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, "/");
20 cc prog.c -o prog -lguestfs
22 cc prog.c -o prog `pkg-config libguestfs --cflags --libs`
26 Libguestfs is a library for accessing and modifying guest disk images.
27 Amongst the things this is good for: making batch configuration
28 changes to guests, getting disk used/free statistics (see also:
29 virt-df), migrating between virtualization systems (see also:
30 virt-p2v), performing partial backups, performing partial guest
31 clones, cloning guests and changing registry/UUID/hostname info, and
34 Libguestfs uses Linux kernel and qemu code, and can access any type of
35 guest filesystem that Linux and qemu can, including but not limited
36 to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
37 schemes, qcow, qcow2, vmdk.
39 Libguestfs provides ways to enumerate guest storage (eg. partitions,
40 LVs, what filesystem is in each LV, etc.). It can also run commands
41 in the context of the guest. Also you can access filesystems over
44 Libguestfs is a library that can be linked with C and C++ management
45 programs (or management programs written in OCaml, Perl, Python, Ruby,
46 Java, PHP, Haskell or C#). You can also use it from shell scripts or the
49 You don't need to be root to use libguestfs, although obviously you do
50 need enough permissions to access the disk images.
52 Libguestfs is a large API because it can do many things. For a gentle
53 introduction, please read the L</API OVERVIEW> section next.
57 This section provides a gentler overview of the libguestfs API. We
58 also try to group API calls together, where that may not be obvious
59 from reading about the individual calls in the main section of this
64 Before you can use libguestfs calls, you have to create a handle.
65 Then you must add at least one disk image to the handle, followed by
66 launching the handle, then performing whatever operations you want,
67 and finally closing the handle. By convention we use the single
68 letter C<g> for the name of the handle variable, although of course
69 you can use any name you want.
71 The general structure of all libguestfs-using programs looks like
74 guestfs_h *g = guestfs_create ();
76 /* Call guestfs_add_drive additional times if there are
77 * multiple disk images.
79 guestfs_add_drive (g, "guest.img");
81 /* Most manipulation calls won't work until you've launched
82 * the handle 'g'. You have to do this _after_ adding drives
83 * and _before_ other commands.
87 /* Now you can examine what partitions, LVs etc are available.
89 char **partitions = guestfs_list_partitions (g);
90 char **logvols = guestfs_lvs (g);
92 /* To access a filesystem in the image, you must mount it.
94 guestfs_mount (g, "/dev/sda1", "/");
96 /* Now you can perform filesystem actions on the guest
99 guestfs_touch (g, "/hello");
101 /* You only need to call guestfs_sync if you have made
102 * changes to the guest image. (But if you've made changes
103 * then you *must* sync). See also: guestfs_umount and
104 * guestfs_umount_all calls.
108 /* Close the handle 'g'. */
111 The code above doesn't include any error checking. In real code you
112 should check return values carefully for errors. In general all
113 functions that return integers return C<-1> on error, and all
114 functions that return pointers return C<NULL> on error. See section
115 L</ERROR HANDLING> below for how to handle errors, and consult the
116 documentation for each function call below to see precisely how they
117 return error indications.
121 The image filename (C<"guest.img"> in the example above) could be a
122 disk image from a virtual machine, a L<dd(1)> copy of a physical hard
123 disk, an actual block device, or simply an empty file of zeroes that
124 you have created through L<posix_fallocate(3)>. Libguestfs lets you
125 do useful things to all of these.
127 The call you should use in modern code for adding drives is
128 L</guestfs_add_drive_opts>. To add a disk image, allowing writes, and
129 specifying that the format is raw, do:
131 guestfs_add_drive_opts (g, filename,
132 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
135 You can add a disk read-only using:
137 guestfs_add_drive_opts (g, filename,
138 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
139 GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
142 or by calling the older function L</guestfs_add_drive_ro>. In either
143 case libguestfs won't modify the file.
145 Be extremely cautious if the disk image is in use, eg. if it is being
146 used by a virtual machine. Adding it read-write will almost certainly
147 cause disk corruption, but adding it read-only is safe.
149 You must add at least one disk image, and you may add multiple disk
150 images. In the API, the disk images are usually referred to as
151 C</dev/sda> (for the first one you added), C</dev/sdb> (for the second
154 Once L</guestfs_launch> has been called you cannot add any more images.
155 You can call L</guestfs_list_devices> to get a list of the device
156 names, in the order that you added them. See also L</BLOCK DEVICE
161 Before you can read or write files, create directories and so on in a
162 disk image that contains filesystems, you have to mount those
163 filesystems using L</guestfs_mount>. If you already know that a disk
164 image contains (for example) one partition with a filesystem on that
165 partition, then you can mount it directly:
167 guestfs_mount (g, "/dev/sda1", "/");
169 where C</dev/sda1> means literally the first partition (C<1>) of the
170 first disk image that we added (C</dev/sda>). If the disk contains
171 Linux LVM2 logical volumes you could refer to those instead (eg. C</dev/VG/LV>).
173 If you are given a disk image and you don't know what it contains then
174 you have to find out. Libguestfs can do that too: use
175 L</guestfs_list_partitions> and L</guestfs_lvs> to list possible
176 partitions and LVs, and either try mounting each to see what is
177 mountable, or else examine them with L</guestfs_vfs_type> or
178 L</guestfs_file>. Libguestfs also has a set of APIs for inspection of
179 disk images (see L</INSPECTION> below). But you might find it easier
180 to look at higher level programs built on top of libguestfs, in
181 particular L<virt-inspector(1)>.
183 To mount a disk image read-only, use L</guestfs_mount_ro>. There are
184 several other variations of the C<guestfs_mount_*> call.
186 =head2 FILESYSTEM ACCESS AND MODIFICATION
188 The majority of the libguestfs API consists of fairly low-level calls
189 for accessing and modifying the files, directories, symlinks etc on
190 mounted filesystems. There are over a hundred such calls which you
191 can find listed in detail below in this man page, and we don't even
192 pretend to cover them all in this overview.
194 Specify filenames as full paths, starting with C<"/"> and including
197 For example, if you mounted a filesystem at C<"/"> and you want to
198 read the file called C<"etc/passwd"> then you could do:
200 char *data = guestfs_cat (g, "/etc/passwd");
202 This would return C<data> as a newly allocated buffer containing the
203 full content of that file (with some conditions: see also
204 L</DOWNLOADING> below), or C<NULL> if there was an error.
206 As another example, to create a top-level directory on that filesystem
207 called C<"var"> you would do:
209 guestfs_mkdir (g, "/var");
211 To create a symlink you could do:
213 guestfs_ln_s (g, "/etc/init.d/portmap",
214 "/etc/rc3.d/S30portmap");
216 Libguestfs will reject attempts to use relative paths and there is no
217 concept of a current working directory.
219 Libguestfs can return errors in many situations: for example if the
220 filesystem isn't writable, or if a file or directory that you
221 requested doesn't exist. If you are using the C API (documented here)
222 you have to check for those error conditions after each call. (Other
223 language bindings turn these errors into exceptions).
225 File writes are affected by the per-handle umask, set by calling
226 L</guestfs_umask> and defaulting to 022. See L</UMASK>.
230 Libguestfs contains API calls to read, create and modify partition
231 tables on disk images.
233 In the common case where you want to create a single partition
234 covering the whole disk, you should use the L</guestfs_part_disk>
237 const char *parttype = "mbr";
238 if (disk_is_larger_than_2TB)
240 guestfs_part_disk (g, "/dev/sda", parttype);
242 Obviously this effectively wipes anything that was on that disk image
247 Libguestfs provides access to a large part of the LVM2 API, such as
248 L</guestfs_lvcreate> and L</guestfs_vgremove>. It won't make much sense
249 unless you familiarize yourself with the concepts of physical volumes,
250 volume groups and logical volumes.
252 This author strongly recommends reading the LVM HOWTO, online at
253 L<http://tldp.org/HOWTO/LVM-HOWTO/>.
257 Use L</guestfs_cat> to download small, text only files. This call
258 is limited to files which are less than 2 MB and which cannot contain
259 any ASCII NUL (C<\0>) characters. However it has a very simple
262 L</guestfs_read_file> can be used to read files which contain
263 arbitrary 8 bit data, since it returns a (pointer, size) pair.
264 However it is still limited to "small" files, less than 2 MB.
266 L</guestfs_download> can be used to download any file, with no
267 limits on content or size (even files larger than 4 GB).
269 To download multiple files, see L</guestfs_tar_out> and
274 It's often the case that you want to write a file or files to the disk
277 To write a small file with fixed content, use L</guestfs_write>. To
278 create a file of all zeroes, use L</guestfs_truncate_size> (sparse) or
279 L</guestfs_fallocate64> (with all disk blocks allocated). There are a
280 variety of other functions for creating test files, for example
281 L</guestfs_fill> and L</guestfs_fill_pattern>.
283 To upload a single file, use L</guestfs_upload>. This call has no
284 limits on file content or size (even files larger than 4 GB).
286 To upload multiple files, see L</guestfs_tar_in> and L</guestfs_tgz_in>.
288 However the fastest way to upload I<large numbers of arbitrary files>
289 is to turn them into a squashfs or CD ISO (see L<mksquashfs(8)> and
290 L<mkisofs(8)>), then attach this using L</guestfs_add_drive_ro>. If
291 you add the drive in a predictable way (eg. adding it last after all
292 other drives) then you can get the device name from
293 L</guestfs_list_devices> and mount it directly using
294 L</guestfs_mount_ro>. Note that squashfs images are sometimes
295 non-portable between kernel versions, and they don't support labels or
296 UUIDs. If you want to pre-build an image or you need to mount it
297 using a label or UUID, use an ISO image instead.
301 There are various different commands for copying between files and
302 devices and in and out of the guest filesystem. These are summarised
307 =item B<file> to B<file>
309 Use L</guestfs_cp> to copy a single file, or
310 L</guestfs_cp_a> to copy directories recursively.
312 =item B<file or device> to B<file or device>
314 Use L</guestfs_dd> which efficiently uses L<dd(1)>
315 to copy between files and devices in the guest.
317 Example: duplicate the contents of an LV:
319 guestfs_dd (g, "/dev/VG/Original", "/dev/VG/Copy");
321 The destination (C</dev/VG/Copy>) must be at least as large as the
322 source (C</dev/VG/Original>). To copy less than the whole
323 source device, use L</guestfs_copy_size>.
325 =item B<file on the host> to B<file or device>
327 Use L</guestfs_upload>. See L</UPLOADING> above.
329 =item B<file or device> to B<file on the host>
331 Use L</guestfs_download>. See L</DOWNLOADING> above.
337 L</guestfs_ll> is just designed for humans to read (mainly when using
338 the L<guestfish(1)>-equivalent command C<ll>).
340 L</guestfs_ls> is a quick way to get a list of files in a directory
341 from programs, as a flat list of strings.
343 L</guestfs_readdir> is a programmatic way to get a list of files in a
344 directory, plus additional information about each one. It is more
345 equivalent to using the L<readdir(3)> call on a local filesystem.
347 L</guestfs_find> and L</guestfs_find0> can be used to recursively list
350 =head2 RUNNING COMMANDS
352 Although libguestfs is primarily an API for manipulating files
353 inside guest images, we also provide some limited facilities for
354 running commands inside guests.
356 There are many limitations to this:
362 The kernel version that the command runs under will be different
363 from what it expects.
367 If the command needs to communicate with daemons, then most likely
368 they won't be running.
372 The command will be running in limited memory.
376 The network may not be available unless you enable it
377 (see L</guestfs_set_network>).
381 Only supports Linux guests (not Windows, BSD, etc).
385 Architecture limitations (eg. won't work for a PPC guest on
390 For SELinux guests, you may need to enable SELinux and load policy
391 first. See L</SELINUX> in this manpage.
395 The two main API calls to run commands are L</guestfs_command> and
396 L</guestfs_sh> (there are also variations).
398 The difference is that L</guestfs_sh> runs commands using the shell, so
399 any shell globs, redirections, etc will work.
401 =head2 CONFIGURATION FILES
403 To read and write configuration files in Linux guest filesystems, we
404 strongly recommend using Augeas. For example, Augeas understands how
405 to read and write, say, a Linux shadow password file or X.org
406 configuration file, and so avoids you having to write that code.
408 The main Augeas calls are bound through the C<guestfs_aug_*> APIs. We
409 don't document Augeas itself here because there is excellent
410 documentation on the L<http://augeas.net/> website.
412 If you don't want to use Augeas (you fool!) then try calling
413 L</guestfs_read_lines> to get the file as a list of lines which
414 you can iterate over.
418 We support SELinux guests. To ensure that labeling happens correctly
419 in SELinux guests, you need to enable SELinux and load the guest's
426 Before launching, do:
428 guestfs_set_selinux (g, 1);
432 After mounting the guest's filesystem(s), load the policy. This
433 is best done by running the L<load_policy(8)> command in the
436 guestfs_sh (g, "/usr/sbin/load_policy");
438 (Older versions of C<load_policy> require you to specify the
439 name of the policy file).
443 Optionally, set the security context for the API. The correct
444 security context to use can only be known by inspecting the
445 guest. As an example:
447 guestfs_setcon (g, "unconfined_u:unconfined_r:unconfined_t:s0");
451 This will work for running commands and editing existing files.
453 When new files are created, you may need to label them explicitly,
454 for example by running the external command
455 C<restorecon pathname>.
459 Certain calls are affected by the current file mode creation mask (the
460 "umask"). In particular ones which create files or directories, such
461 as L</guestfs_touch>, L</guestfs_mknod> or L</guestfs_mkdir>. This
462 affects either the default mode that the file is created with or
463 modifies the mode that you supply.
465 The default umask is C<022>, so files are created with modes such as
466 C<0644> and directories with C<0755>.
468 There are two ways to avoid being affected by umask. Either set umask
469 to 0 (call C<guestfs_umask (g, 0)> early after launching). Or call
470 L</guestfs_chmod> after creating each file or directory.
472 For more information about umask, see L<umask(2)>.
474 =head2 ENCRYPTED DISKS
476 Libguestfs allows you to access Linux guests which have been
477 encrypted using whole disk encryption that conforms to the
478 Linux Unified Key Setup (LUKS) standard. This includes
479 nearly all whole disk encryption systems used by modern
482 Use L</guestfs_vfs_type> to identify LUKS-encrypted block
483 devices (it returns the string C<crypto_LUKS>).
485 Then open these devices by calling L</guestfs_luks_open>.
486 Obviously you will require the passphrase!
488 Opening a LUKS device creates a new device mapper device
489 called C</dev/mapper/mapname> (where C<mapname> is the
490 string you supply to L</guestfs_luks_open>).
491 Reads and writes to this mapper device are decrypted from and
492 encrypted to the underlying block device respectively.
494 LVM volume groups on the device can be made visible by calling
495 L</guestfs_vgscan> followed by L</guestfs_vg_activate_all>.
496 The logical volume(s) can now be mounted in the usual way.
498 Use the reverse process to close a LUKS device. Unmount
499 any logical volumes on it, deactivate the volume groups
500 by caling C<guestfs_vg_activate (g, 0, ["/dev/VG"])>.
501 Then close the mapper device by calling
502 L</guestfs_luks_close> on the C</dev/mapper/mapname>
503 device (I<not> the underlying encrypted block device).
507 Libguestfs has APIs for inspecting an unknown disk image to find out
508 if it contains operating systems. (These APIs used to be in a
509 separate Perl-only library called L<Sys::Guestfs::Lib(3)> but since
510 version 1.5.3 the most frequently used part of this library has been
511 rewritten in C and moved into the core code).
513 Add all disks belonging to the unknown virtual machine and call
514 L</guestfs_launch> in the usual way.
516 Then call L</guestfs_inspect_os>. This function uses other libguestfs
517 calls and certain heuristics, and returns a list of operating systems
518 that were found. An empty list means none were found. A single
519 element is the root filesystem of the operating system. For dual- or
520 multi-boot guests, multiple roots can be returned, each one
521 corresponding to a separate operating system. (Multi-boot virtual
522 machines are extremely rare in the world of virtualization, but since
523 this scenario can happen, we have built libguestfs to deal with it.)
525 For each root, you can then call various C<guestfs_inspect_get_*>
526 functions to get additional details about that operating system. For
527 example, call L</guestfs_inspect_get_type> to return the string
528 C<windows> or C<linux> for Windows and Linux-based operating systems
531 Un*x-like and Linux-based operating systems usually consist of several
532 filesystems which are mounted at boot time (for example, a separate
533 boot partition mounted on C</boot>). The inspection rules are able to
534 detect how filesystems correspond to mount points. Call
535 C<guestfs_inspect_get_mountpoints> to get this mapping. It might
536 return a hash table like this example:
539 / => /dev/vg_guest/lv_root
540 /usr => /dev/vg_guest/lv_usr
542 The caller can then make calls to L</guestfs_mount_options> to
543 mount the filesystems as suggested.
545 Be careful to mount filesystems in the right order (eg. C</> before
546 C</usr>). Sorting the keys of the hash by length, shortest first,
549 Inspection currently only works for some common operating systems.
550 Contributors are welcome to send patches for other operating systems
551 that we currently cannot detect.
553 Encrypted disks must be opened before inspection. See
554 L</ENCRYPTED DISKS> for more details. The L</guestfs_inspect_os>
555 function just ignores any encrypted devices.
557 A note on the implementation: The call L</guestfs_inspect_os> performs
558 inspection and caches the results in the guest handle. Subsequent
559 calls to C<guestfs_inspect_get_*> return this cached information, but
560 I<do not> re-read the disks. If you change the content of the guest
561 disks, you can redo inspection by calling L</guestfs_inspect_os>
564 =head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
566 Libguestfs can mount NTFS partitions. It does this using the
567 L<http://www.ntfs-3g.org/> driver.
569 DOS and Windows still use drive letters, and the filesystems are
570 always treated as case insensitive by Windows itself, and therefore
571 you might find a Windows configuration file referring to a path like
572 C<c:\windows\system32>. When the filesystem is mounted in libguestfs,
573 that directory might be referred to as C</WINDOWS/System32>.
575 Drive letter mappings are outside the scope of libguestfs. You have
576 to use libguestfs to read the appropriate Windows Registry and
577 configuration files, to determine yourself how drives are mapped (see
578 also L<hivex(3)> and L<virt-inspector(1)>).
580 Replacing backslash characters with forward slash characters is also
581 outside the scope of libguestfs, but something that you can easily do.
583 Where we can help is in resolving the case insensitivity of paths.
584 For this, call L</guestfs_case_sensitive_path>.
586 Libguestfs also provides some help for decoding Windows Registry
587 "hive" files, through the library C<hivex> which is part of the
588 libguestfs project although ships as a separate tarball. You have to
589 locate and download the hive file(s) yourself, and then pass them to
590 C<hivex> functions. See also the programs L<hivexml(1)>,
591 L<hivexsh(1)>, L<hivexregedit(1)> and L<virt-win-reg(1)> for more help
594 =head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES
596 Although we don't want to discourage you from using the C API, we will
597 mention here that the same API is also available in other languages.
599 The API is broadly identical in all supported languages. This means
600 that the C call C<guestfs_mount(g,path)> is
601 C<$g-E<gt>mount($path)> in Perl, C<g.mount(path)> in Python,
602 and C<Guestfs.mount g path> in OCaml. In other words, a
603 straightforward, predictable isomorphism between each language.
605 Error messages are automatically transformed
606 into exceptions if the language supports it.
608 We don't try to "object orientify" parts of the API in OO languages,
609 although contributors are welcome to write higher level APIs above
610 what we provide in their favourite languages if they wish.
616 You can use the I<guestfs.h> header file from C++ programs. The C++
617 API is identical to the C API. C++ classes and exceptions are not
622 The C# bindings are highly experimental. Please read the warnings
623 at the top of C<csharp/Libguestfs.cs>.
627 This is the only language binding that is working but incomplete.
628 Only calls which return simple integers have been bound in Haskell,
629 and we are looking for help to complete this binding.
633 Full documentation is contained in the Javadoc which is distributed
638 For documentation see the file C<guestfs.mli>.
642 For documentation see L<Sys::Guestfs(3)>.
646 For documentation see C<README-PHP> supplied with libguestfs
647 sources or in the php-libguestfs package for your distribution.
649 The PHP binding only works correctly on 64 bit machines.
653 For documentation do:
661 Use the Guestfs module. There is no Ruby-specific documentation, but
662 you can find examples written in Ruby in the libguestfs source.
664 =item B<shell scripts>
666 For documentation see L<guestfish(1)>.
670 =head2 LIBGUESTFS GOTCHAS
672 L<http://en.wikipedia.org/wiki/Gotcha_(programming)>: "A feature of a
673 system [...] that works in the way it is documented but is
674 counterintuitive and almost invites mistakes."
676 Since we developed libguestfs and the associated tools, there are
677 several things we would have designed differently, but are now stuck
678 with for backwards compatibility or other reasons. If there is ever a
679 libguestfs 2.0 release, you can expect these to change. Beware of
684 =item Autosync / forgetting to sync.
686 When modifying a filesystem from C or another language, you B<must>
687 unmount all filesystems and call L</guestfs_sync> explicitly before
688 you close the libguestfs handle. You can also call:
690 guestfs_set_autosync (g, 1);
692 to have the unmount/sync done automatically for you when the handle 'g'
693 is closed. (This feature is called "autosync", L</guestfs_set_autosync>
696 If you forget to do this, then it is entirely possible that your
697 changes won't be written out, or will be partially written, or (very
698 rarely) that you'll get disk corruption.
700 Note that in L<guestfish(3)> autosync is the default. So quick and
701 dirty guestfish scripts that forget to sync will work just fine, which
702 can make this very puzzling if you are trying to debug a problem.
704 =item Mount option C<-o sync> should not be the default.
706 If you use L</guestfs_mount>, then C<-o sync,noatime> are added
707 implicitly. However C<-o sync> does not add any reliability benefit,
708 but does have a very large performance impact.
710 The work around is to use L</guestfs_mount_options> and set the mount
711 options that you actually want to use.
713 =item Read-only should be the default.
715 In L<guestfish(3)>, I<--ro> should be the default, and you should
716 have to specify I<--rw> if you want to make changes to the image.
718 This would reduce the potential to corrupt live VM images.
720 Note that many filesystems change the disk when you just mount and
721 unmount, even if you didn't perform any writes. You need to use
722 L</guestfs_add_drive_ro> to guarantee that the disk is not changed.
724 =item guestfish command line is hard to use.
726 C<guestfish disk.img> doesn't do what people expect (open C<disk.img>
727 for examination). It tries to run a guestfish command C<disk.img>
728 which doesn't exist, so it fails. In earlier versions of guestfish
729 the error message was also unintuitive, but we have corrected this
730 since. Like the Bourne shell, we should have used C<guestfish -c
731 command> to run commands.
733 =item guestfish megabyte modifiers don't work right on all commands
735 In recent guestfish you can use C<1M> to mean 1 megabyte (and
736 similarly for other modifiers). What guestfish actually does is to
737 multiply the number part by the modifier part and pass the result to
738 the C API. However this doesn't work for a few APIs which aren't
739 expecting bytes, but are already expecting some other unit
742 The most common is L</guestfs_lvcreate>. The guestfish command:
746 does not do what you might expect. Instead because
747 L</guestfs_lvcreate> is already expecting megabytes, this tries to
748 create a 100 I<terabyte> (100 megabytes * megabytes) logical volume.
749 The error message you get from this is also a little obscure.
751 This could be fixed in the generator by specially marking parameters
752 and return values which take bytes or other units.
754 =item Library should return errno with error messages.
756 It would be a nice-to-have to be able to get the original value of
757 'errno' from inside the appliance along error paths (where set).
758 Currently L<guestmount(1)> goes through hoops to try to reverse the
759 error message string into an errno, see the function error() in
762 In libguestfs 1.5.4, the protocol was changed so that the
763 Linux errno is sent back from the daemon.
765 =item Ambiguity between devices and paths
767 There is a subtle ambiguity in the API between a device name
768 (eg. C</dev/sdb2>) and a similar pathname. A file might just happen
769 to be called C<sdb2> in the directory C</dev> (consider some non-Unix
772 In the current API we usually resolve this ambiguity by having two
773 separate calls, for example L</guestfs_checksum> and
774 L</guestfs_checksum_device>. Some API calls are ambiguous and
775 (incorrectly) resolve the problem by detecting if the path supplied
776 begins with C</dev/>.
778 To avoid both the ambiguity and the need to duplicate some calls, we
779 could make paths/devices into structured names. One way to do this
780 would be to use a notation like grub (C<hd(0,0)>), although nobody
781 really likes this aspect of grub. Another way would be to use a
782 structured type, equivalent to this OCaml type:
784 type path = Path of string | Device of int | Partition of int * int
786 which would allow you to pass arguments like:
789 Device 1 (* /dev/sdb, or perhaps /dev/sda *)
790 Partition (1, 2) (* /dev/sdb2 (or is it /dev/sda2 or /dev/sdb3?) *)
791 Path "/dev/sdb2" (* not a device *)
793 As you can see there are still problems to resolve even with this
794 representation. Also consider how it might work in guestfish.
798 =head2 PROTOCOL LIMITS
800 Internally libguestfs uses a message-based protocol to pass API calls
801 and their responses to and from a small "appliance" (see L</INTERNALS>
802 for plenty more detail about this). The maximum message size used by
803 the protocol is slightly less than 4 MB. For some API calls you may
804 need to be aware of this limit. The API calls which may be affected
805 are individually documented, with a link back to this section of the
808 A simple call such as L</guestfs_cat> returns its result (the file
809 data) in a simple string. Because this string is at some point
810 internally encoded as a message, the maximum size that it can return
811 is slightly under 4 MB. If the requested file is larger than this
812 then you will get an error.
814 In order to transfer large files into and out of the guest filesystem,
815 you need to use particular calls that support this. The sections
816 L</UPLOADING> and L</DOWNLOADING> document how to do this.
818 You might also consider mounting the disk image using our FUSE
819 filesystem support (L<guestmount(1)>).
821 =head2 KEYS AND PASSPHRASES
823 Certain libguestfs calls take a parameter that contains sensitive key
824 material, passed in as a C string.
826 In the future we would hope to change the libguestfs implementation so
827 that keys are L<mlock(2)>-ed into physical RAM, and thus can never end
828 up in swap. However this is I<not> done at the moment, because of the
829 complexity of such an implementation.
831 Therefore you should be aware that any key parameter you pass to
832 libguestfs might end up being written out to the swap partition. If
833 this is a concern, scrub the swap partition or don't use libguestfs on
836 =head1 CONNECTION MANAGEMENT
840 C<guestfs_h> is the opaque type representing a connection handle.
841 Create a handle by calling L</guestfs_create>. Call L</guestfs_close>
842 to free the handle and release all resources used.
844 For information on using multiple handles and threads, see the section
845 L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
847 =head2 guestfs_create
849 guestfs_h *guestfs_create (void);
851 Create a connection handle.
853 You have to call L</guestfs_add_drive_opts> (or one of the equivalent
854 calls) on the handle at least once.
856 This function returns a non-NULL pointer to a handle on success or
859 After configuring the handle, you have to call L</guestfs_launch>.
861 You may also want to configure error handling for the handle. See
862 L</ERROR HANDLING> section below.
866 void guestfs_close (guestfs_h *g);
868 This closes the connection handle and frees up all resources used.
870 =head1 ERROR HANDLING
872 The convention in all functions that return C<int> is that they return
873 C<-1> to indicate an error. You can get additional information on
874 errors by calling L</guestfs_last_error> and/or by setting up an error
875 handler with L</guestfs_set_error_handler>.
877 The default error handler prints the information string to C<stderr>.
879 Out of memory errors are handled differently. The default action is
880 to call L<abort(3)>. If this is undesirable, then you can set a
881 handler using L</guestfs_set_out_of_memory_handler>.
883 =head2 guestfs_last_error
885 const char *guestfs_last_error (guestfs_h *g);
887 This returns the last error message that happened on C<g>. If
888 there has not been an error since the handle was created, then this
891 The lifetime of the returned string is until the next error occurs, or
892 L</guestfs_close> is called.
894 The error string is not localized (ie. is always in English), because
895 this makes searching for error messages in search engines give the
896 largest number of results.
898 =head2 guestfs_set_error_handler
900 typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
903 void guestfs_set_error_handler (guestfs_h *g,
904 guestfs_error_handler_cb cb,
907 The callback C<cb> will be called if there is an error. The
908 parameters passed to the callback are an opaque data pointer and the
909 error message string.
911 Note that the message string C<msg> is freed as soon as the callback
912 function returns, so if you want to stash it somewhere you must make
915 The default handler prints messages on C<stderr>.
917 If you set C<cb> to C<NULL> then I<no> handler is called.
919 =head2 guestfs_get_error_handler
921 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
924 Returns the current error handler callback.
926 =head2 guestfs_set_out_of_memory_handler
928 typedef void (*guestfs_abort_cb) (void);
929 int guestfs_set_out_of_memory_handler (guestfs_h *g,
932 The callback C<cb> will be called if there is an out of memory
933 situation. I<Note this callback must not return>.
935 The default is to call L<abort(3)>.
937 You cannot set C<cb> to C<NULL>. You can't ignore out of memory
940 =head2 guestfs_get_out_of_memory_handler
942 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *g);
944 This returns the current out of memory handler.
948 Libguestfs needs a kernel and initrd.img, which it finds by looking
949 along an internal path.
951 By default it looks for these in the directory C<$libdir/guestfs>
952 (eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
954 Use L</guestfs_set_path> or set the environment variable
955 L</LIBGUESTFS_PATH> to change the directories that libguestfs will
956 search in. The value is a colon-separated list of paths. The current
957 directory is I<not> searched unless the path contains an empty element
958 or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
959 search the current directory and then C</usr/lib/guestfs>.
961 =head1 HIGH-LEVEL API ACTIONS
965 We guarantee the libguestfs ABI (binary interface), for public,
966 high-level actions as outlined in this section. Although we will
967 deprecate some actions, for example if they get replaced by newer
968 calls, we will keep the old actions forever. This allows you the
969 developer to program in confidence against the libguestfs API.
979 =head2 GROUPS OF FUNCTIONALITY IN THE APPLIANCE
981 Using L</guestfs_available> you can test availability of
982 the following groups of functions. This test queries the
983 appliance to see if the appliance you are currently using
984 supports the functionality.
988 =head2 GUESTFISH supported COMMAND
990 In L<guestfish(3)> there is a handy interactive command
991 C<supported> which prints out the available groups and
992 whether they are supported by this build of libguestfs.
993 Note however that you have to do C<run> first.
995 =head2 SINGLE CALLS AT COMPILE TIME
997 Since version 1.5.8, C<E<lt>guestfs.hE<gt>> defines symbols
998 for each C API function, such as:
1000 #define LIBGUESTFS_HAVE_DD 1
1002 if L</guestfs_dd> is available.
1004 Before version 1.5.8, if you needed to test whether a single
1005 libguestfs function is available at compile time, we recommended using
1006 build tools such as autoconf or cmake. For example in autotools you
1009 AC_CHECK_LIB([guestfs],[guestfs_create])
1010 AC_CHECK_FUNCS([guestfs_dd])
1012 which would result in C<HAVE_GUESTFS_DD> being either defined
1013 or not defined in your program.
1015 =head2 SINGLE CALLS AT RUN TIME
1017 Testing at compile time doesn't guarantee that a function really
1018 exists in the library. The reason is that you might be dynamically
1019 linked against a previous I<libguestfs.so> (dynamic library)
1020 which doesn't have the call. This situation unfortunately results
1021 in a segmentation fault, which is a shortcoming of the C dynamic
1022 linking system itself.
1024 You can use L<dlopen(3)> to test if a function is available
1025 at run time, as in this example program (note that you still
1026 need the compile time check as well):
1032 #include <guestfs.h>
1036 #ifdef LIBGUESTFS_HAVE_DD
1040 /* Test if the function guestfs_dd is really available. */
1041 dl = dlopen (NULL, RTLD_LAZY);
1043 fprintf (stderr, "dlopen: %s\n", dlerror ());
1044 exit (EXIT_FAILURE);
1046 has_function = dlsym (dl, "guestfs_dd") != NULL;
1050 printf ("this libguestfs.so does NOT have guestfs_dd function\n");
1052 printf ("this libguestfs.so has guestfs_dd function\n");
1053 /* Now it's safe to call
1054 guestfs_dd (g, "foo", "bar");
1058 printf ("guestfs_dd function was not found at compile time\n");
1062 You may think the above is an awful lot of hassle, and it is.
1063 There are other ways outside of the C linking system to ensure
1064 that this kind of incompatibility never arises, such as using
1067 Requires: libguestfs >= 1.0.80
1069 =head1 CALLS WITH OPTIONAL ARGUMENTS
1071 A recent feature of the API is the introduction of calls which take
1072 optional arguments. In C these are declared 3 ways. The main way is
1073 as a call which takes variable arguments (ie. C<...>), as in this
1076 int guestfs_add_drive_opts (guestfs_h *g, const char *filename, ...);
1078 Call this with a list of optional arguments, terminated by C<-1>.
1079 So to call with no optional arguments specified:
1081 guestfs_add_drive_opts (g, filename, -1);
1083 With a single optional argument:
1085 guestfs_add_drive_opts (g, filename,
1086 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
1091 guestfs_add_drive_opts (g, filename,
1092 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
1093 GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
1096 and so forth. Don't forget the terminating C<-1> otherwise
1097 Bad Things will happen!
1099 =head2 USING va_list FOR OPTIONAL ARGUMENTS
1101 The second variant has the same name with the suffix C<_va>, which
1102 works the same way but takes a C<va_list>. See the C manual for
1103 details. For the example function, this is declared:
1105 int guestfs_add_drive_opts_va (guestfs_h *g, const char *filename,
1108 =head2 CONSTRUCTING OPTIONAL ARGUMENTS
1110 The third variant is useful where you need to construct these
1111 calls. You pass in a structure where you fill in the optional
1112 fields. The structure has a bitmask as the first element which
1113 you must set to indicate which fields you have filled in. For
1114 our example function the structure and call are declared:
1116 struct guestfs_add_drive_opts_argv {
1122 int guestfs_add_drive_opts_argv (guestfs_h *g, const char *filename,
1123 const struct guestfs_add_drive_opts_argv *optargs);
1125 You could call it like this:
1127 struct guestfs_add_drive_opts_argv optargs = {
1128 .bitmask = GUESTFS_ADD_DRIVE_OPTS_READONLY_BITMASK |
1129 GUESTFS_ADD_DRIVE_OPTS_FORMAT_BITMASK,
1134 guestfs_add_drive_opts_argv (g, filename, &optargs);
1142 The C<_BITMASK> suffix on each option name when specifying the
1147 You do not need to fill in all fields of the structure.
1151 There must be a one-to-one correspondence between fields of the
1152 structure that are filled in, and bits set in the bitmask.
1156 =head2 OPTIONAL ARGUMENTS IN OTHER LANGUAGES
1158 In other languages, optional arguments are expressed in the
1159 way that is natural for that language. We refer you to the
1160 language-specific documentation for more details on that.
1162 For guestfish, see L<guestfish(1)/OPTIONAL ARGUMENTS>.
1166 <!-- old anchor for the next section -->
1167 <a name="state_machine_and_low_level_event_api"/>
1173 Internally, libguestfs is implemented by running an appliance (a
1174 special type of small virtual machine) using L<qemu(1)>. Qemu runs as
1175 a child process of the main program.
1181 | | child process / appliance
1182 | | __________________________
1184 +-------------------+ RPC | +-----------------+ |
1185 | libguestfs <--------------------> guestfsd | |
1186 | | | +-----------------+ |
1187 \___________________/ | | Linux kernel | |
1188 | +--^--------------+ |
1189 \_________|________________/
1197 The library, linked to the main program, creates the child process and
1198 hence the appliance in the L</guestfs_launch> function.
1200 Inside the appliance is a Linux kernel and a complete stack of
1201 userspace tools (such as LVM and ext2 programs) and a small
1202 controlling daemon called L</guestfsd>. The library talks to
1203 L</guestfsd> using remote procedure calls (RPC). There is a mostly
1204 one-to-one correspondence between libguestfs API calls and RPC calls
1205 to the daemon. Lastly the disk image(s) are attached to the qemu
1206 process which translates device access by the appliance's Linux kernel
1207 into accesses to the image.
1209 A common misunderstanding is that the appliance "is" the virtual
1210 machine. Although the disk image you are attached to might also be
1211 used by some virtual machine, libguestfs doesn't know or care about
1212 this. (But you will care if both libguestfs's qemu process and your
1213 virtual machine are trying to update the disk image at the same time,
1214 since these usually results in massive disk corruption).
1216 =head1 STATE MACHINE
1218 libguestfs uses a state machine to model the child process:
1229 / | \ \ guestfs_launch
1240 \______/ <------ \________/
1242 The normal transitions are (1) CONFIG (when the handle is created, but
1243 there is no child process), (2) LAUNCHING (when the child process is
1244 booting up), (3) alternating between READY and BUSY as commands are
1245 issued to, and carried out by, the child process.
1247 The guest may be killed by L</guestfs_kill_subprocess>, or may die
1248 asynchronously at any time (eg. due to some internal error), and that
1249 causes the state to transition back to CONFIG.
1251 Configuration commands for qemu such as L</guestfs_add_drive> can only
1252 be issued when in the CONFIG state.
1254 The API offers one call that goes from CONFIG through LAUNCHING to
1255 READY. L</guestfs_launch> blocks until the child process is READY to
1256 accept commands (or until some failure or timeout).
1257 L</guestfs_launch> internally moves the state from CONFIG to LAUNCHING
1258 while it is running.
1260 API actions such as L</guestfs_mount> can only be issued when in the
1261 READY state. These API calls block waiting for the command to be
1262 carried out (ie. the state to transition to BUSY and then back to
1263 READY). There are no non-blocking versions, and no way to issue more
1264 than one command per handle at the same time.
1266 Finally, the child process sends asynchronous messages back to the
1267 main program, such as kernel log messages. You can register a
1268 callback to receive these messages.
1270 =head2 SETTING CALLBACKS TO HANDLE EVENTS
1272 The child process generates events in some situations. Current events
1273 include: receiving a log message, the child process exits.
1275 Use the C<guestfs_set_*_callback> functions to set a callback for
1276 different types of events.
1278 Only I<one callback of each type> can be registered for each handle.
1279 Calling C<guestfs_set_*_callback> again overwrites the previous
1280 callback of that type. Cancel all callbacks of this type by calling
1281 this function with C<cb> set to C<NULL>.
1283 =head2 guestfs_set_log_message_callback
1285 typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
1286 char *buf, int len);
1287 void guestfs_set_log_message_callback (guestfs_h *g,
1288 guestfs_log_message_cb cb,
1291 The callback function C<cb> will be called whenever qemu or the guest
1292 writes anything to the console.
1294 Use this function to capture kernel messages and similar.
1296 Normally there is no log message handler, and log messages are just
1299 =head2 guestfs_set_subprocess_quit_callback
1301 typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
1302 void guestfs_set_subprocess_quit_callback (guestfs_h *g,
1303 guestfs_subprocess_quit_cb cb,
1306 The callback function C<cb> will be called when the child process
1307 quits, either asynchronously or if killed by
1308 L</guestfs_kill_subprocess>. (This corresponds to a transition from
1309 any state to the CONFIG state).
1311 =head2 guestfs_set_launch_done_callback
1313 typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
1314 void guestfs_set_launch_done_callback (guestfs_h *g,
1315 guestfs_launch_done_cb cb,
1318 The callback function C<cb> will be called when the child process
1319 becomes ready first time after it has been launched. (This
1320 corresponds to a transition from LAUNCHING to the READY state).
1322 =head2 guestfs_set_close_callback
1324 typedef void (*guestfs_close_cb) (guestfs_h *g, void *opaque);
1325 void guestfs_set_close_callback (guestfs_h *g,
1326 guestfs_close_cb cb,
1329 The callback function C<cb> will be called while the handle
1330 is being closed (synchronously from L</guestfs_close>).
1332 Note that libguestfs installs an L<atexit(3)> handler to try to
1333 clean up handles that are open when the program exits. This
1334 means that this callback might be called indirectly from
1335 L<exit(3)>, which can cause unexpected problems in higher-level
1336 languages (eg. if your HLL interpreter has already been cleaned
1337 up by the time this is called, and if your callback then jumps
1338 into some HLL function).
1340 =head2 guestfs_set_progress_callback
1342 typedef void (*guestfs_progress_cb) (guestfs_h *g, void *opaque,
1343 int proc_nr, int serial,
1344 uint64_t position, uint64_t total);
1345 void guestfs_set_progress_callback (guestfs_h *g,
1346 guestfs_progress_cb cb,
1349 Some long-running operations can generate progress messages. If
1350 this callback is registered, then it will be called each time a
1351 progress message is generated (usually two seconds after the
1352 operation started, and three times per second thereafter until
1353 it completes, although the frequency may change in future versions).
1355 The callback receives two numbers: C<position> and C<total>.
1356 The units of C<total> are not defined, although for some
1357 operations C<total> may relate in some way to the amount of
1358 data to be transferred (eg. in bytes or megabytes), and
1359 C<position> may be the portion which has been transferred.
1361 The only defined and stable parts of the API are:
1367 The callback can display to the user some type of progress bar or
1368 indicator which shows the ratio of C<position>:C<total>.
1372 0 E<lt>= C<position> E<lt>= C<total>
1376 If any progress notification is sent during a call, then a final
1377 progress notification is always sent when C<position> = C<total>.
1379 This is to simplify caller code, so callers can easily set the
1380 progress indicator to "100%" at the end of the operation, without
1381 requiring special code to detect this case.
1385 The callback also receives the procedure number and serial number of
1386 the call. These are only useful for debugging protocol issues, and
1387 the callback can normally ignore them. The callback may want to
1388 print these numbers in error messages or debugging messages.
1390 =head1 PRIVATE DATA AREA
1392 You can attach named pieces of private data to the libguestfs handle,
1393 and fetch them by name for the lifetime of the handle. This is called
1394 the private data area and is only available from the C API.
1396 To attach a named piece of data, use the following call:
1398 void guestfs_set_private (guestfs_h *g, const char *key, void *data);
1400 C<key> is the name to associate with this data, and C<data> is an
1401 arbitrary pointer (which can be C<NULL>). Any previous item with the
1402 same name is overwritten.
1404 You can use any C<key> you want, but names beginning with an
1405 underscore character are reserved for internal libguestfs purposes
1406 (for implementing language bindings). It is recommended to prefix the
1407 name with some unique string to avoid collisions with other users.
1409 To retrieve the pointer, use:
1411 void *guestfs_get_private (guestfs_h *g, const char *key);
1413 This function returns C<NULL> if either no data is found associated
1414 with C<key>, or if the user previously set the C<key>'s C<data>
1417 Libguestfs does not try to look at or interpret the C<data> pointer in
1418 any way. As far as libguestfs is concerned, it need not be a valid
1419 pointer at all. In particular, libguestfs does I<not> try to free the
1420 data when the handle is closed. If the data must be freed, then the
1421 caller must either free it before calling L</guestfs_close> or must
1422 set up a close callback to do it (see L</guestfs_set_close_callback>,
1423 and note that only one callback can be registered for a handle).
1425 The private data area is implemented using a hash table, and should be
1426 reasonably efficient for moderate numbers of keys.
1428 =head1 BLOCK DEVICE NAMING
1430 In the kernel there is now quite a profusion of schemata for naming
1431 block devices (in this context, by I<block device> I mean a physical
1432 or virtual hard drive). The original Linux IDE driver used names
1433 starting with C</dev/hd*>. SCSI devices have historically used a
1434 different naming scheme, C</dev/sd*>. When the Linux kernel I<libata>
1435 driver became a popular replacement for the old IDE driver
1436 (particularly for SATA devices) those devices also used the
1437 C</dev/sd*> scheme. Additionally we now have virtual machines with
1438 paravirtualized drivers. This has created several different naming
1439 systems, such as C</dev/vd*> for virtio disks and C</dev/xvd*> for Xen
1442 As discussed above, libguestfs uses a qemu appliance running an
1443 embedded Linux kernel to access block devices. We can run a variety
1444 of appliances based on a variety of Linux kernels.
1446 This causes a problem for libguestfs because many API calls use device
1447 or partition names. Working scripts and the recipe (example) scripts
1448 that we make available over the internet could fail if the naming
1451 Therefore libguestfs defines C</dev/sd*> as the I<standard naming
1452 scheme>. Internally C</dev/sd*> names are translated, if necessary,
1453 to other names as required. For example, under RHEL 5 which uses the
1454 C</dev/hd*> scheme, any device parameter C</dev/sda2> is translated to
1455 C</dev/hda2> transparently.
1457 Note that this I<only> applies to parameters. The
1458 L</guestfs_list_devices>, L</guestfs_list_partitions> and similar calls
1459 return the true names of the devices and partitions as known to the
1462 =head2 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
1464 Usually this translation is transparent. However in some (very rare)
1465 cases you may need to know the exact algorithm. Such cases include
1466 where you use L</guestfs_config> to add a mixture of virtio and IDE
1467 devices to the qemu-based appliance, so have a mixture of C</dev/sd*>
1468 and C</dev/vd*> devices.
1470 The algorithm is applied only to I<parameters> which are known to be
1471 either device or partition names. Return values from functions such
1472 as L</guestfs_list_devices> are never changed.
1478 Is the string a parameter which is a device or partition name?
1482 Does the string begin with C</dev/sd>?
1486 Does the named device exist? If so, we use that device.
1487 However if I<not> then we continue with this algorithm.
1491 Replace initial C</dev/sd> string with C</dev/hd>.
1493 For example, change C</dev/sda2> to C</dev/hda2>.
1495 If that named device exists, use it. If not, continue.
1499 Replace initial C</dev/sd> string with C</dev/vd>.
1501 If that named device exists, use it. If not, return an error.
1505 =head2 PORTABILITY CONCERNS
1507 Although the standard naming scheme and automatic translation is
1508 useful for simple programs and guestfish scripts, for larger programs
1509 it is best not to rely on this mechanism.
1511 Where possible for maximum future portability programs using
1512 libguestfs should use these future-proof techniques:
1518 Use L</guestfs_list_devices> or L</guestfs_list_partitions> to list
1519 actual device names, and then use those names directly.
1521 Since those device names exist by definition, they will never be
1526 Use higher level ways to identify filesystems, such as LVM names,
1527 UUIDs and filesystem labels.
1533 =head2 COMMUNICATION PROTOCOL
1535 Don't rely on using this protocol directly. This section documents
1536 how it currently works, but it may change at any time.
1538 The protocol used to talk between the library and the daemon running
1539 inside the qemu virtual machine is a simple RPC mechanism built on top
1540 of XDR (RFC 1014, RFC 1832, RFC 4506).
1542 The detailed format of structures is in C<src/guestfs_protocol.x>
1543 (note: this file is automatically generated).
1545 There are two broad cases, ordinary functions that don't have any
1546 C<FileIn> and C<FileOut> parameters, which are handled with very
1547 simple request/reply messages. Then there are functions that have any
1548 C<FileIn> or C<FileOut> parameters, which use the same request and
1549 reply messages, but they may also be followed by files sent using a
1552 =head3 ORDINARY FUNCTIONS (NO FILEIN/FILEOUT PARAMS)
1554 For ordinary functions, the request message is:
1556 total length (header + arguments,
1557 but not including the length word itself)
1558 struct guestfs_message_header (encoded as XDR)
1559 struct guestfs_<foo>_args (encoded as XDR)
1561 The total length field allows the daemon to allocate a fixed size
1562 buffer into which it slurps the rest of the message. As a result, the
1563 total length is limited to C<GUESTFS_MESSAGE_MAX> bytes (currently
1564 4MB), which means the effective size of any request is limited to
1565 somewhere under this size.
1567 Note also that many functions don't take any arguments, in which case
1568 the C<guestfs_I<foo>_args> is completely omitted.
1570 The header contains the procedure number (C<guestfs_proc>) which is
1571 how the receiver knows what type of args structure to expect, or none
1574 The reply message for ordinary functions is:
1576 total length (header + ret,
1577 but not including the length word itself)
1578 struct guestfs_message_header (encoded as XDR)
1579 struct guestfs_<foo>_ret (encoded as XDR)
1581 As above the C<guestfs_I<foo>_ret> structure may be completely omitted
1582 for functions that return no formal return values.
1584 As above the total length of the reply is limited to
1585 C<GUESTFS_MESSAGE_MAX>.
1587 In the case of an error, a flag is set in the header, and the reply
1588 message is slightly changed:
1590 total length (header + error,
1591 but not including the length word itself)
1592 struct guestfs_message_header (encoded as XDR)
1593 struct guestfs_message_error (encoded as XDR)
1595 The C<guestfs_message_error> structure contains the error message as a
1598 =head3 FUNCTIONS THAT HAVE FILEIN PARAMETERS
1600 A C<FileIn> parameter indicates that we transfer a file I<into> the
1601 guest. The normal request message is sent (see above). However this
1602 is followed by a sequence of file chunks.
1604 total length (header + arguments,
1605 but not including the length word itself,
1606 and not including the chunks)
1607 struct guestfs_message_header (encoded as XDR)
1608 struct guestfs_<foo>_args (encoded as XDR)
1609 sequence of chunks for FileIn param #0
1610 sequence of chunks for FileIn param #1 etc.
1612 The "sequence of chunks" is:
1614 length of chunk (not including length word itself)
1615 struct guestfs_chunk (encoded as XDR)
1617 struct guestfs_chunk (encoded as XDR)
1620 struct guestfs_chunk (with data.data_len == 0)
1622 The final chunk has the C<data_len> field set to zero. Additionally a
1623 flag is set in the final chunk to indicate either successful
1624 completion or early cancellation.
1626 At time of writing there are no functions that have more than one
1627 FileIn parameter. However this is (theoretically) supported, by
1628 sending the sequence of chunks for each FileIn parameter one after
1629 another (from left to right).
1631 Both the library (sender) I<and> the daemon (receiver) may cancel the
1632 transfer. The library does this by sending a chunk with a special
1633 flag set to indicate cancellation. When the daemon sees this, it
1634 cancels the whole RPC, does I<not> send any reply, and goes back to
1635 reading the next request.
1637 The daemon may also cancel. It does this by writing a special word
1638 C<GUESTFS_CANCEL_FLAG> to the socket. The library listens for this
1639 during the transfer, and if it gets it, it will cancel the transfer
1640 (it sends a cancel chunk). The special word is chosen so that even if
1641 cancellation happens right at the end of the transfer (after the
1642 library has finished writing and has started listening for the reply),
1643 the "spurious" cancel flag will not be confused with the reply
1646 This protocol allows the transfer of arbitrary sized files (no 32 bit
1647 limit), and also files where the size is not known in advance
1648 (eg. from pipes or sockets). However the chunks are rather small
1649 (C<GUESTFS_MAX_CHUNK_SIZE>), so that neither the library nor the
1650 daemon need to keep much in memory.
1652 =head3 FUNCTIONS THAT HAVE FILEOUT PARAMETERS
1654 The protocol for FileOut parameters is exactly the same as for FileIn
1655 parameters, but with the roles of daemon and library reversed.
1657 total length (header + ret,
1658 but not including the length word itself,
1659 and not including the chunks)
1660 struct guestfs_message_header (encoded as XDR)
1661 struct guestfs_<foo>_ret (encoded as XDR)
1662 sequence of chunks for FileOut param #0
1663 sequence of chunks for FileOut param #1 etc.
1665 =head3 INITIAL MESSAGE
1667 When the daemon launches it sends an initial word
1668 (C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest and daemon is
1669 alive. This is what L</guestfs_launch> waits for.
1671 =head3 PROGRESS NOTIFICATION MESSAGES
1673 The daemon may send progress notification messages at any time. These
1674 are distinguished by the normal length word being replaced by
1675 C<GUESTFS_PROGRESS_FLAG>, followed by a fixed size progress message.
1677 The library turns them into progress callbacks (see
1678 C<guestfs_set_progress_callback>) if there is a callback registered,
1679 or discards them if not.
1681 The daemon self-limits the frequency of progress messages it sends
1682 (see C<daemon/proto.c:notify_progress>). Not all calls generate
1685 =head1 MULTIPLE HANDLES AND MULTIPLE THREADS
1687 All high-level libguestfs actions are synchronous. If you want
1688 to use libguestfs asynchronously then you must create a thread.
1690 Only use the handle from a single thread. Either use the handle
1691 exclusively from one thread, or provide your own mutex so that two
1692 threads cannot issue calls on the same handle at the same time.
1694 See the graphical program guestfs-browser for one possible
1695 architecture for multithreaded programs using libvirt and libguestfs.
1697 =head1 QEMU WRAPPERS
1699 If you want to compile your own qemu, run qemu from a non-standard
1700 location, or pass extra arguments to qemu, then you can write a
1701 shell-script wrapper around qemu.
1703 There is one important rule to remember: you I<must C<exec qemu>> as
1704 the last command in the shell script (so that qemu replaces the shell
1705 and becomes the direct child of the libguestfs-using program). If you
1706 don't do this, then the qemu process won't be cleaned up correctly.
1708 Here is an example of a wrapper, where I have built my own copy of
1712 qemudir=/home/rjones/d/qemu
1713 exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
1715 Save this script as C</tmp/qemu.wrapper> (or wherever), C<chmod +x>,
1716 and then use it by setting the LIBGUESTFS_QEMU environment variable.
1719 LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
1721 Note that libguestfs also calls qemu with the -help and -version
1722 options in order to determine features.
1724 =head1 LIBGUESTFS VERSION NUMBERS
1726 Since April 2010, libguestfs has started to make separate development
1727 and stable releases, along with corresponding branches in our git
1728 repository. These separate releases can be identified by version
1731 even numbers for stable: 1.2.x, 1.4.x, ...
1732 .-------- odd numbers for development: 1.3.x, 1.5.x, ...
1738 | `-------- sub-version
1740 `------ always '1' because we don't change the ABI
1742 Thus "1.3.5" is the 5th update to the development branch "1.3".
1744 As time passes we cherry pick fixes from the development branch and
1745 backport those into the stable branch, the effect being that the
1746 stable branch should get more stable and less buggy over time. So the
1747 stable releases are ideal for people who don't need new features but
1748 would just like the software to work.
1750 Our criteria for backporting changes are:
1756 Documentation changes which don't affect any code are
1757 backported unless the documentation refers to a future feature
1758 which is not in stable.
1762 Bug fixes which are not controversial, fix obvious problems, and
1763 have been well tested are backported.
1767 Simple rearrangements of code which shouldn't affect how it works get
1768 backported. This is so that the code in the two branches doesn't get
1769 too far out of step, allowing us to backport future fixes more easily.
1773 We I<don't> backport new features, new APIs, new tools etc, except in
1774 one exceptional case: the new feature is required in order to
1775 implement an important bug fix.
1779 A new stable branch starts when we think the new features in
1780 development are substantial and compelling enough over the current
1781 stable branch to warrant it. When that happens we create new stable
1782 and development versions 1.N.0 and 1.(N+1).0 [N is even]. The new
1783 dot-oh release won't necessarily be so stable at this point, but by
1784 backporting fixes from development, that branch will stabilize over
1787 =head1 ENVIRONMENT VARIABLES
1791 =item LIBGUESTFS_APPEND
1793 Pass additional options to the guest kernel.
1795 =item LIBGUESTFS_DEBUG
1797 Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
1798 has the same effect as calling C<guestfs_set_verbose (g, 1)>.
1800 =item LIBGUESTFS_MEMSIZE
1802 Set the memory allocated to the qemu process, in megabytes. For
1805 LIBGUESTFS_MEMSIZE=700
1807 =item LIBGUESTFS_PATH
1809 Set the path that libguestfs uses to search for kernel and initrd.img.
1810 See the discussion of paths in section PATH above.
1812 =item LIBGUESTFS_QEMU
1814 Set the default qemu binary that libguestfs uses. If not set, then
1815 the qemu which was found at compile time by the configure script is
1818 See also L</QEMU WRAPPERS> above.
1820 =item LIBGUESTFS_TRACE
1822 Set C<LIBGUESTFS_TRACE=1> to enable command traces. This
1823 has the same effect as calling C<guestfs_set_trace (g, 1)>.
1827 Location of temporary directory, defaults to C</tmp>.
1829 If libguestfs was compiled to use the supermin appliance then the
1830 real appliance is cached in this directory, shared between all
1831 handles belonging to the same EUID. You can use C<$TMPDIR> to
1832 configure another directory to use in case C</tmp> is not large
1844 L<virt-inspector(1)>,
1845 L<virt-list-filesystems(1)>,
1846 L<virt-list-partitions(1)>,
1855 L<http://libguestfs.org/>.
1857 Tools with a similar purpose:
1866 To get a list of bugs against libguestfs use this link:
1868 L<https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools>
1870 To report a new bug against libguestfs use this link:
1872 L<https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools>
1874 When reporting a bug, please check:
1880 That the bug hasn't been reported already.
1884 That you are testing a recent version.
1888 Describe the bug accurately, and give a way to reproduce it.
1892 Run libguestfs-test-tool and paste the B<complete, unedited>
1893 output into the bug report.
1899 Richard W.M. Jones (C<rjones at redhat dot com>)
1903 Copyright (C) 2009-2010 Red Hat Inc.
1904 L<http://libguestfs.org/>
1906 This library is free software; you can redistribute it and/or
1907 modify it under the terms of the GNU Lesser General Public
1908 License as published by the Free Software Foundation; either
1909 version 2 of the License, or (at your option) any later version.
1911 This library is distributed in the hope that it will be useful,
1912 but WITHOUT ANY WARRANTY; without even the implied warranty of
1913 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
1914 Lesser General Public License for more details.
1916 You should have received a copy of the GNU Lesser General Public
1917 License along with this library; if not, write to the Free Software
1918 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA