POT files to Transifex. Then run:
2963 which is a wrapper to pull the latest translated C<*.po> files.
2967 Create new stable and development directories under
2968 L<http://libguestfs.org/download>.
2972 Create the branch in git:
2974 git tag -a 1.XX.0 -m "Version 1.XX.0 (stable)"
2975 git tag -a 1.YY.0 -m "Version 1.YY.0 (development)"
2976 git branch stable-1.XX
2977 git push origin tag 1.XX.0 1.YY.0 stable-1.XX
2983 =head2 PROTOCOL LIMITS
2985 Internally libguestfs uses a message-based protocol to pass API calls
2986 and their responses to and from a small "appliance" (see L</INTERNALS>
2987 for plenty more detail about this). The maximum message size used by
2988 the protocol is slightly less than 4 MB. For some API calls you may
2989 need to be aware of this limit. The API calls which may be affected
2990 are individually documented, with a link back to this section of the
2993 A simple call such as L</guestfs_cat> returns its result (the file
2994 data) in a simple string. Because this string is at some point
2995 internally encoded as a message, the maximum size that it can return
2996 is slightly under 4 MB. If the requested file is larger than this
2997 then you will get an error.
2999 In order to transfer large files into and out of the guest filesystem,
3000 you need to use particular calls that support this. The sections
3001 L</UPLOADING> and L</DOWNLOADING> document how to do this.
3003 You might also consider mounting the disk image using our FUSE
3004 filesystem support (L<guestmount(1)>).
3006 =head2 MAXIMUM NUMBER OF DISKS
3008 When using virtio disks (the default) the current limit is B<25>
3011 Virtio itself consumes 1 virtual PCI slot per disk, and PCI is limited
3012 to 31 slots. However febootstrap only understands disks with names
3013 C</dev/vda> through C</dev/vdz> (26 letters) and it reserves one disk
3014 for its own purposes.
3016 We are working to substantially raise this limit in future versions
3017 but it requires complex changes to qemu.
3019 In future versions of libguestfs it should also be possible to "hot
3020 plug" disks (add and remove disks after calling L</guestfs_launch>).
3021 This also requires changes to qemu.
3023 =head2 MAXIMUM NUMBER OF PARTITIONS PER DISK
3025 Virtio limits the maximum number of partitions per disk to B<15>.
3027 This is because it reserves 4 bits for the minor device number (thus
3028 C</dev/vda>, and C</dev/vda1> through C</dev/vda15>).
3030 If you attach a disk with more than 15 partitions, the extra
3031 partitions are ignored by libguestfs.
3033 =head2 MAXIMUM SIZE OF A DISK
3035 Probably the limit is between 2**63-1 and 2**64-1 bytes.
3037 We have tested block devices up to 1 exabyte (2**60 or
3038 1,152,921,504,606,846,976 bytes) using sparse files backed by an XFS
3041 Although libguestfs probably does not impose any limit, the underlying
3042 host storage will. If you store disk images on a host ext4
3043 filesystem, then the maximum size will be limited by the maximum ext4
3044 file size (currently 16 TB). If you store disk images as host logical
3045 volumes then you are limited by the maximum size of an LV.
3047 For the hugest disk image files, we recommend using XFS on the host
3050 =head2 MAXIMUM SIZE OF A PARTITION
3052 The MBR (ie. classic MS-DOS) partitioning scheme uses 32 bit sector
3053 numbers. Assuming a 512 byte sector size, this means that MBR cannot
3054 address a partition located beyond 2 TB on the disk.
3056 It is recommended that you use GPT partitions on disks which are
3057 larger than this size. GPT uses 64 bit sector numbers and so can
3058 address partitions which are theoretically larger than the largest
3059 disk we could support.
3061 =head2 MAXIMUM SIZE OF A FILESYSTEM, FILES, DIRECTORIES
3063 This depends on the filesystem type. libguestfs itself does not
3064 impose any known limit. Consult Wikipedia or the filesystem
3065 documentation to find out what these limits are.
3067 =head2 MAXIMUM UPLOAD AND DOWNLOAD
3069 The API functions L</guestfs_upload>, L</guestfs_download>,
3070 L</guestfs_tar_in>, L</guestfs_tar_out> and the like allow unlimited
3071 sized uploads and downloads.
3073 =head2 INSPECTION LIMITS
3075 The inspection code has several arbitrary limits on things like the
3076 size of Windows Registry hive it will read, and the length of product
3077 name. These are intended to stop a malicious guest from consuming
3078 arbitrary amounts of memory and disk space on the host, and should not
3079 be reached in practice. See the source code for more information.
3081 =head1 ENVIRONMENT VARIABLES
3085 =item FEBOOTSTRAP_KERNEL
3087 =item FEBOOTSTRAP_MODULES
3089 These two environment variables allow the kernel that libguestfs uses
3090 in the appliance to be selected. If C<$FEBOOTSTRAP_KERNEL> is not
3091 set, then the most recent host kernel is chosen. For more information
3092 about kernel selection, see L<febootstrap-supermin-helper(8)>. This
3093 feature is only available in febootstrap E<ge> 3.8.
3095 =item LIBGUESTFS_APPEND
3097 Pass additional options to the guest kernel.
3099 =item LIBGUESTFS_DEBUG
3101 Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
3102 has the same effect as calling C<guestfs_set_verbose (g, 1)>.
3104 =item LIBGUESTFS_MEMSIZE
3106 Set the memory allocated to the qemu process, in megabytes. For
3109 LIBGUESTFS_MEMSIZE=700
3111 =item LIBGUESTFS_PATH
3113 Set the path that libguestfs uses to search for a supermin appliance.
3114 See the discussion of paths in section L</PATH> above.
3116 =item LIBGUESTFS_QEMU
3118 Set the default qemu binary that libguestfs uses. If not set, then
3119 the qemu which was found at compile time by the configure script is
3122 See also L</QEMU WRAPPERS> above.
3124 =item LIBGUESTFS_TRACE
3126 Set C<LIBGUESTFS_TRACE=1> to enable command traces. This
3127 has the same effect as calling C<guestfs_set_trace (g, 1)>.
3131 Location of temporary directory, defaults to C</tmp> except for the
3132 cached supermin appliance which defaults to C</var/tmp>.
3134 If libguestfs was compiled to use the supermin appliance then the
3135 real appliance is cached in this directory, shared between all
3136 handles belonging to the same EUID. You can use C<$TMPDIR> to
3137 configure another directory to use in case C</var/tmp> is not large
3144 L<guestfs-examples(3)>,
3146 L<guestfs-ocaml(3)>,
3148 L<guestfs-python(3)>,
3154 L<virt-copy-out(1)>,
3157 L<virt-filesystems(1)>,
3158 L<virt-inspector(1)>,
3159 L<virt-list-filesystems(1)>,
3160 L<virt-list-partitions(1)>,
3170 L<febootstrap-supermin-helper(8)>,
3172 L<http://libguestfs.org/>.
3174 Tools with a similar purpose:
3183 To get a list of bugs against libguestfs use this link:
3185 L<https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools>
3187 To report a new bug against libguestfs use this link:
3189 L<https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools>
3191 When reporting a bug, please check:
3197 That the bug hasn't been reported already.
3201 That you are testing a recent version.
3205 Describe the bug accurately, and give a way to reproduce it.
3209 Run libguestfs-test-tool and paste the B<complete, unedited>
3210 output into the bug report.
3216 Richard W.M. Jones (C<rjones at redhat dot com>)
3220 Copyright (C) 2009-2011 Red Hat Inc.
3221 L<http://libguestfs.org/>
3223 This library is free software; you can redistribute it and/or
3224 modify it under the terms of the GNU Lesser General Public
3225 License as published by the Free Software Foundation; either
3226 version 2 of the License, or (at your option) any later version.
3228 This library is distributed in the hope that it will be useful,
3229 but WITHOUT ANY WARRANTY; without even the implied warranty of
3230 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
3231 Lesser General Public License for more details.
3233 You should have received a copy of the GNU Lesser General Public
3234 License along with this library; if not, write to the Free Software
3235 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA