24.6 Invoking grub-mount

The program grub-mount performs a read-only mount of any file system or file system image that GRUB understands, using GRUB’s file system drivers via FUSE. (It is only available if FUSE development files were present when GRUB was built.) This has a number of uses:

• It provides a convenient way to check how GRUB will view a file system at boot time. You can use normal command-line tools to compare that view with that of your operating system, making it easy to find bugs.
• It offers true read-only mounts. Linux does not have these for journalling file systems, because it will always attempt to replay the journal at mount time; while you can temporarily mark the block device read-only to avoid this, that causes the mount to fail. Since GRUB intentionally contains no code for writing to file systems, it can easily provide a guaranteed read-only mount mechanism.
• It allows you to examine any file system that GRUB understands without needing to load additional modules into your running kernel, which may be useful in constrained environments such as installers.
• Since it can examine file system images (contained in regular files) just as easily as file systems on block devices, you can use it to inspect any file system image that GRUB understands with only enough privileges to use FUSE, even if nobody has yet written a FUSE module specifically for that file system type.

Using grub-mount is normally as simple as:

grub-mount /dev/sda1 /mnt

grub-mount must be given one or more images and a mount point as non-option arguments (if it is given more than one image, it will treat them as a RAID set), and also accepts the following options:

--help

Print a summary of the command-line options and exit.

--version

Print the version number of GRUB and exit.

-C

--crypto

Mount encrypted devices, prompting for a passphrase if necessary.

-d string

--debug=string

Show debugging output for conditions matching string.

-K prompt|file

--zfs-key=prompt|file

Load a ZFS encryption key. If you use ‘prompt’ as the argument, grub-mount will read a passphrase from the terminal; otherwise, it will read key material from the specified file.

-r device

--root=device

Set the GRUB root device to device. You do not normally need to set this; grub-mount will automatically set the root device to the root of the supplied file system.

If device is just a number, then it will be treated as a partition number within the supplied image. This means that, if you have an image of an entire disk in disk.img, then you can use this command to mount its second partition:

grub-mount -r 2 disk.img mount-point

-v

--verbose

Print verbose messages.