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HDIUTIL(1) BSD General Commands Manual HDIUTIL(1)
NAME
hdiutil -- manipulate disk images (attach, verify, burn, etc)
SYNOPSIS
hdiutil verb [options]
DESCRIPTION
hdiutil uses the DiskImages framework to manipulate disk images. Common verbs include attach, detach,
verify, create, convert, compact, and burn.
The rest of the verbs are currently: help, info, checksum, chpass, unflatten, flatten, imageinfo,
isencrypted, mountvol, unmount, plugins, udifrez, udifderez, internet-enable, resize, segment,
makehybrid, and pmap.
BACKGROUND
Disk images are containers that emulate disks. Like disks, they can be partitioned and formatted.
Many uses of disk images blur the distinction between the disk image container and its content, but
this distinction is critical to understanding disk images. The terms "attach" and "detach" are used to
distinguish the way disk images are connected to and disconnected from the system.
For example, when you double-click a disk image in the Mac OS X Finder, two separate things happen.
First, the image is "attached" to the system just like an external drive. Then, the kernel and Disk
Arbitration probe the new device for recognized file structures. If any file structures are under-stood, understood,
stood, the associated volumes will mount and appear in the Finder.
Always consider whether a "disk image" operation applies to the blocks of the disk image device or to
the (often file-oriented) content of the image. For example, verify verifies that the blocks stored in
a read-only disk image have not changed since it was created. On the other hand, create -srcfolder
creates a disk image container, puts a filesystem in it, and then copies the specified files to the new
filesystem.
COMMON OPTIONS
The following option descriptions apply to all verbs:
-verbose be verbose: produce extra progress output and error diagnostics. This option can help the
user decipher why a particular operation failed. At a minimum, the probing of any specified
images will be detailed.
-quiet close stdout and stderr, leaving only hdiutil's exit status to indicate success or failure.
-debug and -verbose disable -quiet.
-debug be very verbose. This option is good if a large amount of progress information is needed. As
of Mac OS X 10.6, -debug enables -verbose.
Many hdiutil verbs understand the following options:
-plist provide result output in plist format. Other programs invoking hdiutil are expected to
use -plist rather than try to parse the human-readable output. The usual output is
consistent but generally unstructured.
-puppetstrings provide progress output that is easy for another program to parse. PERCENTAGE outputs
can include the value -1 which means hdiutil is performing an operation that will take
an indeterminate amount of time to complete. Any program trying to interpret hdiutil's
progress should use -puppetstrings.
-srcimagekey key=value
specify a key/value pair for the disk image recognition system. (-imagekey is normally
a synonym)
-tgtimagekey key=value
specify a key/value pair for any image created. (-imagekey is only a synonym if there
is no input image).
-encryption [AES-128|AES-256]
specify a particular type of encryption or, if not specified, the default encryption
algorithm. The default algorithm is the AES cipher with a 128-bit key.
-stdinpass read a null-terminated passphrase from standard input. If the standard input is a tty,
the passphrase will be read with readpassphrase(3). -stdinpass replaces -passphrase
though the latter is still supported for compatibility. Beware that the password will
contain any newlines before the NULL. See EXAMPLES.
-agentpass force the default behavior of prompting for a passphrase. Useful with -pubkey to cre-ate create
ate an image protected by both a passphrase and a public key.
-recover keychain_file
specify a keychain containing the secret corresponding to the certificate specified
with -certificate when the image was created.
-certificate cert_file
specify a secondary access certificate for an encrypted image. cert_file must be DER-encoded DERencoded
encoded certificate data, which can be created by Keychain Access or openssl(1).
-pubkey PK1,PK2,...,PKn
specify a list of public keys, identified by their hexadecimal hashes, to be used to
protect the encrypted image being created.
-cacert cert specify a certificate authority certificate. cert can be either a PEM file or a direc-tory directory
tory of certificates processed by c_rehash(1). See also --capath and --cacert in
curl(1).
-insecurehttp ignore SSL host validation failures. Useful for self-signed servers for which the
appropriate certificates are unavailable or if access to a server is desired when the
server name doesn't match what is in the certificate.
-shadow [shadowfile]
Use a shadow file in conjunction with the data in the primary image file. This option
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. All data written to an attached device will be
redirected to the shadow file. If not specified, shadowfile defaults to image.shadow.
If the shadow file does not exist, it is created. hdiutil verbs taking images as input
accept -shadow, -cacert, and -insecurehttp.
Verbs that create images automatically append the correct extension to any filenames if the extension
is not already present. The creation engine also examines the filename extension of the provided file-name filename
name and changes its behavior accordingly. For example, a sparse image can be created without specify-ing specifying
ing -type SPARSEBUNDLE simply by appending the .sparsebundle extension to the provided filename.
VERBS
Each verb is listed with its description and individual arguments. Arguments to the verbs can be
passed in any order. A sector is 512 bytes.
help display minimal usage information for each verb. hdiutil verb -help will provide basic
usage information for that verb.
attach image [options]
attach a disk image as a device. attach will return information about an already-attached
image as if it had attached it. mount is a poorly-named synonym for attach. See BACK-GROUND. BACKGROUND.
GROUND.
Beware that an image freshly created and attached is treated as a new removable device. See
hdid(8) and the EXAMPLES section below for more details about how owners are ignored on
filesystems on such devices.
The output of attach has been stable since OS X 10.0 (though it was called hdid(8) then) and
is intended to be program-readable. It consists of the /dev node, a tab, a content hint (if
applicable), another tab, and a mount point (if any filesystems were mounted). Because con-tent content
tent hints are derived from the partition data, GUID Partition Table types may leak through.
Common GUIDs such as "48465300-0000-11AA-AA11-0030654" are mapped to their human-readable
counterparts (here "Apple_HFS").
Common options: -encryption, -stdinpass, -recover, -imagekey, -shadow, -puppetstrings, and
-plist.
Options:
-readonly force the resulting device to be read-only
-readwrite attempt to override the DiskImages framework's decision to attach a par-ticular particular
ticular image read-only. For example, -readwrite can be used to modify
the HFS filesystem on a HFS/ISO hybrid CD image.
-nokernel attach with a helper process. This is again the default as of OS X 10.5.
-kernel attempt to attach this image without a helper process; fail if unsup-ported. unsupported.
ported. Only UDRW, UDRO, UDZO, and UDSP images are supported in-kernel.
Encryption and HTTP-backed images are also supported.
-notremovable prevent this image from being detached. Only root can use this option.
-mount required|optional|suppressed
indicate whether filesystems in the image should be mounted or not. The
default is required (attach will fail if no filesystems mount).
-nomount identical to -mount suppressed.
-mountroot path mount volumes on subdirectories of path instead of under /Volumes. path
must exist. Full mount point paths must be less than MNAMELEN characters
(increased from 90 to 1024 in OS X 10.6).
-mountrandom path like -mountroot, but mount point directory names are randomized with
mkdtemp(3).
-mountpoint path assuming only one volume, mount it at path instead of in /Volumes. See
fstab(5) for ways a system administrator can make particular volumes
automatically mount in particular filesystem locations by editing the
file /etc/fstab.
-union attempt a union mount over the mount point specified by -mountpoint.
Union mounts are no longer supported in Mac OS X, so this flag is cur-rently currently
rently a no-op.
-private suppress filesystem mount notifications. -private confuses programs
using the Carbon File Manager and should be avoided in favor of
-nobrowse.
-nobrowse render any volumes invisible in applications such as the OS X Finder.
-owners on|off specify that owners on any filesystems be honored or not.
-drivekey key=value
specify a key/value pair to be attached to the device in the IOKit reg-istry. registry.
istry.
The following options have corresponding elements in the com.apple.frameworks.diskimages
preferences domain and thus can be rendered in both the positive and the negative to over-ride override
ride any existing preferences.
-[no]verify do [not] verify the image. By default, hdiutil attach attempts to intel-ligently intelligently
ligently verify images that contain checksums before attaching them. If
hdiutil can write to an image it has verified, attach will store an
attribute with the image so that it will not be verified again unless its
timestamp changes. To maintain backwards compatibility, hdid(8) does not
attempt to verify images before attaching them.
Preferences keys: skip-verify, skip-verify-remote, skip-verify-locked,
skip-previously-verified
-[no]ignorebadchecksums
specify whether bad checksums should be ignored. The default is to abort
when a bad checksum is detected.
Preferences key: ignore-bad-checksums
-[no]idme do [not] perform IDME actions on IDME images. IDME actions are normally
only performed when Safari downloads and attaches an image.
Preferences key: skip-idme
-[no]idmereveal do [not] reveal (in the Finder) the results of IDME processing.
Preferences key: skip-idme-reveal
-[no]idmetrash do [not] put IDME images in the trash after processing.
Preferences key: skip-idme-trash
-[no]autoopen do [not] auto-open volumes (in the Finder) after attaching an image. By
default, read-only volumes are opened in the Finder.
-[no]autoopenro do [not] auto-open read-only volumes.
Preferences key: auto-open-ro-root
-[no]autoopenrw do [not] auto-open read/write volumes.
Preferences key: auto-open-rw-root
-[no]autofsck do [not] force automatic file system checking before mounting a disk
image. By default, only quarantined images (e.g. downloaded from the
Internet) that have not previously passed fsck are checked.
Preferences key: auto-fsck
detach dev_name [-force]
detach a disk image and terminate any associated process. dev_name is a partial /dev node
path (e.g. "disk1"). As of OS X 10.4, dev_name can also be a mountpoint. If Disk Arbitra-tion Arbitration
tion is running, detach will use it to unmount any filesystems and detach the image. If
not, detach will attempt to unmount any filesystems and detach the image directly (using the
`eject' ioctl). If Disk Arbitration is not running, it may be necessary to unmount the
filesystems with umount(8) before detaching the image. eject is a synonym for detach.
Options:
-force ignore open files on mounted volumes, etc.
verify image [options]
compute the checksum of a "read-only" or "compressed" image and verify it against the value
stored in the image. Read/write images don't contain checksums and thus can't be verified.
verify accepts the common options -encryption, -stdinpass, -srcimagekey, -puppetstrings, and
-plist.
create size_spec image
create a new image of the given size or from the provided data. If image already exists,
-ov must be specified or create will fail. To make a cross-platform CD or DVD, use
makehybrid instead. See also EXAMPLES below.
The size specified is the size of the image to be created. Filesystem and partition layout
overhead (80 sectors for the default GPTSPUD layout on Intel machines) may not be available
for the filesystem and user data in the image.
Size specifiers:
-size ??b|??k|??m|??g|??t|??p|??e
Specify the size of the image in the style of mkfile(8) with the addition of
tera-, peta-, and exa-bytes sizes (note that 'b' specifies a number of sectors,
not bytes). The larger sizes are useful for large sparse images.
-sectors sector_count
Specify the size of the image file in 512-byte sectors.
-megabytes size
Specify the size of the image file in megabytes (1024*1024 bytes).
-srcfolder source
copies file-by-file the contents of source into image, creating a fresh (theoret-ically (theoretically
ically defragmented) filesystem on the destination. The resulting image is thus
recommended for use with asr(8)since it will have a minimal amount of unused
space. Its size will be that of the source data plus some padding for filesystem
overhead. The filesystem type of the image volume will match that of the source
as closely as possible unless overridden with -fs. Other size specifiers, such
as -size, will override the default size calculation based on the source content,
allowing for more or less free space in the resulting filesystem. -srcfolder can
be specified more than once, in which case the image volume will be populated at
the top level with a copy of each specified filesystem object. -srcdir is a syn-onym. synonym.
onym.
-srcdevice device
specifies that the blocks of device should be used to create a new image. The
image size will match the size of device. resize can be used to adjust the size
of resizable filesystems and writable images. Both -srcdevice and -srcfolder can
run into errors if there are bad blocks on a disk. One way around this problem
is to write over the files in question in the hopes that the drive will remap the
bad blocks. Data will be lost, but the image creation operation will subse-quently subsequently
quently succeed. Filesystem options (like -fs, -volname, -stretch, or -size) are
invalid and ignored when using -srcdevice.
Common options: -encryption, -stdinpass, -certificate, -pubkey, -plist, -imagekey,
-tgtimagekey, -puppetstrings, and -plist.
-imagekey di-sparse-puma-compatible=TRUE and -imagekey di-shadow-puma-compatible=TRUE will
create, respectively, sparse and shadow images that can be attached on OS X 10.1. -imagekey
encrypted-encoding-version can select between version 1 and version 2 of the encrypted
encoding. The framework preferences have a corresponding key to change the default for all
images. Version 2 is not compatible with OS X 10.2 but is more robust for SPARSE (UDSP)
images. Version 1 is the default for non-sparse images. As of OS X 10.4.7, sparse
encrypted images always use version 2 and as of OS X 10.5, all encrypted images default to
version 2.
General options:
-align alignment
specifies a size to which the final data partition will be aligned. The default
is 4K.
-type UDIF|SPARSE|SPARSEBUNDLE
-type is particular to create and is used to specify the format of empty
read/write images. It is independent of -format which is used to specify the
final read-only image format when populating an image with pre-existing content.
UDIF is the default type. If specified, a UDRW of the specified size will be cre-ated. created.
ated. SPARSE creates a UDSP: a read/write single-file image which expands as is
is filled with data. SPARSEBUNDLE creates a UDSB: a read/write image backed by a
directory bundle.
By default, UDSP images grow one megabyte at a time. Introduced in 10.5, UDSB
images use 8 MB band files which grow as they are written to.. -imagekey
sparse-band-size=size can be used to specify the number of 512-byte sectors that
will be added each time the image grows. Valid values for SPARSEBUNDLE range from
2048 to 262144 sectors (1 MB to 128 MB).
The maximum size of a SPARSE image is 128 petabytes; the maximum for SPARSEBUNDLE
is just under 8 exabytes (2^63 - 512 bytes minus 1 byte). The amount of data that
can be stored in either type of sparse image is additionally bounded by the
filesystem in the image and by any partition map. compact can reclaim unused
bands in sparse images backing HFS+ filesystems. resize will only change the vir-tual virtual
tual size of a sparse image. See also USING PERSISTENT SPARSE IMAGES below.
-fs filesystem
where filesystem is one of HFS+, HFS+J (JHFS+), HFSX, JHFS+X, MS-DOS, or UDF. -fs
causes a filesystem of the specified type to be written to the image. -fs may
change the partition scheme and type appropriately. -fs will not make any size
adjustments: if the image is the wrong size for the specified filesystem, create
will fail. -fs is invalid and ignored when using -srcdevice.
-volname volname
The newly-created filesystem will be named volname. The default depends the
filesystem being used; HFS+'s default volume name is `untitled'. -volname is
invalid and ignored when using -srcdevice.
-uid uid the root of the newly-created volume will be owned by the given numeric user id.
99 maps to the magic `unknown' user (see hdid(8)).
-gid gid the root of the newly-created volume will be owned by the given numeric group id.
99 maps to `unknown'.
-mode mode the root of the newly-created volume will have mode (in octal) mode. The default
mode is determined by the filesystem's newfs unless -srcfolder is specified, in
which case the default mode is derived from the specified filesystem object.
-[no]autostretch
do [not] suppress automatically making backwards-compatible stretchable volumes
when the volume size crosses the auto-stretch-size threshold (default: 256 MB).
See also asr(8).
-stretch max_stretch
-stretch initializes HFS+ filesystem data such that it can later be stretched on
older systems (which could only stretch within predefined limits) using hdiutil
resize or by asr(8). max_stretch is specified like -size. -stretch is invalid
and ignored when using -srcdevice.
-fsargs newfs_args
additional arguments to pass to whatever newfs program is implied by -fs.
newfs_hfs(8) has a number of options that can reduce the amount of space needed by
the filesystem's data structures. Suppressing the journal with -fs HFS+ and pass-ing passing
ing arguments such as -c c=64,a=16,e=16 to -fsargs will minimize gaps at the front
of the filesystem, allowing resize to squeeze more space from the filesystem. For
truly optimal filesystems, use makehybrid.
-layout layout
Specify the partition layout of the image. layout can be anything supported by
MediaKit.framework. NONE creates an image with no partition map. When such an
image is attached, a single /dev entry will be created (e.g. /dev/disk1).
`SPUD' causes a DDM and an Apple Partition Scheme partition map with a single
entry to be written. `GPTSPUD' creates a similar image but with a GUID Partition
Scheme map instead. When attached, multiple /dev entries will be created, with
either slice 1 (GPT) or slice 2 (APM) as the data partition. (e.g. /dev/disk1,
/dev/disk1s1, /dev/disk1s2).
Unless overridden by -fs, the default layout is `GPTSPUD' (PPC systems used `SPUD'
prior to OS X 10.6). Other layouts include `MBRSPUD' and `ISOCD'. create -help
lists all supported layouts.
-library bundle
specify an alternate layout library. The default is MediaKit's MKDrivers.bundle.
-partitionType partition_type
Change the type of partition in a single-partition disk image. The default is
Apple_HFS unless -fs implies otherwise.
-ov overwrite an existing file. The default is not to overwrite existing files.
-attach attach the image after creating it. If no filesystem is specified via -fs, the
attach will fail per the default attach -mount required behavior.
Image from source options (for -srcfolder and -srcdevice):
-format format Specify the final image format. The default when a source is specified is
UDZO. format can be any of the format parameters used by convert.
Options specific to -srcdevice:
-segmentSize size_spec
Specify that the image should be written in segments no bigger than size_spec
(which follows -size conventions).
Options specific to -srcfolder:
-[no]crossdev do [not] cross device boundaries on the source filesystem.
-[no]scrub do [not] skip temporary files when imaging a volume. Scrubbing is the
default when the source is the root of a mounted volume. Scrubbed items
include trashes, temporary directories, swap files, etc.
-[no]anyowners do not fail if the user invoking hdiutil can't ensure correct file ownership
for the files in the image.
-skipunreadable skip files that can't be read by the copying user and don't authenticate.
-copyuid user perform the copy as the given user. Requires root privilege. If user can't
read or create files with the needed owners, -anyowners or -skipunreadable
must be used to prevent the operation from failing.
By default, create -srcfolder attempts to maintain the permissions present in the source
directory. It prompts for authentication if it detects an unreadable file, a file owned by
someone other than the user creating the image, or a SGID file in a group that the copying
user is not in.
convert image -format format -o outfile
convert image to type format and write the result to outfile.
As with create, the correct filename extension will be added only if it isn't part of the
provided name. Format is one of:
UDRW - UDIF read/write image
UDRO - UDIF read-only image
UDCO - UDIF ADC-compressed image
UDZO - UDIF zlib-compressed image
UDBZ - UDIF bzip2-compressed image (OS X 10.4+ only)
UFBI - UDIF entire image with MD5 checksum
UDRo - UDIF read-only (obsolete format)
UDCo - UDIF compressed (obsolete format)
UDTO - DVD/CD-R master for export
UDxx - UDIF stub image
UDSP - SPARSE (grows with content)
UDSB - SPARSEBUNDLE (grows with content; bundle-backed)
RdWr - NDIF read/write image (deprecated)
Rdxx - NDIF read-only image (Disk Copy 6.3.3 format)
ROCo - NDIF compressed image (deprecated)
Rken - NDIF compressed (obsolete format)
DC42 - Disk Copy 4.2 image
In addition to the compression offered by some formats, the UDIF and NDIF read-only formats
skip unused space in HFS, UFS, and MS-DOS (FAT) filesystems. For UDZO, -imagekey
zlib-level=value allows the zlib compression level to be specified ala gzip(1). The default
compression level is 1 (fastest).
Common options: -encryption, -stdinpass, -certificate, -srcimagekey, -tgtimagekey, -shadow
and related, -puppetstrings, and -plist.
Other options:
-align alignment
The default is 4 (2K).
-pmap add partition map.
When converting a NDIF to a any variety of UDIF, or when converting an unparti-tioned unpartitioned
tioned UDIF, the default is true.
-segmentSize [size_spec]
Specify segmentation into size_spec-sized segments as outfile is being written.
The default size_spec when -segmentSize is specified alone is 2*1024*1024 (1 GB
worth of sectors) for UDTO images and 4*1024*1024 (2 GB segments) for all other
image types. size_spec can also be specified ??b|??k|??m|??g|??t??p|??e like
create's -size flag.
-tasks task_count
When converting an image into a compressed format, specify the number of
threads to use for the compression operation. The default is the number of
processors active in the current system.
burn image
Burn image to optical media in an attached burning device. In all cases, a prompt for media
will be printed once an appropriate drive has been found. Common options: -shadow and
related, -srcimagekey, -encryption, -puppetstrings, and -stdinpass.
Other options:
-device specify a device to use for burning. See -list.
-testburn don't turn on laser (laser defaults to on).
-anydevice explicitly allow burning to devices not qualified by Apple (kept for back-wards backwards
wards compatibility as burn will burn to any device by default as of OS X
10.4).
-[no]eject do [not] eject disc after burning. The default is to eject the disc.
-[no]verifyburn do [not] verify disc contents after burn. The default is to verify.
-[no]addpmap do [not] add partition map if necessary. Some filesystem types will not be
recognized when stored on optical media unless they are enclosed in a par-tition partition
tition map. This option will add a partition map to any bare filesystem
which needs a partition map in order to be recognized when burned to opti-cal optical
cal media. The default is to add the partition map if needed.
-[no]skipfinalfree do [not] skip final free partition. If there is a partition map on the
image specifying an Apple_Free partition as the last partition, that
Apple_Free partition will not be burned. The burned partition map will
still reference the empty space. The default is to skip burning a final
free partition.
-[no]optimizeimage do [not] optimize filesystem for burning. Optimization can reduce the
size of an HFS or HFS+ volume to the size of the data contained on the vol-ume. volume.
ume. This option will change what is burned such that the disc will have a
different checksum than the image it came from. The default is to burn all
blocks of the disk image (minus any trailing Apple_Free).
-[no]forceclose do [not] force the disc to be closed after burning. Further burns to the
disc will be impossible. The default is not to close the disc.
-nounderrun Disable the default buffer underrun protection.
-[no]synthesize [Don't] Synthesize a hybrid filesystem for the disc. The default is to
create a new (HFS/ISO) filesystem when the source image's blocks could not
be legally burned to a disc.
-speed x_factor 1, 2, 4, 6, ... `max'
The desired "x-factor". e.g. 8 means the drive will be instructed burn at
"8x speed". `max' will cause the burn to proceed at the maximum speed of
the drive. `max' is the default speed. Slower speeds can produce more
reliable burns. The speed factor is relative to the media being burned
(e.g. -speed 2 has a different data rate when used for a DVD burn vs. a CD
burn). Note that some drives have a minimum burn speed in which case any
slower speed specified will result in a burn at the drive's minimum speed.
-sizequery calculate the size of disc required (the size returned is in sectors) with-out without
out burning anything.
-erase prompt for optical media (DVD-RW/CD-RW) and then, if the hardware supports
it, quickly erase the media. If an image is specified, it will be burned
to the media after the media has been erased.
-fullerase erase all sectors of the disc (this usually takes quit a bit longer than
-erase).
-list list all burning devices, with OpenFirmware paths suitable for -device.
makehybrid -o image source
Generate a potentially-hybrid filesystem in a read-only disk image using the DiscRecording
framework's content creation system. This disk image will represent a data disc. drutil(1)
can be used to make audio discs.
source can either be a directory or a disk image. The generated image can later be burned
using burn, or converted to another read-only format with convert. By default, the filesys-tem filesystem
tem will be readable on most modern computing platforms. The generated filesystem is not
intended for conversion to read/write, but can safely have its files copied to a read/write
filesystem by ditto(8) or asr(8) (in file-copy mode).
hdiutil supports generating El Torito-style bootable ISO9660 filesystems, which is commonly
used for booting x86-based hardware. The specification includes several emulation modes. By
default, an El Torito boot image emulates either a 1.2MB, 1.44MB, or 2.88MB floppy drive,
depending on the size of the image. Also available are "No Emulation" and "Hard Disk
Emulation" modes, which allow the boot image to either be loaded directly into memory, or be
virtualized as a partitioned hard disk, respectively. The El Torito options should not be
used for data CDs.
Filesystem options:
-hfs Generate an HFS+ filesystem. This filesystem can be present on an image simultane-ously simultaneously
ously with an ISO9660 or Joliet or UDF filesystem. On operating systems that under-stand understand
stand HFS+ as well as ISO9660 and UDF, like Mac OS 9 or Mac OS X, it is usually the
preferred filesystem.
-iso Generate an ISO9660 Level 2 filesystem with Rock Ridge extensions. This filesystem
can be present on an image simultaneously with an HFS+ or Joliet or UDF filesystem.
ISO9660 is the standard cross-platform interchange format for CDs and some DVDs, and
is understood by virtually all operating systems. If an ISO9660 or Joliet filesys-tem filesystem
tem is present on a disk image or CD, but not HFS+, Mac OS X will use the ISO9660
(or Joliet) filesystem.
-joliet Generate Joliet extensions to ISO9660. This view of the filesystem can be present
on an image simultaneously with HFS+, and requires the presence of an ISO9660
filesystem. Joliet supports Unicode filenames, but is only supported on some oper-ating operating
ating systems. If both an ISO9660 and Joliet filesystem are present on a disk image
or CD, but not HFS+, Mac OS X will prefer the Joliet filesystem.
-udf Generate a UDF filesystem. This filesystem can be present on an image simultaneously
with HFS+, ISO9660, and Joliet. UDF is the standard interchange format for DVDs,
although operating system support varies based on OS version and UDF version.
By default, if no filesystem is specified, the image will be created with all four filesys-tems filesystems
tems as a hybrid image. When multiple filesystems are selected, the data area of the image
is shared between all filesystems, and only directory information and volume meta-data are
unique to each filesystem. This means that creating a cross-platform ISO9660/HFS+ hybrid
has a minimal overhead when compared to a single filesystem image.
Other options (most take a single argument):
-hfs-blessed-directory Path to directory which should be "blessed" for Mac OS X booting on
the generated filesystem. This assumes the directory has been other-wise otherwise
wise prepared, for example with bless -bootinfo to create a valid
BootX file. (HFS+ only).
-hfs-openfolder Path to a directory that will be opened by the Finder automatically.
See also the -openfolder option in bless(8) (HFS+ only).
-hfs-startupfile-size Allocate an empty HFS+ Startup File of the specified size, in bytes
(HFS+ only).
-abstract-file Path to a file in the source directory (and thus the root of the gen-erated generated
erated filesystem) for use as the ISO9660/Joliet Abstract file
(ISO9660/Joliet).
-bibliography-file Path to a file in the source directory (and thus the root of the gen-erated generated
erated filesystem) for use as the ISO9660/Joliet Bibliography file
(ISO9660/Joliet).
-copyright-file Path to a file in the source directory (and thus the root of the gen-erated generated
erated filesystem) for use as the ISO9660/Joliet Copyright file
(ISO9660/Joliet).
-application Application string (ISO9660/Joliet).
-preparer Preparer string (ISO9660/Joliet).
-publisher Publisher string (ISO9660/Joliet).
-system-id System Identification string (ISO9660/Joliet).
-keep-mac-specific Expose Macintosh-specific files (such as .DS_Store) in non-HFS+
filesystems (ISO9660/Joliet).
-eltorito-boot Path to an El Torito boot image within the source directory. By
default, floppy drive emulation is used, so the image must be one of
1200KB, 1440KB, or 2880KB. If the image has a different size, either
-no-emul-boot or -hard-disk-boot must be used to enable "No
Emulation" or "Hard Disk Emulation" mode, respectively
(ISO9660/Joliet).
-hard-disk-boot Use El Torito Hard Disk Emulation mode. The image must represent a
virtual device with an MBR partition map and a single partition
-no-emul-boot Use El Torito No Emulation mode. The system firmware will load the
number of sectors specified by -boot-load-size and execute it, with-out without
out emulating any devices (ISO9660/Joliet).
-no-boot Mark the El Torito image as non-bootable. The system firmware may
still create a virtual device backed by this data. This option is not
recommended (ISO9660/Joliet).
-boot-load-seg For a No Emulation boot image, load the data at the specified segment
address. This options is not recommended, so that the system
firmware can use its default address (ISO9660/Joliet)
-boot-load-size For a No Emulation boot image, load the specified number of 512-byte
emulated sectors into memory and execute it. By default, 4 sectors
(2KB) will be loaded (ISO9660/Joliet).
-eltorito-platform Use the specified numeric platform ID in the El Torito Boot Catalog
Validation Entry or Section Header. Defaults to 0 to identify x86
hardware (ISO/Joliet).
-eltorito-specification For complex layouts involving multiple boot images, a plist-format-ted plist-formatted
ted string can be provided, using either OpenStep-style syntax or XML
syntax, representing an array of dictionaries. Any of the El Torito
options can be set in the sub-dictionaries and will apply to that
boot image only. If -eltorito-specification is provided in addition
to the normal El Torito command-line options, the specification will
be used to populate secondary non-default boot entries.
-udf-version Version of UDF filesystem to generate. This can be either "1.02" or
"1.50". If not specified, it defaults to "1.50" (UDF).
-default-volume-name Default volume name for all filesystems, unless overridden. If not
specified, defaults to the last path component of source.
-hfs-volume-name Volume name for just the HFS+ filesystem if it should be different
(HFS+ only).
-iso-volume-name Volume name for just the ISO9660 filesystem if it should be different
(ISO9660 only).
-joliet-volume-name Volume name for just the Joliet filesystem if it should be different
(Joliet only).
-udf-volume-name Volume name for just the UDF filesystem if it should be different
(UDF only).
-hide-all A glob expression of files and directories that should not be exposed
in the generated filesystems. The string may need to be quoted to
avoid shell expansion, and will be passed to glob(3) for evaluation.
Although this option cannot be used multiple times, an arbitrarily
complex glob expression can be used.
-hide-hfs A glob expression of files and directories that should not be exposed
via the HFS+ filesystem, although the data may still be present for
use by other filesystems (HFS+ only).
-hide-iso A glob expression of files and directories that should not be exposed
via the ISO filesystem, although the data may still be present for
use by other filesystems (ISO9660 only). Per above, the Joliet hier-archy hierarchy
archy will supersede the ISO hierarchy when the hybrid is mounted as
an ISO 9660 filesystem on Mac OS X. Therefore, if Joliet is being
generated (the default) -hide-joliet will also be needed to hide the
file from mount_cd9660(8).
-hide-joliet A glob expression of files and directories that should not be exposed
via the Joliet filesystem, although the data may still be present for
use by other filesystems (Joliet only). Because OS X's ISO 9660
filesystem uses the Joliet catalog if it is available, -hide-joliet
effectively supersedes -hide-iso when the resulting filesystem is
mounted as ISO on OS X.
-hide-udf A glob expression of files and directories that should not be exposed
via the UDF filesystem, although the data may still be present for
use by other filesystems (UDF only).
-only-udf A glob expression of objects that should only be exposed in UDF.
-only-iso A glob expression of objects that should only be exposed in ISO.
-only-joliet A glob expression of objects that should only be exposed in Joliet.
-print-size Preflight the data and calculate an upper bound on the size of the
image. The actual size of the generated image is guaranteed to be
less than or equal to this estimate.
-plistin Instead of using command-line parameters, use a standard plist from
standard input to specific the parameters of the hybrid image genera-tion. generation.
tion. Each command-line option should be a key in the dictionary,
without the leading "-", and the value should be a string for path
and string arguments, a number for number arguments, and a boolean
for toggle options. The source argument should use a key of "source"
and the image should use a key of "output".
If a disk image was specified for source, the image will be attached and paths will be eval-uated evaluated
uated relative to the mountpoint of the image. No absolute paths can be used in this case.
If source is a directory, all argument paths should point to files or directories either via
an absolute path, or via a relative path to the current working directory.
The volume name options, just like files in the filesystems, may need to be mapped onto the
legal character set for a given filesystem or otherwise changed to obey naming restrictions.
Use drutil(1) as drutil filename myname to see how a given string would be remapped.
The -abstract-file, -bibliography-file, -and -copyright-file must exist directly in the
source directory, not a sub-directory, and must have an 8.3 name for compatibility with
ISO9660 Level 1.
compact image
scans the bands of a sparse (SPARSE or SPARSEBUNDLE) disk image containing an HFS filesys-tem, filesystem,
tem, removing those parts of the image which are no longer being used by the filesystem.
Depending on the location of files in the hosted filesystem, compact may or may not shrink
the image. For SPARSEBUNDLE images, completely unused band files are simply removed.
Common options: -encryption, -stdinpass, -srcimagekey, -shadow and related, -puppetstrings,
and -plist.
info display information about DiskImages.framework, the disk image driver, and any images that
are currently attached. hdiutil info accepts -plist.
checksum image -type type
Calculate the specified checksum on the image data, regardless of image type.
Common options: -shadow and related, -encryption, -stdinpass. -srcimagekey, -puppetstrings,
and -plist,
type is one of:
UDIF-CRC32 - CRC-32 image checksum
UDIF-MD5 - MD5 image checksum
DC42 - Disk Copy 4.2
CRC28 - CRC-32 (NDIF)
CRC32 - CRC-32
MD5 - MD5
SHA - SHA
SHA1 - SHA-1
SHA256 - SHA-256
SHA384 - SHA-384
SHA512 - SHA-512
chpass image
change the passphrase for an encrypted image. The default is to change the password inter-actively. interactively.
actively.
Common options: -recover and -srcimagekey. The options -oldstdinpass and -newstdinpass
allow, in the order specified, the null-terminated old and new passwords to be read from the
standard input in the same manner as with -stdinpass.
unflatten image
unflatten a UDIF disk image, creating an OS 9-style dual-fork image file (no XML metadata).
If the resource fork representation of the metadata becomes greater than 16 MB, the opera-tion operation
tion will fail with error -39 ("End of fork").
Common options: -encryption, -stdinpass, and -srcimagekey.
flatten image
Flatten a read-only (or compressed) UDIF disk image into a single-fork file. By default,
metadata will be stored both as XML (for the kernel's use) and in an embedded resource fork
(for OS X 10.1 and earlier).
Common options: -srcimagekey, -encryption, and -stdinpass. Since images are created "flat"
by default, flatten is only required if the UDIF has previously been unflattened.
Other options:
-noxml don't embed XML data for in-kernel attachment. The image will never attach in-kernel. inkernel.
kernel.
-norsrcfork don't embed resource fork data. The image will not attach on OS X versions
prior to OS X 10.2.
fsid image
Print information about file systems on a given disk image. As usual, image can be a /dev
entry corresponding to a physical disk. See the NOTE ON DEV ENTRY ACCESS section. More
detailed information is presented for HFS file systems.
Common options: -encryption, -stdinpass, -srcimagekey, and -shadow and related.
mountvol dev_name
mount the filesystem in dev_name using Disk Arbitration (similar to diskutil(8)'s mount).
XML output is available from -plist. Note that mountvol (rather than mount, though it often
works in OS X 10.5 and later) is the correct way to remount a volume after it has been
unmounted by unmount.
Prior to OS X 10.5, mount/attach would treat a /dev entry as a disk image to be attached
(creating another /dev entry). That behavior was undesirable.
unmount volume [-force]
unmount a mounted volume without detaching any associated image. Volume is a /dev entry or
mountpoint. NOTE: unmount does NOT detach any disk image associated with the volume.
Images are attached and detached; volumes are mounted and unmounted. mountvol will remount
a volume that has been unmounted by unmount.
Options:
-force unmount filesystem regardless of open files on that filesystem. Similar to umount
-f.
imageinfo image
Print out information about a disk image.
Common options: -encryption, -stdinpass, -srcimagekey, -shadow and related, and -plist.
Options are any of:
-format just print out the image format
-checksum just print out the image checksum
isencrypted image
print a line indicating whether image is encrypted. If it is, additional details are
printed.
Common options: -plist.
plugins print information about DiskImages framework plugins. The user, system, local, and network
domains are searched for plugins (i.e. ~/Library/Plug-ins/DiskImages,
/System/Library/Plug-ins/DiskImages, /Library/Plug-ins/DiskImages,
/Network/Library/Plug-ins/DiskImages).
Common options: -plist.
internet-enable [-yes] | -no | -query image
Enable or disable download post-processing (IDME). -yes is the default. When enabled, a
browser (or Disk Copy 10.2.3+) will "unpack" the contents: the image's visible contents will
be copied into the directory containing the image and the image will be put into the trash
with IDME disabled.
Common options: -encryption, -stdinpass, -srcimagekey, and -plist.
resize size_spec image
Resize a disk image or the containers within it. For an image containing a trailing
Apple_HFS partition, the default behavior is to resize the image container, the partition,
and the filesystem within it by aligning the end of the latter with the end of the image.
On older systems, resize was limited to pre-defined limits that depended on how the filesys-tem filesystem
tem was created. As of OS X 10.4, resize can be used to grow an HFS filesystem within an
image to any size supported by HFS and the filesystem hosting the image.
resize is often used when a device image needs to be shrunk so that the HFS/HFS+ partition
can be converted to CD-R/DVD-R format and still be burned. Note that gaps cannot be
reclaimed as resize does not move data. diskutil(8) resize can be used to move filesystem
data so that hdiutil resize can make an image barely larger than the data within it.
-fsargs can sometimes be used to minimize filesystem gaps in the image contents. resize can
grow a filesystem and image within the bounds of the image and filesystem formats (e.g.
roughly 2^63 bytes for HFS+ inside of a UDRW on HFS+).
hdiutil burn does not burn Apple_Free partitions at the end of the devices, so an image with
a resized filesystem can be burned to create a CD-R/DVD-R master that contains only the
actual data in the hosted filesystem (assuming minimal data fragmentation).
Common options: -encryption, -stdinpass, -srcimagekey, -shadow and related, and -plist.
Size specifiers:
-size ??b|??k|??m|??g|??t??p|??e
-sectors sector_count | min
Specify the number of 512-byte sectors to which the partition should be
resized. If this falls outside the mininum valid value or space remaining
on the underlying file system, an error will be returned and the partition
will not be resized. min automatically determines the smallest possible
size.
Other options:
-imageonly only resize the image file, not the partition(s) and filesystems inside of
it.
-partitiononly only resize a partition / filesystem in the image, not the image.
-partitiononly will fail if the new size won't fit inside the image. On
APM, shrinking a partition results in an explicit Apple_Free entry taking
up the remaining space in the image.
-partitionNumber partitionNumber
specifies which partition to resize (UDIF only -- see HISTORY below).
partitionNumber is 0-based, but, per hdiutil pmap, partition 0 is the par-tition partition
tition map itself.
-growonly only allow the image to grow
-shrinkonly only allow the image to shrink
-nofinalgap allow resize to entirely eliminate the trailing free partition in an APM
map. Restoring such images to very old hardware may interfere with boot-ing. booting.
ing.
-limits Displays the minimum, current, and maximum sizes (in 512-byte sectors) for
the image. In addition to any hosted filesystem constraints, UDRW images
are constrained by available disk space in the filesystem hosting the
image. -limits does not modify the image.
segment
segment -o firstSegname -segmentCount #segs image [opts]
segment -o firstSegname -segmentSize size image [opts]
segment a NDIF or UDIF disk image. Segmented images work around limitations in file size
which are sometimes imposed by filesystems, network protocols, or media. Note: whether or
not the segments are encrypted is determined by the options passed to segment and not by the
state of the source image.
Common options: -encryption, -stdinpass, -srcimagekey, -tgtimagekey, -puppetstrings, and
-plist.
Options:
-segmentCount segment_count
Specify the number of segments. Only one of -segmentCount or -segmentSize will
be honored.
-segmentSize segment_size
Specify the segment size in sectors or in the style of mkfile(8) (here unquali-fied unqualified
fied numbers are still sectors). If the original image size is not an exact
multiple of the segment size, the last segment will be shorter than the others.
Only one of -segmentCount or -segmentSize will be honored. Segmenting
read/write (UDRW) images is not supported (as of OS X 10.3).
-firstSegmentSize segment_size
Specify the first segment size in sectors in the same form as for -segmentSize.
Used for multi-CD restores.
-restricted Make restricted segments for use in multi-CD restores.
-ov overwrite any existing files.
pmap [options image]
display the partition map of an image or device. By default, this report includes offsets
and significant amounts of free space. image is either a plain or special file (i.e. a
/dev/disk entry). See the NOTE ON DEV ENTRY ACCESS below.
Common options: -encryption, -stdinpass, -srcimagekey, and -shadow and related.
-simple generate MediaKit's minimal report: partition types, names, and sizes in
human-readable units.
-standard generate MediaKit's standard report, which adds partition offsets and uses
512-byte sectors.
-complete generate MediaKit's comprehensive report, with end offsets, significant free
space, etc.
-endoffsets indicate last block of each partition.
-nofreespace suppress all free space reporting.
-shims report free space < 32 sectors
-uuids show per-instance UUIDs for each partition. APM does not store instance UUIDs
so these will be randomly generated for APM entries.
udifrez [options] image
embed resources (e.g. a software license agreement) in a disk image.
You must specify one of the following options:
-xml file
Copy resources from the XML in file.
-rsrcfork file
Copy resources from file's resource fork.
-replaceall
Delete all pre-existing resources in image.
udifderez [options] image
extract resources from image.
Options:
-xml emit XML output (default)
-rez emit Rez format output
Common options: -encryption, -stdinpass, and -srcimagekey.
EXAMPLES
Verifying:
hdiutil verify myimage.img
Verifies an image against its internal checksum.
Segmenting:
hdiutil segment -segmentSize 10m -o /tmp/aseg 30m.dmg
creates aseg.dmg, aseg.002.dmgpart, and aseg.003.dmgpart
Converting:
hdiutil convert master.dmg -format UDTO -o master
Converts master.dmg to a CD-R export image named master.cdr
hdiutil convert /dev/disk1 -format UDRW -o devimage
Converts the disk /dev/disk1 to a read/write device image file. authopen(1) will
be used if read access to /dev/rdisk1 is not available. Note use of the block-special
device.
Burning:
hdiutil burn myImage.dmg
Burns the image to available optical media and verifies the burn.
hdiutil burn myRawImage.cdr -noverifyburn -noeject
Burns the image without verifying the burn or ejecting the disc. Volumes will be
mounted after burning.
Creating a 50 MB encrypted image:
hdiutil create -encryption -size 50m e.dmg -fs HFS+J
Creating a 50 MB encrypted image protected with public key only:
hdiutil create -encryption -size 50m e.dmg -fs HFS+J
-pubkey F534A3B0C2AEE3B988308CC89AA04ABE7FDB5F30
Creating a 50 MB encrypted image protected with public key and password:
hdiutil create -encryption -size 50m e.dmg -fs HFS+J -agentpass
-pubkey F534A3B0C2AEE3B988308CC89AA04ABE7FDB5F30
Creating an encrypted single-partition image without user interaction:
printf pp|hdiutil create -encryption -stdinpass -size 9m sp.dmg
Creating a "1 GB" SPARSE image (a 1 GB filesystem in a growable file):
hdiutil create -type SPARSE -size 1g -fs HFS+ growableTo1g
Creating a "1 GB" SPARSEBUNDLE (a 1 GB filesystem in a growable bundle):
hdiutil create -type SPARSEBUNDLE -size 1g -fs HFS+ growableTo1g
Creating a new mounted volume backed by an image:
hdiutil create -volname Dick -size 1.3m -fs HFS+ -attach Moby.dmg
Using a shadow file to attach a read-only image read-write to modify it, then convert it back to a
read-only image. This method eliminates the time/space required to convert a image to read-write before
modifying it.
hdiutil attach -owners on Moby.dmg -shadow
/dev/disk2 Apple_partition_scheme
/dev/disk2s1 Apple_partition_map
/dev/disk2s2 Apple_HFS /Volumes/Moby
ditto /Applications/Preview.app /Volumes/Moby
hdiutil detach /dev/disk2
hdiutil convert -format UDZO Moby.dmg -shadow
Using makehybrid to create cross-platform data with files overlapping between filesystem views. With
these files:
albumlist.txt song2.wma song4.m4a song6.mp3 song8.mp3
song1.wma song3.m4a song5.mp3 song7.mp3
hdiutil makehybrid -o MusicBackup.iso Music -hfs -iso -joliet \
-hide-hfs 'Music/*.wma' -hide-joliet 'Music/{*.m4a,*.mp3}' \
-hide-iso 'Music/*.{wma,m4a}'
will create an image with three filesystems pointing to the same blocks. The HFS+ filesystem, typi-
cally only visible on Macintosh systems, will not include the .wma files, but will show the .m4a and
.mp3 files. The Joliet filesystem will not show the .m4a and .mp3 files, but will show the .wma files.
The ISO9660 filesystem, typically the default filesystem for optical media on many platforms, will only
show the .mp3 files. All three filesystems will include the "albumlist.txt" files.
Image from directory (new-style):
hdiutil create -srcfolder mydir mydir.dmg
Image from directory (10.1-style; of historical interest):
du -s myFolder # du(1) will count resource forks
10542
hdiutil create -sectors 10642 folder # add ~1% for filesytem
hdid -nomount folder.dmg
...
/dev/disk1s2 Apple_HFS
newfs_hfs -v myFolderImage /dev/rdisk1s2
hdiutil detach disk1
hdid folder.dmg
...
/dev/disk1s2 Apple_HFS /Volumes/myFolderImage
sudo mount -u -t hfs -o perm /dev/disk1s2 /Volumes/myFolderImage
# optionally enable owners; sudo unneeded if manually mounted
ditto -rsrcFork myFolder /Volumes/myFolderImage
hdiutil detach disk1s2 # all done
hdiutil convert -format UDZO -o folder.z.dmg folder.dmg # compress
Manually changing ownership settings of a read-only disk image:
hdiutil attach myimage.dmg
...
/dev/disk1s2 Apple_HFS /Volumes/myVolume
diskutil unmount disk1s2
mkdir /Volumes/myVolume
sudo mount -r -t hfs -o owners /dev/disk1s2 /Volumes/myVolume
# -o owners is the default for manual mounts
Forcing a known image to attach:
hdiutil attach -imagekey diskimage-class=CRawDiskImage myBlob.bar
ENVIRONMENT
The following environment variables affect hdiutil and DiskImages:
com_apple_hdid_verbose
enable -verbose behavior for attach.
com_apple_hdid_debug
enable -debug behavior for attach.
com_apple_hdid_nokernel
similar to -nokernel but works even with, for example, create -attach.
com_apple_hdid_kernel
attempt to attach in-kernel first (like attach -kernel). In OS X 10.4.x, in-kernel was the
default behavior for UDRW and SPARSE images. On OS X 10.5, these and other kernel-compati-ble kernel-compatible
ble images, including RAM-based images described in hdid(8), will attach with a user process
unless attach -kernel is used or the corresponding variable is set. If an image is not
"kernel-compatible" and -kernel is specified, the attach will fail. (WARNING: ram:// images
currently use wired memory when attached in-kernel).
com_apple_diskimages_insecureHTTP
disable SSL peer verification the same way -insecurehttp does. Useful for clients of
DiskImages such as asr(8) which don't support a similar command line option.
ERRORS
DiskImages uses many frameworks and can encounter many error codes. In general, it tries to turn these
errors numbers into localized strings for the user. For background, intro(2) is a good explanation of
our primary error domain: the BSD errno values. For debugging, -verbose should generally provide
enough information to figure out what has gone wrong. The following is a list of interesting errors
that hdiutil may encounter:
[ENXIO] Device not configured. This error is returned explicitly by DiskImages when its
kernel driver or framework helper cannot be contacted. It also often shows up when
a device has been removed while I/O is still active. One common case of the helper
not being found is when Foundation's Distributed Objects RPC mechanism cannot be
configured. D.O. doesn't work under dead Mach bootstrap contexts such as can exist
in a reattached screen(1) session. Root users can take advantage of
StartupItemContext(8) (in /usr/libexec) to access the startup item Mach bootstrap
context.
[EINVAL] Invalid argument. This error is used in many contexts and is often a clue that
hdiutil's arguments are subtly non-sensical (e.g. an invalid layout name passed to
create -layout).
[EFBIG] File too large. DiskImages uses this error explicitly when attempting to access a
disk image over HTTP that is too large for the server to support Range requests.
This error can also occur when the Resource fork of an old-style UDIF overflows.
[EAUTH] Authentication error. Used by DiskImages when libcurl(3) is unable to verify its
SSL peer or when Security.framework indicates that the user failed to enter the cor-rect correct
rect password. See -insecurehttp and -cacert for more information about verifica-tion verification
tion of SSL peers.
[EBUSY] Resource busy. Used if necessary exclusive access cannot be obtained. This error
often appears when a volume can't be unmounted.
[EAGAIN] Resource temporarily unavailable. As of OS X 10.5, DiskImages uses reader/writer
locks on its image files to prevent images from being attached on more than one
machine at a time (e.g. over the network). EAGAIN is returned if the appropriate
read or write lock can't be obtained.
EACCES vs. EPERM EACCES and EPERM are subtly different. The latter "operation not permitted" tends
to refer to an operation that cannot be performed, often due to an incorrect effec-tive effective
tive user ID. On the other hand, "permission denied" tends to mean that a particu-lar particular
lar file access mode prevented the operation.
USING PERSISTENT SPARSE IMAGES
As of OS X 10.5, a more reliable, efficient, and scalable sparse format, UDSB (SPARSEBUNDLE), is recom-mended recommended
mended for persistent sparse images as long as a backing bundle (directory) is acceptable. OS X 10.5
also introduced F_FULLFSYNC over AFP (on client and server), allowing proper journal flushes for HFS+J-bearing HFS+Jbearing
bearing images. Critical data should never be stored in sparse disk images on file servers that don't
support F_FULLFSYNC.
SPARSE (UDSP) images and shadow files were designed for intermediate use when creating other images
(e.g. UDZO) when final image sizes are unknown. As of OS X 10.3.2, partially-updated SPARSE images are
properly handled and are thus safe for persistent storage. SPARSE images are not recommended for per-sistent persistent
sistent storage on versions of OS X earlier than 10.3.2 and should be avoided in favor of SPARSEBUNDLE
images or UDRW images and resize.
If more space is needed than is referenced by the hosted filesystem, hdiutil resize or diskutil(8)
resize can help to grow or shrink the filesystem in an image. compact reclaims unused space in sparse
images. Though they request that hosted HFS+ filesystems use a special "front first" allocation pol-icy, policy,
icy, beware that sparse images can enhance the effects of any fragmentation in the hosted filesystem.
To prevent errors when a filesystem inside of a sparse image has more free space than the volume hold-ing holding
ing the sparse image, HFS volumes inside sparse images will report an amount of free space slightly
less than the amount of free space on the volume on which image resides. The image filesystem cur-rently currently
rently only behaves this way as a result of a direct attach action and will not behave this way if, for
example, the filesystem is unmounted and remounted.
NOTE ON DEV ENTRY ACCESS
Since any /dev entry can be treated as a raw disk image, it is worth noting which devices can be
accessed when and how. /dev/rdisk nodes are character-special devices, but are "raw" in the BSD sense
and force block-aligned I/O. They are closer to the physical disk than the buffer cache. /dev/disk
nodes, on the other hand, are buffered block-special devices and are used primarily by the kernel's
filesystem code.
It is not possible to read from a /dev/disk node while a filesystem is mounted from it, but anyone with
read access to the appropriate /dev/rdisk node can use hdiutil verbs such as fsid or pmap with it. The
DiskImages framework will attempt to use authopen(1) to open any device which it can't open (due to
EACCES) for reading with open(2). This may cause apparent hangs while trying to access /dev entries
while logged in remotely (an authorization panel is waiting on console).
Generally, the /dev/disk node is preferred for imaging devices (e.g. convert or create -srcdevice
operations), while /dev/rdisk is usable for the quick pmap or fsid. In particular, converting the
blocks of a mounted journaled filesystem to a read-only image will prevent the volume in the image from
mounting (the journal will be permanently dirty).
COMPATIBILITY
OS X 10.0 supported the disk images of Disk Copy 6 on Mac OS 9. OS X 10.1 added sparse, encrypted, and
zlib-compressed images. These images will not be recognized on OS X 10.0 (or will attach read/write,
possibly allowing for their destruction). As the sparse, shadow, and encrypted formats have evolved,
switches have been added to facilitate the creation of images that are compatible with older OS ver-sions versions
sions (at the expense of the performance and reliability improvements offered by the format enhance-ments). enhancements).
ments). In particular, sparse images should not be expected to attach on versions of OS X older than
that which created them.
With OS X 10.2, the most common image formats went "in-kernel" (i.e. the DiskImages kernel extension
served them without a helper process), image meta-data began being stored both as XML and in the embed-ded embedded
ded resource fork, and the default Disk Copy.app "compressed" format became UDZO (breaking compatibil-ity compatibility
ity with 10.0). OS X 10.4 introduced bzip2 compression in the UDBZ format which provides smaller
images (especially when combined with makehybrid) at the expense of backwards compatibility.
In OS X 10.4.7, the resource forks previously embedded in UDIF images were abandoned entirely to avoid
metadata length limitations imposed by resource fork structures. As a result, UDIF images created on
10.4.7 and later will not, by default, be recognized by either OS X 10.1 or OS X 10.0. flatten can be
used to customize the type of metadata stored in the image.
OS X 10.5 introduced sparse bundle images which compact quickly but are not recognized by previous OS
versions. OS X 10.6 removed support for attaching SPARSEBUNDLE images from network file servers that
don't support F_FULLFSYNC.
HISTORY
Disk images were first invented to electronically store and transmit representations of floppy disks
for manufacturing replication. These images of floppies are typically referred to as 'Disk Copy 4.2'
images, in reference to the application that created and restored them to floppy disks. Disk Copy 4.2
images were block-for-block representations of a floppy disk, with no notion of compression. DART is a
variant of the Disk Copy 4.2 format that supported compression.
NDIF (New Disk Image Format) images were developed to replace the Disk Copy 4.2 and DART image formats
and to support images larger than a floppy disk. With NDIF and Disk Copy version 6, images could be
"attached" as mass storage devices under Mac OS 9. Apple Data Compression (ADC) -- which carefully
optimizes for fast decompression -- was used to compress images that were typically created once and
restored many times during manufacturing.
UDIF (Universal Disk Image Format) device images picked up where NDIF left off, allowing images to rep-resent represent
resent entire block devices and all the data therein: DDM, partition map, disk-based drivers, etc. For
example, it can represent bootable CDs which can then be replicated from an image. To ensure single-fork singlefork
fork files (NDIF was dual-fork), it began embedding its resource fork in the data fork. UDIF is the
native image format for OS X.
Raw disk images from other operating systems (e.g. .iso files) will be recognized as disk images and
can be attached and mounted if OS X recognizes the filesystems. They can also be burned with hdiutil
burn.
WHAT'S NEW
In OS X 10.6, pmap was rewritten to use MediaKit's latest reporting routines so that it can properly
support GPT partition maps. Also -debug now implies -verbose for all verbs.
OS X 10.5 changed the behavior of attach when run on an existing image or /dev node: if the image was
attached but no volume was mounted, the volume would be mounted. Prior systems would return the /dev
without mounting the volume. This change effectively removes the ability to create a second /dev node
from an existing one.
SEE ALSO
authopen(1), hdid(8), diskutil, ditto(8), ioreg(8), drutil(1), ufs.util(8), msdos.util(8), hfs.util(8),
diskarbitrationd(8), /usr/sbin/disktool (run with no arguments for usage),
/System/Library/CoreServices/DiskImageMounter.app.
Mac OS X 22 Apr 2009 Mac OS X
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