HDIUTIL(1) General Commands Manual HDIUTIL(1)
NAME
hdiutil – manipulate disk images (attach, verify, create, etc)
SYNOPSIS
hdiutil verb [options]
DESCRIPTION
hdiutil uses the DiskImages framework to manipulate disk images. Common
verbs include attach, detach, verify, create, convert, and compact.
The rest of the verbs are currently: help, info, burn, checksum, chpass,
erasekeys, imageinfo, isencrypted, mountvol, unmount, plugins, udifrez,
udifderez, resize, segment, makehybrid, and pmap.
BACKGROUND
Disk images are data containers that emulate disks. Like disks, they can
be partitioned and formatted. Many common uses of disk images blur the
distinction between the disk image container and its content, but this
distinction is critical to understanding how disk images work. The terms
"attach" and "detach" are used to distinguish the way disk images are
connected to and disconnected from a system. "Mount" and "unmount" are the
parallel filesystems options.
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 are discovered that
should be mounted, the associated volumes will mount and appear on the
desktop.
When using disk images, always consider whether an operation applies to the
blocks of the disk image container or to the (often file-oriented) content
of the image. For example, hdiutil verify verifies that the blocks stored
in a read-only disk image have not changed since it was created. It does
not check whether the filesystem stored within the image is self-consistent
(as diskutil verifyVolume would). On the other hand, hdiutil 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. No /dev entries or mount points will
be printed. -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. As of OS X
10.7, the default algorithm is the AES cipher running in
CBC mode on 512-byte blocks 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). Otherwise, the password is read
from stdin. -stdinpass replaces -passphrase which has been
deprecated. -passphrase is insecure because its argument
appears in the output of ps(1) where it is visible to other
users and processes on the system. 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
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 directory 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 filename and changes
its behavior accordingly. For example, a sparse bundle image can be
created without specifying -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. If
any associated volumes are unmounted (and mounting is not
suppressed), they will be remounted. mount is a poorly-named
synonym for attach. See BACKGROUND.
By default, the system applies additional mount options to
filesystems backed by untrusted devices like disk images:
options like nosuid and quarantine. PERMISSIONS VS. OWNERS
explains the behavior of such filesystems and EXAMPLES shows how
to override some of the default behavior.
The output of attach has been stable since Mac 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 content 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 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 Mac OS X 10.5.
-kernel attempt to attach this image without a helper
process; fail if unsupported. Only UDRW,
UDRO, UDZO, ULFO, and UDSP images are
supported in-kernel. Encryption and HTTP are
supported by the kernel driver.
-notremovable prevent this image from being detached. Only
root can use this option. A reboot is
necessary to cleanly detach an image attached
with -notremovable.
-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 Mac 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.
-nobrowse render any volumes invisible in applications
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 set on 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 abort 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, double-
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 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 Mac
OS X 10.4, dev_name can also be a mountpoint. If Disk
Arbitration 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. In common
operation, detach is very similar to diskutil(8)'s eject.
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 (theoretically 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 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.
With APFS, imaging from a device that is an
individual APFS volume is invalid. To create a valid
APFS disk image, device needs to be an APFS container
or contain an APFS container partition.
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 Mac 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 Mac OS X 10.2 but
is more robust for SPARSE (UDSP) images. Version 1 is the
default for non-sparse images. As of Mac OS X 10.4.7, sparse
encrypted images always use version 2 and as of Mac 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 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 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 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). 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 APFS or HFS+ filesystems.
resize will only change the virtual size of a sparse
image. See also USING PERSISTENT SPARSE IMAGES below.
-fs filesystem
where filesystem is one of several options such as
HFS+, HFS+J (JHFS+), HFSX, JHFS+X, APFS, FAT32, ExFAT,
or UDF. A full list of supported filesystems can be
found in create -help. -fs causes a filesystem of the
specified type to be written to the image. The
default file system is APFS. If -partitionType and/or
-layout are specified, but -fs is not specified, no
file system will be created. -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; The
default volume name in both HFS+ and APFS 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 PERMISSIONS VS. OWNERS).
-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 whichever newfs
program is implied by -fs. As an example with HFS+,
newfs_hfs(8) has a number of options that can control
the amount of space used by the filesystem's data
structures.
-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 Mac 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.
-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 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
qualified by Apple (kept for backwards
compatibility as burn will burn to any device
by default as of Mac 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 partition 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 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 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+
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
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 burning the source
image's blocks would not result in a valid
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 without
burning anything. The size is returned in
sectors.
-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 quite 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 (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, without 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-formatted 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 hierarchy will supersede the
ISO hierarchy when the hybrid is mounted
as an ISO 9660 filesystem on 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 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
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
delete keys used to access an encrypted image, quickly rendering
the image inaccessible. This does not prevent other copies of
the keys from later being broken and used to decrypt the data,
such as from a copy or backup of the image. In addition, modern
storage systems such as solid state disks do not securely
overwrite data. As a result, erasekeys cannot protect against
all attacks, but it may prevent trivial access.
Common options: -plist and -quiet.
fsid image
Print information about filesystems on a given disk image. Per
DEVICE SPECIAL FILES, image can be a /dev entry corresponding to
a disk. More detailed information is presented for HFS+
filesystems.
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
Mac OS X 10.5 and later) is the correct way to remount a volume
after it has been unmounted by unmount.
Prior to Mac 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.
hdiutil mountvol (or diskutil mount) will remount a volume that
has been unmounted by hdiutil unmount.
Options:
-force unmount filesystem regardless of open files on that
filesystem. Similar to umount -f.
imageinfo image [options]
Print out information about a disk image.
Options are any of:
-format only print out the image format
-checksum only print out the image checksum
Common options: -encryption, -stdinpass, -srcimagekey, -shadow
and related, and -plist.
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.
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 filesystems
other than HFS+ and its variants.
resize can shrink an image so that its 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 Mac OS X
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 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.
-partitionID partitionID
specifies which partition to resize (UDIF only --
see HISTORY below). partitionID is 1-based.
-nofinalgap allow resize to entirely eliminate the trailing
free partition in an APM map. Restoring such
images to very old hardware may interfere with
booting.
-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
NOTE: hdiutil segment command is deprecated
segment -o firstSegname -segmentCount #segs image [opts]
segment -o firstSegname -segmentSize size image [opts]
segment an 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 Mac 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 starting offsets and significant amounts of
free space. image is either a disk image or /dev/disk entry
(see DEVICE SPECIAL FILES).
Common options: -encryption, -stdinpass, -srcimagekey, and
-shadow and related.
-simple generate MediaKit's minimal report: basic
partition types, names, and sizes in human-
readable units.
-standard generate MediaKit's standard report, which adds
partition offsets and uses 512-byte sectors. This
is the default.
-complete generate MediaKit's comprehensive report, with end
offsets, significant free space, etc.
-diagnostic generate MediaKit's diagnostic report, which shows
all partition schemes encountered. Useful for
Boot Camp troubleshooting.
-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 (deprecated)
embed resources in a disk image.
You must specify one of the following options:
-xml file
Copy resources from the XML in file.
-replaceall
Delete all pre-existing resources in image.
udifderez [options] image (deprecated)
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.
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.
hdiutil convert image.dmg -o image.sparsebundle
converts image.dmg to format UDSB by automatically detecting
the file extension .sparsebundle.
hdiutil convert files.sparsebundle -format UDZO \
-imagekey zlib-level=5 -o files
converts files.sparsebundle to files.dmg: a read-only,
compressed disk image using zlib level 5 instead of the
default.
hdiutil convert stuff.dmg -format UDZO -encryption -o stuff-enc
create a copy of stuff.dmg named stuff-enc.dmg which is
encrypted with AES-128.
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 read/write encrypted image:
hdiutil create -encryption -size 50m e.dmg -fs HFS+J
Creating a 50 MB read/write encrypted image protected with public key only:
hdiutil create -encryption -size 50m e.dmg -fs HFS+J \
-pubkey F534A3B0C2AEE3B988308CC89AA04ABE7FDB5F30
Creating a 50 MB read/write 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
corresponding to this public key is currently in the user's keychain or
smart card. For additional information on smart card authorization setup
see sc_auth(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+J growableTo1g
Creating a "1 GB" SPARSEBUNDLE (a 1 GB filesystem in a growable bundle):
hdiutil create -type SPARSEBUNDLE -size 1g -fs HFS+J growableTo1g
Creating a new mounted volume backed by an image:
hdiutil create -volname Dick -size 1.3m -fs HFS+ -attach Moby.dmg
Attaching an image on a web server to the system, with any writes going to
a local file:
hdiutil attach https://my.webserver.com/master.dmg \
-shadow /tmp/mastershadowfile
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/Dick
ditto /Applications/Preview.app /Volumes/Dick
hdiutil detach /dev/disk2
hdiutil convert -format UDZO Moby.dmg -shadow
Creating a RAM-backed device and filesystem:
NUMSECTORS=128000 # a sector is 512 bytes
mydev=`hdiutil attach -nomount ram://$NUMSECTORS`
newfs_hfs $mydev
mkdir /tmp/mymount
mount -t hfs $mydev /tmp/mymount
Using makehybrid to create cross-platform data with files overlapping
between filesystem views, containing 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:
hdiutil create -srcfolder mydir mydir.dmg
This method uses the least disk space during image creation,
but the resulting image may be slightly less space efficient.
Image from directory using an intermediate sparse bundle:
hdiutil create -srcfolder mydir -format UDSB mydir.sparsebundle
hdiutil convert mydir.sparsebundle -format UDZO -o mydir.dmg
This method produces space-optimal images, but requires much
more disk space during image creation. The intermediate sparse
bundle image can be removed after the process is complete.
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
Make attach behave as if -kernel was passed. In Mac OS X
10.4.x, in-kernel was the default behavior for UDRW and SPARSE
images. In Mac OS X 10.5 and later, these and other kernel-
compatible images again default to attaching with a user
process. If an image is not "kernel-compatible" and in-kernel
mounting is specified, the attach will fail. WARNING: ram://
images 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
generally provide enough information to figure out what has gone wrong.
The following is a list of interesting errors that hdiutil may encounter:
No mountable filesystems
The "No mountable filesystems" error from hdiutil attach
means that no filesystems could be recognized or mounted
after the disk image was attached. The default behavior
in this case is to detach the disk image. See attach
for options modifying this behavior. This error can
occur if the disk image or contained filesystem is
corrupt. It can also occur if an image was created from
a block device containing a mounted, journaled
filesystem (in which case the image contains a dirty
journal that can't be replayed without making the image
read/write, such as with attach -shadow).
[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 reports this error when
attempting to access a disk image over HTTP that is too
large for the server to support access via Range
requests. Segmented images can sometimes be used to
work around this limitation of older HTTP servers. This
error can also occur if an overflow occurs with an old-
style UDIF resource fork.
[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. lsof(8) may help determine
which open files could be causing the error.
[EAGAIN] Resource temporarily unavailable. As of Mac OS X 10.5,
DiskImages uses read/write 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
effective user ID. On the other hand, "permission
denied" tends to mean that a particular file access mode
prevented the operation.
USING PERSISTENT SPARSE IMAGES
As of Mac OS X 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. Mac OS X 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.
Generally speaking, SPARSE images are not recommended for persistent
storage, though they are relatively safe on Mac OS X 10.3.2 and later. On
versions earlier than 10.3.2, SPARSE should be avoided in favor of UDRW
images and resize. On Mac OS X 10.5 and later, the more robust and faster
SPARSEBUNDLE type is preferred.
Note that both sparse formats, UDSP and UDSB, are growable only up to a
limit: the size parameter specified when they were created. They will take
up less space on the hosting filesystem if they contain less data than
their created size, and grow up to that size as data is added.
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. Moving the image file to a different volume with sufficient
free space will allow the image's filesystem to grow to its full size.
DEVICE SPECIAL FILES
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. Beware that
information read from a raw device while a filesystem is mounted may not be
consistent because the consistent data is stored in memory or in the
filesystem's journal.
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). Depending on
session characteristics, this behavior can 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).
PERMISSIONS VS. OWNERS
Some filesystems support permissions including users and groups. While
important for security on a managed filesystem, users and groups ("owners")
pose challenges for unmanaged, shared filesystems such as those typically
present in disk images. macOS's solution to this problem is to make owners
optional, both while creating files and enforcing permissions.
By default, unknown HFS+ filesystems on "external" devices (including disk
images) mount with their owners ignored (mount -o noowners). Normally when
owners are ignored, the system uses a special _unknown user and group to
dynamically substitute the current user's identity for any owners recorded
in the filesystem. These _unknown owners are even written to the volume
when creating new files. The new files will continue to have "floating"
ownership when mounted with owners honored. The net result is that shared
volumes behave as expected regardless of how they are accessed.
The behavior is different when disk images are attached. With disk images,
the owner of all files in a filesystem mount for which owners are ignored
is the user attaching the disk image. The attaching owner is also used
when creating new files.
On modern macOS systems, root (UID 0) can "see through" the "owners
ignored" user mappings. Thus
sudo ls -l /Volumes/imageVol
will show whatever is really stored in the filesystem (possibly _unknown)
regardless of whether owners are currently being honored on that volume.
In contrast, non-root users will see themselves any time _unknown is in
effect, whether the default for the mount when owners are ignored or
because _unknown is stored on disk. For disk images, non-root users will
see owners matching the user that attached the disk image.
Unlike owners, permissions are never optional. A non-writable file will
not be writable just because owners are ignored. However, a file that is
writable by its owner will be writable by everyone if _unknown is the
effective owner of the file for that file. Because anyone accessing an
owners-ignored file is treated as the owner, everyone is effectively the
owner. Because the default behavior for disk image filesystems is for all
files to be owned by the user attaching the disk image, other users will be
treated per the 'group' (if applicable) and 'other' permission modes.
diskutil(8)'s enableOwnership or the Finder's Get Info window can be used
to configure a system to respect the on-disk owners for a filesystem in the
future.
COMPATIBILITY
The DiskImages framework supports a variety of image formats, including
read/write, read-only, and read-only compressed (which are decompressed in
small chunks as I/O requests are made). It is capable of mounting most
images directly from http:// URLs. Because DiskImages can make many
requests over a single connection, responsiveness can be improved by
modifying HTTP server settings such as apache's MaxKeepAliveRequests and
KeepAliveTimeout.
Mac 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 Mac 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 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 OS X older than that which created them.
With Mac 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 embedded resource
fork, and the default Disk Copy.app "compressed" format became UDZO
(breaking compatibility with 10.0). Mac 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,
some performance, and kernel compatibility.
In Mac 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 Mac OS X 10.1 or Mac OS
X 10.0. flatten can be used to customize the type of metadata stored in
the image.
Mac OS X 10.5 introduced sparse bundle images which compact quickly but are
not recognized by previous OS versions. Mac OS X 10.6 removed support for
attaching SPARSEBUNDLE images from network file servers that don't support
F_FULLFSYNC, although this requirement was relaxed in macOS 10.12. OS X
10.7 removed double-click support for images using legacy metadata; these
can be rehabilitated using flatten and unflatten, or simply convert.
OS X 10.11 introduced lzfse compression in the ULFO format, providing
faster, more efficient compression and smaller images compared to UDZO.
These images are also supported in-kernel, but will not work on any earlier
versions of the OS.
macOS 10.12 included a pre-release version of the Apple File System called
APFS which was meant for evaluation and development purposes only. Files
stored in APFS-based images may not be accessible in future releases of
macOS, and won't work in past ones. All data to be stored in APFS volumes
should be backed up prior to using APFS and regularly backed up while using
APFS.
macOS 10.15:
• Introduced lzma compression in the ULMO format, providing smaller
images compared to ULFO. These images are not supported in-
kernel, and will not work on any earlier versions of the OS.
• Deprecated OS 9-style dual-fork file support (hdiutil
flatten/unflatten).
• Removed the deprecated "hdiutil internet-enable" command and the
IDME attach flags.
macOS 11.0:
• Removed support for DiskCopy42, DART and NDIF formats.
• Removed support for AppleSingle and MacBinary encodings.
• Removed the deprecated OS 9-style dual-fork file support (hdiutil
flatten/unflatten).
• Default file system for new images has changed to APFS (instead
of an empty disk image with no partition map). To create an empty
disk image add "-layout NONE" to the creation flags. This change
does not apply to images created with -srcfolder or -srcdevice
arguments.
macOS 12.0:
• Deprecated UDBZ format (bzip2 compression)
• Deprecated segmented UDIF images (hdiutil segment, -segmentSize
argument in hdiutil create & convert)
• Deprecated hdiutil udifrez/udifderez (embed and extract
resources)
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 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 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 macOS
recognizes the filesystems. They can also be burned with hdiutil burn.
WHAT'S NEW
macOS 10.15 added ULMO format images compressed with lzma. These images
are smaller than comparable ULFO images compressed with lzfse. These
images are not supported in-kernel, and are not usable on earlier OSes.
macOS 10.12 introduced the pre-release APFS for evaluation (see
COMPATIBILITY above). 10.12 also added an option to disable atomic copying
during image from folder operations, -noatomic, which may result in
slightly faster image creation. pmap added a new switch, -diagnostic,
which captures troubleshooting information for Boot Camp configurations.
OS X 10.11 added ULFO format images compressed with lzfse. These images
are more efficient and smaller than comparable UDZO images compressed with
zlib, and retain kernel compatibility, but are not usable on earlier OSes.
OS X 10.10 quadrupled the default UDIF chunk size without affecting
backward compatibility. UDIF images created or converted on 10.10 will
benefit from smaller metadata and more efficient compression for UDZO and
especially UDBZ formats.
OS X 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 Mac 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.
Mac 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
diskutil(8), asr(8), ioreg(8), hfs.util(8), apfs.util(8), msdos.util(8),
exfat.util(8), authopen(1), ditto(8), drutil(1), diskarbitrationd(8).
macOS 09 Dec 2020 macOS