5 guestfs - Library for accessing and modifying virtual machine images
11 guestfs_h *handle = guestfs_create ();
12 guestfs_add_drive (handle, "guest.img");
13 guestfs_launch (handle);
14 guestfs_wait_ready (handle);
15 guestfs_mount (handle, "/dev/sda1", "/");
16 guestfs_touch (handle, "/hello");
17 guestfs_sync (handle);
18 guestfs_close (handle);
22 Libguestfs is a library for accessing and modifying guest disk images.
23 Amongst the things this is good for: making batch configuration
24 changes to guests, getting disk used/free statistics (see also:
25 virt-df), migrating between virtualization systems (see also:
26 virt-p2v), performing partial backups, performing partial guest
27 clones, cloning guests and changing registry/UUID/hostname info, and
30 Libguestfs uses Linux kernel and qemu code, and can access any type of
31 guest filesystem that Linux and qemu can, including but not limited
32 to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
33 schemes, qcow, qcow2, vmdk.
35 Libguestfs provides ways to enumerate guest storage (eg. partitions,
36 LVs, what filesystem is in each LV, etc.). It can also run commands
37 in the context of the guest. Also you can access filesystems over FTP.
39 Libguestfs is a library that can be linked with C and C++ management
40 programs (or management programs written in OCaml or Perl).
41 You can also use it from shell scripts or the command line.
43 You don't need to be root to use libguestfs, although obviously you do
44 need enough permissions to access the disk images.
46 =head1 CONNECTION MANAGEMENT
48 If you are using the high-level API, then you should call the
49 functions in the following order:
51 guestfs_h *handle = guestfs_create ();
53 guestfs_add_drive (handle, "guest.img");
54 /* call guestfs_add_drive additional times if the guest has
58 guestfs_launch (handle);
59 guestfs_wait_ready (handle);
61 /* now you can examine what partitions, LVs etc are available
62 * you have to mount / at least
64 guestfs_mount (handle, "/dev/sda1", "/");
66 /* now you can perform actions on the guest disk image */
67 guestfs_touch (handle, "/hello");
69 /* you only need to call guestfs_sync if you have made
70 * changes to the guest image
72 guestfs_sync (handle);
74 guestfs_close (handle);
76 C<guestfs_wait_ready> and all of the actions including C<guestfs_sync>
77 are blocking calls. You can use the low-level event API to do
78 non-blocking operations instead.
80 All functions that return integers, return C<-1> on error. See
81 section ERROR HANDLING below for how to handle errors.
85 C<guestfs_h> is the opaque type representing a connection handle.
86 Create a handle by calling C<guestfs_create>. Call C<guestfs_close>
87 to free the handle and release all resources used.
89 Handles and operations on handles are not thread safe. However you
90 can use a separate handle for each thread (but not on the same disk
95 guestfs_h *guestfs_create (void);
97 Create a connection handle.
99 You have to call C<guestfs_add_drive> on the handle at least once.
100 See CONFIGURATION MANAGEMENT section below.
102 This function returns a non-NULL pointer to a handle on success or
105 After configuring the handle, you have to call C<guestfs_launch> and
106 C<guestfs_wait_ready>.
108 You may also want to configure error handling for the handle. See
109 ERROR HANDLING section below.
113 void guestfs_close (guestfs_h *handle);
115 This closes the connection handle and frees up all resources used.
117 =head2 guestfs_launch, guestfs_wait_ready
119 int guestfs_launch (guestfs_h *handle);
120 int guestfs_wait_ready (guestfs_h *handle);
122 Internally libguestfs is implemented by running a virtual machine
123 using L<qemu(1)>. These calls are necessary in order to boot the
124 virtual machine. More discussion of this is available in the section
125 STATE MACHINE AND LOW-LEVEL EVENT API below.
127 You should call these two functions after configuring the handle
128 (eg. adding drives) but before performing any actions.
130 =head2 guestfs_kill_subprocess
132 int guestfs_kill_subprocess (guestfs_h *handle);
134 This kills the qemu subprocess. You should never need to call this.
136 =head1 CONFIGURATION MANAGEMENT
138 The configuration functions allow you to configure which drive images
139 will be examined or modified, and set other aspects of the L<qemu(1)>
140 virtual machine that we will be running. You need to call only
141 C<guestfs_add_drive> at least once for each guest image that you want
144 =head2 guestfs_add_drive
146 int guestfs_add_drive (guestfs_h *handle, const char *filename);
148 This function adds a virtual machine disk image C<filename> to the
149 guest. The first time you call this function, the disk appears as IDE
150 disk 0 (C</dev/sda>) in the guest, the second time as C</dev/sdb>, and
153 You don't necessarily need to be root when using libguestfs. However
154 you obviously do need sufficient permissions to access the filename
155 for whatever operations you want to perform (ie. read access if you
156 just want to read the image or write access if you want to modify the
159 This is equivalent to the qemu parameter C<-drive file=filename>.
161 =head2 guestfs_add_cdrom
163 int guestfs_add_cdrom (guestfs_h *handle, const char *filename);
165 This function adds a virtual CD-ROM disk image to the guest.
167 This is equivalent to the qemu parameter C<-cdrom filename>.
169 =head2 guestfs_config
171 int guestfs_config (guestfs_h *handle,
172 const char *qemu_param, const char *qemu_value);
174 This can be used to add arbitrary qemu command line parameters
175 of the form C<-param value>. Actually it's not quite arbitrary - we
176 prevent you from setting some parameters which would interfere with
177 parameters that we use.
179 The first character of C<qemu_param> string must be a C<-> (dash).
181 C<qemu_value> can be NULL.
183 =head1 ERROR HANDLING
185 The convention in all functions that return C<int> is that they return
186 C<-1> to indicate an error. You can get additional information on
187 errors by calling C<guestfs_set_error_handler>. The default error
188 handler prints the information string to C<stderr>.
190 Out of memory errors are handled differently. The default action is
191 to call L<abort(3)>. If this is undesirable, then you can set a
192 handler using C<guestfs_set_out_of_memory_handler>.
194 =head2 guestfs_set_error_handler
196 typedef void (*guestfs_error_handler_cb) (guestfs_h *handle,
199 void guestfs_set_error_handler (guestfs_h *handle,
200 guestfs_error_handler_cb cb,
203 The callback C<cb> will be called if there is an error. The
204 parameters passed to the callback are an opaque data pointer and the
205 error message string.
207 Note that the message string C<msg> is freed as soon as the callback
208 function returns, so if you want to stash it somewhere you must make
211 The default handler prints messages on C<stderr>.
213 If you set C<cb> to C<NULL> then I<no> handler is called and the error
214 message is completely discarded.
216 =head2 guestfs_get_error_handler
218 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *handle,
221 Returns the current error handler callback.
223 =head2 guestfs_set_out_of_memory_handler
225 typedef void (*guestfs_abort_cb) (void);
226 int guestfs_set_out_of_memory_handler (guestfs_h *handle,
229 The callback C<cb> will be called if there is an out of memory
230 situation. I<Note this callback must not return>.
232 The default is to call L<abort(3)>.
234 You cannot set C<cb> to C<NULL>. You can't ignore out of memory
237 =head2 guestfs_get_out_of_memory_handler
239 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *handle);
241 This returns the current out of memory handler.
245 Libguestfs needs a kernel and initrd.img, which it finds by looking
246 along an internal path.
248 By default it looks for these in the directory C<$libdir/guestfs>
249 (eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
251 Use C<guestfs_set_path> or set the environment variable
252 C<LIBGUESTFS_PATH> to change the directories that libguestfs will
253 search in. The value is a colon-separated list of paths. The current
254 directory is I<not> searched unless the path contains an empty element
255 or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
256 search the current directory and then C</usr/lib/guestfs>.
258 =head2 guestfs_set_path
260 void guestfs_set_path (guestfs_h *handle, const char *path);
262 Set the path that libguestfs searches for kernel and initrd.img.
264 The default is C<$libdir/guestfs> unless overridden by setting
265 C<LIBGUESTFS_PATH> environment variable.
267 The string C<path> is stashed in the libguestfs handle, so the caller
268 must make sure it remains valid for the lifetime of the handle.
270 Setting C<path> to C<NULL> restores the default path.
272 =head2 guestfs_get_path
274 const char *guestfs_get_path (guestfs_h *handle);
276 Return the current search path.
278 This is always non-NULL. If it wasn't set already, then this will
279 return the default path.
283 =head2 guestfs_set_autosync
285 void guestfs_set_autosync (guestfs_h *handle, int autosync);
287 If C<autosync> is true, this enables autosync. Libguestfs will make a
288 best effort attempt to run C<guestfs_sync> when the handle is closed
289 (also if the program exits without closing handles).
291 =head2 guestfs_get_autosync
293 int guestfs_get_autosync (guestfs_h *handle);
295 Get the autosync flag.
297 =head1 VERBOSE MESSAGES
299 =head2 guestfs_set_verbose
301 void guestfs_set_verbose (guestfs_h *handle, int verbose);
303 If C<verbose> is true, this turns on verbose messages (to C<stderr>).
305 Verbose messages are disabled unless the environment variable
306 C<LIBGUESTFS_DEBUG> is defined and set to C<1>.
308 =head2 guestfs_get_verbose
310 int guestfs_get_verbose (guestfs_h *handle);
312 This returns the verbose messages flag.
314 =head1 HIGH-LEVEL API ACTIONS
322 =head1 STATE MACHINE AND LOW-LEVEL EVENT API
324 Internally, libguestfs is implemented by running a virtual machine
325 using L<qemu(1)>. QEmu runs as a child process of the main program,
326 and most of this discussion won't make sense unless you understand
327 that the complexity is dealing with the (asynchronous) actions of the
331 ___________________ _________________________
333 | main program | | qemu +-----------------+|
334 | | | | Linux kernel ||
335 +-------------------+ | +-----------------+|
336 | libguestfs <-------------->| guestfsd ||
337 | | | +-----------------+|
338 \___________________/ \_________________________/
340 The diagram above shows libguestfs communicating with the guestfsd
341 daemon running inside the qemu child process. There are several
342 points of failure here: qemu can fail to start, the virtual machine
343 inside qemu can fail to boot, guestfsd can fail to start or not
344 establish communication, any component can start successfully but fail
345 asynchronously later, and so on.
349 libguestfs uses a state machine to model the child process:
360 / | \ \ guestfs_launch
366 / | guestfs_wait_ready
371 \______/ <------ \________/
373 The normal transitions are (1) CONFIG (when the handle is created, but
374 there is no child process), (2) LAUNCHING (when the child process is
375 booting up), (3) alternating between READY and BUSY as commands are
376 issued to, and carried out by, the child process.
378 The guest may be killed by C<guestfs_kill_subprocess>, or may die
379 asynchronously at any time (eg. due to some internal error), and that
380 causes the state to transition back to CONFIG.
382 Configuration commands for qemu such as C<guestfs_add_drive> can only
383 be issued when in the CONFIG state.
385 The high-level API offers two calls that go from CONFIG through
386 LAUNCHING to READY. C<guestfs_launch> is a non-blocking call that
387 starts up the child process, immediately moving from CONFIG to
388 LAUNCHING. C<guestfs_wait_ready> blocks until the child process is
389 READY to accept commands (or until some failure or timeout). The
390 low-level event API described below provides a non-blocking way to
391 replace C<guestfs_wait_ready>.
393 High-level API actions such as C<guestfs_mount> can only be issued
394 when in the READY state. These high-level API calls block waiting for
395 the command to be carried out (ie. the state to transition to BUSY and
396 then back to READY). But using the low-level event API, you get
397 non-blocking versions. (But you can still only carry out one
398 operation per handle at a time - that is a limitation of the
399 communications protocol we use).
401 Finally, the child process sends asynchronous messages back to the
402 main program, such as kernel log messages. Mostly these are ignored
403 by the high-level API, but using the low-level event API you can
404 register to receive these messages.
406 =head2 SETTING CALLBACKS TO HANDLE EVENTS
408 The child process generates events in some situations. Current events
409 include: receiving a reply message after some action, receiving a log
410 message, the child process exits, &c.
412 Use the C<guestfs_set_*_callback> functions to set a callback for
413 different types of events.
415 Only I<one callback of each type> can be registered for each handle.
416 Calling C<guestfs_set_*_callback> again overwrites the previous
417 callback of that type. Cancel all callbacks of this type by calling
418 this function with C<cb> set to C<NULL>.
420 =head2 NON-BLOCKING ACTIONS
422 XXX NOT IMPLEMENTED YET XXX
424 C<guestfs_set_reply_callback> is the most interesting callback to
425 play with, since it allows you to perform actions without blocking.
432 guestfs_main_loop_run (); /* --> blocks, then calls my_cb */
437 guestfs_set_reply_callback (handle, my_cb, data);
438 guestfs_nb_[action] (handle, [other parameters ...]);
439 /* returns immediately */
442 my_cb (guestfs_h *handle, void *data, XDR *xdr)
444 retval = guestfs_nb_[action]_r (handle, xdr);
448 There are C<guestfs_nb_*> and C<guestfs_nb_*_r> functions
449 corresponding to every C<guestfs_*> action in the high-level API.
451 =head2 guestfs_set_reply_callback
453 typedef void (*guestfs_reply_cb) (guestfs_h *g, void *opaque, XDR *xdr);
454 void guestfs_set_reply_callback (guestfs_h *handle,
458 The callback function C<cb> will be called whenever a reply is
459 received from the child process. (This corresponds to a transition
460 from the BUSY state to the READY state).
462 Note that the C<xdr> that you get in the callback is in C<XDR_DECODE>
463 mode, and you need to consume it before you return from the callback
464 function (since it gets destroyed after).
466 =head2 guestfs_set_log_message_callback
468 typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
470 void guestfs_set_log_message_callback (guestfs_h *handle,
471 guestfs_log_message_cb cb,
474 The callback function C<cb> will be called whenever qemu or the guest
475 writes anything to the console.
477 Use this function to capture kernel messages and similar.
479 Normally there is no log message handler, and log messages are just
482 =head2 guestfs_set_subprocess_quit_callback
484 typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
485 void guestfs_set_subprocess_quit_callback (guestfs_h *handle,
486 guestfs_subprocess_quit_cb cb,
489 The callback function C<cb> will be called when the child process
490 quits, either asynchronously or if killed by
491 C<guestfs_kill_subprocess>. (This corresponds to a transition from
492 any state to the CONFIG state).
494 =head2 guestfs_set_launch_done_callback
496 typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
497 void guestfs_set_launch_done_callback (guestfs_h *handle,
501 The callback function C<cb> will be called when the child process
502 becomes ready first time after it has been launched. (This
503 corresponds to a transition from LAUNCHING to the READY state).
505 You can use this instead of C<guestfs_wait_ready> to implement a
506 non-blocking wait for the child process to finish booting up.
508 =head2 EVENT MAIN LOOP
510 To use the low-level event API, you have to provide an event "main
511 loop". You can write your own, but if you don't want to write one,
512 two are provided for you:
516 =item libguestfs-select
518 A simple main loop that is implemented using L<select(2)>.
520 This is the default main loop unless you call C<guestfs_set_main_loop>
521 or C<guestfs_glib_set_main_loop>.
523 =item libguestfs-glib
525 An implementation which can be used with GLib and GTK+ programs. You
526 can use this to write graphical (GTK+) programs which use libguestfs
527 without hanging during long or slow operations.
531 =head2 guestfs_set_main_loop
533 void guestfs_set_main_loop (guestfs_main_loop *);
535 This call sets the current main loop to the list of callbacks
536 contained in the C<guestfs_main_loop> structure.
538 Only one main loop implementation can be used by libguestfs, so
539 calling this replaces the previous one. (So this is something that
540 has to be done by the main program, but only the main program "knows"
541 that it is a GTK+ program or whatever).
543 You should call this early in the main program, certainly before
544 calling C<guestfs_create>.
546 =head2 guestfs_glib_set_main_loop
548 void guestfs_glib_set_main_loop (GMainLoop *);
550 This helper calls C<guestfs_set_main_loop> with the correct callbacks
551 for integrating with the GLib main loop.
553 The libguestfs-glib main loop is contained in a separate library, so
554 that libguestfs doesn't depend on the whole of GLib:
557 #include <guestfs-glib.h>
562 g_main_loop_new (g_main_context_default (), 1);
564 guestfs_glib_set_main_loop (loop);
566 g_main_loop_run (loop);
569 To use this main loop you must link with C<-lguestfs-glib>. (See also
570 the GLib and GTK+ documentation).
572 =head2 guestfs_main_loop_run
574 void guestfs_main_loop_run (void);
576 This calls the main loop.
578 For some types of main loop you may want or prefer to call another
579 function, eg. C<g_main_loop_run>, or the main loop may already be
580 invoked by another part of your program. In those cases, ignore this
583 =head2 guestfs_main_loop_quit
585 void guestfs_main_loop_quit (void);
587 This instructs the main loop to quit. In other words,
588 C<guestfs_main_loop_run> will return.
590 For some types of main loop you may want or prefer to call another
591 function, eg. C<g_main_loop_quit>. In those cases, ignore this call.
593 =head2 WRITING A CUSTOM MAIN LOOP
595 This isn't documented. Please see the libguestfs-select and
596 libguestfs-glib implementations.
598 =head1 ENVIRONMENT VARIABLES
602 =item LIBGUESTFS_DEBUG
604 Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
605 has the same effect as calling C<guestfs_set_verbose (handle, 1)>.
607 =item LIBGUESTFS_PATH
609 Set the path that libguestfs uses to search for kernel and initrd.img.
610 See the discussion of paths in C<guestfs_set_path> above.
619 L<http://et.redhat.com/~rjones/libguestfs>.
623 Richard W.M. Jones (C<rjones at redhat dot com>)
627 Copyright (C) 2009 Red Hat Inc.
628 L<http://et.redhat.com/~rjones/libguestfs>
630 This library is free software; you can redistribute it and/or
631 modify it under the terms of the GNU Lesser General Public
632 License as published by the Free Software Foundation; either
633 version 2 of the License, or (at your option) any later version.
635 This library is distributed in the hope that it will be useful,
636 but WITHOUT ANY WARRANTY; without even the implied warranty of
637 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
638 Lesser General Public License for more details.
640 You should have received a copy of the GNU Lesser General Public
641 License along with this library; if not, write to the Free Software
642 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA