Manipulate disk images (attach, verify, burn, etc).
Syntax
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,
erasekeys, 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 macOS 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 understood, 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 opera-
tion 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 macOS 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 speci-
fied, 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 com-
patibility. 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 create 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 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 hexa-
decimal 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 directory of certificates pro-
cessed 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 filename and
changes its behavior accordingly. For example, a sparse image can be
created without specifying -type SPARSEBUNDLE 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 BACKGROUND.
Beware that an image freshly created and attached is treated
as a new removable device. See hdid(8) and the EXAMPLES sec-
tion below for more details about how owners are ignored on
filesystems on such devices.
The output of attach has been stable since macOS 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 content hints are derived
from the partition data, GUID Partition Table types can 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 frame-
work’s decision to attach a particular
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 macOS 10.5.
-kernel attempt to attach this image without a
helper process; fail if unsupported. Only
UDRW, UDRO, UDZO, and UDSP images are sup-
ported 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 filesys-
tems 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 macOS 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 par-
ticular volumes automatically mount in par-
ticular filesystem locations by editing the
file /etc/fstab.
-nobrowse Render any volumes invisible in applica-
tions such as the macOS 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 registry.
-section subspec Attach a subsection of a disk image.
subspec is any of <offset>, <first-last>, or <start,count>
in 0-based sectors. Ranges are inclusive
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 override any existing preferences.
-[no]verify Do [not] verify the image. By default, hdiutil attach
attempts to intelligently 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 cancel when a bad
checksum is detected.
Preferences key: ignore-bad-checksums
-[no]autoopen do [not] auto-open volumes (in the Finder) after attaching
an image. By default, dou ble-clicking a read-only
disk image causes the resulting volume to be opened in the
Finder. hdiutil defaults to -noautoopen.
-[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 check-
ing before mounting a disk image. By
default, only quarantined images (e.g. down-
loaded from the Internet) that have not pre-
viously 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 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 can 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) might 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 use-
ful for large sparse images.
-sectors sector_count
Specify the size of the image file in 512-byte sec-
tors.
-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 (theoretically defrag-
mented) filesystem on the destination. The result-
ing 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 over-
ridden 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 synonym.
-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 subsequently succeed.
Filesystem options (like -fs, -volname, -stretch,
or -size) are invalid and ignored when using
-srcdevice.
Common options: -encryption, -stdinpass, -certificate,
-pubkey, -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 macOS 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 macOS 10.2 but is more robust for
SPARSE (UDSP) images. Version 1 is the default for non-sparse images.
As of macOS 10.4.7, sparse encrypted images always use version 2 and as
of macOS 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 inde-
pendent 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 created. 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 bun-
dle.
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 16777216 sectors (1 MB to 8 GB).
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 filesys-
tem 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 size of a sparse image. See also USING PERSIS-
TENT SPARSE IMAGES below.
-fs filesystem
where filesystem is one of HFS+, HFS+J (JHFS+),
HFSX, JHFS+X, MS-DOS, or UDF. -fs causes a filesys-
tem of the specified type to be written to the
image. -fs can change the partition scheme and type
appropriately. -fs will not make any size adjust-
ments: if the image is the wrong size for the speci-
fied 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 speci-
fied, 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 speci-
fied like -size. -stretch is invalid and ignored
when using -srcdevice.
-fsargs newfs_args
additional arguments to pass to whatever newfs pro-
gram 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. Sup-
pressing the journal with -fs HFS+ and passing argu-
ments such as -c c=64,a=16,e=16 to -fsargs will min-
imize 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, multi-
ple /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 macOS
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
Note that segmented images are deprecated.
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.
-[no]atomic Do [not] copy files to a temporary location and then rename them to their
destination. Atomic copies are the default.
Non-atomic copying may be slightly faster.
-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
ULFO - UDIF lzfse-compressed image (OS X 10.11+ only)
ULMO - UDIF lzma-compressed image (macOS 10.15+ only)
UDBZ - UDIF bzip2-compressed image (deprecated)
UDTO - DVD/CD-R master for export
UDSP - SPARSE (grows with content)
UDSB - SPARSEBUNDLE (grows with content; bundle-backed)
UFBI - UDIF entire image with MD5 checksum
In addition to the compression offered by some formats, the UDIF read-only format skips
unused space in HFS, APFS, ExFAT, and MS-DOS (FAT, FAT32) filesystems.
For UDZO, -imagekey zlib-level=value allows the zlib compression level to be specified
a la 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 unpartitioned UDIF, the
default is true.
-segmentSize [size_spec]
Note that segmented images are deprecated.
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 qual-
ified by Apple (kept for backwards compati-
bility as burn will burn to any device by
default as of macOS 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 partition map. This option
will add a partition map to any bare filesys-
tem which needs a partition map in order to
be recognized when burned to optical 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 speci-
fying 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 volume. This option will change what
is burned such that the disc will have a dif-
ferent 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 protec-
tion.
-[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) without burning any-
thing.
-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 filesystem 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 using ditto(8).
hdiutil supports generating El Torito-style bootable ISO9660 filesystems, which are
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 simultaneously with an ISO9660
or Joliet or UDF filesystem. On Operating Systems that understand HFS+ as well
as ISO9660 and UDF, like Mac OS 9 or OS X, HFS+ is usually the preferred
filesystem for hybrid images.
-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 filesystem is present on a disk image or CD, but not
HFS+, 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 Operating Systems.
If both an ISO9660 and Joliet filesystem are present on a disk image
or CD, but not HFS+, 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
filesystems 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 OS X booting
on the generated filesystem.
This assumes the directory has been otherwise 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 generated
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 generated
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 generated
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 (suchas .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, without emulating any
devices (ISO9660/Joliet).
-no-boot Mark the El Torito image as non-bootable. The system firmware can 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 Valida-
tion Entry or Section Header. Defaults to 0 to identify x86 hardware
(ISO/Joliet).
-eltorito-specification For complex layouts involving multiple boot images, a plist-formatted string
can be provided, using either OpenStep-style syntax or XML syntax, represent-
ing 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 com-
mand-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 might
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 can
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 can
still be present for use by other filesystems (ISO9660 only). Per above,
the Joliet hierarchy will supersede the ISO hierarchy when the hybrid is
mounted as an ISO 9660 filesystem on macOS. 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 can 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 macOS.
-hide-udf A glob expression of files and directories that should not
be exposed via the UDF filesystem, although the data can
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
generation. 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
evaluated 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 options
scans the bands of a sparse (SPARSE or SPARSEBUNDLE) disk image containing an APFS or HFS+
filesystem, 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.
Options:
-batteryallowed Allow compacting on battery power.
SPARSE images could be damaged if power is lost during a compact operation.
The default is not allowed.
-sleepallowed Allow machine to idle sleep while compacting, which cancels the compact operation.
The default is not allowed, which prevents idle sleep until
compact completes.
User-initiated sleep, such as a lid close, will always cancel compact.
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 interactively.
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.
erasekeys image
securely overwrite keys used to access an encrypted image,
quickly rendering the image completely inaccessible. Once
erasekeys has been run on an encrypted image, there is no fea-
sible way to recover data from the image file.
Common options: -plist and -quiet.
unflatten image
unflatten a UDIF disk image, creating an OS 9-style dual-fork
image file (no XML metadata). If the resource fork represen-
tation of the metadata becomes greater than 16 MB, the opera-
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 macOS 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.
-norsrcfork don’t embed resource fork data. The image will
not attach on macOS versions prior to macOS 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 physi-
cal 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 (simi-
lar to diskutil(8)’s mount). XML output is available from
-plist. Note that mountvol (rather than mount, though it
often works in macOS 10.5 and later) is the correct way to
remount a volume after it has been unmounted by unmount.
Prior to macOS 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 is to
resize the image container, the partition, and the filesystem
within it by aligning the end of the hosted structures with
the end of the image. hdiutil resize cannot resize filesys-
tems other than HFS+ and its variants.
resize can shrink an image so that its HFS/HFS+ partition can
be converted to CD-R/DVD-R format and still be burned.
hdiutil resize will not reclaim gaps because it does not move
data. diskutil(8)’s resize can move filesystem data which can
help hdiutil resize create a minimally-sized image. -fsargs
can also be used to minimize filesystem gaps inside an image.
resize is limited by the disk image container format (e.g.
UDSP vs. UDSB), any partition scheme, the hosted filesystem,
and the filesystem hosting the image. In the case of HFS+
inside of GPT inside of a UDRW on HFS+ with adequate free
space, the limit is approximately 2^63 bytes. Older images
created with an APM partition scheme are limited by it to 2TB.
Before macOS 10.4, resize was limited by how the filesystem was
created (see hdiutil create -stretch).
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 sys-
tem, an error will be returned and the parti-
tion will not be resized. min automatically
determines the smallest possible size.
Other options:
-imageonly only resize the image file, not the parti-
tion(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 partition map itself.
-growonly only allow the image to grow
-shrinkonly only allow the image to shrink
-nofinalgap allow resize to entirely eliminate the trail-
ing free partition in an APM map. Restoring
such images to very old hardware can inter-
fere with booting.
-limits Displays the minimum, current, and maximum
sizes (in 512-byte sectors) for the image.
In addition to any hosted filesystem con-
straints, UDRW images are constrained by
available disk space in the filesystem host-
ing 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 unqualified 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 macOS 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 starting offsets and significant amounts
of free space. image is either a plain or special file (for
example, a /dev/disk entry). See NOTE ON DEV ENTRY ACCESS.
Common options: -encryption, -stdinpass, -srcimagekey, and
-shadow and related.
-simple generate MediaKit’s minimal report: basic parti-
tion 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. Not valid
with -shims.
-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 maps.
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 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
Note that these two -pubkey usage examples assume a certificate corre-
sponding to this public key is currently in the user’s keychain or smart
card. For additional information on smart card authorization setup see
sc_autch(8).
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, typically 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 macOS 10.5, these and other kernel-compati-
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 error 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 gen-
erally provide enough information to figure out what has gone wrong. The
following is a list of interesting errors that hdiutil can encounter:
[ENXIO] Device not configured. This error is returned explic-
itly 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 reat-
tached screen(1) session. Root users can take advan-
tage 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 sub-
tly 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 correct password. See -insecurehttp and
-cacert for more information about verification 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 macOS 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 opera-
tion that cannot be performed, often due to an incor-
rect effective user ID. On the other hand, "permis-
sion denied" tends to mean that a particular file
access mode prevented the operation.
USING PERSISTENT SPARSE IMAGES
As of macOS 10.5, a more reliable, efficient, and scalable sparse format, UDSB (SPARSEBUNDLE), is recommended for persistent sparse images as long
as a backing bundle (directory) is acceptable. macOS 10.5 also introduced
F_FULLFSYNC over AFP (on client and server), allowing proper journal flushes for HFS+J-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 macOS 10.3.2, partially-updated SPARSE images are properly handled and are thus safe for persistent storage. SPARSE images are not
recommended for persistent storage on versions of macOS 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 policy, 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 holding 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 currently 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.
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 might 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).
macOS 10.0 supported the disk images of Disk Copy 6 on Mac OS 9. macOS 10.1 added sparse, encrypted, and zlib-compressed images. These images will not be recognized on macOS 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 versions (at the expense of the performance and reliability improvements offered by the format enhancements). In particular, sparse images should not be expected to attach on versions of macOS older than that which created them.
With macOS 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 embedded resource fork, and the default Disk Copy.app "compressed" format became UDZO (breaking compatibility with 10.0). macOS 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 macOS 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 macOS 10.1 or macOS 10.0. flatten can be used to customize the type of metadata stored in the image.
macOS 10.5 introduced sparse bundle images which compact quickly but are not recognized by previous OS versions. macOS 10.6 removed support for attaching SPARSEBUNDLE images from network file servers that don’t support F_FULLFSYNC.
macOS 10.7 removed double-click support for images using legacy metadata; these can be rehabilitated using flatten and unflatten, or convert.
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 represent 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 files (NDIF was dual-fork), it began embedding its resource fork in the data fork. UDIF is the native image format for macOS.
Raw disk images from other Operating Systems (e.g. .iso files) will be recognized as disk images and can be attached and mounted if macOS recognizes the filesystems. They can also be burned with hdiutil burn.
In macOS 10.12 Apple will provide an updated hdutil command able to work with the new file system.
macOS 10.7 added the ability to quickly render encrypted images inaccessible using the new erasekeys verb, which saves time versus securely overwriting the entire image.
In macOS 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.
macOS 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.
Mount a Disk Image:
$ hdiutil attach /path/to/diskimage.dmg
Unmount a Disk Image:
$ hdiutil detach /dev/disk2s1
Create a Disk Image from a folders contents:
$ hdiutil create -volname "Volume Name" -srcfolder /path/to/folder -ov diskimage.dmg
Create an encrypted Disk Image from a folders contents:
$ hdiutil create -encryption -stdinpass -volname "Volume Name" -srcfolder /path/to/folder -ov encrypted.dmg
The required password can be piped into the hdiutil command:
echo -n SEcurePa$$w0rd | hdiutil...
Burn a Disk Image file (.iso, .img or .dmg) to a DVD:
$ hdiutil burn /path/to/image_file
“The beginning of wisdom is to call things by their right names” ~ Chinese Proverb
asr - Apple Software Restore.
dd - Convert and copy a file, clone disks.
diskutil - Disk utilities - Format, Verify, Repair.
ditto - Copy files and folders.
authopen(1), hdid(8), ioreg(8), drutil(1), msdos.util(8), hfs.util(8), diskarbitrationd(8), /System/Library/CoreServices/DiskImageMounter.app.