hdid(8) hdid(8)
NAME
hdid - HDI driver backing store service
SYNOPSIS
hdid [ options ] image
DESCRIPTION
Historically, hdid has been the user-level process handling the loading
and decompression of disk image data for the hard disk image (HDI)
driver in the Mac OS X kernel. With Mac OS X version 10.2 and later,
certain read/write images and 10.2+-generated zlib-compressed (UDZO)
images attach in-kernel without a persistent user process.
With Mac OS X version 10.3, hdid calls the DiskImages.framework and its
helpers take care of any out-of-kernel image serving duties. As of Mac
OS X 10.4, hdid calls through to hdiutil attach. hdid exists primarily
for backwards compatibility. Generally, hdiutil attach should be used
instead of hdid. This man page continues to document certain DiskIm-
ages features that are not tool-specific.
The DiskImages framework supports a variety of flat-file and dual-fork
image formats, including read/write, read-only, and read-only com-
pressed formats (which it decompresses on the fly). It automatically
decodes AppleSingle and MacBinary file formats and is capable of mount-
ing most images directly from http:// URLs.
hdiutil detach or diskutil eject should be used to detach (aka "eject")
images attached to the system via hdid.
Beware that an image you have created and attached is considered an
unknown removable device. For HFS filesystems on such a device, being
unknown to the system means that the on-disk ownership of files and
directories are initially ignored. On 10.2, the owner values were
dynamically replaced with the owner of /dev/console and the group
unknown (gid 99). On 10.3, the group remains unknown, but the owner is
whoever is currently accessing the file (joe sees that he owns files
when he looks at the volume; mary sees that she owns files when she
looks). Owners can be enabled for a particular volume permanently (see
disktool/"get info" in the Finder) or temporarily (see EXAMPLES section
of hdiutil(1)). Aside from whether owners are enabled, being removable
means that disk arbitration will mount any volumes with special options
such as nosuid.
The error "no mountable filesystems" generally means that there is no
filesystem in the image or that any filesystem is corrupt. Unfortu-
nately, read-only device images made from mounted journaled volumes
will not mount because the journal can't be replayed. It should be
noted, however, that the error was common on older systems when
remotely logged in to a machine with no one logged in on console. Disk
arbitration wouldn't mount removable media until the SystemUIServer
process was running. On 10.2 systems, 'disktool -c `id -u`' would
allow image-based volumes to mount in such situations. With 10.3, vol-
umes automatically mount on non-managed systems regardless of whether
anyone is logged in on console. Image-based filesystems can also be
manually mounted after attaching the image with -nomount.
Please see the section below on setting up HTTP image servers if you
plan to regularly mount images from web servers or are wondering why a
particular image isn't mounting over HTTP.
ARGUMENTS
-help show available options
-shadow [ ]
Use a shadow file in conjunction with the data in the image.
This prevents modification of the original image and allows
read-only images to be attached read/write. When blocks are
being read from the image, blocks present in the shadow file
override blocks in the base image. When blocks are being writ-
ten, the writes will be redirected to the shadow file. If not
specified, -shadow defaults to .shadow. If the
shadow file does not exist, it is created.
-readonly
Attach the image read only. Has no effect on read-only images.
-readwrite
Attach the image read/write. Has no effect on read-only (or
compressed) images. Used in some cases where a read/write image
might default to being attached read-only.
-nomount
Suppress automatic mounting of any filesystems in the image.
This will result in /dev entries being created and (for non-ker-
nel-attached images) a process in the background, but no volumes
will be mounted.
-notremovable
Make the image appear to the system as a fixed disk. A reboot
will be required to cleanly detach the image, though filesystems
can be unmounted and remounted. This option requires root
access, e.g. via sudo(8).
-encryption [ ]
This option specifies a particular encrypted encoding. The
default CEncryptedEncoding automatically recognizes its images
so this option should rarely be needed. Be careful what you are
asking for if the argument to -encryption comes directly before
the image name on the command line.
-stdinpass
causes hdid to read a null-terminated passphrase from its stan-
dard input. ^@ (control-@) can be typed to explicitly insert
the terminator. This option is designed for automation in which
standard input would be attached to a file or pipe. -passphrase
This option is provided for automation purposes but
is very insecure as the passphrase value will be visible in the
output of ps(1) (and thus to other users). -passphrase has been
deprecated.
-imagekey =
Specify a key/value pair for the disk image recognition and cre-
ation system. See hdiutil(1) for more information.
-drivekey =
Specify a key/value pair for the IOHDIXHDDrive object created
(shows up in the IOKit registry of devices which is viewable
with ioreg(8)).
-section subspec
Attach a subset of the disk image. subspec is any of ,
, or . All sector numbers are zero-
based and ranges are inclusive.
-kernel
hand the image directly to the IOHDIXController module in the
kernel even if this image would not normally be sent "in-ker-
nel." If the image cannot be attached, no attempt will be made
to attach it with a user process.
-nokernel
attach the image with a persistent process instead of attaching
in-kernel, even if the default for this type of image is to
attach in-kernel. Use hdiutil(1)'s imageinfo verb to determine
if an image will default to mounting in-kernel.
-plist output a plist describing the image and system entities (dev
entries, mount points, etc) that were created as a result of
attaching the given image.
-verbose
verbose output when attaching an image
-debug diagnostic output when attaching an image
-quiet Don't print out resulting /dev entries and filesystems. Also do
not print any errors. hdid's exit status will indicate whether
the attach was successful.
EXAMPLES
$ hdid funstuff.img
Present funstuff.img as a device so that its filesystems can be
mounted.
$ hdid master.dmg -shadow
Present master.dmg to the filesystems for potential mounting, redirect-
ing all write operations to the shadow file master.dmg.shadow.
$ hdid http://my.webserver.com/master.img -shadow /tmp/master-
shadowfile
Present master.img to the filesystems for potential mounting, redirect-
ing all write operations to the shadow file mastershadowfile in /tmp.
The shadow file can be on any mounted read/write filesystem -- keep in
mind the consequences of using a remote filesystems (NFS, AFP) for such
shadow files.
hdid -nomount ram://
will attach a ram disk that can be mounted and used after being format-
ted with a newfs utility or Disk Utility.app. A sector is 512 bytes.
A small shell script to create and mount a ram disk:
#!/bin/sh
NUMSECTORS=128000
mydev=`hdid -nomount ram://$NUMSECTORS`
newfs_hfs $mydev
mkdir /tmp/mymount
mount -t hfs $mydev /tmp/mymount
OUTPUT
Unless -plist is specified, hdid returns one line of output per /dev
entry created. Each line contains up to three tab-delimited columns.
The first column always contains the full path to the /dev entry cre-
ated. The second column will contain the partition type if the image
contained a partition map. The third column will contain the mount-
point if the particular /dev entry was mounted.
If hdid is asked to attach an image that is already attached, it will
attempt to return the usual information for the attached image, as if
it had just been attached. However, if there are unmounted partitions
on the attached image, they will not be remounted.
Mounting Images via HTTP
In addition to mounting images from local or remote mounted filesys-
tems, one can also mount images from HTTP servers without downloading
the entire image. For flat images (UDIF images, or AppleSingle/MacBi-
nary encoded NDIF image files) mounting an image is a matter of passing
the http:// URL to hdid:
hdid http://server.company.com/Images/stuff.dmg
It should be noted that some web servers (Apache in particular) do not
support byte-range requests beyond 2 (Apache 1.x) or 4 GB (Apache 2.x)
and thus image files larger than those sizes will not be accessible
over HTTP. Read/write images may attach, but will not be fully acces-
sible. Segmented images do work correctly over HTTP (assuming they are
named properly) and can be used to work around the file size limita-
tion.
Browsing images via HTTP is much more pleasant if the server settings
are modified to be more friendly to highly-persistent clients. In par-
ticular for Apache, MaxKeepAliveRequests should be increased signifi-
cantly beyond 100 or set to 0 (unlimited) and KeepAliveTimeout should
be boosted to at least 30 (seconds). Increasing the number of simulta-
neous clients may also be desirable because of the increased delay
before clients are forcibly disconnected.
If the image to be served via HTTP is a dual fork NDIF image that is
not encoded into a flat-file format such as AppleSingle and the HTTP
server is running on Mac OS X, dual fork files may be detected and sup-
ported. Such dual-fork files must be moved or copied using the Finder,
or some other resource-fork-aware tool. Properly copied dual-fork
files on a UFS volume have a ._filename file in addition to the file-
name you see in the Finder (i.e. stuff.img would also have ._stuff.img
in the same directory).
In either case, one would specify the URL to the data fork, and DiskIm-
ages will determine if it is necessary to access the secondary file.
Accessing dual fork images on HFS+ filesystems via HTTP is only sup-
ported if the HTTP server is on a Mac OS X system. It is possible that
the web server's configuration could prevent access to the resource
fork. For example, Mac OS X 10.3 security updates have disabled access
to the /..namedfork/ paths necessary to access resource forks on HFS.
Thus it may be necessary to tweak web server settings to successfully
serve dual-fork images.
While it is not directly related to mounting via hdid(1), informing
your web server that '.dmg' (and others) are extensions associated with
the MIME type application/octet-stream will allow web browsers to down-
load the files rather than try to display them. For apache, you add
the extensions to the appropriate line in /etc/httpd/mime.types.
SEE ALSO
hdiutil(1), load_hdi(8), ditto(8), diskutil(8), diskarbitrationd(8),
ioreg(8)
25 June 2002 hdid(8)
