5 guestfs - Library for accessing and modifying virtual machine images
11 guestfs_h *g = guestfs_create ();
12 guestfs_add_drive (g, "guest.img");
14 guestfs_mount (g, "/dev/sda1", "/");
15 guestfs_touch (g, "/hello");
16 guestfs_umount (g, "/");
19 cc prog.c -o prog -lguestfs
21 cc prog.c -o prog `pkg-config libguestfs --cflags --libs`
25 Libguestfs is a library for accessing and modifying guest disk images.
26 Amongst the things this is good for: making batch configuration
27 changes to guests, getting disk used/free statistics (see also:
28 virt-df), migrating between virtualization systems (see also:
29 virt-p2v), performing partial backups, performing partial guest
30 clones, cloning guests and changing registry/UUID/hostname info, and
33 Libguestfs uses Linux kernel and qemu code, and can access any type of
34 guest filesystem that Linux and qemu can, including but not limited
35 to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
36 schemes, qcow, qcow2, vmdk.
38 Libguestfs provides ways to enumerate guest storage (eg. partitions,
39 LVs, what filesystem is in each LV, etc.). It can also run commands
40 in the context of the guest. Also you can access filesystems over
43 Libguestfs is a library that can be linked with C and C++ management
44 programs (or management programs written in OCaml, Perl, Python, Ruby,
45 Java, PHP, Haskell or C#). You can also use it from shell scripts or the
48 You don't need to be root to use libguestfs, although obviously you do
49 need enough permissions to access the disk images.
51 Libguestfs is a large API because it can do many things. For a gentle
52 introduction, please read the L</API OVERVIEW> section next.
54 There are also some example programs in the L<guestfs-examples(3)>
59 This section provides a gentler overview of the libguestfs API. We
60 also try to group API calls together, where that may not be obvious
61 from reading about the individual calls in the main section of this
66 Before you can use libguestfs calls, you have to create a handle.
67 Then you must add at least one disk image to the handle, followed by
68 launching the handle, then performing whatever operations you want,
69 and finally closing the handle. By convention we use the single
70 letter C<g> for the name of the handle variable, although of course
71 you can use any name you want.
73 The general structure of all libguestfs-using programs looks like
76 guestfs_h *g = guestfs_create ();
78 /* Call guestfs_add_drive additional times if there are
79 * multiple disk images.
81 guestfs_add_drive (g, "guest.img");
83 /* Most manipulation calls won't work until you've launched
84 * the handle 'g'. You have to do this _after_ adding drives
85 * and _before_ other commands.
89 /* Now you can examine what partitions, LVs etc are available.
91 char **partitions = guestfs_list_partitions (g);
92 char **logvols = guestfs_lvs (g);
94 /* To access a filesystem in the image, you must mount it.
96 guestfs_mount (g, "/dev/sda1", "/");
98 /* Now you can perform filesystem actions on the guest
101 guestfs_touch (g, "/hello");
103 /* This is only needed for libguestfs < 1.5.24. Since then
104 * it is done automatically when you close the handle. See
105 * discussion of autosync in this page.
109 /* Close the handle 'g'. */
112 The code above doesn't include any error checking. In real code you
113 should check return values carefully for errors. In general all
114 functions that return integers return C<-1> on error, and all
115 functions that return pointers return C<NULL> on error. See section
116 L</ERROR HANDLING> below for how to handle errors, and consult the
117 documentation for each function call below to see precisely how they
118 return error indications. See L<guestfs-examples(3)> for fully worked
123 The image filename (C<"guest.img"> in the example above) could be a
124 disk image from a virtual machine, a L<dd(1)> copy of a physical hard
125 disk, an actual block device, or simply an empty file of zeroes that
126 you have created through L<posix_fallocate(3)>. Libguestfs lets you
127 do useful things to all of these.
129 The call you should use in modern code for adding drives is
130 L</guestfs_add_drive_opts>. To add a disk image, allowing writes, and
131 specifying that the format is raw, do:
133 guestfs_add_drive_opts (g, filename,
134 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
137 You can add a disk read-only using:
139 guestfs_add_drive_opts (g, filename,
140 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
141 GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
144 or by calling the older function L</guestfs_add_drive_ro>. In either
145 case libguestfs won't modify the file.
147 Be extremely cautious if the disk image is in use, eg. if it is being
148 used by a virtual machine. Adding it read-write will almost certainly
149 cause disk corruption, but adding it read-only is safe.
151 You must add at least one disk image, and you may add multiple disk
152 images. In the API, the disk images are usually referred to as
153 C</dev/sda> (for the first one you added), C</dev/sdb> (for the second
156 Once L</guestfs_launch> has been called you cannot add any more images.
157 You can call L</guestfs_list_devices> to get a list of the device
158 names, in the order that you added them. See also L</BLOCK DEVICE
163 Before you can read or write files, create directories and so on in a
164 disk image that contains filesystems, you have to mount those
165 filesystems using L</guestfs_mount_options> or L</guestfs_mount_ro>.
166 If you already know that a disk image contains (for example) one
167 partition with a filesystem on that partition, then you can mount it
170 guestfs_mount_options (g, "", "/dev/sda1", "/");
172 where C</dev/sda1> means literally the first partition (C<1>) of the
173 first disk image that we added (C</dev/sda>). If the disk contains
174 Linux LVM2 logical volumes you could refer to those instead
175 (eg. C</dev/VG/LV>). Note that these are libguestfs virtual devices,
176 and are nothing to do with host devices.
178 If you are given a disk image and you don't know what it contains then
179 you have to find out. Libguestfs can do that too: use
180 L</guestfs_list_partitions> and L</guestfs_lvs> to list possible
181 partitions and LVs, and either try mounting each to see what is
182 mountable, or else examine them with L</guestfs_vfs_type> or
183 L</guestfs_file>. To list just filesystems, use
184 L</guestfs_list_filesystems>.
186 Libguestfs also has a set of APIs for inspection of unknown disk
187 images (see L</INSPECTION> below). But you might find it easier to
188 look at higher level programs built on top of libguestfs, in
189 particular L<virt-inspector(1)>.
191 To mount a filesystem read-only, use L</guestfs_mount_ro>. There are
192 several other variations of the C<guestfs_mount_*> call.
194 =head2 FILESYSTEM ACCESS AND MODIFICATION
196 The majority of the libguestfs API consists of fairly low-level calls
197 for accessing and modifying the files, directories, symlinks etc on
198 mounted filesystems. There are over a hundred such calls which you
199 can find listed in detail below in this man page, and we don't even
200 pretend to cover them all in this overview.
202 Specify filenames as full paths, starting with C<"/"> and including
205 For example, if you mounted a filesystem at C<"/"> and you want to
206 read the file called C<"etc/passwd"> then you could do:
208 char *data = guestfs_cat (g, "/etc/passwd");
210 This would return C<data> as a newly allocated buffer containing the
211 full content of that file (with some conditions: see also
212 L</DOWNLOADING> below), or C<NULL> if there was an error.
214 As another example, to create a top-level directory on that filesystem
215 called C<"var"> you would do:
217 guestfs_mkdir (g, "/var");
219 To create a symlink you could do:
221 guestfs_ln_s (g, "/etc/init.d/portmap",
222 "/etc/rc3.d/S30portmap");
224 Libguestfs will reject attempts to use relative paths and there is no
225 concept of a current working directory.
227 Libguestfs can return errors in many situations: for example if the
228 filesystem isn't writable, or if a file or directory that you
229 requested doesn't exist. If you are using the C API (documented here)
230 you have to check for those error conditions after each call. (Other
231 language bindings turn these errors into exceptions).
233 File writes are affected by the per-handle umask, set by calling
234 L</guestfs_umask> and defaulting to 022. See L</UMASK>.
238 Libguestfs contains API calls to read, create and modify partition
239 tables on disk images.
241 In the common case where you want to create a single partition
242 covering the whole disk, you should use the L</guestfs_part_disk>
245 const char *parttype = "mbr";
246 if (disk_is_larger_than_2TB)
248 guestfs_part_disk (g, "/dev/sda", parttype);
250 Obviously this effectively wipes anything that was on that disk image
255 Libguestfs provides access to a large part of the LVM2 API, such as
256 L</guestfs_lvcreate> and L</guestfs_vgremove>. It won't make much sense
257 unless you familiarize yourself with the concepts of physical volumes,
258 volume groups and logical volumes.
260 This author strongly recommends reading the LVM HOWTO, online at
261 L<http://tldp.org/HOWTO/LVM-HOWTO/>.
265 Use L</guestfs_cat> to download small, text only files. This call is
266 limited to files which are less than 2 MB and which cannot contain any
267 ASCII NUL (C<\0>) characters. However the API is very simple to use.
269 L</guestfs_read_file> can be used to read files which contain
270 arbitrary 8 bit data, since it returns a (pointer, size) pair.
271 However it is still limited to "small" files, less than 2 MB.
273 L</guestfs_download> can be used to download any file, with no
274 limits on content or size (even files larger than 4 GB).
276 To download multiple files, see L</guestfs_tar_out> and
281 It's often the case that you want to write a file or files to the disk
284 To write a small file with fixed content, use L</guestfs_write>. To
285 create a file of all zeroes, use L</guestfs_truncate_size> (sparse) or
286 L</guestfs_fallocate64> (with all disk blocks allocated). There are a
287 variety of other functions for creating test files, for example
288 L</guestfs_fill> and L</guestfs_fill_pattern>.
290 To upload a single file, use L</guestfs_upload>. This call has no
291 limits on file content or size (even files larger than 4 GB).
293 To upload multiple files, see L</guestfs_tar_in> and L</guestfs_tgz_in>.
295 However the fastest way to upload I<large numbers of arbitrary files>
296 is to turn them into a squashfs or CD ISO (see L<mksquashfs(8)> and
297 L<mkisofs(8)>), then attach this using L</guestfs_add_drive_ro>. If
298 you add the drive in a predictable way (eg. adding it last after all
299 other drives) then you can get the device name from
300 L</guestfs_list_devices> and mount it directly using
301 L</guestfs_mount_ro>. Note that squashfs images are sometimes
302 non-portable between kernel versions, and they don't support labels or
303 UUIDs. If you want to pre-build an image or you need to mount it
304 using a label or UUID, use an ISO image instead.
308 There are various different commands for copying between files and
309 devices and in and out of the guest filesystem. These are summarised
314 =item B<file> to B<file>
316 Use L</guestfs_cp> to copy a single file, or
317 L</guestfs_cp_a> to copy directories recursively.
319 =item B<file or device> to B<file or device>
321 Use L</guestfs_dd> which efficiently uses L<dd(1)>
322 to copy between files and devices in the guest.
324 Example: duplicate the contents of an LV:
326 guestfs_dd (g, "/dev/VG/Original", "/dev/VG/Copy");
328 The destination (C</dev/VG/Copy>) must be at least as large as the
329 source (C</dev/VG/Original>). To copy less than the whole
330 source device, use L</guestfs_copy_size>.
332 =item B<file on the host> to B<file or device>
334 Use L</guestfs_upload>. See L</UPLOADING> above.
336 =item B<file or device> to B<file on the host>
338 Use L</guestfs_download>. See L</DOWNLOADING> above.
342 =head2 UPLOADING AND DOWNLOADING TO PIPES AND FILE DESCRIPTORS
344 Calls like L</guestfs_upload>, L</guestfs_download>,
345 L</guestfs_tar_in>, L</guestfs_tar_out> etc appear to only take
346 filenames as arguments, so it appears you can only upload and download
347 to files. However many Un*x-like hosts let you use the special device
348 files C</dev/stdin>, C</dev/stdout>, C</dev/stderr> and C</dev/fd/N>
349 to read and write from stdin, stdout, stderr, and arbitrary file
352 For example, L<virt-cat(1)> writes its output to stdout by
355 guestfs_download (g, filename, "/dev/stdout");
357 and you can write tar output to a pipe C<fd> by doing:
360 snprintf (devfd, sizeof devfd, "/dev/fd/%d", fd);
361 guestfs_tar_out (g, "/", devfd);
365 L</guestfs_ll> is just designed for humans to read (mainly when using
366 the L<guestfish(1)>-equivalent command C<ll>).
368 L</guestfs_ls> is a quick way to get a list of files in a directory
369 from programs, as a flat list of strings.
371 L</guestfs_readdir> is a programmatic way to get a list of files in a
372 directory, plus additional information about each one. It is more
373 equivalent to using the L<readdir(3)> call on a local filesystem.
375 L</guestfs_find> and L</guestfs_find0> can be used to recursively list
378 =head2 RUNNING COMMANDS
380 Although libguestfs is primarily an API for manipulating files
381 inside guest images, we also provide some limited facilities for
382 running commands inside guests.
384 There are many limitations to this:
390 The kernel version that the command runs under will be different
391 from what it expects.
395 If the command needs to communicate with daemons, then most likely
396 they won't be running.
400 The command will be running in limited memory.
404 The network may not be available unless you enable it
405 (see L</guestfs_set_network>).
409 Only supports Linux guests (not Windows, BSD, etc).
413 Architecture limitations (eg. won't work for a PPC guest on
418 For SELinux guests, you may need to enable SELinux and load policy
419 first. See L</SELINUX> in this manpage.
423 I<Security:> It is not safe to run commands from untrusted, possibly
424 malicious guests. These commands may attempt to exploit your program
425 by sending unexpected output. They could also try to exploit the
426 Linux kernel or qemu provided by the libguestfs appliance. They could
427 use the network provided by the libguestfs appliance to bypass
428 ordinary network partitions and firewalls. They could use the
429 elevated privileges or different SELinux context of your program
432 A secure alternative is to use libguestfs to install a "firstboot"
433 script (a script which runs when the guest next boots normally), and
434 to have this script run the commands you want in the normal context of
435 the running guest, network security and so on. For information about
436 other security issues, see L</SECURITY>.
440 The two main API calls to run commands are L</guestfs_command> and
441 L</guestfs_sh> (there are also variations).
443 The difference is that L</guestfs_sh> runs commands using the shell, so
444 any shell globs, redirections, etc will work.
446 =head2 CONFIGURATION FILES
448 To read and write configuration files in Linux guest filesystems, we
449 strongly recommend using Augeas. For example, Augeas understands how
450 to read and write, say, a Linux shadow password file or X.org
451 configuration file, and so avoids you having to write that code.
453 The main Augeas calls are bound through the C<guestfs_aug_*> APIs. We
454 don't document Augeas itself here because there is excellent
455 documentation on the L<http://augeas.net/> website.
457 If you don't want to use Augeas (you fool!) then try calling
458 L</guestfs_read_lines> to get the file as a list of lines which
459 you can iterate over.
463 We support SELinux guests. To ensure that labeling happens correctly
464 in SELinux guests, you need to enable SELinux and load the guest's
471 Before launching, do:
473 guestfs_set_selinux (g, 1);
477 After mounting the guest's filesystem(s), load the policy. This
478 is best done by running the L<load_policy(8)> command in the
481 guestfs_sh (g, "/usr/sbin/load_policy");
483 (Older versions of C<load_policy> require you to specify the
484 name of the policy file).
488 Optionally, set the security context for the API. The correct
489 security context to use can only be known by inspecting the
490 guest. As an example:
492 guestfs_setcon (g, "unconfined_u:unconfined_r:unconfined_t:s0");
496 This will work for running commands and editing existing files.
498 When new files are created, you may need to label them explicitly,
499 for example by running the external command
500 C<restorecon pathname>.
504 Certain calls are affected by the current file mode creation mask (the
505 "umask"). In particular ones which create files or directories, such
506 as L</guestfs_touch>, L</guestfs_mknod> or L</guestfs_mkdir>. This
507 affects either the default mode that the file is created with or
508 modifies the mode that you supply.
510 The default umask is C<022>, so files are created with modes such as
511 C<0644> and directories with C<0755>.
513 There are two ways to avoid being affected by umask. Either set umask
514 to 0 (call C<guestfs_umask (g, 0)> early after launching). Or call
515 L</guestfs_chmod> after creating each file or directory.
517 For more information about umask, see L<umask(2)>.
519 =head2 ENCRYPTED DISKS
521 Libguestfs allows you to access Linux guests which have been
522 encrypted using whole disk encryption that conforms to the
523 Linux Unified Key Setup (LUKS) standard. This includes
524 nearly all whole disk encryption systems used by modern
527 Use L</guestfs_vfs_type> to identify LUKS-encrypted block
528 devices (it returns the string C<crypto_LUKS>).
530 Then open these devices by calling L</guestfs_luks_open>.
531 Obviously you will require the passphrase!
533 Opening a LUKS device creates a new device mapper device
534 called C</dev/mapper/mapname> (where C<mapname> is the
535 string you supply to L</guestfs_luks_open>).
536 Reads and writes to this mapper device are decrypted from and
537 encrypted to the underlying block device respectively.
539 LVM volume groups on the device can be made visible by calling
540 L</guestfs_vgscan> followed by L</guestfs_vg_activate_all>.
541 The logical volume(s) can now be mounted in the usual way.
543 Use the reverse process to close a LUKS device. Unmount
544 any logical volumes on it, deactivate the volume groups
545 by caling C<guestfs_vg_activate (g, 0, ["/dev/VG"])>.
546 Then close the mapper device by calling
547 L</guestfs_luks_close> on the C</dev/mapper/mapname>
548 device (I<not> the underlying encrypted block device).
552 Libguestfs has APIs for inspecting an unknown disk image to find out
553 if it contains operating systems, an install CD or a live CD. (These
554 APIs used to be in a separate Perl-only library called
555 L<Sys::Guestfs::Lib(3)> but since version 1.5.3 the most frequently
556 used part of this library has been rewritten in C and moved into the
559 Add all disks belonging to the unknown virtual machine and call
560 L</guestfs_launch> in the usual way.
562 Then call L</guestfs_inspect_os>. This function uses other libguestfs
563 calls and certain heuristics, and returns a list of operating systems
564 that were found. An empty list means none were found. A single
565 element is the root filesystem of the operating system. For dual- or
566 multi-boot guests, multiple roots can be returned, each one
567 corresponding to a separate operating system. (Multi-boot virtual
568 machines are extremely rare in the world of virtualization, but since
569 this scenario can happen, we have built libguestfs to deal with it.)
571 For each root, you can then call various C<guestfs_inspect_get_*>
572 functions to get additional details about that operating system. For
573 example, call L</guestfs_inspect_get_type> to return the string
574 C<windows> or C<linux> for Windows and Linux-based operating systems
577 Un*x-like and Linux-based operating systems usually consist of several
578 filesystems which are mounted at boot time (for example, a separate
579 boot partition mounted on C</boot>). The inspection rules are able to
580 detect how filesystems correspond to mount points. Call
581 C<guestfs_inspect_get_mountpoints> to get this mapping. It might
582 return a hash table like this example:
585 / => /dev/vg_guest/lv_root
586 /usr => /dev/vg_guest/lv_usr
588 The caller can then make calls to L</guestfs_mount_options> to
589 mount the filesystems as suggested.
591 Be careful to mount filesystems in the right order (eg. C</> before
592 C</usr>). Sorting the keys of the hash by length, shortest first,
595 Inspection currently only works for some common operating systems.
596 Contributors are welcome to send patches for other operating systems
597 that we currently cannot detect.
599 Encrypted disks must be opened before inspection. See
600 L</ENCRYPTED DISKS> for more details. The L</guestfs_inspect_os>
601 function just ignores any encrypted devices.
603 A note on the implementation: The call L</guestfs_inspect_os> performs
604 inspection and caches the results in the guest handle. Subsequent
605 calls to C<guestfs_inspect_get_*> return this cached information, but
606 I<do not> re-read the disks. If you change the content of the guest
607 disks, you can redo inspection by calling L</guestfs_inspect_os>
608 again. (L</guestfs_inspect_list_applications> works a little
609 differently from the other calls and does read the disks. See
610 documentation for that function for details).
612 =head3 INSPECTING INSTALL DISKS
614 Libguestfs (since 1.9.4) can detect some install disks, install
615 CDs, live CDs and more.
617 Call L</guestfs_inspect_get_format> to return the format of the
618 operating system, which currently can be C<installed> (a regular
619 operating system) or C<installer> (some sort of install disk).
621 Further information is available about the operating system that can
622 be installed using the regular inspection APIs like
623 L</guestfs_inspect_get_product_name>,
624 L</guestfs_inspect_get_major_version> etc.
626 Some additional information specific to installer disks is also
627 available from the L</guestfs_inspect_is_live>,
628 L</guestfs_inspect_is_netinst> and L</guestfs_inspect_is_multipart>
631 =head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
633 Libguestfs can mount NTFS partitions. It does this using the
634 L<http://www.ntfs-3g.org/> driver.
636 =head3 DRIVE LETTERS AND PATHS
638 DOS and Windows still use drive letters, and the filesystems are
639 always treated as case insensitive by Windows itself, and therefore
640 you might find a Windows configuration file referring to a path like
641 C<c:\windows\system32>. When the filesystem is mounted in libguestfs,
642 that directory might be referred to as C</WINDOWS/System32>.
644 Drive letter mappings are outside the scope of libguestfs. You have
645 to use libguestfs to read the appropriate Windows Registry and
646 configuration files, to determine yourself how drives are mapped (see
647 also L<hivex(3)> and L<virt-inspector(1)>).
649 Replacing backslash characters with forward slash characters is also
650 outside the scope of libguestfs, but something that you can easily do.
652 Where we can help is in resolving the case insensitivity of paths.
653 For this, call L</guestfs_case_sensitive_path>.
655 =head3 ACCESSING THE WINDOWS REGISTRY
657 Libguestfs also provides some help for decoding Windows Registry
658 "hive" files, through the library C<hivex> which is part of the
659 libguestfs project although ships as a separate tarball. You have to
660 locate and download the hive file(s) yourself, and then pass them to
661 C<hivex> functions. See also the programs L<hivexml(1)>,
662 L<hivexsh(1)>, L<hivexregedit(1)> and L<virt-win-reg(1)> for more help
665 =head3 SYMLINKS ON NTFS-3G FILESYSTEMS
667 Ntfs-3g tries to rewrite "Junction Points" and NTFS "symbolic links"
668 to provide something which looks like a Linux symlink. The way it
669 tries to do the rewriting is described here:
671 L<http://www.tuxera.com/community/ntfs-3g-advanced/junction-points-and-symbolic-links/>
673 The essential problem is that ntfs-3g simply does not have enough
674 information to do a correct job. NTFS links can contain drive letters
675 and references to external device GUIDs that ntfs-3g has no way of
676 resolving. It is almost certainly the case that libguestfs callers
677 should ignore what ntfs-3g does (ie. don't use L</guestfs_readlink> on
680 Instead if you encounter a symbolic link on an ntfs-3g filesystem, use
681 L</guestfs_lgetxattr> to read the C<system.ntfs_reparse_data> extended
682 attribute, and read the raw reparse data from that (you can find the
683 format documented in various places around the web).
685 =head3 EXTENDED ATTRIBUTES ON NTFS-3G FILESYSTEMS
687 There are other useful extended attributes that can be read from
688 ntfs-3g filesystems (using L</guestfs_getxattr>). See:
690 L<http://www.tuxera.com/community/ntfs-3g-advanced/extended-attributes/>
692 =head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES
694 Although we don't want to discourage you from using the C API, we will
695 mention here that the same API is also available in other languages.
697 The API is broadly identical in all supported languages. This means
698 that the C call C<guestfs_add_drive_ro(g,file)> is
699 C<$g-E<gt>add_drive_ro($file)> in Perl, C<g.add_drive_ro(file)> in Python,
700 and C<g#add_drive_ro file> in OCaml. In other words, a
701 straightforward, predictable isomorphism between each language.
703 Error messages are automatically transformed
704 into exceptions if the language supports it.
706 We don't try to "object orientify" parts of the API in OO languages,
707 although contributors are welcome to write higher level APIs above
708 what we provide in their favourite languages if they wish.
714 You can use the I<guestfs.h> header file from C++ programs. The C++
715 API is identical to the C API. C++ classes and exceptions are not
720 The C# bindings are highly experimental. Please read the warnings
721 at the top of C<csharp/Libguestfs.cs>.
725 This is the only language binding that is working but incomplete.
726 Only calls which return simple integers have been bound in Haskell,
727 and we are looking for help to complete this binding.
731 Full documentation is contained in the Javadoc which is distributed
736 See L<guestfs-ocaml(3)>.
740 See L<guestfs-perl(3)> and L<Sys::Guestfs(3)>.
744 For documentation see C<README-PHP> supplied with libguestfs
745 sources or in the php-libguestfs package for your distribution.
747 The PHP binding only works correctly on 64 bit machines.
751 See L<guestfs-python(3)>.
755 See L<guestfs-ruby(3)>.
757 =item B<shell scripts>
763 =head2 LIBGUESTFS GOTCHAS
765 L<http://en.wikipedia.org/wiki/Gotcha_(programming)>: "A feature of a
766 system [...] that works in the way it is documented but is
767 counterintuitive and almost invites mistakes."
769 Since we developed libguestfs and the associated tools, there are
770 several things we would have designed differently, but are now stuck
771 with for backwards compatibility or other reasons. If there is ever a
772 libguestfs 2.0 release, you can expect these to change. Beware of
777 =item Autosync / forgetting to sync.
779 When modifying a filesystem from C or another language, you B<must>
780 unmount all filesystems and call L</guestfs_sync> explicitly before
781 you close the libguestfs handle. You can also call:
783 guestfs_set_autosync (g, 1);
785 to have the unmount/sync done automatically for you when the handle 'g'
786 is closed. (This feature is called "autosync", L</guestfs_set_autosync>
789 If you forget to do this, then it is entirely possible that your
790 changes won't be written out, or will be partially written, or (very
791 rarely) that you'll get disk corruption.
793 Note that in L<guestfish(3)> autosync is the default. So quick and
794 dirty guestfish scripts that forget to sync will work just fine, which
795 can make this very puzzling if you are trying to debug a problem.
797 Update: Autosync is enabled by default for all API users starting from
800 =item Mount option C<-o sync> should not be the default.
802 If you use L</guestfs_mount>, then C<-o sync,noatime> are added
803 implicitly. However C<-o sync> does not add any reliability benefit,
804 but does have a very large performance impact.
806 The work around is to use L</guestfs_mount_options> and set the mount
807 options that you actually want to use.
809 =item Read-only should be the default.
811 In L<guestfish(3)>, I<--ro> should be the default, and you should
812 have to specify I<--rw> if you want to make changes to the image.
814 This would reduce the potential to corrupt live VM images.
816 Note that many filesystems change the disk when you just mount and
817 unmount, even if you didn't perform any writes. You need to use
818 L</guestfs_add_drive_ro> to guarantee that the disk is not changed.
820 =item guestfish command line is hard to use.
822 C<guestfish disk.img> doesn't do what people expect (open C<disk.img>
823 for examination). It tries to run a guestfish command C<disk.img>
824 which doesn't exist, so it fails. In earlier versions of guestfish
825 the error message was also unintuitive, but we have corrected this
826 since. Like the Bourne shell, we should have used C<guestfish -c
827 command> to run commands.
829 =item guestfish megabyte modifiers don't work right on all commands
831 In recent guestfish you can use C<1M> to mean 1 megabyte (and
832 similarly for other modifiers). What guestfish actually does is to
833 multiply the number part by the modifier part and pass the result to
834 the C API. However this doesn't work for a few APIs which aren't
835 expecting bytes, but are already expecting some other unit
838 The most common is L</guestfs_lvcreate>. The guestfish command:
842 does not do what you might expect. Instead because
843 L</guestfs_lvcreate> is already expecting megabytes, this tries to
844 create a 100 I<terabyte> (100 megabytes * megabytes) logical volume.
845 The error message you get from this is also a little obscure.
847 This could be fixed in the generator by specially marking parameters
848 and return values which take bytes or other units.
850 =item Ambiguity between devices and paths
852 There is a subtle ambiguity in the API between a device name
853 (eg. C</dev/sdb2>) and a similar pathname. A file might just happen
854 to be called C<sdb2> in the directory C</dev> (consider some non-Unix
857 In the current API we usually resolve this ambiguity by having two
858 separate calls, for example L</guestfs_checksum> and
859 L</guestfs_checksum_device>. Some API calls are ambiguous and
860 (incorrectly) resolve the problem by detecting if the path supplied
861 begins with C</dev/>.
863 To avoid both the ambiguity and the need to duplicate some calls, we
864 could make paths/devices into structured names. One way to do this
865 would be to use a notation like grub (C<hd(0,0)>), although nobody
866 really likes this aspect of grub. Another way would be to use a
867 structured type, equivalent to this OCaml type:
869 type path = Path of string | Device of int | Partition of int * int
871 which would allow you to pass arguments like:
874 Device 1 (* /dev/sdb, or perhaps /dev/sda *)
875 Partition (1, 2) (* /dev/sdb2 (or is it /dev/sda2 or /dev/sdb3?) *)
876 Path "/dev/sdb2" (* not a device *)
878 As you can see there are still problems to resolve even with this
879 representation. Also consider how it might work in guestfish.
883 =head2 PROTOCOL LIMITS
885 Internally libguestfs uses a message-based protocol to pass API calls
886 and their responses to and from a small "appliance" (see L</INTERNALS>
887 for plenty more detail about this). The maximum message size used by
888 the protocol is slightly less than 4 MB. For some API calls you may
889 need to be aware of this limit. The API calls which may be affected
890 are individually documented, with a link back to this section of the
893 A simple call such as L</guestfs_cat> returns its result (the file
894 data) in a simple string. Because this string is at some point
895 internally encoded as a message, the maximum size that it can return
896 is slightly under 4 MB. If the requested file is larger than this
897 then you will get an error.
899 In order to transfer large files into and out of the guest filesystem,
900 you need to use particular calls that support this. The sections
901 L</UPLOADING> and L</DOWNLOADING> document how to do this.
903 You might also consider mounting the disk image using our FUSE
904 filesystem support (L<guestmount(1)>).
906 =head2 KEYS AND PASSPHRASES
908 Certain libguestfs calls take a parameter that contains sensitive key
909 material, passed in as a C string.
911 In the future we would hope to change the libguestfs implementation so
912 that keys are L<mlock(2)>-ed into physical RAM, and thus can never end
913 up in swap. However this is I<not> done at the moment, because of the
914 complexity of such an implementation.
916 Therefore you should be aware that any key parameter you pass to
917 libguestfs might end up being written out to the swap partition. If
918 this is a concern, scrub the swap partition or don't use libguestfs on
921 =head2 MULTIPLE HANDLES AND MULTIPLE THREADS
923 All high-level libguestfs actions are synchronous. If you want
924 to use libguestfs asynchronously then you must create a thread.
926 Only use the handle from a single thread. Either use the handle
927 exclusively from one thread, or provide your own mutex so that two
928 threads cannot issue calls on the same handle at the same time.
930 See the graphical program guestfs-browser for one possible
931 architecture for multithreaded programs using libvirt and libguestfs.
935 Libguestfs needs a kernel and initrd.img, which it finds by looking
936 along an internal path.
938 By default it looks for these in the directory C<$libdir/guestfs>
939 (eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
941 Use L</guestfs_set_path> or set the environment variable
942 L</LIBGUESTFS_PATH> to change the directories that libguestfs will
943 search in. The value is a colon-separated list of paths. The current
944 directory is I<not> searched unless the path contains an empty element
945 or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
946 search the current directory and then C</usr/lib/guestfs>.
950 If you want to compile your own qemu, run qemu from a non-standard
951 location, or pass extra arguments to qemu, then you can write a
952 shell-script wrapper around qemu.
954 There is one important rule to remember: you I<must C<exec qemu>> as
955 the last command in the shell script (so that qemu replaces the shell
956 and becomes the direct child of the libguestfs-using program). If you
957 don't do this, then the qemu process won't be cleaned up correctly.
959 Here is an example of a wrapper, where I have built my own copy of
963 qemudir=/home/rjones/d/qemu
964 exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
966 Save this script as C</tmp/qemu.wrapper> (or wherever), C<chmod +x>,
967 and then use it by setting the LIBGUESTFS_QEMU environment variable.
970 LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
972 Note that libguestfs also calls qemu with the -help and -version
973 options in order to determine features.
975 =head2 ATTACHING TO RUNNING DAEMONS
977 I<Note (1):> This is B<highly experimental> and has a tendency to eat
978 babies. Use with caution.
980 I<Note (2):> This section explains how to attach to a running daemon
981 from a low level perspective. For most users, simply using virt tools
982 such as L<guestfish(1)> with the I<--live> option will "just work".
984 =head3 Using guestfs_set_attach_method
986 By calling L</guestfs_set_attach_method> you can change how the
987 library connects to the C<guestfsd> daemon in L</guestfs_launch>
988 (read L</ARCHITECTURE> for some background).
990 The normal attach method is C<appliance>, where a small appliance is
991 created containing the daemon, and then the library connects to this.
993 Setting attach method to C<unix:I<path>> (where I<path> is the path of
994 a Unix domain socket) causes L</guestfs_launch> to connect to an
995 existing daemon over the Unix domain socket.
997 The normal use for this is to connect to a running virtual machine
998 that contains a C<guestfsd> daemon, and send commands so you can read
999 and write files inside the live virtual machine.
1001 =head3 Using guestfs_add_domain with live flag
1003 L</guestfs_add_domain> provides some help for getting the
1004 correct attach method. If you pass the C<live> option to this
1005 function, then (if the virtual machine is running) it will
1006 examine the libvirt XML looking for a virtio-serial channel
1013 <channel type='unix'>
1014 <source mode='bind' path='/path/to/socket'/>
1015 <target type='virtio' name='org.libguestfs.channel.0'/>
1021 L</guestfs_add_domain> extracts C</path/to/socket> and sets the attach
1022 method to C<unix:/path/to/socket>.
1024 Some of the libguestfs tools (including guestfish) support a I<--live>
1025 option which is passed through to L</guestfs_add_domain> thus allowing
1026 you to attach to and modify live virtual machines.
1028 The virtual machine needs to have been set up beforehand so that it
1029 has the virtio-serial channel and so that guestfsd is running inside
1032 =head2 ABI GUARANTEE
1034 We guarantee the libguestfs ABI (binary interface), for public,
1035 high-level actions as outlined in this section. Although we will
1036 deprecate some actions, for example if they get replaced by newer
1037 calls, we will keep the old actions forever. This allows you the
1038 developer to program in confidence against the libguestfs API.
1040 =head2 BLOCK DEVICE NAMING
1042 In the kernel there is now quite a profusion of schemata for naming
1043 block devices (in this context, by I<block device> I mean a physical
1044 or virtual hard drive). The original Linux IDE driver used names
1045 starting with C</dev/hd*>. SCSI devices have historically used a
1046 different naming scheme, C</dev/sd*>. When the Linux kernel I<libata>
1047 driver became a popular replacement for the old IDE driver
1048 (particularly for SATA devices) those devices also used the
1049 C</dev/sd*> scheme. Additionally we now have virtual machines with
1050 paravirtualized drivers. This has created several different naming
1051 systems, such as C</dev/vd*> for virtio disks and C</dev/xvd*> for Xen
1054 As discussed above, libguestfs uses a qemu appliance running an
1055 embedded Linux kernel to access block devices. We can run a variety
1056 of appliances based on a variety of Linux kernels.
1058 This causes a problem for libguestfs because many API calls use device
1059 or partition names. Working scripts and the recipe (example) scripts
1060 that we make available over the internet could fail if the naming
1063 Therefore libguestfs defines C</dev/sd*> as the I<standard naming
1064 scheme>. Internally C</dev/sd*> names are translated, if necessary,
1065 to other names as required. For example, under RHEL 5 which uses the
1066 C</dev/hd*> scheme, any device parameter C</dev/sda2> is translated to
1067 C</dev/hda2> transparently.
1069 Note that this I<only> applies to parameters. The
1070 L</guestfs_list_devices>, L</guestfs_list_partitions> and similar calls
1071 return the true names of the devices and partitions as known to the
1074 =head3 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
1076 Usually this translation is transparent. However in some (very rare)
1077 cases you may need to know the exact algorithm. Such cases include
1078 where you use L</guestfs_config> to add a mixture of virtio and IDE
1079 devices to the qemu-based appliance, so have a mixture of C</dev/sd*>
1080 and C</dev/vd*> devices.
1082 The algorithm is applied only to I<parameters> which are known to be
1083 either device or partition names. Return values from functions such
1084 as L</guestfs_list_devices> are never changed.
1090 Is the string a parameter which is a device or partition name?
1094 Does the string begin with C</dev/sd>?
1098 Does the named device exist? If so, we use that device.
1099 However if I<not> then we continue with this algorithm.
1103 Replace initial C</dev/sd> string with C</dev/hd>.
1105 For example, change C</dev/sda2> to C</dev/hda2>.
1107 If that named device exists, use it. If not, continue.
1111 Replace initial C</dev/sd> string with C</dev/vd>.
1113 If that named device exists, use it. If not, return an error.
1117 =head3 PORTABILITY CONCERNS WITH BLOCK DEVICE NAMING
1119 Although the standard naming scheme and automatic translation is
1120 useful for simple programs and guestfish scripts, for larger programs
1121 it is best not to rely on this mechanism.
1123 Where possible for maximum future portability programs using
1124 libguestfs should use these future-proof techniques:
1130 Use L</guestfs_list_devices> or L</guestfs_list_partitions> to list
1131 actual device names, and then use those names directly.
1133 Since those device names exist by definition, they will never be
1138 Use higher level ways to identify filesystems, such as LVM names,
1139 UUIDs and filesystem labels.
1145 This section discusses security implications of using libguestfs,
1146 particularly with untrusted or malicious guests or disk images.
1148 =head2 GENERAL SECURITY CONSIDERATIONS
1150 Be careful with any files or data that you download from a guest (by
1151 "download" we mean not just the L</guestfs_download> command but any
1152 command that reads files, filenames, directories or anything else from
1153 a disk image). An attacker could manipulate the data to fool your
1154 program into doing the wrong thing. Consider cases such as:
1160 the data (file etc) not being present
1164 being present but empty
1168 being much larger than normal
1172 containing arbitrary 8 bit data
1176 being in an unexpected character encoding
1180 containing homoglyphs.
1184 =head2 SECURITY OF MOUNTING FILESYSTEMS
1186 When you mount a filesystem under Linux, mistakes in the kernel
1187 filesystem (VFS) module can sometimes be escalated into exploits by
1188 deliberately creating a malicious, malformed filesystem. These
1189 exploits are very severe for two reasons. Firstly there are very many
1190 filesystem drivers in the kernel, and many of them are infrequently
1191 used and not much developer attention has been paid to the code.
1192 Linux userspace helps potential crackers by detecting the filesystem
1193 type and automatically choosing the right VFS driver, even if that
1194 filesystem type is obscure or unexpected for the administrator.
1195 Secondly, a kernel-level exploit is like a local root exploit (worse
1196 in some ways), giving immediate and total access to the system right
1197 down to the hardware level.
1199 That explains why you should never mount a filesystem from an
1200 untrusted guest on your host kernel. How about libguestfs? We run a
1201 Linux kernel inside a qemu virtual machine, usually running as a
1202 non-root user. The attacker would need to write a filesystem which
1203 first exploited the kernel, and then exploited either qemu
1204 virtualization (eg. a faulty qemu driver) or the libguestfs protocol,
1205 and finally to be as serious as the host kernel exploit it would need
1206 to escalate its privileges to root. This multi-step escalation,
1207 performed by a static piece of data, is thought to be extremely hard
1208 to do, although we never say 'never' about security issues.
1210 In any case callers can reduce the attack surface by forcing the
1211 filesystem type when mounting (use L</guestfs_mount_vfs>).
1213 =head2 PROTOCOL SECURITY
1215 The protocol is designed to be secure, being based on RFC 4506 (XDR)
1216 with a defined upper message size. However a program that uses
1217 libguestfs must also take care - for example you can write a program
1218 that downloads a binary from a disk image and executes it locally, and
1219 no amount of protocol security will save you from the consequences.
1221 =head2 INSPECTION SECURITY
1223 Parts of the inspection API (see L</INSPECTION>) return untrusted
1224 strings directly from the guest, and these could contain any 8 bit
1225 data. Callers should be careful to escape these before printing them
1226 to a structured file (for example, use HTML escaping if creating a web
1229 Guest configuration may be altered in unusual ways by the
1230 administrator of the virtual machine, and may not reflect reality
1231 (particularly for untrusted or actively malicious guests). For
1232 example we parse the hostname from configuration files like
1233 C</etc/sysconfig/network> that we find in the guest, but the guest
1234 administrator can easily manipulate these files to provide the wrong
1237 The inspection API parses guest configuration using two external
1238 libraries: Augeas (Linux configuration) and hivex (Windows Registry).
1239 Both are designed to be robust in the face of malicious data, although
1240 denial of service attacks are still possible, for example with
1241 oversized configuration files.
1243 =head2 RUNNING UNTRUSTED GUEST COMMANDS
1245 Be very cautious about running commands from the guest. By running a
1246 command in the guest, you are giving CPU time to a binary that you do
1247 not control, under the same user account as the library, albeit
1248 wrapped in qemu virtualization. More information and alternatives can
1249 be found in the section L</RUNNING COMMANDS>.
1251 =head2 CVE-2010-3851
1253 https://bugzilla.redhat.com/642934
1255 This security bug concerns the automatic disk format detection that
1256 qemu does on disk images.
1258 A raw disk image is just the raw bytes, there is no header. Other
1259 disk images like qcow2 contain a special header. Qemu deals with this
1260 by looking for one of the known headers, and if none is found then
1261 assuming the disk image must be raw.
1263 This allows a guest which has been given a raw disk image to write
1264 some other header. At next boot (or when the disk image is accessed
1265 by libguestfs) qemu would do autodetection and think the disk image
1266 format was, say, qcow2 based on the header written by the guest.
1268 This in itself would not be a problem, but qcow2 offers many features,
1269 one of which is to allow a disk image to refer to another image
1270 (called the "backing disk"). It does this by placing the path to the
1271 backing disk into the qcow2 header. This path is not validated and
1272 could point to any host file (eg. "/etc/passwd"). The backing disk is
1273 then exposed through "holes" in the qcow2 disk image, which of course
1274 is completely under the control of the attacker.
1276 In libguestfs this is rather hard to exploit except under two
1283 You have enabled the network or have opened the disk in write mode.
1287 You are also running untrusted code from the guest (see
1288 L</RUNNING COMMANDS>).
1292 The way to avoid this is to specify the expected disk format when
1293 adding disks (the optional C<format> option to
1294 L</guestfs_add_drive_opts>). You should always do this if the disk is
1295 raw format, and it's a good idea for other cases too.
1297 For disks added from libvirt using calls like L</guestfs_add_domain>,
1298 the format is fetched from libvirt and passed through.
1300 For libguestfs tools, use the I<--format> command line parameter as
1303 =head1 CONNECTION MANAGEMENT
1307 C<guestfs_h> is the opaque type representing a connection handle.
1308 Create a handle by calling L</guestfs_create>. Call L</guestfs_close>
1309 to free the handle and release all resources used.
1311 For information on using multiple handles and threads, see the section
1312 L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
1314 =head2 guestfs_create
1316 guestfs_h *guestfs_create (void);
1318 Create a connection handle.
1320 You have to call L</guestfs_add_drive_opts> (or one of the equivalent
1321 calls) on the handle at least once.
1323 This function returns a non-NULL pointer to a handle on success or
1326 After configuring the handle, you have to call L</guestfs_launch>.
1328 You may also want to configure error handling for the handle. See
1329 L</ERROR HANDLING> section below.
1331 =head2 guestfs_close
1333 void guestfs_close (guestfs_h *g);
1335 This closes the connection handle and frees up all resources used.
1337 =head1 ERROR HANDLING
1339 API functions can return errors. For example, almost all functions
1340 that return C<int> will return C<-1> to indicate an error.
1342 Additional information is available for errors: an error message
1343 string and optionally an error number (errno) if the thing that failed
1346 You can get at the additional information about the last error on the
1347 handle by calling L</guestfs_last_error>, L</guestfs_last_errno>,
1348 and/or by setting up an error handler with
1349 L</guestfs_set_error_handler>.
1351 When the handle is created, a default error handler is installed which
1352 prints the error message string to C<stderr>. For small short-running
1353 command line programs it is sufficient to do:
1355 if (guestfs_launch (g) == -1)
1356 exit (EXIT_FAILURE);
1358 since the default error handler will ensure that an error message has
1359 been printed to C<stderr> before the program exits.
1361 For other programs the caller will almost certainly want to install an
1362 alternate error handler or do error handling in-line like this:
1364 g = guestfs_create ();
1366 /* This disables the default behaviour of printing errors
1368 guestfs_set_error_handler (g, NULL, NULL);
1370 if (guestfs_launch (g) == -1) {
1371 /* Examine the error message and print it etc. */
1372 char *msg = guestfs_last_error (g);
1373 int errnum = guestfs_last_errno (g);
1374 fprintf (stderr, "%s\n", msg);
1378 Out of memory errors are handled differently. The default action is
1379 to call L<abort(3)>. If this is undesirable, then you can set a
1380 handler using L</guestfs_set_out_of_memory_handler>.
1382 L</guestfs_create> returns C<NULL> if the handle cannot be created,
1383 and because there is no handle if this happens there is no way to get
1384 additional error information. However L</guestfs_create> is supposed
1385 to be a lightweight operation which can only fail because of
1386 insufficient memory (it returns NULL in this case).
1388 =head2 guestfs_last_error
1390 const char *guestfs_last_error (guestfs_h *g);
1392 This returns the last error message that happened on C<g>. If
1393 there has not been an error since the handle was created, then this
1396 The lifetime of the returned string is until the next error occurs, or
1397 L</guestfs_close> is called.
1399 =head2 guestfs_last_errno
1401 int guestfs_last_errno (guestfs_h *g);
1403 This returns the last error number (errno) that happened on C<g>.
1405 If successful, an errno integer not equal to zero is returned.
1407 If no error, this returns 0. This call can return 0 in three
1414 There has not been any error on the handle.
1418 There has been an error but the errno was meaningless. This
1419 corresponds to the case where the error did not come from a
1420 failed system call, but for some other reason.
1424 There was an error from a failed system call, but for some
1425 reason the errno was not captured and returned. This usually
1426 indicates a bug in libguestfs.
1430 Libguestfs tries to convert the errno from inside the applicance into
1431 a corresponding errno for the caller (not entirely trivial: the
1432 appliance might be running a completely different operating system
1433 from the library and error numbers are not standardized across
1434 Un*xen). If this could not be done, then the error is translated to
1435 C<EINVAL>. In practice this should only happen in very rare
1438 =head2 guestfs_set_error_handler
1440 typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
1443 void guestfs_set_error_handler (guestfs_h *g,
1444 guestfs_error_handler_cb cb,
1447 The callback C<cb> will be called if there is an error. The
1448 parameters passed to the callback are an opaque data pointer and the
1449 error message string.
1451 C<errno> is not passed to the callback. To get that the callback must
1452 call L</guestfs_last_errno>.
1454 Note that the message string C<msg> is freed as soon as the callback
1455 function returns, so if you want to stash it somewhere you must make
1458 The default handler prints messages on C<stderr>.
1460 If you set C<cb> to C<NULL> then I<no> handler is called.
1462 =head2 guestfs_get_error_handler
1464 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
1467 Returns the current error handler callback.
1469 =head2 guestfs_set_out_of_memory_handler
1471 typedef void (*guestfs_abort_cb) (void);
1472 int guestfs_set_out_of_memory_handler (guestfs_h *g,
1475 The callback C<cb> will be called if there is an out of memory
1476 situation. I<Note this callback must not return>.
1478 The default is to call L<abort(3)>.
1480 You cannot set C<cb> to C<NULL>. You can't ignore out of memory
1483 =head2 guestfs_get_out_of_memory_handler
1485 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *g);
1487 This returns the current out of memory handler.
1499 =head2 GROUPS OF FUNCTIONALITY IN THE APPLIANCE
1501 Using L</guestfs_available> you can test availability of
1502 the following groups of functions. This test queries the
1503 appliance to see if the appliance you are currently using
1504 supports the functionality.
1508 =head2 GUESTFISH supported COMMAND
1510 In L<guestfish(3)> there is a handy interactive command
1511 C<supported> which prints out the available groups and
1512 whether they are supported by this build of libguestfs.
1513 Note however that you have to do C<run> first.
1515 =head2 SINGLE CALLS AT COMPILE TIME
1517 Since version 1.5.8, C<E<lt>guestfs.hE<gt>> defines symbols
1518 for each C API function, such as:
1520 #define LIBGUESTFS_HAVE_DD 1
1522 if L</guestfs_dd> is available.
1524 Before version 1.5.8, if you needed to test whether a single
1525 libguestfs function is available at compile time, we recommended using
1526 build tools such as autoconf or cmake. For example in autotools you
1529 AC_CHECK_LIB([guestfs],[guestfs_create])
1530 AC_CHECK_FUNCS([guestfs_dd])
1532 which would result in C<HAVE_GUESTFS_DD> being either defined
1533 or not defined in your program.
1535 =head2 SINGLE CALLS AT RUN TIME
1537 Testing at compile time doesn't guarantee that a function really
1538 exists in the library. The reason is that you might be dynamically
1539 linked against a previous I<libguestfs.so> (dynamic library)
1540 which doesn't have the call. This situation unfortunately results
1541 in a segmentation fault, which is a shortcoming of the C dynamic
1542 linking system itself.
1544 You can use L<dlopen(3)> to test if a function is available
1545 at run time, as in this example program (note that you still
1546 need the compile time check as well):
1552 #include <guestfs.h>
1556 #ifdef LIBGUESTFS_HAVE_DD
1560 /* Test if the function guestfs_dd is really available. */
1561 dl = dlopen (NULL, RTLD_LAZY);
1563 fprintf (stderr, "dlopen: %s\n", dlerror ());
1564 exit (EXIT_FAILURE);
1566 has_function = dlsym (dl, "guestfs_dd") != NULL;
1570 printf ("this libguestfs.so does NOT have guestfs_dd function\n");
1572 printf ("this libguestfs.so has guestfs_dd function\n");
1573 /* Now it's safe to call
1574 guestfs_dd (g, "foo", "bar");
1578 printf ("guestfs_dd function was not found at compile time\n");
1582 You may think the above is an awful lot of hassle, and it is.
1583 There are other ways outside of the C linking system to ensure
1584 that this kind of incompatibility never arises, such as using
1587 Requires: libguestfs >= 1.0.80
1589 =head1 CALLS WITH OPTIONAL ARGUMENTS
1591 A recent feature of the API is the introduction of calls which take
1592 optional arguments. In C these are declared 3 ways. The main way is
1593 as a call which takes variable arguments (ie. C<...>), as in this
1596 int guestfs_add_drive_opts (guestfs_h *g, const char *filename, ...);
1598 Call this with a list of optional arguments, terminated by C<-1>.
1599 So to call with no optional arguments specified:
1601 guestfs_add_drive_opts (g, filename, -1);
1603 With a single optional argument:
1605 guestfs_add_drive_opts (g, filename,
1606 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
1611 guestfs_add_drive_opts (g, filename,
1612 GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
1613 GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
1616 and so forth. Don't forget the terminating C<-1> otherwise
1617 Bad Things will happen!
1619 =head2 USING va_list FOR OPTIONAL ARGUMENTS
1621 The second variant has the same name with the suffix C<_va>, which
1622 works the same way but takes a C<va_list>. See the C manual for
1623 details. For the example function, this is declared:
1625 int guestfs_add_drive_opts_va (guestfs_h *g, const char *filename,
1628 =head2 CONSTRUCTING OPTIONAL ARGUMENTS
1630 The third variant is useful where you need to construct these
1631 calls. You pass in a structure where you fill in the optional
1632 fields. The structure has a bitmask as the first element which
1633 you must set to indicate which fields you have filled in. For
1634 our example function the structure and call are declared:
1636 struct guestfs_add_drive_opts_argv {
1642 int guestfs_add_drive_opts_argv (guestfs_h *g, const char *filename,
1643 const struct guestfs_add_drive_opts_argv *optargs);
1645 You could call it like this:
1647 struct guestfs_add_drive_opts_argv optargs = {
1648 .bitmask = GUESTFS_ADD_DRIVE_OPTS_READONLY_BITMASK |
1649 GUESTFS_ADD_DRIVE_OPTS_FORMAT_BITMASK,
1654 guestfs_add_drive_opts_argv (g, filename, &optargs);
1662 The C<_BITMASK> suffix on each option name when specifying the
1667 You do not need to fill in all fields of the structure.
1671 There must be a one-to-one correspondence between fields of the
1672 structure that are filled in, and bits set in the bitmask.
1676 =head2 OPTIONAL ARGUMENTS IN OTHER LANGUAGES
1678 In other languages, optional arguments are expressed in the
1679 way that is natural for that language. We refer you to the
1680 language-specific documentation for more details on that.
1682 For guestfish, see L<guestfish(1)/OPTIONAL ARGUMENTS>.
1684 =head2 SETTING CALLBACKS TO HANDLE EVENTS
1686 The child process generates events in some situations. Current events
1687 include: receiving a log message, the child process exits.
1689 Use the C<guestfs_set_*_callback> functions to set a callback for
1690 different types of events.
1692 Only I<one callback of each type> can be registered for each handle.
1693 Calling C<guestfs_set_*_callback> again overwrites the previous
1694 callback of that type. Cancel all callbacks of this type by calling
1695 this function with C<cb> set to C<NULL>.
1697 =head2 guestfs_set_log_message_callback
1699 typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
1700 char *buf, int len);
1701 void guestfs_set_log_message_callback (guestfs_h *g,
1702 guestfs_log_message_cb cb,
1705 The callback function C<cb> will be called whenever qemu or the guest
1706 writes anything to the console.
1708 Use this function to capture kernel messages and similar.
1710 Normally there is no log message handler, and log messages are just
1713 =head2 guestfs_set_subprocess_quit_callback
1715 typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
1716 void guestfs_set_subprocess_quit_callback (guestfs_h *g,
1717 guestfs_subprocess_quit_cb cb,
1720 The callback function C<cb> will be called when the child process
1721 quits, either asynchronously or if killed by
1722 L</guestfs_kill_subprocess>. (This corresponds to a transition from
1723 any state to the CONFIG state).
1725 =head2 guestfs_set_launch_done_callback
1727 typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
1728 void guestfs_set_launch_done_callback (guestfs_h *g,
1729 guestfs_launch_done_cb cb,
1732 The callback function C<cb> will be called when the child process
1733 becomes ready first time after it has been launched. (This
1734 corresponds to a transition from LAUNCHING to the READY state).
1736 =head2 guestfs_set_close_callback
1738 typedef void (*guestfs_close_cb) (guestfs_h *g, void *opaque);
1739 void guestfs_set_close_callback (guestfs_h *g,
1740 guestfs_close_cb cb,
1743 The callback function C<cb> will be called while the handle
1744 is being closed (synchronously from L</guestfs_close>).
1746 Note that libguestfs installs an L<atexit(3)> handler to try to
1747 clean up handles that are open when the program exits. This
1748 means that this callback might be called indirectly from
1749 L<exit(3)>, which can cause unexpected problems in higher-level
1750 languages (eg. if your HLL interpreter has already been cleaned
1751 up by the time this is called, and if your callback then jumps
1752 into some HLL function).
1754 =head2 guestfs_set_progress_callback
1756 typedef void (*guestfs_progress_cb) (guestfs_h *g, void *opaque,
1757 int proc_nr, int serial,
1758 uint64_t position, uint64_t total);
1759 void guestfs_set_progress_callback (guestfs_h *g,
1760 guestfs_progress_cb cb,
1763 Some long-running operations can generate progress messages. If
1764 this callback is registered, then it will be called each time a
1765 progress message is generated (usually two seconds after the
1766 operation started, and three times per second thereafter until
1767 it completes, although the frequency may change in future versions).
1769 The callback receives two numbers: C<position> and C<total>.
1770 The units of C<total> are not defined, although for some
1771 operations C<total> may relate in some way to the amount of
1772 data to be transferred (eg. in bytes or megabytes), and
1773 C<position> may be the portion which has been transferred.
1775 The only defined and stable parts of the API are:
1781 The callback can display to the user some type of progress bar or
1782 indicator which shows the ratio of C<position>:C<total>.
1786 0 E<lt>= C<position> E<lt>= C<total>
1790 If any progress notification is sent during a call, then a final
1791 progress notification is always sent when C<position> = C<total>.
1793 This is to simplify caller code, so callers can easily set the
1794 progress indicator to "100%" at the end of the operation, without
1795 requiring special code to detect this case.
1799 The callback also receives the procedure number and serial number of
1800 the call. These are only useful for debugging protocol issues, and
1801 the callback can normally ignore them. The callback may want to
1802 print these numbers in error messages or debugging messages.
1804 =head1 PRIVATE DATA AREA
1806 You can attach named pieces of private data to the libguestfs handle,
1807 and fetch them by name for the lifetime of the handle. This is called
1808 the private data area and is only available from the C API.
1810 To attach a named piece of data, use the following call:
1812 void guestfs_set_private (guestfs_h *g, const char *key, void *data);
1814 C<key> is the name to associate with this data, and C<data> is an
1815 arbitrary pointer (which can be C<NULL>). Any previous item with the
1816 same name is overwritten.
1818 You can use any C<key> you want, but names beginning with an
1819 underscore character are reserved for internal libguestfs purposes
1820 (for implementing language bindings). It is recommended to prefix the
1821 name with some unique string to avoid collisions with other users.
1823 To retrieve the pointer, use:
1825 void *guestfs_get_private (guestfs_h *g, const char *key);
1827 This function returns C<NULL> if either no data is found associated
1828 with C<key>, or if the user previously set the C<key>'s C<data>
1831 Libguestfs does not try to look at or interpret the C<data> pointer in
1832 any way. As far as libguestfs is concerned, it need not be a valid
1833 pointer at all. In particular, libguestfs does I<not> try to free the
1834 data when the handle is closed. If the data must be freed, then the
1835 caller must either free it before calling L</guestfs_close> or must
1836 set up a close callback to do it (see L</guestfs_set_close_callback>,
1837 and note that only one callback can be registered for a handle).
1839 The private data area is implemented using a hash table, and should be
1840 reasonably efficient for moderate numbers of keys.
1844 <!-- old anchor for the next section -->
1845 <a name="state_machine_and_low_level_event_api"/>
1851 Internally, libguestfs is implemented by running an appliance (a
1852 special type of small virtual machine) using L<qemu(1)>. Qemu runs as
1853 a child process of the main program.
1859 | | child process / appliance
1860 | | __________________________
1862 +-------------------+ RPC | +-----------------+ |
1863 | libguestfs <--------------------> guestfsd | |
1864 | | | +-----------------+ |
1865 \___________________/ | | Linux kernel | |
1866 | +--^--------------+ |
1867 \_________|________________/
1875 The library, linked to the main program, creates the child process and
1876 hence the appliance in the L</guestfs_launch> function.
1878 Inside the appliance is a Linux kernel and a complete stack of
1879 userspace tools (such as LVM and ext2 programs) and a small
1880 controlling daemon called L</guestfsd>. The library talks to
1881 L</guestfsd> using remote procedure calls (RPC). There is a mostly
1882 one-to-one correspondence between libguestfs API calls and RPC calls
1883 to the daemon. Lastly the disk image(s) are attached to the qemu
1884 process which translates device access by the appliance's Linux kernel
1885 into accesses to the image.
1887 A common misunderstanding is that the appliance "is" the virtual
1888 machine. Although the disk image you are attached to might also be
1889 used by some virtual machine, libguestfs doesn't know or care about
1890 this. (But you will care if both libguestfs's qemu process and your
1891 virtual machine are trying to update the disk image at the same time,
1892 since these usually results in massive disk corruption).
1894 =head1 STATE MACHINE
1896 libguestfs uses a state machine to model the child process:
1907 / | \ \ guestfs_launch
1918 \______/ <------ \________/
1920 The normal transitions are (1) CONFIG (when the handle is created, but
1921 there is no child process), (2) LAUNCHING (when the child process is
1922 booting up), (3) alternating between READY and BUSY as commands are
1923 issued to, and carried out by, the child process.
1925 The guest may be killed by L</guestfs_kill_subprocess>, or may die
1926 asynchronously at any time (eg. due to some internal error), and that
1927 causes the state to transition back to CONFIG.
1929 Configuration commands for qemu such as L</guestfs_add_drive> can only
1930 be issued when in the CONFIG state.
1932 The API offers one call that goes from CONFIG through LAUNCHING to
1933 READY. L</guestfs_launch> blocks until the child process is READY to
1934 accept commands (or until some failure or timeout).
1935 L</guestfs_launch> internally moves the state from CONFIG to LAUNCHING
1936 while it is running.
1938 API actions such as L</guestfs_mount> can only be issued when in the
1939 READY state. These API calls block waiting for the command to be
1940 carried out (ie. the state to transition to BUSY and then back to
1941 READY). There are no non-blocking versions, and no way to issue more
1942 than one command per handle at the same time.
1944 Finally, the child process sends asynchronous messages back to the
1945 main program, such as kernel log messages. You can register a
1946 callback to receive these messages.
1950 =head2 COMMUNICATION PROTOCOL
1952 Don't rely on using this protocol directly. This section documents
1953 how it currently works, but it may change at any time.
1955 The protocol used to talk between the library and the daemon running
1956 inside the qemu virtual machine is a simple RPC mechanism built on top
1957 of XDR (RFC 1014, RFC 1832, RFC 4506).
1959 The detailed format of structures is in C<src/guestfs_protocol.x>
1960 (note: this file is automatically generated).
1962 There are two broad cases, ordinary functions that don't have any
1963 C<FileIn> and C<FileOut> parameters, which are handled with very
1964 simple request/reply messages. Then there are functions that have any
1965 C<FileIn> or C<FileOut> parameters, which use the same request and
1966 reply messages, but they may also be followed by files sent using a
1969 =head3 ORDINARY FUNCTIONS (NO FILEIN/FILEOUT PARAMS)
1971 For ordinary functions, the request message is:
1973 total length (header + arguments,
1974 but not including the length word itself)
1975 struct guestfs_message_header (encoded as XDR)
1976 struct guestfs_<foo>_args (encoded as XDR)
1978 The total length field allows the daemon to allocate a fixed size
1979 buffer into which it slurps the rest of the message. As a result, the
1980 total length is limited to C<GUESTFS_MESSAGE_MAX> bytes (currently
1981 4MB), which means the effective size of any request is limited to
1982 somewhere under this size.
1984 Note also that many functions don't take any arguments, in which case
1985 the C<guestfs_I<foo>_args> is completely omitted.
1987 The header contains the procedure number (C<guestfs_proc>) which is
1988 how the receiver knows what type of args structure to expect, or none
1991 For functions that take optional arguments, the optional arguments are
1992 encoded in the C<guestfs_I<foo>_args> structure in the same way as
1993 ordinary arguments. A bitmask in the header indicates which optional
1994 arguments are meaningful. The bitmask is also checked to see if it
1995 contains bits set which the daemon does not know about (eg. if more
1996 optional arguments were added in a later version of the library), and
1997 this causes the call to be rejected.
1999 The reply message for ordinary functions is:
2001 total length (header + ret,
2002 but not including the length word itself)
2003 struct guestfs_message_header (encoded as XDR)
2004 struct guestfs_<foo>_ret (encoded as XDR)
2006 As above the C<guestfs_I<foo>_ret> structure may be completely omitted
2007 for functions that return no formal return values.
2009 As above the total length of the reply is limited to
2010 C<GUESTFS_MESSAGE_MAX>.
2012 In the case of an error, a flag is set in the header, and the reply
2013 message is slightly changed:
2015 total length (header + error,
2016 but not including the length word itself)
2017 struct guestfs_message_header (encoded as XDR)
2018 struct guestfs_message_error (encoded as XDR)
2020 The C<guestfs_message_error> structure contains the error message as a
2023 =head3 FUNCTIONS THAT HAVE FILEIN PARAMETERS
2025 A C<FileIn> parameter indicates that we transfer a file I<into> the
2026 guest. The normal request message is sent (see above). However this
2027 is followed by a sequence of file chunks.
2029 total length (header + arguments,
2030 but not including the length word itself,
2031 and not including the chunks)
2032 struct guestfs_message_header (encoded as XDR)
2033 struct guestfs_<foo>_args (encoded as XDR)
2034 sequence of chunks for FileIn param #0
2035 sequence of chunks for FileIn param #1 etc.
2037 The "sequence of chunks" is:
2039 length of chunk (not including length word itself)
2040 struct guestfs_chunk (encoded as XDR)
2042 struct guestfs_chunk (encoded as XDR)
2045 struct guestfs_chunk (with data.data_len == 0)
2047 The final chunk has the C<data_len> field set to zero. Additionally a
2048 flag is set in the final chunk to indicate either successful
2049 completion or early cancellation.
2051 At time of writing there are no functions that have more than one
2052 FileIn parameter. However this is (theoretically) supported, by
2053 sending the sequence of chunks for each FileIn parameter one after
2054 another (from left to right).
2056 Both the library (sender) I<and> the daemon (receiver) may cancel the
2057 transfer. The library does this by sending a chunk with a special
2058 flag set to indicate cancellation. When the daemon sees this, it
2059 cancels the whole RPC, does I<not> send any reply, and goes back to
2060 reading the next request.
2062 The daemon may also cancel. It does this by writing a special word
2063 C<GUESTFS_CANCEL_FLAG> to the socket. The library listens for this
2064 during the transfer, and if it gets it, it will cancel the transfer
2065 (it sends a cancel chunk). The special word is chosen so that even if
2066 cancellation happens right at the end of the transfer (after the
2067 library has finished writing and has started listening for the reply),
2068 the "spurious" cancel flag will not be confused with the reply
2071 This protocol allows the transfer of arbitrary sized files (no 32 bit
2072 limit), and also files where the size is not known in advance
2073 (eg. from pipes or sockets). However the chunks are rather small
2074 (C<GUESTFS_MAX_CHUNK_SIZE>), so that neither the library nor the
2075 daemon need to keep much in memory.
2077 =head3 FUNCTIONS THAT HAVE FILEOUT PARAMETERS
2079 The protocol for FileOut parameters is exactly the same as for FileIn
2080 parameters, but with the roles of daemon and library reversed.
2082 total length (header + ret,
2083 but not including the length word itself,
2084 and not including the chunks)
2085 struct guestfs_message_header (encoded as XDR)
2086 struct guestfs_<foo>_ret (encoded as XDR)
2087 sequence of chunks for FileOut param #0
2088 sequence of chunks for FileOut param #1 etc.
2090 =head3 INITIAL MESSAGE
2092 When the daemon launches it sends an initial word
2093 (C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest and daemon is
2094 alive. This is what L</guestfs_launch> waits for.
2096 =head3 PROGRESS NOTIFICATION MESSAGES
2098 The daemon may send progress notification messages at any time. These
2099 are distinguished by the normal length word being replaced by
2100 C<GUESTFS_PROGRESS_FLAG>, followed by a fixed size progress message.
2102 The library turns them into progress callbacks (see
2103 C<guestfs_set_progress_callback>) if there is a callback registered,
2104 or discards them if not.
2106 The daemon self-limits the frequency of progress messages it sends
2107 (see C<daemon/proto.c:notify_progress>). Not all calls generate
2110 =head1 LIBGUESTFS VERSION NUMBERS
2112 Since April 2010, libguestfs has started to make separate development
2113 and stable releases, along with corresponding branches in our git
2114 repository. These separate releases can be identified by version
2117 even numbers for stable: 1.2.x, 1.4.x, ...
2118 .-------- odd numbers for development: 1.3.x, 1.5.x, ...
2124 | `-------- sub-version
2126 `------ always '1' because we don't change the ABI
2128 Thus "1.3.5" is the 5th update to the development branch "1.3".
2130 As time passes we cherry pick fixes from the development branch and
2131 backport those into the stable branch, the effect being that the
2132 stable branch should get more stable and less buggy over time. So the
2133 stable releases are ideal for people who don't need new features but
2134 would just like the software to work.
2136 Our criteria for backporting changes are:
2142 Documentation changes which don't affect any code are
2143 backported unless the documentation refers to a future feature
2144 which is not in stable.
2148 Bug fixes which are not controversial, fix obvious problems, and
2149 have been well tested are backported.
2153 Simple rearrangements of code which shouldn't affect how it works get
2154 backported. This is so that the code in the two branches doesn't get
2155 too far out of step, allowing us to backport future fixes more easily.
2159 We I<don't> backport new features, new APIs, new tools etc, except in
2160 one exceptional case: the new feature is required in order to
2161 implement an important bug fix.
2165 A new stable branch starts when we think the new features in
2166 development are substantial and compelling enough over the current
2167 stable branch to warrant it. When that happens we create new stable
2168 and development versions 1.N.0 and 1.(N+1).0 [N is even]. The new
2169 dot-oh release won't necessarily be so stable at this point, but by
2170 backporting fixes from development, that branch will stabilize over
2173 =head1 EXTENDING LIBGUESTFS
2175 =head2 ADDING A NEW API ACTION
2177 Large amounts of boilerplate code in libguestfs (RPC, bindings,
2178 documentation) are generated, and this makes it easy to extend the
2181 To add a new API action there are two changes:
2187 You need to add a description of the call (name, parameters, return
2188 type, tests, documentation) to C<generator/generator_actions.ml>.
2190 There are two sorts of API action, depending on whether the call goes
2191 through to the daemon in the appliance, or is serviced entirely by the
2192 library (see L</ARCHITECTURE> above). L</guestfs_sync> is an example
2193 of the former, since the sync is done in the appliance.
2194 L</guestfs_set_trace> is an example of the latter, since a trace flag
2195 is maintained in the handle and all tracing is done on the library
2198 Most new actions are of the first type, and get added to the
2199 C<daemon_functions> list. Each function has a unique procedure number
2200 used in the RPC protocol which is assigned to that action when we
2201 publish libguestfs and cannot be reused. Take the latest procedure
2202 number and increment it.
2204 For library-only actions of the second type, add to the
2205 C<non_daemon_functions> list. Since these functions are serviced by
2206 the library and do not travel over the RPC mechanism to the daemon,
2207 these functions do not need a procedure number, and so the procedure
2208 number is set to C<-1>.
2212 Implement the action (in C):
2214 For daemon actions, implement the function C<do_E<lt>nameE<gt>> in the
2215 C<daemon/> directory.
2217 For library actions, implement the function C<guestfs__E<lt>nameE<gt>>
2218 (note: double underscore) in the C<src/> directory.
2220 In either case, use another function as an example of what to do.
2224 After making these changes, use C<make> to compile.
2226 Note that you don't need to implement the RPC, language bindings,
2227 manual pages or anything else. It's all automatically generated from
2228 the OCaml description.
2230 =head2 ADDING TESTS FOR AN API ACTION
2232 You can supply zero or as many tests as you want per API call. The
2233 tests can either be added as part of the API description
2234 (C<generator/generator_actions.ml>), or in some rarer cases you may
2235 want to drop a script into C<regressions/>. Note that adding a script
2236 to C<regressions/> is slower, so if possible use the first method.
2238 The following describes the test environment used when you add an API
2239 test in C<generator_actions.ml>.
2241 The test environment has 4 block devices:
2245 =item C</dev/sda> 500MB
2247 General block device for testing.
2249 =item C</dev/sdb> 50MB
2251 C</dev/sdb1> is an ext2 filesystem used for testing
2252 filesystem write operations.
2254 =item C</dev/sdc> 10MB
2256 Used in a few tests where two block devices are needed.
2260 ISO with fixed content (see C<images/test.iso>).
2264 To be able to run the tests in a reasonable amount of time, the
2265 libguestfs appliance and block devices are reused between tests. So
2266 don't try testing L</guestfs_kill_subprocess> :-x
2268 Each test starts with an initial scenario, selected using one of the
2269 C<Init*> expressions, described in C<generator/generator_types.ml>.
2270 These initialize the disks mentioned above in a particular way as
2271 documented in C<generator_types.ml>. You should not assume anything
2272 about the previous contents of other disks that are not initialized.
2274 You can add a prerequisite clause to any individual test. This is a
2275 run-time check, which, if it fails, causes the test to be skipped.
2276 Useful if testing a command which might not work on all variations of
2277 libguestfs builds. A test that has prerequisite of C<Always> means to
2278 run unconditionally.
2280 In addition, packagers can skip individual tests by setting
2281 environment variables before running C<make check>.
2283 SKIP_TEST_<CMD>_<NUM>=1
2285 eg: C<SKIP_TEST_COMMAND_3=1> skips test #3 of L</guestfs_command>.
2291 eg: C<SKIP_TEST_ZEROFREE=1> skips all L</guestfs_zerofree> tests.
2293 Packagers can run only certain tests by setting for example:
2295 TEST_ONLY="vfs_type zerofree"
2297 See C<capitests/tests.c> for more details of how these environment
2300 =head2 DEBUGGING NEW API ACTIONS
2302 Test new actions work before submitting them.
2304 You can use guestfish to try out new commands.
2306 Debugging the daemon is a problem because it runs inside a minimal
2307 environment. However you can fprintf messages in the daemon to
2308 stderr, and they will show up if you use C<guestfish -v>.
2310 =head2 FORMATTING CODE AND OTHER CONVENTIONS
2312 Our C source code generally adheres to some basic code-formatting
2313 conventions. The existing code base is not totally consistent on this
2314 front, but we do prefer that contributed code be formatted similarly.
2315 In short, use spaces-not-TABs for indentation, use 2 spaces for each
2316 indentation level, and other than that, follow the K&R style.
2318 If you use Emacs, add the following to one of one of your start-up files
2319 (e.g., ~/.emacs), to help ensure that you get indentation right:
2321 ;;; In libguestfs, indent with spaces everywhere (not TABs).
2322 ;;; Exceptions: Makefile and ChangeLog modes.
2323 (add-hook 'find-file-hook
2324 '(lambda () (if (and buffer-file-name
2325 (string-match "/libguestfs\\>"
2327 (not (string-equal mode-name "Change Log"))
2328 (not (string-equal mode-name "Makefile")))
2329 (setq indent-tabs-mode nil))))
2331 ;;; When editing C sources in libguestfs, use this style.
2332 (defun libguestfs-c-mode ()
2333 "C mode with adjusted defaults for use with libguestfs."
2336 (setq c-indent-level 2)
2337 (setq c-basic-offset 2))
2338 (add-hook 'c-mode-hook
2339 '(lambda () (if (string-match "/libguestfs\\>"
2341 (libguestfs-c-mode))))
2343 Enable warnings when compiling (and fix any problems this
2346 ./configure --enable-gcc-warnings
2350 make syntax-check # checks the syntax of the C code
2351 make check # runs the test suite
2353 =head2 DAEMON CUSTOM PRINTF FORMATTERS
2355 In the daemon code we have created custom printf formatters C<%Q> and
2356 C<%R>, which are used to do shell quoting.
2362 Simple shell quoted string. Any spaces or other shell characters are
2367 Same as C<%Q> except the string is treated as a path which is prefixed
2374 asprintf (&cmd, "cat %R", path);
2376 would produce C<cat /sysroot/some\ path\ with\ spaces>
2378 I<Note:> Do I<not> use these when you are passing parameters to the
2379 C<command{,r,v,rv}()> functions. These parameters do NOT need to be
2380 quoted because they are not passed via the shell (instead, straight to
2381 exec). You probably want to use the C<sysroot_path()> function
2384 =head2 SUBMITTING YOUR NEW API ACTIONS
2386 Submit patches to the mailing list:
2387 L<http://www.redhat.com/mailman/listinfo/libguestfs>
2388 and CC to L<rjones@redhat.com>.
2390 =head2 INTERNATIONALIZATION (I18N) SUPPORT
2392 We support i18n (gettext anyhow) in the library.
2394 However many messages come from the daemon, and we don't translate
2395 those at the moment. One reason is that the appliance generally has
2396 all locale files removed from it, because they take up a lot of space.
2397 So we'd have to readd some of those, as well as copying our PO files
2400 Debugging messages are never translated, since they are intended for
2403 =head2 SOURCE CODE SUBDIRECTORIES
2409 The libguestfs appliance, build scripts and so on.
2413 Automated tests of the C API.
2417 The L<virt-cat(1)>, L<virt-filesystems(1)> and L<virt-ls(1)> commands
2422 Outside contributions, experimental parts.
2426 The daemon that runs inside the libguestfs appliance and carries out
2431 L<virt-df(1)> command and documentation.
2439 L<guestfish(1)>, the command-line shell, and various shell scripts
2440 built on top such as L<virt-copy-in(1)>, L<virt-copy-out(1)>,
2441 L<virt-tar-in(1)>, L<virt-tar-out(1)>.
2445 L<guestmount(1)>, FUSE (userspace filesystem) built on top of libguestfs.
2449 The crucially important generator, used to automatically generate
2450 large amounts of boilerplate C code for things like RPC and bindings.
2454 Files used by the test suite.
2456 Some "phony" guest images which we test against.
2460 L<virt-inspector(1)>, the virtual machine image inspector.
2464 Logo used on the website. The fish is called Arthur by the way.
2468 M4 macros used by autoconf.
2472 Translations of simple gettext strings.
2476 The build infrastructure and PO files for translations of manpages and
2477 POD files. Eventually this will be combined with the C<po> directory,
2478 but that is rather complicated.
2480 =item C<regressions>
2486 L<virt-rescue(1)> command and documentation.
2490 Source code to the C library.
2494 Command line tools written in Perl (L<virt-resize(1)> and many others).
2498 Test tool for end users to test if their qemu/kernel combination
2499 will work with libguestfs.
2521 =head1 ENVIRONMENT VARIABLES
2525 =item LIBGUESTFS_APPEND
2527 Pass additional options to the guest kernel.
2529 =item LIBGUESTFS_DEBUG
2531 Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
2532 has the same effect as calling C<guestfs_set_verbose (g, 1)>.
2534 =item LIBGUESTFS_MEMSIZE
2536 Set the memory allocated to the qemu process, in megabytes. For
2539 LIBGUESTFS_MEMSIZE=700
2541 =item LIBGUESTFS_PATH
2543 Set the path that libguestfs uses to search for kernel and initrd.img.
2544 See the discussion of paths in section PATH above.
2546 =item LIBGUESTFS_QEMU
2548 Set the default qemu binary that libguestfs uses. If not set, then
2549 the qemu which was found at compile time by the configure script is
2552 See also L</QEMU WRAPPERS> above.
2554 =item LIBGUESTFS_TRACE
2556 Set C<LIBGUESTFS_TRACE=1> to enable command traces. This
2557 has the same effect as calling C<guestfs_set_trace (g, 1)>.
2561 Location of temporary directory, defaults to C</tmp> except for the
2562 cached supermin appliance which defaults to C</var/tmp>.
2564 If libguestfs was compiled to use the supermin appliance then the
2565 real appliance is cached in this directory, shared between all
2566 handles belonging to the same EUID. You can use C<$TMPDIR> to
2567 configure another directory to use in case C</var/tmp> is not large
2574 L<guestfs-examples(3)>,
2575 L<guestfs-ocaml(3)>,
2576 L<guestfs-python(3)>,
2582 L<virt-copy-out(1)>,
2585 L<virt-filesystems(1)>,
2586 L<virt-inspector(1)>,
2587 L<virt-list-filesystems(1)>,
2588 L<virt-list-partitions(1)>,
2599 L<http://libguestfs.org/>.
2601 Tools with a similar purpose:
2610 To get a list of bugs against libguestfs use this link:
2612 L<https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools>
2614 To report a new bug against libguestfs use this link:
2616 L<https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools>
2618 When reporting a bug, please check:
2624 That the bug hasn't been reported already.
2628 That you are testing a recent version.
2632 Describe the bug accurately, and give a way to reproduce it.
2636 Run libguestfs-test-tool and paste the B<complete, unedited>
2637 output into the bug report.
2643 Richard W.M. Jones (C<rjones at redhat dot com>)
2647 Copyright (C) 2009-2010 Red Hat Inc.
2648 L<http://libguestfs.org/>
2650 This library is free software; you can redistribute it and/or
2651 modify it under the terms of the GNU Lesser General Public
2652 License as published by the Free Software Foundation; either
2653 version 2 of the License, or (at your option) any later version.
2655 This library is distributed in the hope that it will be useful,
2656 but WITHOUT ANY WARRANTY; without even the implied warranty of
2657 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
2658 Lesser General Public License for more details.
2660 You should have received a copy of the GNU Lesser General Public
2661 License along with this library; if not, write to the Free Software
2662 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA