You don't need to be root to use libguestfs, although obviously you do
need enough permissions to access the disk images.
-=head1 CONNECTION MANAGEMENT
+Libguestfs is a large API because it can do many things. For a gentle
+introduction, please read the L</API OVERVIEW> section next.
+
+=head1 API OVERVIEW
+
+This section provides a gentler overview of the libguestfs API. We
+also try to group API calls together, where that may not be obvious
+from reading about the individual calls below.
+
+=head2 HANDLES
-If you are using the high-level API, then you should call the
-functions in the following order:
+Before you can use libguestfs calls, you have to create a handle.
+Then you must add at least one disk image to the handle, followed by
+launching the handle, then performing whatever operations you want,
+and finally closing the handle. So the general structure of all
+libguestfs-using programs looks like this:
guestfs_h *handle = guestfs_create ();
- guestfs_add_drive (handle, "guest.img");
- /* call guestfs_add_drive additional times if the guest has
- * multiple disks
+ /* Call guestfs_add_drive additional times if there are
+ * multiple disk images.
*/
+ guestfs_add_drive (handle, "guest.img");
+ /* Most manipulation calls won't work until you've launched
+ * the handle. You have to do this _after_ adding drives
+ * and _before_ other commands.
+ */
guestfs_launch (handle);
- /* now you can examine what partitions, LVs etc are available
- * you have to mount / at least
+ /* Now you can examine what partitions, LVs etc are available.
+ */
+ char **partitions = guestfs_list_partitions (handle);
+ char **logvols = guestfs_lvs (handle);
+
+ /* To access a filesystem in the image, you must mount it.
*/
guestfs_mount (handle, "/dev/sda1", "/");
- /* now you can perform actions on the guest disk image */
+ /* Now you can perform filesystem actions on the guest disk image. */
guestfs_touch (handle, "/hello");
- /* you only need to call guestfs_sync if you have made
- * changes to the guest image
+ /* You only need to call guestfs_sync if you have made
+ * changes to the guest image.
*/
guestfs_sync (handle);
+ /* Close the handle. */
guestfs_close (handle);
-C<guestfs_launch> and all of the actions including C<guestfs_sync>
-are blocking calls.
-
-All functions that return integers, return C<-1> on error. See
-section L</ERROR HANDLING> below for how to handle errors.
-
-=head2 guestfs_h *
-
-C<guestfs_h> is the opaque type representing a connection handle.
-Create a handle by calling C<guestfs_create>. Call C<guestfs_close>
-to free the handle and release all resources used.
-
-For information on using multiple handles and threads, see the section
-L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
-
-=head2 guestfs_create
-
- guestfs_h *guestfs_create (void);
-
-Create a connection handle.
-
-You have to call C<guestfs_add_drive> on the handle at least once.
-
-This function returns a non-NULL pointer to a handle on success or
-NULL on error.
-
-After configuring the handle, you have to call C<guestfs_launch>.
-
-You may also want to configure error handling for the handle. See
-L</ERROR HANDLING> section below.
-
-=head2 guestfs_close
-
- void guestfs_close (guestfs_h *handle);
-
-This closes the connection handle and frees up all resources used.
-
-=head1 ERROR HANDLING
+The code above doesn't include any error checking. In real code you
+should check return values carefully for errors. In general all
+functions that return integers return C<-1> on error, and all
+functions that return pointers return C<NULL> on error. See section
+L</ERROR HANDLING> below for how to handle errors, and consult the
+documentation for each function call below to see precisely how they
+return error indications.
-The convention in all functions that return C<int> is that they return
-C<-1> to indicate an error. You can get additional information on
-errors by calling C<guestfs_last_error> and/or by setting up an error
-handler with C<guestfs_set_error_handler>.
+=head2 DISK IMAGES
-The default error handler prints the information string to C<stderr>.
-
-Out of memory errors are handled differently. The default action is
-to call L<abort(3)>. If this is undesirable, then you can set a
-handler using C<guestfs_set_out_of_memory_handler>.
-
-=head2 guestfs_last_error
-
- const char *guestfs_last_error (guestfs_h *handle);
+The image filename (C<"guest.img"> in the example above) could be a
+disk image from a virtual machine, a L<dd(1)> copy of a physical block
+device, an actual block device, or simply an empty file of zeroes that
+you have created through L<posix_fallocate(3)>. Libguestfs lets you
+do useful things to all of these.
-This returns the last error message that happened on C<handle>. If
-there has not been an error since the handle was created, then this
-returns C<NULL>.
+You can add a disk read-only using C<guestfs_add_drive_ro>, in which
+case libguestfs won't modify the file.
-The lifetime of the returned string is until the next error occurs, or
-C<guestfs_close> is called.
+Be extremely cautious if the disk image is in use, eg. if it is being
+used by a virtual machine. Adding it read-write will almost certainly
+cause disk corruption, but adding it read-only is safe.
-The error string is not localized (ie. is always in English), because
-this makes searching for error messages in search engines give the
-largest number of results.
+You must add at least one disk image, and you may add multiple disk
+images. In the API, the disk images are usually referred to as
+C</dev/sda> (for the first one you added), C</dev/sdb> (for the second
+one you added), etc.
-=head2 guestfs_set_error_handler
+Once C<guestfs_launch> has been called you cannot add any more images.
+You can call C<guestfs_list_devices> to get a list of the device
+names, in the order that you added them. See also L</BLOCK DEVICE
+NAMING> below.
- typedef void (*guestfs_error_handler_cb) (guestfs_h *handle,
- void *data,
- const char *msg);
- void guestfs_set_error_handler (guestfs_h *handle,
- guestfs_error_handler_cb cb,
- void *data);
+=head2 MOUNTING
-The callback C<cb> will be called if there is an error. The
-parameters passed to the callback are an opaque data pointer and the
-error message string.
+Before you can read or write files, create directories and so on in a
+disk image that contains filesystems, you have to mount those
+filesystems using C<guestfs_mount>. If you already know that a disk
+image contains (for example) one partition with a filesystem on that
+partition, then you can mount it directly:
-Note that the message string C<msg> is freed as soon as the callback
-function returns, so if you want to stash it somewhere you must make
-your own copy.
-
-The default handler prints messages on C<stderr>.
-
-If you set C<cb> to C<NULL> then I<no> handler is called.
-
-=head2 guestfs_get_error_handler
-
- guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *handle,
- void **data_rtn);
+ guestfs_mount (handle, "/dev/sda1", "/");
-Returns the current error handler callback.
+where C</dev/sda1> means literally the first partition (C<1>) of the
+first disk image that we added (C</dev/sda>). If the disk contains
+Linux LVM2 logical volumes you could refer to those instead (eg. C</dev/VG/LV>).
-=head2 guestfs_set_out_of_memory_handler
+If you are given a disk image and you don't know what it contains then
+you have to find out. Libguestfs can also do that: use
+C<guestfs_list_partitions> and C<guestfs_lvs> to list possible
+partitions and LVs, and either try mounting each to see what is
+mountable, or else examine them with C<guestfs_file>. But you might
+find it easier to look at higher level programs built on top of
+libguestfs, in particular L<virt-inspector(1)>.
- typedef void (*guestfs_abort_cb) (void);
- int guestfs_set_out_of_memory_handler (guestfs_h *handle,
- guestfs_abort_cb);
+To mount a disk image read-only, use C<guestfs_mount_ro>. There are
+several other variations of the C<guestfs_mount_*> call.
-The callback C<cb> will be called if there is an out of memory
-situation. I<Note this callback must not return>.
+=head2 FILESYSTEM ACCESS AND MODIFICATION
-The default is to call L<abort(3)>.
+The majority of the libguestfs API consists of fairly low-level calls
+for accessing and modifying the files, directories, symlinks etc on
+mounted filesystems. There are over a hundred such calls which you
+can find listed in detail below in this man page, and we don't even
+pretend to cover them all in this overview.
-You cannot set C<cb> to C<NULL>. You can't ignore out of memory
-situations.
+Specify filenames as full paths including the mount point.
-=head2 guestfs_get_out_of_memory_handler
+For example, if you mounted a filesystem at C<"/"> and you want to
+read the file called C<"etc/passwd"> then you could do:
- guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *handle);
+ char *data = guestfs_cat (handle, "/etc/passwd");
-This returns the current out of memory handler.
+This would return C<data> as a newly allocated buffer containing the
+full content of that file (with some conditions: see also
+L</DOWNLOADING> below), or C<NULL> if there was an error.
-=head1 PATH
+As another example, to create a top-level directory on that filesystem
+called C<"var"> you would do:
-Libguestfs needs a kernel and initrd.img, which it finds by looking
-along an internal path.
+ guestfs_mkdir (handle, "/var");
-By default it looks for these in the directory C<$libdir/guestfs>
-(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
+To create a symlink you could do:
-Use C<guestfs_set_path> or set the environment variable
-C<LIBGUESTFS_PATH> to change the directories that libguestfs will
-search in. The value is a colon-separated list of paths. The current
-directory is I<not> searched unless the path contains an empty element
-or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
-search the current directory and then C</usr/lib/guestfs>.
+ guestfs_ln_s (handle, "/etc/init.d/portmap",
+ "/etc/rc3.d/S30portmap");
-=head1 API OVERVIEW
+Libguestfs will reject attempts to use relative paths. There is no
+concept of a current working directory. Libguestfs can return errors
+in many situations: for example if the filesystem isn't writable, or
+if a file or directory that you requested doesn't exist. If you are
+using the C API (documented here) you have to check for those error
+conditions after each call. (Other language bindings turn these
+errors into exceptions).
-This section provides additional documentation for groups of API
-calls, which may not be obvious from reading about the individual
-calls below.
-
-=head2 LVM2
-
-Libguestfs provides access to a large part of the LVM2 API. It won't
-make much sense unless you familiarize yourself with the concepts of
-physical volumes, volume groups and logical volumes.
-
-This author strongly recommends reading the LVM HOWTO, online at
-L<http://tldp.org/HOWTO/LVM-HOWTO/>.
+File writes are affected by the per-handle umask, set by calling
+C<guestfs_umask> and defaulting to 022.
=head2 PARTITIONING
+Libguestfs contains API calls to read, create and modify partition
+tables on disk images.
+
In the common case where you want to create a single partition
covering the whole disk, you should use the C<guestfs_part_disk>
call:
parttype = "gpt";
guestfs_part_disk (g, "/dev/sda", parttype);
+Obviously this effectively wipes anything that was on that disk image
+before.
+
In general MBR partitions are both unnecessarily complicated and
depend on archaic details, namely the Cylinder-Head-Sector (CHS)
geometry of the disk. C<guestfs_sfdiskM> can be used to
My advice: make a single partition to cover the whole disk, then use
LVM on top.
+=head2 LVM2
+
+Libguestfs provides access to a large part of the LVM2 API, such as
+C<guestfs_lvcreate> and C<guestfs_vgremove>. It won't make much sense
+unless you familiarize yourself with the concepts of physical volumes,
+volume groups and logical volumes.
+
+This author strongly recommends reading the LVM HOWTO, online at
+L<http://tldp.org/HOWTO/LVM-HOWTO/>.
+
+=head2 DOWNLOADING
+
+Use C<guestfs_cat> to download small, text only files. This call
+is limited to files which are less than 2 MB and which cannot contain
+any ASCII NUL (C<\0>) characters. However it has a very simple
+to use API.
+
+C<guestfs_read_file> can be used to read files which contain
+arbitrary 8 bit data, since it returns a (pointer, size) pair.
+However it is still limited to "small" files, less than 2 MB.
+
+C<guestfs_download> can be used to download any file, with no
+limits on content or size (even files larger than 4 GB).
+
+To download multiple files, see C<guestfs_tar_out> and
+C<guestfs_tgz_out>.
+
=head2 UPLOADING
-For small, single files, use C<guestfs_write_file>. In some versions
-of libguestfs there was a bug which limited this call to text files
+It's often the case that you want to write a file or files to the disk
+image.
+
+For small, single files, use C<guestfs_write_file>. This call
+currently contains a bug which limited the call to plain text files
(not containing ASCII NUL characters).
To upload a single file, use C<guestfs_upload>. This call has no
UUIDs. If you want to pre-build an image or you need to mount it
using a label or UUID, use an ISO image instead.
-=head2 DOWNLOADING
+=head2 LISTING FILES
-Use C<guestfs_cat> to download small, text only files. This call
-is limited to files which are less than 2 MB and which cannot contain
-any ASCII NUL (C<\0>) characters. However it has a very simple
-to use API.
+C<guestfs_ll> is just designed for humans to read (mainly when using
+the L<guestfish(1)>-equivalent command C<ll>).
-C<guestfs_read_file> can be used to read files which contain
-arbitrary 8 bit data, since it returns a (pointer, size) pair.
-However it is still limited to "small" files, less than 2 MB.
+C<guestfs_ls> is a quick way to get a list of files in a directory
+from programs, as a flat list of strings.
-C<guestfs_download> can be used to download any file, with no
-limits on content or size (even files larger than 4 GB).
+C<guestfs_readdir> is a programmatic way to get a list of files in a
+directory, plus additional information about each one. It is more
+equivalent to using the L<readdir(3)> call on a local filesystem.
-To download multiple files, see C<guestfs_tar_out> and
-C<guestfs_tgz_out>.
+C<guestfs_find> can be used to recursively list files.
=head2 RUNNING COMMANDS
The difference is that C<guestfs_sh> runs commands using the shell, so
any shell globs, redirections, etc will work.
-=head2 LISTING FILES
+=head2 CONFIGURATION FILES
-C<guestfs_ll> is just designed for humans to read (mainly when using
-the L<guestfish(1)>-equivalent command C<ll>).
+To read and write configuration files in Linux guest filesystems, we
+strongly recommend using Augeas. For example, Augeas understands how
+to read and write, say, a Linux shadow password file or X.org
+configuration file, and so avoids you having to write that code.
-C<guestfs_ls> is a quick way to get a list of files in a directory
-from programs.
-
-C<guestfs_readdir> is a programmatic way to get a list of files in a
-directory, plus additional information about each one.
+The main Augeas calls are bound through the C<guestfs_aug_*> APIs. We
+don't document Augeas itself here because there is excellent
+documentation on the L<http://augeas.net/> website.
-C<guestfs_find> can be used to recursively list files.
+If you don't want to use Augeas (you fool!) then try calling
+C<guestfs_read_lines> to get the file as a list of lines which
+you can iterate over.
=head2 SELINUX
for example by running the external command
C<restorecon pathname>.
+=head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
+
+Libguestfs can mount NTFS partitions. It does this using the
+L<http://www.ntfs-3g.org/> driver.
+
+DOS and Windows still use drive letters, and the filesystems are
+always treated as case insensitive by Windows itself, and therefore
+you might find a Windows configuration file referring to a path like
+C<c:\windows\system32>. When the filesystem is mounted in libguestfs,
+that directory might be referred to as C</WINDOWS/System32>.
+
+Drive letter mappings are outside the scope of libguestfs. You have
+to use libguestfs to read the appropriate Windows Registry and
+configuration files, to determine yourself how drives are mapped (see
+also L<virt-inspector(1)>).
+
+Replacing backslash characters with forward slash characters is also
+outside the scope of libguestfs, but something that you can easily do.
+
+Where we can help is in resolving the case insensitivity of paths.
+For this, call C<guestfs_case_sensitive_path>.
+
+Libguestfs also provides some help for decoding Windows Registry
+"hive" files, through the library C<libhivex> which is part of
+libguestfs. You have to locate and download the hive file(s)
+yourself, and then pass them to C<libhivex> functions. See also the
+programs L<hivexml(1)>, L<hivexget(1)> and L<virt-win-reg(1)> for more
+help on this issue.
+
+=head1 CONNECTION MANAGEMENT
+
+=head2 guestfs_h *
+
+C<guestfs_h> is the opaque type representing a connection handle.
+Create a handle by calling C<guestfs_create>. Call C<guestfs_close>
+to free the handle and release all resources used.
+
+For information on using multiple handles and threads, see the section
+L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
+
+=head2 guestfs_create
+
+ guestfs_h *guestfs_create (void);
+
+Create a connection handle.
+
+You have to call C<guestfs_add_drive> on the handle at least once.
+
+This function returns a non-NULL pointer to a handle on success or
+NULL on error.
+
+After configuring the handle, you have to call C<guestfs_launch>.
+
+You may also want to configure error handling for the handle. See
+L</ERROR HANDLING> section below.
+
+=head2 guestfs_close
+
+ void guestfs_close (guestfs_h *handle);
+
+This closes the connection handle and frees up all resources used.
+
+=head1 ERROR HANDLING
+
+The convention in all functions that return C<int> is that they return
+C<-1> to indicate an error. You can get additional information on
+errors by calling C<guestfs_last_error> and/or by setting up an error
+handler with C<guestfs_set_error_handler>.
+
+The default error handler prints the information string to C<stderr>.
+
+Out of memory errors are handled differently. The default action is
+to call L<abort(3)>. If this is undesirable, then you can set a
+handler using C<guestfs_set_out_of_memory_handler>.
+
+=head2 guestfs_last_error
+
+ const char *guestfs_last_error (guestfs_h *handle);
+
+This returns the last error message that happened on C<handle>. If
+there has not been an error since the handle was created, then this
+returns C<NULL>.
+
+The lifetime of the returned string is until the next error occurs, or
+C<guestfs_close> is called.
+
+The error string is not localized (ie. is always in English), because
+this makes searching for error messages in search engines give the
+largest number of results.
+
+=head2 guestfs_set_error_handler
+
+ typedef void (*guestfs_error_handler_cb) (guestfs_h *handle,
+ void *data,
+ const char *msg);
+ void guestfs_set_error_handler (guestfs_h *handle,
+ guestfs_error_handler_cb cb,
+ void *data);
+
+The callback C<cb> will be called if there is an error. The
+parameters passed to the callback are an opaque data pointer and the
+error message string.
+
+Note that the message string C<msg> is freed as soon as the callback
+function returns, so if you want to stash it somewhere you must make
+your own copy.
+
+The default handler prints messages on C<stderr>.
+
+If you set C<cb> to C<NULL> then I<no> handler is called.
+
+=head2 guestfs_get_error_handler
+
+ guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *handle,
+ void **data_rtn);
+
+Returns the current error handler callback.
+
+=head2 guestfs_set_out_of_memory_handler
+
+ typedef void (*guestfs_abort_cb) (void);
+ int guestfs_set_out_of_memory_handler (guestfs_h *handle,
+ guestfs_abort_cb);
+
+The callback C<cb> will be called if there is an out of memory
+situation. I<Note this callback must not return>.
+
+The default is to call L<abort(3)>.
+
+You cannot set C<cb> to C<NULL>. You can't ignore out of memory
+situations.
+
+=head2 guestfs_get_out_of_memory_handler
+
+ guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *handle);
+
+This returns the current out of memory handler.
+
+=head1 PATH
+
+Libguestfs needs a kernel and initrd.img, which it finds by looking
+along an internal path.
+
+By default it looks for these in the directory C<$libdir/guestfs>
+(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
+
+Use C<guestfs_set_path> or set the environment variable
+C<LIBGUESTFS_PATH> to change the directories that libguestfs will
+search in. The value is a colon-separated list of paths. The current
+directory is I<not> searched unless the path contains an empty element
+or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
+search the current directory and then C</usr/lib/guestfs>.
+
=head1 HIGH-LEVEL API ACTIONS
=head2 ABI GUARANTEE
git.annexia.org / libguestfs.git / commitdiff