Name
vndevice
Synopsis
vndevice { attach | shadow }device pathname
vndevice detachdevice
Attaches or detaches a virtual device node to or from a disk image
file. (Note that the functionality of vndevice
is
incorporated within hdiutil
.) Modifications to
data on the attached disk image will instead be written to the
virtual node, or shadow image
, and subsequent
access to that data will be from the shadow. This allows effective
read/write access to data on a disk image which
shouldn’t or can’t be modified.
Options
-
attach
Attach a device node to a disk image designated by
pathname
.-
detach
Detach a device node from a disk image.
-
shadow
Associate an attached device node to a shadow disk image designated by
pathname
.-
device
The device node filename, e.g.,
/dev/vn0
.
Examples
Create a disk image, attach a virtual device node to it, and mount it:
$hdiutil create test.dmg -volname test -size 5m -fs HFS+ -layout NONE
$sudo vndevice attach /dev/vn0 test.dmg
$mkdir mount_point
$sudo mount -t hfs /dev/vn0 mount_point
Wait a minute, and then:
$touch mount_point/test_file
$ls -l test.dmg
Note that the modification time on the disk image is current, reflecting the change you made by creating a test file.
Now set up shadowing. Unmount the volume first, then create the shadow disk image, attach the virtual node to it, and mount it again:
$sudo umount /dev/vn0
$hdiutil create shadow.dmg -volname shadow -size 5m -fs HFS+ -layout NONE
$sudo vndevice shadow /dev/vn0 shadow.dmg
$sudo mount -t hfs /dev/vn0 ...
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