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, 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 You can add a disk read-only using L</guestfs_add_drive_ro>, in which
128 case libguestfs won't modify the file.
130 Be extremely cautious if the disk image is in use, eg. if it is being
131 used by a virtual machine. Adding it read-write will almost certainly
132 cause disk corruption, but adding it read-only is safe.
134 You must add at least one disk image, and you may add multiple disk
135 images. In the API, the disk images are usually referred to as
136 C</dev/sda> (for the first one you added), C</dev/sdb> (for the second
139 Once L</guestfs_launch> has been called you cannot add any more images.
140 You can call L</guestfs_list_devices> to get a list of the device
141 names, in the order that you added them. See also L</BLOCK DEVICE
146 Before you can read or write files, create directories and so on in a
147 disk image that contains filesystems, you have to mount those
148 filesystems using L</guestfs_mount>. If you already know that a disk
149 image contains (for example) one partition with a filesystem on that
150 partition, then you can mount it directly:
152 guestfs_mount (g, "/dev/sda1", "/");
154 where C</dev/sda1> means literally the first partition (C<1>) of the
155 first disk image that we added (C</dev/sda>). If the disk contains
156 Linux LVM2 logical volumes you could refer to those instead (eg. C</dev/VG/LV>).
158 If you are given a disk image and you don't know what it contains then
159 you have to find out. Libguestfs can do that too: use
160 L</guestfs_list_partitions> and L</guestfs_lvs> to list possible
161 partitions and LVs, and either try mounting each to see what is
162 mountable, or else examine them with L</guestfs_vfs_type> or
163 L</guestfs_file>. Libguestfs also has a set of APIs for inspection of
164 disk images (see L</INSPECTION> below). But you might find it easier
165 to look at higher level programs built on top of libguestfs, in
166 particular L<virt-inspector(1)>.
168 To mount a disk image read-only, use L</guestfs_mount_ro>. There are
169 several other variations of the C<guestfs_mount_*> call.
171 =head2 FILESYSTEM ACCESS AND MODIFICATION
173 The majority of the libguestfs API consists of fairly low-level calls
174 for accessing and modifying the files, directories, symlinks etc on
175 mounted filesystems. There are over a hundred such calls which you
176 can find listed in detail below in this man page, and we don't even
177 pretend to cover them all in this overview.
179 Specify filenames as full paths, starting with C<"/"> and including
182 For example, if you mounted a filesystem at C<"/"> and you want to
183 read the file called C<"etc/passwd"> then you could do:
185 char *data = guestfs_cat (g, "/etc/passwd");
187 This would return C<data> as a newly allocated buffer containing the
188 full content of that file (with some conditions: see also
189 L</DOWNLOADING> below), or C<NULL> if there was an error.
191 As another example, to create a top-level directory on that filesystem
192 called C<"var"> you would do:
194 guestfs_mkdir (g, "/var");
196 To create a symlink you could do:
198 guestfs_ln_s (g, "/etc/init.d/portmap",
199 "/etc/rc3.d/S30portmap");
201 Libguestfs will reject attempts to use relative paths and there is no
202 concept of a current working directory.
204 Libguestfs can return errors in many situations: for example if the
205 filesystem isn't writable, or if a file or directory that you
206 requested doesn't exist. If you are using the C API (documented here)
207 you have to check for those error conditions after each call. (Other
208 language bindings turn these errors into exceptions).
210 File writes are affected by the per-handle umask, set by calling
211 L</guestfs_umask> and defaulting to 022. See L</UMASK>.
215 Libguestfs contains API calls to read, create and modify partition
216 tables on disk images.
218 In the common case where you want to create a single partition
219 covering the whole disk, you should use the L</guestfs_part_disk>
222 const char *parttype = "mbr";
223 if (disk_is_larger_than_2TB)
225 guestfs_part_disk (g, "/dev/sda", parttype);
227 Obviously this effectively wipes anything that was on that disk image
232 Libguestfs provides access to a large part of the LVM2 API, such as
233 L</guestfs_lvcreate> and L</guestfs_vgremove>. It won't make much sense
234 unless you familiarize yourself with the concepts of physical volumes,
235 volume groups and logical volumes.
237 This author strongly recommends reading the LVM HOWTO, online at
238 L<http://tldp.org/HOWTO/LVM-HOWTO/>.
242 Use L</guestfs_cat> to download small, text only files. This call
243 is limited to files which are less than 2 MB and which cannot contain
244 any ASCII NUL (C<\0>) characters. However it has a very simple
247 L</guestfs_read_file> can be used to read files which contain
248 arbitrary 8 bit data, since it returns a (pointer, size) pair.
249 However it is still limited to "small" files, less than 2 MB.
251 L</guestfs_download> can be used to download any file, with no
252 limits on content or size (even files larger than 4 GB).
254 To download multiple files, see L</guestfs_tar_out> and
259 It's often the case that you want to write a file or files to the disk
262 To write a small file with fixed content, use L</guestfs_write>. To
263 create a file of all zeroes, use L</guestfs_truncate_size> (sparse) or
264 L</guestfs_fallocate64> (with all disk blocks allocated). There are a
265 variety of other functions for creating test files, for example
266 L</guestfs_fill> and L</guestfs_fill_pattern>.
268 To upload a single file, use L</guestfs_upload>. This call has no
269 limits on file content or size (even files larger than 4 GB).
271 To upload multiple files, see L</guestfs_tar_in> and L</guestfs_tgz_in>.
273 However the fastest way to upload I<large numbers of arbitrary files>
274 is to turn them into a squashfs or CD ISO (see L<mksquashfs(8)> and
275 L<mkisofs(8)>), then attach this using L</guestfs_add_drive_ro>. If
276 you add the drive in a predictable way (eg. adding it last after all
277 other drives) then you can get the device name from
278 L</guestfs_list_devices> and mount it directly using
279 L</guestfs_mount_ro>. Note that squashfs images are sometimes
280 non-portable between kernel versions, and they don't support labels or
281 UUIDs. If you want to pre-build an image or you need to mount it
282 using a label or UUID, use an ISO image instead.
286 There are various different commands for copying between files and
287 devices and in and out of the guest filesystem. These are summarised
292 =item B<file> to B<file>
294 Use L</guestfs_cp> to copy a single file, or
295 L</guestfs_cp_a> to copy directories recursively.
297 =item B<file or device> to B<file or device>
299 Use L</guestfs_dd> which efficiently uses L<dd(1)>
300 to copy between files and devices in the guest.
302 Example: duplicate the contents of an LV:
304 guestfs_dd (g, "/dev/VG/Original", "/dev/VG/Copy");
306 The destination (C</dev/VG/Copy>) must be at least as large as the
307 source (C</dev/VG/Original>). To copy less than the whole
308 source device, use L</guestfs_copy_size>.
310 =item B<file on the host> to B<file or device>
312 Use L</guestfs_upload>. See L</UPLOADING> above.
314 =item B<file or device> to B<file on the host>
316 Use L</guestfs_download>. See L</DOWNLOADING> above.
322 L</guestfs_ll> is just designed for humans to read (mainly when using
323 the L<guestfish(1)>-equivalent command C<ll>).
325 L</guestfs_ls> is a quick way to get a list of files in a directory
326 from programs, as a flat list of strings.
328 L</guestfs_readdir> is a programmatic way to get a list of files in a
329 directory, plus additional information about each one. It is more
330 equivalent to using the L<readdir(3)> call on a local filesystem.
332 L</guestfs_find> and L</guestfs_find0> can be used to recursively list
335 =head2 RUNNING COMMANDS
337 Although libguestfs is a primarily an API for manipulating files
338 inside guest images, we also provide some limited facilities for
339 running commands inside guests.
341 There are many limitations to this:
347 The kernel version that the command runs under will be different
348 from what it expects.
352 If the command needs to communicate with daemons, then most likely
353 they won't be running.
357 The command will be running in limited memory.
361 Only supports Linux guests (not Windows, BSD, etc).
365 Architecture limitations (eg. won't work for a PPC guest on
370 For SELinux guests, you may need to enable SELinux and load policy
371 first. See L</SELINUX> in this manpage.
375 The two main API calls to run commands are L</guestfs_command> and
376 L</guestfs_sh> (there are also variations).
378 The difference is that L</guestfs_sh> runs commands using the shell, so
379 any shell globs, redirections, etc will work.
381 =head2 CONFIGURATION FILES
383 To read and write configuration files in Linux guest filesystems, we
384 strongly recommend using Augeas. For example, Augeas understands how
385 to read and write, say, a Linux shadow password file or X.org
386 configuration file, and so avoids you having to write that code.
388 The main Augeas calls are bound through the C<guestfs_aug_*> APIs. We
389 don't document Augeas itself here because there is excellent
390 documentation on the L<http://augeas.net/> website.
392 If you don't want to use Augeas (you fool!) then try calling
393 L</guestfs_read_lines> to get the file as a list of lines which
394 you can iterate over.
398 We support SELinux guests. To ensure that labeling happens correctly
399 in SELinux guests, you need to enable SELinux and load the guest's
406 Before launching, do:
408 guestfs_set_selinux (g, 1);
412 After mounting the guest's filesystem(s), load the policy. This
413 is best done by running the L<load_policy(8)> command in the
416 guestfs_sh (g, "/usr/sbin/load_policy");
418 (Older versions of C<load_policy> require you to specify the
419 name of the policy file).
423 Optionally, set the security context for the API. The correct
424 security context to use can only be known by inspecting the
425 guest. As an example:
427 guestfs_setcon (g, "unconfined_u:unconfined_r:unconfined_t:s0");
431 This will work for running commands and editing existing files.
433 When new files are created, you may need to label them explicitly,
434 for example by running the external command
435 C<restorecon pathname>.
439 Certain calls are affected by the current file mode creation mask (the
440 "umask"). In particular ones which create files or directories, such
441 as L</guestfs_touch>, L</guestfs_mknod> or L</guestfs_mkdir>. This
442 affects either the default mode that the file is created with or
443 modifies the mode that you supply.
445 The default umask is C<022>, so files are created with modes such as
446 C<0644> and directories with C<0755>.
448 There are two ways to avoid being affected by umask. Either set umask
449 to 0 (call C<guestfs_umask (g, 0)> early after launching). Or call
450 L</guestfs_chmod> after creating each file or directory.
452 For more information about umask, see L<umask(2)>.
454 =head2 ENCRYPTED DISKS
456 Libguestfs allows you to access Linux guests which have been
457 encrypted using whole disk encryption that conforms to the
458 Linux Unified Key Setup (LUKS) standard. This includes
459 nearly all whole disk encryption systems used by modern
462 Use L</guestfs_vfs_type> to identify LUKS-encrypted block
463 devices (it returns the string C<crypto_LUKS>).
465 Then open these devices by calling L</guestfs_luks_open>.
466 Obviously you will require the passphrase!
468 Opening a LUKS device creates a new device mapper device
469 called C</dev/mapper/mapname> (where C<mapname> is the
470 string you supply to L</guestfs_luks_open>).
471 Reads and writes to this mapper device are decrypted from and
472 encrypted to the underlying block device respectively.
474 LVM volume groups on the device can be made visible by calling
475 L</guestfs_vgscan> followed by L</guestfs_vg_activate_all>.
476 The logical volume(s) can now be mounted in the usual way.
478 Use the reverse process to close a LUKS device. Unmount
479 any logical volumes on it, deactivate the volume groups
480 by caling C<guestfs_vg_activate (g, 0, ["/dev/VG"])>.
481 Then close the mapper device by calling
482 L</guestfs_luks_close> on the C</dev/mapper/mapname>
483 device (I<not> the underlying encrypted block device).
487 Libguestfs has APIs for inspecting an unknown disk image to find out
488 if it contains operating systems. (These APIs used to be in a
489 separate Perl-only library called L<Sys::Guestfs::Lib(3)> but since
490 version 1.5.3 the most frequently used part of this library has been
491 rewritten in C and moved into the core code).
493 Add all disks belonging to the unknown virtual machine and call
494 L</guestfs_launch> in the usual way.
496 Then call L</guestfs_inspect_os>. This function uses other libguestfs
497 calls and certain heuristics, and returns a list of operating systems
498 that were found. An empty list means none were found. A single
499 element is the root filesystem of the operating system. For dual- or
500 multi-boot guests, multiple roots can be returned, each one
501 corresponding to a separate operating system. (Multi-boot virtual
502 machines are extremely rare in the world of virtualization, but since
503 this scenario can happen, we have built libguestfs to deal with it.)
505 For each root, you can then call various C<guestfs_inspect_get_*>
506 functions to get additional details about that operating system. For
507 example, call L</guestfs_inspect_get_type> to return the string
508 C<windows> or C<linux> for Windows and Linux-based operating systems
511 Un*x-like and Linux-based operating systems usually consist of several
512 filesystems which are mounted at boot time (for example, a separate
513 boot partition mounted on C</boot>). The inspection rules are able to
514 detect how filesystems correspond to mount points. Call
515 C<guestfs_inspect_get_mountpoints> to get this mapping. It might
516 return a hash table like this example:
519 / => /dev/vg_guest/lv_root
520 /usr => /dev/vg_guest/lv_usr
522 The caller can then make calls to L</guestfs_mount_options> to
523 mount the filesystems as suggested.
525 Be careful to mount filesystems in the right order (eg. C</> before
526 C</usr>). Sorting the keys of the hash by length, shortest first,
529 Inspection currently only works for some common operating systems.
530 Contributors are welcome to send patches for other operating systems
531 that we currently cannot detect.
533 Encrypted disks must be opened before inspection. See
534 L</ENCRYPTED DISKS> for more details. The L</guestfs_inspect_os>
535 function just ignores any encrypted devices.
537 A note on the implementation: The call L</guestfs_inspect_os> performs
538 inspection and caches the results in the guest handle. Subsequent
539 calls to C<guestfs_inspect_get_*> return this cached information, but
540 I<do not> re-read the disks. If you change the content of the guest
541 disks, you can redo inspection by calling L</guestfs_inspect_os>
544 =head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
546 Libguestfs can mount NTFS partitions. It does this using the
547 L<http://www.ntfs-3g.org/> driver.
549 DOS and Windows still use drive letters, and the filesystems are
550 always treated as case insensitive by Windows itself, and therefore
551 you might find a Windows configuration file referring to a path like
552 C<c:\windows\system32>. When the filesystem is mounted in libguestfs,
553 that directory might be referred to as C</WINDOWS/System32>.
555 Drive letter mappings are outside the scope of libguestfs. You have
556 to use libguestfs to read the appropriate Windows Registry and
557 configuration files, to determine yourself how drives are mapped (see
558 also L<hivex(3)> and L<virt-inspector(1)>).
560 Replacing backslash characters with forward slash characters is also
561 outside the scope of libguestfs, but something that you can easily do.
563 Where we can help is in resolving the case insensitivity of paths.
564 For this, call L</guestfs_case_sensitive_path>.
566 Libguestfs also provides some help for decoding Windows Registry
567 "hive" files, through the library C<hivex> which is part of the
568 libguestfs project although ships as a separate tarball. You have to
569 locate and download the hive file(s) yourself, and then pass them to
570 C<hivex> functions. See also the programs L<hivexml(1)>,
571 L<hivexsh(1)>, L<hivexregedit(1)> and L<virt-win-reg(1)> for more help
574 =head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES
576 Although we don't want to discourage you from using the C API, we will
577 mention here that the same API is also available in other languages.
579 The API is broadly identical in all supported languages. This means
580 that the C call C<guestfs_mount(g,path)> is
581 C<$g-E<gt>mount($path)> in Perl, C<g.mount(path)> in Python,
582 and C<Guestfs.mount g path> in OCaml. In other words, a
583 straightforward, predictable isomorphism between each language.
585 Error messages are automatically transformed
586 into exceptions if the language supports it.
588 We don't try to "object orientify" parts of the API in OO languages,
589 although contributors are welcome to write higher level APIs above
590 what we provide in their favourite languages if they wish.
596 You can use the I<guestfs.h> header file from C++ programs. The C++
597 API is identical to the C API. C++ classes and exceptions are not
602 The C# bindings are highly experimental. Please read the warnings
603 at the top of C<csharp/Libguestfs.cs>.
607 This is the only language binding that is working but incomplete.
608 Only calls which return simple integers have been bound in Haskell,
609 and we are looking for help to complete this binding.
613 Full documentation is contained in the Javadoc which is distributed
618 For documentation see the file C<guestfs.mli>.
622 For documentation see L<Sys::Guestfs(3)>.
626 For documentation do:
634 Use the Guestfs module. There is no Ruby-specific documentation, but
635 you can find examples written in Ruby in the libguestfs source.
637 =item B<shell scripts>
639 For documentation see L<guestfish(1)>.
643 =head2 LIBGUESTFS GOTCHAS
645 L<http://en.wikipedia.org/wiki/Gotcha_(programming)>: "A feature of a
646 system [...] that works in the way it is documented but is
647 counterintuitive and almost invites mistakes."
649 Since we developed libguestfs and the associated tools, there are
650 several things we would have designed differently, but are now stuck
651 with for backwards compatibility or other reasons. If there is ever a
652 libguestfs 2.0 release, you can expect these to change. Beware of
657 =item Autosync / forgetting to sync.
659 When modifying a filesystem from C or another language, you B<must>
660 unmount all filesystems and call L</guestfs_sync> explicitly before
661 you close the libguestfs handle. You can also call:
663 guestfs_set_autosync (g, 1);
665 to have the unmount/sync done automatically for you when the handle 'g'
666 is closed. (This feature is called "autosync", L</guestfs_set_autosync>
669 If you forget to do this, then it is entirely possible that your
670 changes won't be written out, or will be partially written, or (very
671 rarely) that you'll get disk corruption.
673 Note that in L<guestfish(3)> autosync is the default. So quick and
674 dirty guestfish scripts that forget to sync will work just fine, which
675 can make this very puzzling if you are trying to debug a problem.
677 =item Mount option C<-o sync> should not be the default.
679 If you use L</guestfs_mount>, then C<-o sync,noatime> are added
680 implicitly. However C<-o sync> does not add any reliability benefit,
681 but does have a very large performance impact.
683 The work around is to use L</guestfs_mount_options> and set the mount
684 options that you actually want to use.
686 =item Read-only should be the default.
688 In L<guestfish(3)>, I<--ro> should be the default, and you should
689 have to specify I<--rw> if you want to make changes to the image.
691 This would reduce the potential to corrupt live VM images.
693 Note that many filesystems change the disk when you just mount and
694 unmount, even if you didn't perform any writes. You need to use
695 L</guestfs_add_drive_ro> to guarantee that the disk is not changed.
697 =item guestfish command line is hard to use.
699 C<guestfish disk.img> doesn't do what people expect (open C<disk.img>
700 for examination). It tries to run a guestfish command C<disk.img>
701 which doesn't exist, so it fails. In earlier versions of guestfish
702 the error message was also unintuitive, but we have corrected this
703 since. Like the Bourne shell, we should have used C<guestfish -c
704 command> to run commands.
706 =item guestfish megabyte modifiers don't work right on all commands
708 In recent guestfish you can use C<1M> to mean 1 megabyte (and
709 similarly for other modifiers). What guestfish actually does is to
710 multiply the number part by the modifier part and pass the result to
711 the C API. However this doesn't work for a few APIs which aren't
712 expecting bytes, but are already expecting some other unit
715 The most common is L</guestfs_lvcreate>. The guestfish command:
719 does not do what you might expect. Instead because
720 L</guestfs_lvcreate> is already expecting megabytes, this tries to
721 create a 100 I<terabyte> (100 megabytes * megabytes) logical volume.
722 The error message you get from this is also a little obscure.
724 This could be fixed in the generator by specially marking parameters
725 and return values which take bytes or other units.
727 =item Protocol limit of 256 characters for error messages
729 This limit is both rather small and quite unnecessary. We should be
730 able to return error messages up to the length of the protocol message
733 Note that we cannot change the protocol without some breakage, because
734 there are distributions that repackage the Fedora appliance.
736 =item Protocol should return errno with error messages.
738 It would be a nice-to-have to be able to get the original value of
739 'errno' from inside the appliance along error paths (where set).
740 Currently L<guestmount(1)> goes through hoops to try to reverse the
741 error message string into an errno, see the function error() in
746 =head2 PROTOCOL LIMITS
748 Internally libguestfs uses a message-based protocol to pass API calls
749 and their responses to and from a small "appliance" (see L</INTERNALS>
750 for plenty more detail about this). The maximum message size used by
751 the protocol is slightly less than 4 MB. For some API calls you may
752 need to be aware of this limit. The API calls which may be affected
753 are individually documented, with a link back to this section of the
756 A simple call such as L</guestfs_cat> returns its result (the file
757 data) in a simple string. Because this string is at some point
758 internally encoded as a message, the maximum size that it can return
759 is slightly under 4 MB. If the requested file is larger than this
760 then you will get an error.
762 In order to transfer large files into and out of the guest filesystem,
763 you need to use particular calls that support this. The sections
764 L</UPLOADING> and L</DOWNLOADING> document how to do this.
766 You might also consider mounting the disk image using our FUSE
767 filesystem support (L<guestmount(1)>).
769 =head2 KEYS AND PASSPHRASES
771 Certain libguestfs calls take a parameter that contains sensitive key
772 material, passed in as a C string.
774 In the future we would hope to change the libguestfs implementation so
775 that keys are L<mlock(2)>-ed into physical RAM, and thus can never end
776 up in swap. However this is I<not> done at the moment, because of the
777 complexity of such an implementation.
779 Therefore you should be aware that any key parameter you pass to
780 libguestfs might end up being written out to the swap partition. If
781 this is a concern, scrub the swap partition or don't use libguestfs on
784 =head1 CONNECTION MANAGEMENT
788 C<guestfs_h> is the opaque type representing a connection handle.
789 Create a handle by calling L</guestfs_create>. Call L</guestfs_close>
790 to free the handle and release all resources used.
792 For information on using multiple handles and threads, see the section
793 L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
795 =head2 guestfs_create
797 guestfs_h *guestfs_create (void);
799 Create a connection handle.
801 You have to call L</guestfs_add_drive> on the handle at least once.
803 This function returns a non-NULL pointer to a handle on success or
806 After configuring the handle, you have to call L</guestfs_launch>.
808 You may also want to configure error handling for the handle. See
809 L</ERROR HANDLING> section below.
813 void guestfs_close (guestfs_h *g);
815 This closes the connection handle and frees up all resources used.
817 =head1 ERROR HANDLING
819 The convention in all functions that return C<int> is that they return
820 C<-1> to indicate an error. You can get additional information on
821 errors by calling L</guestfs_last_error> and/or by setting up an error
822 handler with L</guestfs_set_error_handler>.
824 The default error handler prints the information string to C<stderr>.
826 Out of memory errors are handled differently. The default action is
827 to call L<abort(3)>. If this is undesirable, then you can set a
828 handler using L</guestfs_set_out_of_memory_handler>.
830 =head2 guestfs_last_error
832 const char *guestfs_last_error (guestfs_h *g);
834 This returns the last error message that happened on C<g>. If
835 there has not been an error since the handle was created, then this
838 The lifetime of the returned string is until the next error occurs, or
839 L</guestfs_close> is called.
841 The error string is not localized (ie. is always in English), because
842 this makes searching for error messages in search engines give the
843 largest number of results.
845 =head2 guestfs_set_error_handler
847 typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
850 void guestfs_set_error_handler (guestfs_h *g,
851 guestfs_error_handler_cb cb,
854 The callback C<cb> will be called if there is an error. The
855 parameters passed to the callback are an opaque data pointer and the
856 error message string.
858 Note that the message string C<msg> is freed as soon as the callback
859 function returns, so if you want to stash it somewhere you must make
862 The default handler prints messages on C<stderr>.
864 If you set C<cb> to C<NULL> then I<no> handler is called.
866 =head2 guestfs_get_error_handler
868 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
871 Returns the current error handler callback.
873 =head2 guestfs_set_out_of_memory_handler
875 typedef void (*guestfs_abort_cb) (void);
876 int guestfs_set_out_of_memory_handler (guestfs_h *g,
879 The callback C<cb> will be called if there is an out of memory
880 situation. I<Note this callback must not return>.
882 The default is to call L<abort(3)>.
884 You cannot set C<cb> to C<NULL>. You can't ignore out of memory
887 =head2 guestfs_get_out_of_memory_handler
889 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *g);
891 This returns the current out of memory handler.
895 Libguestfs needs a kernel and initrd.img, which it finds by looking
896 along an internal path.
898 By default it looks for these in the directory C<$libdir/guestfs>
899 (eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
901 Use L</guestfs_set_path> or set the environment variable
902 L</LIBGUESTFS_PATH> to change the directories that libguestfs will
903 search in. The value is a colon-separated list of paths. The current
904 directory is I<not> searched unless the path contains an empty element
905 or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
906 search the current directory and then C</usr/lib/guestfs>.
908 =head1 HIGH-LEVEL API ACTIONS
912 We guarantee the libguestfs ABI (binary interface), for public,
913 high-level actions as outlined in this section. Although we will
914 deprecate some actions, for example if they get replaced by newer
915 calls, we will keep the old actions forever. This allows you the
916 developer to program in confidence against the libguestfs API.
926 =head2 GROUPS OF FUNCTIONALITY IN THE APPLIANCE
928 Using L</guestfs_available> you can test availability of
929 the following groups of functions. This test queries the
930 appliance to see if the appliance you are currently using
931 supports the functionality.
935 =head2 GUESTFISH supported COMMAND
937 In L<guestfish(3)> there is a handy interactive command
938 C<supported> which prints out the available groups and
939 whether they are supported by this build of libguestfs.
940 Note however that you have to do C<run> first.
942 =head2 SINGLE CALLS AT COMPILE TIME
944 If you need to test whether a single libguestfs function is
945 available at compile time, we recommend using build tools
946 such as autoconf or cmake. For example in autotools you could
949 AC_CHECK_LIB([guestfs],[guestfs_create])
950 AC_CHECK_FUNCS([guestfs_dd])
952 which would result in C<HAVE_GUESTFS_DD> being either defined
953 or not defined in your program.
955 =head2 SINGLE CALLS AT RUN TIME
957 Testing at compile time doesn't guarantee that a function really
958 exists in the library. The reason is that you might be dynamically
959 linked against a previous I<libguestfs.so> (dynamic library)
960 which doesn't have the call. This situation unfortunately results
961 in a segmentation fault, which is a shortcoming of the C dynamic
962 linking system itself.
964 You can use L<dlopen(3)> to test if a function is available
965 at run time, as in this example program (note that you still
966 need the compile time check as well):
978 #ifdef HAVE_GUESTFS_DD
982 /* Test if the function guestfs_dd is really available. */
983 dl = dlopen (NULL, RTLD_LAZY);
985 fprintf (stderr, "dlopen: %s\n", dlerror ());
988 has_function = dlsym (dl, "guestfs_dd") != NULL;
992 printf ("this libguestfs.so does NOT have guestfs_dd function\n");
994 printf ("this libguestfs.so has guestfs_dd function\n");
995 /* Now it's safe to call
996 guestfs_dd (g, "foo", "bar");
1000 printf ("guestfs_dd function was not found at compile time\n");
1004 You may think the above is an awful lot of hassle, and it is.
1005 There are other ways outside of the C linking system to ensure
1006 that this kind of incompatibility never arises, such as using
1009 Requires: libguestfs >= 1.0.80
1013 <!-- old anchor for the next section -->
1014 <a name="state_machine_and_low_level_event_api"/>
1020 Internally, libguestfs is implemented by running an appliance (a
1021 special type of small virtual machine) using L<qemu(1)>. Qemu runs as
1022 a child process of the main program.
1028 | | child process / appliance
1029 | | __________________________
1031 +-------------------+ RPC | +-----------------+ |
1032 | libguestfs <--------------------> guestfsd | |
1033 | | | +-----------------+ |
1034 \___________________/ | | Linux kernel | |
1035 | +--^--------------+ |
1036 \_________|________________/
1044 The library, linked to the main program, creates the child process and
1045 hence the appliance in the L</guestfs_launch> function.
1047 Inside the appliance is a Linux kernel and a complete stack of
1048 userspace tools (such as LVM and ext2 programs) and a small
1049 controlling daemon called L</guestfsd>. The library talks to
1050 L</guestfsd> using remote procedure calls (RPC). There is a mostly
1051 one-to-one correspondence between libguestfs API calls and RPC calls
1052 to the daemon. Lastly the disk image(s) are attached to the qemu
1053 process which translates device access by the appliance's Linux kernel
1054 into accesses to the image.
1056 A common misunderstanding is that the appliance "is" the virtual
1057 machine. Although the disk image you are attached to might also be
1058 used by some virtual machine, libguestfs doesn't know or care about
1059 this. (But you will care if both libguestfs's qemu process and your
1060 virtual machine are trying to update the disk image at the same time,
1061 since these usually results in massive disk corruption).
1063 =head1 STATE MACHINE
1065 libguestfs uses a state machine to model the child process:
1076 / | \ \ guestfs_launch
1087 \______/ <------ \________/
1089 The normal transitions are (1) CONFIG (when the handle is created, but
1090 there is no child process), (2) LAUNCHING (when the child process is
1091 booting up), (3) alternating between READY and BUSY as commands are
1092 issued to, and carried out by, the child process.
1094 The guest may be killed by L</guestfs_kill_subprocess>, or may die
1095 asynchronously at any time (eg. due to some internal error), and that
1096 causes the state to transition back to CONFIG.
1098 Configuration commands for qemu such as L</guestfs_add_drive> can only
1099 be issued when in the CONFIG state.
1101 The high-level API offers two calls that go from CONFIG through
1102 LAUNCHING to READY. L</guestfs_launch> blocks until the child process
1103 is READY to accept commands (or until some failure or timeout).
1104 L</guestfs_launch> internally moves the state from CONFIG to LAUNCHING
1105 while it is running.
1107 High-level API actions such as L</guestfs_mount> can only be issued
1108 when in the READY state. These high-level API calls block waiting for
1109 the command to be carried out (ie. the state to transition to BUSY and
1110 then back to READY). But using the low-level event API, you get
1111 non-blocking versions. (But you can still only carry out one
1112 operation per handle at a time - that is a limitation of the
1113 communications protocol we use).
1115 Finally, the child process sends asynchronous messages back to the
1116 main program, such as kernel log messages. Mostly these are ignored
1117 by the high-level API, but using the low-level event API you can
1118 register to receive these messages.
1120 =head2 SETTING CALLBACKS TO HANDLE EVENTS
1122 The child process generates events in some situations. Current events
1123 include: receiving a log message, the child process exits.
1125 Use the C<guestfs_set_*_callback> functions to set a callback for
1126 different types of events.
1128 Only I<one callback of each type> can be registered for each handle.
1129 Calling C<guestfs_set_*_callback> again overwrites the previous
1130 callback of that type. Cancel all callbacks of this type by calling
1131 this function with C<cb> set to C<NULL>.
1133 =head2 guestfs_set_log_message_callback
1135 typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
1136 char *buf, int len);
1137 void guestfs_set_log_message_callback (guestfs_h *g,
1138 guestfs_log_message_cb cb,
1141 The callback function C<cb> will be called whenever qemu or the guest
1142 writes anything to the console.
1144 Use this function to capture kernel messages and similar.
1146 Normally there is no log message handler, and log messages are just
1149 =head2 guestfs_set_subprocess_quit_callback
1151 typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
1152 void guestfs_set_subprocess_quit_callback (guestfs_h *g,
1153 guestfs_subprocess_quit_cb cb,
1156 The callback function C<cb> will be called when the child process
1157 quits, either asynchronously or if killed by
1158 L</guestfs_kill_subprocess>. (This corresponds to a transition from
1159 any state to the CONFIG state).
1161 =head2 guestfs_set_launch_done_callback
1163 typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
1164 void guestfs_set_launch_done_callback (guestfs_h *g,
1165 guestfs_launch_done_cb cb,
1168 The callback function C<cb> will be called when the child process
1169 becomes ready first time after it has been launched. (This
1170 corresponds to a transition from LAUNCHING to the READY state).
1172 =head2 guestfs_set_close_callback
1174 typedef void (*guestfs_close_cb) (guestfs_h *g, void *opaque);
1175 void guestfs_set_close_callback (guestfs_h *g,
1176 guestfs_close_cb cb,
1179 The callback function C<cb> will be called while the handle
1180 is being closed (synchronously from L</guestfs_close>).
1182 Note that libguestfs installs an L<atexit(3)> handler to try to
1183 clean up handles that are open when the program exits. This
1184 means that this callback might be called indirectly from
1185 L<exit(3)>, which can cause unexpected problems in higher-level
1186 languages (eg. if your HLL interpreter has already been cleaned
1187 up by the time this is called, and if your callback then jumps
1188 into some HLL function).
1190 =head1 BLOCK DEVICE NAMING
1192 In the kernel there is now quite a profusion of schemata for naming
1193 block devices (in this context, by I<block device> I mean a physical
1194 or virtual hard drive). The original Linux IDE driver used names
1195 starting with C</dev/hd*>. SCSI devices have historically used a
1196 different naming scheme, C</dev/sd*>. When the Linux kernel I<libata>
1197 driver became a popular replacement for the old IDE driver
1198 (particularly for SATA devices) those devices also used the
1199 C</dev/sd*> scheme. Additionally we now have virtual machines with
1200 paravirtualized drivers. This has created several different naming
1201 systems, such as C</dev/vd*> for virtio disks and C</dev/xvd*> for Xen
1204 As discussed above, libguestfs uses a qemu appliance running an
1205 embedded Linux kernel to access block devices. We can run a variety
1206 of appliances based on a variety of Linux kernels.
1208 This causes a problem for libguestfs because many API calls use device
1209 or partition names. Working scripts and the recipe (example) scripts
1210 that we make available over the internet could fail if the naming
1213 Therefore libguestfs defines C</dev/sd*> as the I<standard naming
1214 scheme>. Internally C</dev/sd*> names are translated, if necessary,
1215 to other names as required. For example, under RHEL 5 which uses the
1216 C</dev/hd*> scheme, any device parameter C</dev/sda2> is translated to
1217 C</dev/hda2> transparently.
1219 Note that this I<only> applies to parameters. The
1220 L</guestfs_list_devices>, L</guestfs_list_partitions> and similar calls
1221 return the true names of the devices and partitions as known to the
1224 =head2 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
1226 Usually this translation is transparent. However in some (very rare)
1227 cases you may need to know the exact algorithm. Such cases include
1228 where you use L</guestfs_config> to add a mixture of virtio and IDE
1229 devices to the qemu-based appliance, so have a mixture of C</dev/sd*>
1230 and C</dev/vd*> devices.
1232 The algorithm is applied only to I<parameters> which are known to be
1233 either device or partition names. Return values from functions such
1234 as L</guestfs_list_devices> are never changed.
1240 Is the string a parameter which is a device or partition name?
1244 Does the string begin with C</dev/sd>?
1248 Does the named device exist? If so, we use that device.
1249 However if I<not> then we continue with this algorithm.
1253 Replace initial C</dev/sd> string with C</dev/hd>.
1255 For example, change C</dev/sda2> to C</dev/hda2>.
1257 If that named device exists, use it. If not, continue.
1261 Replace initial C</dev/sd> string with C</dev/vd>.
1263 If that named device exists, use it. If not, return an error.
1267 =head2 PORTABILITY CONCERNS
1269 Although the standard naming scheme and automatic translation is
1270 useful for simple programs and guestfish scripts, for larger programs
1271 it is best not to rely on this mechanism.
1273 Where possible for maximum future portability programs using
1274 libguestfs should use these future-proof techniques:
1280 Use L</guestfs_list_devices> or L</guestfs_list_partitions> to list
1281 actual device names, and then use those names directly.
1283 Since those device names exist by definition, they will never be
1288 Use higher level ways to identify filesystems, such as LVM names,
1289 UUIDs and filesystem labels.
1295 =head2 COMMUNICATION PROTOCOL
1297 Don't rely on using this protocol directly. This section documents
1298 how it currently works, but it may change at any time.
1300 The protocol used to talk between the library and the daemon running
1301 inside the qemu virtual machine is a simple RPC mechanism built on top
1302 of XDR (RFC 1014, RFC 1832, RFC 4506).
1304 The detailed format of structures is in C<src/guestfs_protocol.x>
1305 (note: this file is automatically generated).
1307 There are two broad cases, ordinary functions that don't have any
1308 C<FileIn> and C<FileOut> parameters, which are handled with very
1309 simple request/reply messages. Then there are functions that have any
1310 C<FileIn> or C<FileOut> parameters, which use the same request and
1311 reply messages, but they may also be followed by files sent using a
1314 =head3 ORDINARY FUNCTIONS (NO FILEIN/FILEOUT PARAMS)
1316 For ordinary functions, the request message is:
1318 total length (header + arguments,
1319 but not including the length word itself)
1320 struct guestfs_message_header (encoded as XDR)
1321 struct guestfs_<foo>_args (encoded as XDR)
1323 The total length field allows the daemon to allocate a fixed size
1324 buffer into which it slurps the rest of the message. As a result, the
1325 total length is limited to C<GUESTFS_MESSAGE_MAX> bytes (currently
1326 4MB), which means the effective size of any request is limited to
1327 somewhere under this size.
1329 Note also that many functions don't take any arguments, in which case
1330 the C<guestfs_I<foo>_args> is completely omitted.
1332 The header contains the procedure number (C<guestfs_proc>) which is
1333 how the receiver knows what type of args structure to expect, or none
1336 The reply message for ordinary functions is:
1338 total length (header + ret,
1339 but not including the length word itself)
1340 struct guestfs_message_header (encoded as XDR)
1341 struct guestfs_<foo>_ret (encoded as XDR)
1343 As above the C<guestfs_I<foo>_ret> structure may be completely omitted
1344 for functions that return no formal return values.
1346 As above the total length of the reply is limited to
1347 C<GUESTFS_MESSAGE_MAX>.
1349 In the case of an error, a flag is set in the header, and the reply
1350 message is slightly changed:
1352 total length (header + error,
1353 but not including the length word itself)
1354 struct guestfs_message_header (encoded as XDR)
1355 struct guestfs_message_error (encoded as XDR)
1357 The C<guestfs_message_error> structure contains the error message as a
1360 =head3 FUNCTIONS THAT HAVE FILEIN PARAMETERS
1362 A C<FileIn> parameter indicates that we transfer a file I<into> the
1363 guest. The normal request message is sent (see above). However this
1364 is followed by a sequence of file chunks.
1366 total length (header + arguments,
1367 but not including the length word itself,
1368 and not including the chunks)
1369 struct guestfs_message_header (encoded as XDR)
1370 struct guestfs_<foo>_args (encoded as XDR)
1371 sequence of chunks for FileIn param #0
1372 sequence of chunks for FileIn param #1 etc.
1374 The "sequence of chunks" is:
1376 length of chunk (not including length word itself)
1377 struct guestfs_chunk (encoded as XDR)
1379 struct guestfs_chunk (encoded as XDR)
1382 struct guestfs_chunk (with data.data_len == 0)
1384 The final chunk has the C<data_len> field set to zero. Additionally a
1385 flag is set in the final chunk to indicate either successful
1386 completion or early cancellation.
1388 At time of writing there are no functions that have more than one
1389 FileIn parameter. However this is (theoretically) supported, by
1390 sending the sequence of chunks for each FileIn parameter one after
1391 another (from left to right).
1393 Both the library (sender) I<and> the daemon (receiver) may cancel the
1394 transfer. The library does this by sending a chunk with a special
1395 flag set to indicate cancellation. When the daemon sees this, it
1396 cancels the whole RPC, does I<not> send any reply, and goes back to
1397 reading the next request.
1399 The daemon may also cancel. It does this by writing a special word
1400 C<GUESTFS_CANCEL_FLAG> to the socket. The library listens for this
1401 during the transfer, and if it gets it, it will cancel the transfer
1402 (it sends a cancel chunk). The special word is chosen so that even if
1403 cancellation happens right at the end of the transfer (after the
1404 library has finished writing and has started listening for the reply),
1405 the "spurious" cancel flag will not be confused with the reply
1408 This protocol allows the transfer of arbitrary sized files (no 32 bit
1409 limit), and also files where the size is not known in advance
1410 (eg. from pipes or sockets). However the chunks are rather small
1411 (C<GUESTFS_MAX_CHUNK_SIZE>), so that neither the library nor the
1412 daemon need to keep much in memory.
1414 =head3 FUNCTIONS THAT HAVE FILEOUT PARAMETERS
1416 The protocol for FileOut parameters is exactly the same as for FileIn
1417 parameters, but with the roles of daemon and library reversed.
1419 total length (header + ret,
1420 but not including the length word itself,
1421 and not including the chunks)
1422 struct guestfs_message_header (encoded as XDR)
1423 struct guestfs_<foo>_ret (encoded as XDR)
1424 sequence of chunks for FileOut param #0
1425 sequence of chunks for FileOut param #1 etc.
1427 =head3 INITIAL MESSAGE
1429 Because the underlying channel (QEmu -net channel) doesn't have any
1430 sort of connection control, when the daemon launches it sends an
1431 initial word (C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest
1432 and daemon is alive. This is what L</guestfs_launch> waits for.
1434 =head1 MULTIPLE HANDLES AND MULTIPLE THREADS
1436 All high-level libguestfs actions are synchronous. If you want
1437 to use libguestfs asynchronously then you must create a thread.
1439 Only use the handle from a single thread. Either use the handle
1440 exclusively from one thread, or provide your own mutex so that two
1441 threads cannot issue calls on the same handle at the same time.
1443 =head1 QEMU WRAPPERS
1445 If you want to compile your own qemu, run qemu from a non-standard
1446 location, or pass extra arguments to qemu, then you can write a
1447 shell-script wrapper around qemu.
1449 There is one important rule to remember: you I<must C<exec qemu>> as
1450 the last command in the shell script (so that qemu replaces the shell
1451 and becomes the direct child of the libguestfs-using program). If you
1452 don't do this, then the qemu process won't be cleaned up correctly.
1454 Here is an example of a wrapper, where I have built my own copy of
1458 qemudir=/home/rjones/d/qemu
1459 exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
1461 Save this script as C</tmp/qemu.wrapper> (or wherever), C<chmod +x>,
1462 and then use it by setting the LIBGUESTFS_QEMU environment variable.
1465 LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
1467 Note that libguestfs also calls qemu with the -help and -version
1468 options in order to determine features.
1470 =head1 LIBGUESTFS VERSION NUMBERS
1472 Since April 2010, libguestfs has started to make separate development
1473 and stable releases, along with corresponding branches in our git
1474 repository. These separate releases can be identified by version
1477 even numbers for stable: 1.2.x, 1.4.x, ...
1478 .-------- odd numbers for development: 1.3.x, 1.5.x, ...
1484 | `-------- sub-version
1486 `------ always '1' because we don't change the ABI
1488 Thus "1.3.5" is the 5th update to the development branch "1.3".
1490 As time passes we cherry pick fixes from the development branch and
1491 backport those into the stable branch, the effect being that the
1492 stable branch should get more stable and less buggy over time. So the
1493 stable releases are ideal for people who don't need new features but
1494 would just like the software to work.
1496 Our criteria for backporting changes are:
1502 Documentation changes which don't affect any code are
1503 backported unless the documentation refers to a future feature
1504 which is not in stable.
1508 Bug fixes which are not controversial, fix obvious problems, and
1509 have been well tested are backported.
1513 Simple rearrangements of code which shouldn't affect how it works get
1514 backported. This is so that the code in the two branches doesn't get
1515 too far out of step, allowing us to backport future fixes more easily.
1519 We I<don't> backport new features, new APIs, new tools etc, except in
1520 one exceptional case: the new feature is required in order to
1521 implement an important bug fix.
1525 A new stable branch starts when we think the new features in
1526 development are substantial and compelling enough over the current
1527 stable branch to warrant it. When that happens we create new stable
1528 and development versions 1.N.0 and 1.(N+1).0 [N is even]. The new
1529 dot-oh release won't necessarily be so stable at this point, but by
1530 backporting fixes from development, that branch will stabilize over
1533 =head1 ENVIRONMENT VARIABLES
1537 =item LIBGUESTFS_APPEND
1539 Pass additional options to the guest kernel.
1541 =item LIBGUESTFS_DEBUG
1543 Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
1544 has the same effect as calling C<guestfs_set_verbose (g, 1)>.
1546 =item LIBGUESTFS_MEMSIZE
1548 Set the memory allocated to the qemu process, in megabytes. For
1551 LIBGUESTFS_MEMSIZE=700
1553 =item LIBGUESTFS_PATH
1555 Set the path that libguestfs uses to search for kernel and initrd.img.
1556 See the discussion of paths in section PATH above.
1558 =item LIBGUESTFS_QEMU
1560 Set the default qemu binary that libguestfs uses. If not set, then
1561 the qemu which was found at compile time by the configure script is
1564 See also L</QEMU WRAPPERS> above.
1566 =item LIBGUESTFS_TRACE
1568 Set C<LIBGUESTFS_TRACE=1> to enable command traces. This
1569 has the same effect as calling C<guestfs_set_trace (g, 1)>.
1573 Location of temporary directory, defaults to C</tmp>.
1575 If libguestfs was compiled to use the supermin appliance then each
1576 handle will require rather a large amount of space in this directory
1577 for short periods of time (~ 80 MB). You can use C<$TMPDIR> to
1578 configure another directory to use in case C</tmp> is not large
1590 L<virt-inspector(1)>,
1591 L<virt-list-filesystems(1)>,
1592 L<virt-list-partitions(1)>,
1601 L<http://libguestfs.org/>.
1603 Tools with a similar purpose:
1612 To get a list of bugs against libguestfs use this link:
1614 L<https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools>
1616 To report a new bug against libguestfs use this link:
1618 L<https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools>
1620 When reporting a bug, please check:
1626 That the bug hasn't been reported already.
1630 That you are testing a recent version.
1634 Describe the bug accurately, and give a way to reproduce it.
1638 Run libguestfs-test-tool and paste the B<complete, unedited>
1639 output into the bug report.
1645 Richard W.M. Jones (C<rjones at redhat dot com>)
1649 Copyright (C) 2009-2010 Red Hat Inc.
1650 L<http://libguestfs.org/>
1652 This library is free software; you can redistribute it and/or
1653 modify it under the terms of the GNU Lesser General Public
1654 License as published by the Free Software Foundation; either
1655 version 2 of the License, or (at your option) any later version.
1657 This library is distributed in the hope that it will be useful,
1658 but WITHOUT ANY WARRANTY; without even the implied warranty of
1659 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
1660 Lesser General Public License for more details.
1662 You should have received a copy of the GNU Lesser General Public
1663 License along with this library; if not, write to the Free Software
1664 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA