guestmount(1) Virtualization Support guestmount(1)NAMEguestmount - Mount a guest filesystem on the host using FUSE and
libguestfs
SYNOPSISguestmount [--options] -a disk.img -m device [--ro] mountpoint
guestmount [--options] -a disk.img -i [--ro] mountpoint
guestmount [--options] -d Guest -i [--ro] mountpoint
WARNING
You must not use "guestmount" in read-write mode on live virtual
machines. If you do this, you risk disk corruption in the VM.
DESCRIPTION
The guestmount program can be used to mount virtual machine filesystems
and other disk images on the host. It uses libguestfs for access to
the guest filesystem, and FUSE (the "filesystem in userspace") to make
it appear as a mountable device.
Along with other options, you have to give at least one device (-a
option) or libvirt domain (-d option), and at least one mountpoint (-m
option) or use the -i inspection option or the --live option. How this
works is better explained in the guestfish(1) manual page, or by
looking at the examples below.
FUSE lets you mount filesystems as non-root. The mountpoint must be
owned by you, and the filesystem will not be visible to any other users
unless you make certain global configuration changes to
"/etc/fuse.conf". To unmount the filesystem, use the "fusermount -u"
command.
EXAMPLES
For a typical Windows guest which has its main filesystem on the first
partition:
guestmount-a windows.img -m /dev/sda1 --ro /mnt
For a typical Linux guest which has a /boot filesystem on the first
partition, and the root filesystem on a logical volume:
guestmount-a linux.img -m /dev/VG/LV -m /dev/sda1:/boot --ro /mnt
To get libguestfs to detect guest mountpoints for you:
guestmount-a guest.img -i --ro /mnt
For a libvirt guest called "Guest" you could do:
guestmount-d Guest -i --ro /mnt
If you don't know what filesystems are contained in a guest or disk
image, use virt-filesystems(1) first:
virt-filesystems -d MyGuest
If you want to trace the libguestfs calls but without excessive
debugging information, we recommend:
guestmount [...] --trace /mnt
If you want to debug the program, we recommend:
guestmount [...] --trace --verbose /mnt
NOTES
Other users cannot see the filesystem by default
If you mount a filesystem as one user (eg. root), then other users will
not be able to see it by default. The fix is to add the FUSE
"allow_other" option when mounting:
sudo guestmount [...] -o allow_other /mnt
Enabling FUSE
On some distros, you may need to add yourself to a special group (eg.
"fuse") before you can use any FUSE filesystem. This is necessary on
Debian and derivatives.
On other distros, no special group is required. It is not necessary on
Fedora or Red Hat Enterprise Linux.
fusermount error: "Device or resource busy"
You can see this error when another process on the system jumps into
the mountpoint you have just created, holding it open and preventing
you from unmounting it. The usual culprits are various GUI "indexing"
programs.
The popular workaround for this problem is to retry the "fusermount -u"
command a few times until it works. Unfortunately this isn't a
reliable fix if (for example) the mounted filesystem is particularly
large and the intruding program particularly persistent.
timeout=10
count=$timeout
while ! fusermount -u $mountpoint && [ $count -gt 0 ]; do
sleep 1
((count--))
done
if [ $count -eq 0 ]; then
echo "$0: fusermount failed after $timeout seconds"
exit 1
fi
A proper fix is to use a private mountpoint by creating a new mount
namespace using the Linux-specific clone(2)/unshare(2) flag
"CLONE_NEWNS". Unfortunately at the moment this requires root and we
would also probably need to add it as a feature to guestmount.
Race conditions possible when shutting down the connection
When "fusermount -u" exits, guestmount may still be running and
cleaning up the mountpoint. The disk image will not be fully
finalized.
This means that scripts like the following have a nasty race condition:
guestmount-a disk.img -i /mnt
# copy things into /mnt
fusermount -u /mnt
# immediately try to use 'disk.img' ** UNSAFE **
The solution is to use the --pid-file option to write the guestmount
PID to a file, then after fusermount spin waiting for this PID to exit.
guestmount-a disk.img -i --pid-file guestmount.pid /mnt
# ...
# ...
# Save the PID of guestmount *before* calling fusermount.
pid="$(cat guestmount.pid)"
timeout=10
# fusermount retry code, see above
# ...
# ...
count=$timeout
while kill -0 "$pid" 2>/dev/null && [ $count -gt 0 ]; do
sleep 1
((count--))
done
if [ $count -eq 0 ]; then
echo "$0: wait for guestmount to exit failed after $timeout seconds"
exit 1
fi
# Now it is safe to use the disk image.
Note that if you use the "guestfs_mount_local" API directly (see "MOUNT
LOCAL" in guestfs(3)) then it is much easier to write a safe, race-free
program.
OPTIONS-a image
--add image
Add a block device or virtual machine image.
The format of the disk image is auto-detected. To override this
and force a particular format use the --format=.. option.
-c URI
--connect URI
When used in conjunction with the -d option, this specifies the
libvirt URI to use. The default is to use the default libvirt
connection.
-d libvirt-domain
--domain libvirt-domain
Add disks from the named libvirt domain. If the --ro option is
also used, then any libvirt domain can be used. However in write
mode, only libvirt domains which are shut down can be named here.
Domain UUIDs can be used instead of names.
--dir-cache-timeout N
Set the readdir cache timeout to N seconds, the default being 60
seconds. The readdir cache [actually, there are several semi-
independent caches] is populated after a readdir(2) call with the
stat and extended attributes of the files in the directory, in
anticipation that they will be requested soon after.
There is also a different attribute cache implemented by FUSE (see
the FUSE option -o attr_timeout), but the FUSE cache does not
anticipate future requests, only cache existing ones.
--echo-keys
When prompting for keys and passphrases, guestfish normally turns
echoing off so you cannot see what you are typing. If you are not
worried about Tempest attacks and there is no one else in the room
you can specify this flag to see what you are typing.
--format=raw|qcow2|..
--format
The default for the -a option is to auto-detect the format of the
disk image. Using this forces the disk format for -a options which
follow on the command line. Using --format with no argument
switches back to auto-detection for subsequent -a options.
If you have untrusted raw-format guest disk images, you should use
this option to specify the disk format. This avoids a possible
security problem with malicious guests (CVE-2010-3851). See also
"guestfs_add_drive_opts" in guestfs(3).
--fuse-help
Display help on special FUSE options (see -o below).
--help
Display brief help and exit.
-i
--inspector
Using virt-inspector(1) code, inspect the disks looking for an
operating system and mount filesystems as they would be mounted on
the real virtual machine.
--keys-from-stdin
Read key or passphrase parameters from stdin. The default is to
try to read passphrases from the user by opening "/dev/tty".
--live
Connect to a live virtual machine. (Experimental, see "ATTACHING
TO RUNNING DAEMONS" in guestfs(3)).
-m dev[:mountpoint[:options]]
--mount dev[:mountpoint[:options]]
Mount the named partition or logical volume on the given mountpoint
in the guest (this has nothing to do with mountpoints in the host).
If the mountpoint is omitted, it defaults to "/". You have to
mount something on "/".
The third (and rarely used) part of the mount parameter is the list
of mount options used to mount the underlying filesystem. If this
is not given, then the mount options are either the empty string or
"ro" (the latter if the --ro flag is used). By specifying the
mount options, you override this default choice. Probably the only
time you would use this is to enable ACLs and/or extended
attributes if the filesystem can support them:
-m /dev/sda1:/:acl,user_xattr
-n
--no-sync
By default, we attempt to sync the guest disk when the FUSE
mountpoint is unmounted. If you specify this option, then we don't
attempt to sync the disk. See the discussion of autosync in the
guestfs(3) manpage.
-o option
--option option
Pass extra options to FUSE.
To get a list of all the extra options supported by FUSE, use the
command below. Note that only the FUSE -o options can be passed,
and only some of them are a good idea.
guestmount--fuse-help
Some potentially useful FUSE options:
-o allow_other
Allow other users to see the filesystem.
-o attr_timeout=N
Enable attribute caching by FUSE, and set the timeout to N
seconds.
-o kernel_cache
Allow the kernel to cache files (reduces the number of reads
that have to go through the guestfs(3) API). This is generally
a good idea if you can afford the extra memory usage.
-o uid=N -o gid=N
Use these options to map all UIDs and GIDs inside the guest
filesystem to the chosen values.
--pid-file filename
Write the PID of the guestmount worker process to "filename".
-r
--ro
Add devices and mount everything read-only. Also disallow writes
and make the disk appear read-only to FUSE.
This is highly recommended if you are not going to edit the guest
disk. If the guest is running and this option is not supplied,
then there is a strong risk of disk corruption in the guest. We
try to prevent this from happening, but it is not always possible.
See also "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
--selinux
Enable SELinux support for the guest.
-v
--verbose
Enable verbose messages from underlying libguestfs.
-V
--version
Display the program version and exit.
-w
--rw
This changes the -a, -d and -m options so that disks are added and
mounts are done read-write.
See "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
-x
--trace
Trace libguestfs calls and entry into each FUSE function.
This also stops the daemon from forking into the background.
FILES
$HOME/.libguestfs-tools.rc
/etc/libguestfs-tools.conf
This configuration file controls the default read-only or read-
write mode (--ro or --rw).
See "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
EXIT STATUS
This program returns 0 if successful, or non-zero if there was an
error.
SEE ALSOguestfish(1), virt-inspector(1), virt-cat(1), virt-edit(1),
virt-tar(1), "MOUNT LOCAL" in guestfs(3), http://libguestfs.org/,
http://fuse.sf.net/.
AUTHORS
Richard W.M. Jones ("rjones at redhat dot com")
COPYRIGHT
Copyright (C) 2009-2013 Red Hat Inc.
LICENSE
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
BUGS
To get a list of bugs against libguestfs, use this link:
https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools
To report a new bug against libguestfs, use this link:
https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools
When reporting a bug, please supply:
· The version of libguestfs.
· Where you got libguestfs (eg. which Linux distro, compiled from
source, etc)
· Describe the bug accurately and give a way to reproduce it.
· Run libguestfs-test-tool(1) and paste the complete, unedited output
into the bug report.
libguestfs-1.20.4 2013-03-12 guestmount(1)
