C<value> can be NULL.
+=head2 debug
+
+ debug subcmd 'extraargs ...'
+
+The C<debug> command exposes some internals of
+C<guestfsd> (the guestfs daemon) that runs inside the
+qemu subprocess.
+
+There is no comprehensive help for this command. You have
+to look at the file C<daemon/debug.c> in the libguestfs source
+to find out what you can do.
+
=head2 download
download remotefilename (filename|-)
particular that the filename is not prepended to the output
(the C<-b> option).
+=head2 fsck
+
+ fsck fstype device
+
+This runs the filesystem checker (fsck) on C<device> which
+should have filesystem type C<fstype>.
+
+The returned integer is the status. See L<fsck(8)> for the
+list of status codes from C<fsck>.
+
+Notes:
+
+=over 4
+
+=item *
+
+Multiple status codes can be summed together.
+
+=item *
+
+A non-zero return code can mean "success", for example if
+errors have been corrected on the filesystem.
+
+=item *
+
+Checking or repairing NTFS volumes is not supported
+(by linux-ntfs).
+
+=back
+
+This command is entirely equivalent to running C<fsck -a -t fstype device>.
+
=head2 get-autosync
get-autosync
Get the autosync flag.
+=head2 get-e2label
+
+ get-e2label device
+
+This returns the ext2/3/4 filesystem label of the filesystem on
+C<device>.
+
+=head2 get-e2uuid
+
+ get-e2uuid device
+
+This returns the ext2/3/4 filesystem UUID of the filesystem on
+C<device>.
+
=head2 get-path
get-path
This returns the verbose messages flag.
+=head2 grub-install
+
+ grub-install root device
+
+This command installs GRUB (the Grand Unified Bootloader) on
+C<device>, with the root directory being C<root>.
+
=head2 is-busy
is-busy
B<This command is dangerous. Without careful use you
can easily destroy all your data>.
+=head2 lvremove
+
+ lvremove device
+
+Remove an LVM logical volume C<device>, where C<device> is
+the path to the LV, such as C</dev/VG/LV>.
+
+You can also remove all LVs in a volume group by specifying
+the VG name, C</dev/VG>.
+
=head2 lvs
lvs
where C<device> should usually be a partition name such
as C</dev/sda1>.
+=head2 pvremove
+
+ pvremove device
+
+This wipes a physical volume C<device> so that LVM will no longer
+recognise it.
+
+The implementation uses the C<pvremove> command which refuses to
+wipe physical volumes that contain any volume groups, so you have
+to remove those first.
+
=head2 pvs
pvs
set-autosync true|false
If C<autosync> is true, this enables autosync. Libguestfs will make a
-best effort attempt to run C<sync> when the handle is closed
+best effort attempt to run C<umount-all> followed by
+C<sync> when the handle is closed
(also if the program exits without closing handles).
+This is disabled by default (except in guestfish where it is
+enabled by default).
+
+=head2 set-e2label
+
+ set-e2label device label
+
+This sets the ext2/3/4 filesystem label of the filesystem on
+C<device> to C<label>. Filesystem labels are limited to
+16 characters.
+
+You can use either C<tune2fs-l> or C<get-e2label>
+to return the existing label on a filesystem.
+
+=head2 set-e2uuid
+
+ set-e2uuid device uuid
+
+This sets the ext2/3/4 filesystem UUID of the filesystem on
+C<device> to C<uuid>. The format of the UUID and alternatives
+such as C<clear>, C<random> and C<time> are described in the
+L<tune2fs(8)> manpage.
+
+You can use either C<tune2fs-l> or C<get-e2uuid>
+to return the existing UUID of a filesystem.
+
=head2 set-path | path
set-path path
tune2fs-l device
-This returns the contents of the ext2 or ext3 filesystem superblock
-on C<device>.
+This returns the contents of the ext2, ext3 or ext4 filesystem
+superblock on C<device>.
It is the same as running C<tune2fs -l device>. See L<tune2fs(8)>
manpage for more details. The list of fields returned isn't
This creates an LVM volume group called C<volgroup>
from the non-empty list of physical volumes C<physvols>.
+=head2 vgremove
+
+ vgremove vgname
+
+Remove an LVM volume group C<vgname>, (for example C<VG>).
+
+This also forcibly removes all logical volumes in the volume
+group (if any).
+
=head2 vgs
vgs
of somewhere between 2MB and 4MB. To transfer large files you should use
FTP.
+=head2 zero
+
+ zero device
+
+This command writes zeroes over the first few blocks of C<device>.
+
+How many blocks are zeroed isn't specified (but it's I<not> enough
+to securely wipe the device). It should be sufficient to remove
+any partition tables, filesystem superblocks and so on.
+