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hdiutil(1) [osx man page]

HDIUTIL(1)						    BSD General Commands Manual 						HDIUTIL(1)

hdiutil -- manipulate disk images (attach, verify, burn, etc) SYNOPSIS
hdiutil verb [options] DESCRIPTION
hdiutil uses the DiskImages framework to manipulate disk images. Common verbs include attach, detach, verify, create, convert, compact, and burn. The rest of the verbs are currently: help, info, checksum, chpass, erasekeys, unflatten, flatten, imageinfo, isencrypted, mountvol, unmount, plugins, udifrez, udifderez, internet-enable, 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 Mac OS X Finder, two separate things happen. First, the image is "attached" to the system just like an external drive. Then, the kernel and Disk Arbitration probe the new device for recognized file structures. If any 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-ori- ented) 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 inter- pret 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 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 cre- ated. -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 cre- ated. -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 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 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, 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 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 OS X Finder. -owners on|off specify that owners on any filesystems be honored or not. -drivekey key=value specify a key/value pair to be 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 preferences domain and thus can be ren- dered 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 back- wards compatibility, hdid(8) does not attempt to verify images before attaching them. Preferences keys: skip-verify, skip-verify-remote, skip-verify-locked, skip-previously-verified -[no]ignorebadchecksums specify whether bad checksums should be ignored. The default is to abort when a bad checksum is detected. Preferences key: ignore-bad-checksums -[no]idme do [not] perform IDME actions on IDME images. IDME actions are not performed by default. Preferences key: skip-idme -[no]idmereveal do [not] reveal (in the Finder) the results of IDME processing. Preferences key: skip-idme-reveal -[no]idmetrash do [not] put IDME images in the trash after processing. Preferences key: skip-idme-trash -[no]autoopen do [not] auto-open volumes (in the Finder) after attaching an image. By default, 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 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. 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 OS X 10.1. -imagekey encrypted-encoding-version can select between version 1 and version 2 of the encrypted encoding. The framework preferences have a corresponding key to change the default for all images. Version 2 is not compatible with OS X 10.2 but is more robust for SPARSE (UDSP) images. Version 1 is the default for non-sparse images. As of OS X 10.4.7, sparse encrypted images always use version 2 and as of OS X 10.5, all encrypted images default to version 2. General options: -align alignment specifies a size to which the final data partition will be aligned. The default is 4K. -type UDIF|SPARSE|SPARSEBUNDLE -type is particular to create and is used to specify the format of empty read/write images. It is independent of -format which is used to specify the final read-only image format when populating an image with pre-existing content. UDIF is the default type. If specified, a UDRW of the specified size will be 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 minus 1 byte). The amount of data that can be stored in either type of sparse image is additionally bounded by the filesystem in the image and by any partition map. compact can reclaim unused bands in sparse images backing HFS+ filesystems. resize will only change the virtual size of a sparse image. See also USING PERSISTENT SPARSE IMAGES below. -fs filesystem where filesystem is one of HFS+, HFS+J (JHFS+), HFSX, JHFS+X, MS-DOS, or UDF. -fs causes a filesystem of the specified type to be written to the image. -fs may change the partition scheme and type appropriately. -fs will not make any size adjustments: if the image is the wrong size for the specified filesystem, create will fail. -fs is invalid and ignored when using -srcdevice. -volname volname The newly-created filesystem will be named volname. The default depends the filesystem being used; HFS+'s default vol- ume 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 filesys- tem's newfs unless -srcfolder is specified, in which case the default mode is derived from the specified filesystem object. -[no]autostretch do [not] suppress automatically making backwards-compatible stretchable volumes when the volume size crosses the auto- stretch-size threshold (default: 256 MB). See also asr(8). -stretch max_stretch -stretch initializes HFS+ filesystem data such that it can later be stretched on older systems (which could only stretch within predefined limits) using hdiutil resize or by asr(8). max_stretch is specified like -size. -stretch is invalid and ignored when using -srcdevice. -fsargs newfs_args additional arguments to pass to whatever newfs program is implied by -fs. newfs_hfs(8) has a number of options that can reduce the amount of space needed by the filesystem's data structures. Suppressing the journal with -fs HFS+ and pass- ing arguments such as -c c=64,a=16,e=16 to -fsargs will minimize gaps at the front of the filesystem, allowing resize to squeeze more space from the filesystem. For truly optimal filesystems, use makehybrid. -layout layout Specify the partition layout of the image. layout can be anything supported by MediaKit.framework. NONE creates an image with no partition map. When such an image is attached, a single /dev entry will be created (e.g. /dev/disk1). 'SPUD' causes a DDM and an Apple Partition Scheme partition map with a single entry to be written. 'GPTSPUD' creates a similar image but with a GUID Partition Scheme map instead. When attached, multiple /dev entries will be created, with either slice 1 (GPT) or slice 2 (APM) as the data partition. (e.g. /dev/disk1, /dev/disk1s1, /dev/disk1s2). Unless overridden by -fs, the default layout is 'GPTSPUD' (PPC systems used 'SPUD' prior to OS X 10.6). Other layouts include 'MBRSPUD' and 'ISOCD'. create -help lists all supported layouts. -library bundle specify an alternate layout library. The default is MediaKit's MKDrivers.bundle. -partitionType partition_type Change the type of partition in a single-partition disk image. The default is Apple_HFS unless -fs implies otherwise. -ov overwrite an existing file. The default is not to overwrite existing files. -attach attach the image after creating it. If no filesystem is specified via -fs, the attach will fail per the default attach -mount required behavior. Image from source options (for -srcfolder and -srcdevice): -format format Specify the final image format. The default when a source is specified is UDZO. format can be any of the format parameters used by convert. Options specific to -srcdevice: -segmentSize size_spec Specify that the image should be written in segments no bigger than size_spec (which follows -size conventions). Options specific to -srcfolder: -[no]crossdev do [not] cross device boundaries on the source filesystem. -[no]scrub do [not] skip temporary files when imaging a volume. Scrubbing is the default when the source is the root of a mounted volume. Scrubbed items include trashes, temporary directories, swap files, etc. -[no]anyowners do not fail if the user invoking hdiutil can't ensure correct file ownership for the files in the image. -skipunreadable skip files that can't be read by the copying user and don't authenticate. -copyuid user perform the copy as the given user. Requires root privilege. If user can't read or create files with the needed owners, -anyowners or -skipunreadable must be used to prevent the operation from failing. By default, create -srcfolder attempts to maintain the permissions present in the source directory. It prompts for authentication if it detects an unreadable file, a file owned by someone other than the user creating the image, or a SGID file in a group that the copying user is not in. convert image -format format -o outfile convert image to type format and write the result to outfile. As with create, the correct filename extension will be added only if it isn't part of the provided name. Format is one of: UDRW - UDIF read/write image UDRO - UDIF read-only image UDCO - UDIF ADC-compressed image UDZO - UDIF zlib-compressed image UDBZ - UDIF bzip2-compressed image (OS X 10.4+ only) UFBI - UDIF entire image with MD5 checksum UDRo - UDIF read-only (obsolete format) UDCo - UDIF compressed (obsolete format) UDTO - DVD/CD-R master for export UDxx - UDIF stub image UDSP - SPARSE (grows with content) UDSB - SPARSEBUNDLE (grows with content; bundle-backed) RdWr - NDIF read/write image (deprecated) Rdxx - NDIF read-only image (Disk Copy 6.3.3 format) ROCo - NDIF compressed image (deprecated) Rken - NDIF compressed (obsolete format) DC42 - Disk Copy 4.2 image In addition to the compression offered by some formats, the UDIF and NDIF read-only formats skip unused space in HFS, UFS, and MS- DOS (FAT) filesystems. For UDZO, -imagekey zlib-level=value allows the zlib compression level to be specified ala gzip(1). The default compression level is 1 (fastest). Common options: -encryption, -stdinpass, -certificate, -srcimagekey, -tgtimagekey, -shadow and related, -puppetstrings, and -plist. Other options: -align alignment The default is 4 (2K). -pmap add partition map. When converting a NDIF to a any variety of UDIF, or when converting an unpartitioned UDIF, the default is true. -segmentSize [size_spec] Specify segmentation into size_spec-sized segments as outfile is being written. The default size_spec when -segmentSize is specified alone is 2*1024*1024 (1 GB worth of sectors) for UDTO images and 4*1024*1024 (2 GB seg- ments) 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 opera- tion. 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 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 parti- tion 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 different checksum than the image it came from. The default is to burn all blocks of the disk image (minus any trailing Apple_Free). -[no]forceclose do [not] force the disc to be closed after burning. Further burns to the disc will be impossible. The default is not to close the disc. -nounderrun Disable the default buffer underrun protection. -[no]synthesize [Don't] Synthesize a hybrid filesystem for the disc. The default is to create a new (HFS/ISO) filesystem when the source image's blocks could not be legally burned to a disc. -speed x_factor 1, 2, 4, 6, ... 'max' The desired "x-factor". e.g. 8 means the drive will be instructed burn at "8x speed". 'max' will cause the burn to proceed at the maximum speed of the drive. 'max' is the default speed. Slower speeds can produce more reli- able 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 anything. -erase prompt for optical media (DVD-RW/CD-RW) and then, if the hardware supports it, quickly erase the media. If an image is specified, it will be burned to the media after the media has been erased. -fullerase erase all sectors of the disc (this usually takes quit a bit longer than -erase). -list list all burning devices, with OpenFirmware paths suitable for -device. makehybrid -o image source Generate a potentially-hybrid filesystem in a read-only disk image using the DiscRecording framework's content creation system. This disk image will represent a data disc. drutil(1) can be used to make audio discs. source can either be a directory or a disk image. The generated image can later be burned using burn, or converted to another read-only format with convert. By default, the 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 by ditto(8) or asr(8) (in file-copy mode). 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 Mac OS X, it is usu- ally the preferred filesystem. -iso Generate an ISO9660 Level 2 filesystem with Rock Ridge extensions. This filesystem can be present on an image simultane- ously 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+, Mac OS X will use the ISO9660 (or Joliet) filesystem. -joliet Generate Joliet extensions to ISO9660. This view of the filesystem can be present on an image simultaneously with HFS+, and requires the presence of an ISO9660 filesystem. Joliet supports Unicode filenames, but is only supported on some operating systems. If both an ISO9660 and Joliet filesystem are present on a disk image or CD, but not HFS+, Mac OS X will prefer the Joliet filesystem. -udf Generate a UDF filesystem. This filesystem can be present on an image simultaneously with HFS+, ISO9660, and Joliet. UDF is the standard interchange format for DVDs, although operating system support varies based on OS version and UDF version. By default, if no filesystem is specified, the image will be created with all four 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 Mac 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 recom- mended, 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 exe- cute 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 popu- late 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 Mac OS X. There- fore, 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 filesys- tem 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 parame- ters 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 argu- ments, 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 direc- tories either via an absolute path, or via a relative path to the current working directory. The volume name options, just like files in the filesystems, may need to be mapped onto the legal character set for a given filesystem or otherwise changed to obey naming restrictions. Use drutil(1) as drutil filename myname to see how a given string would be remapped. The -abstract-file, -bibliography-file, -and -copyright-file must exist directly in the source directory, not a sub-directory, and must have an 8.3 name for compatibility with ISO9660 Level 1. compact image scans the bands of a sparse (SPARSE or SPARSEBUNDLE) disk image containing an HFS 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. 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 feasible 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 representation of the metadata becomes greater than 16 MB, the operation will fail with error -39 ("End of fork"). Common options: -encryption, -stdinpass, and -srcimagekey. flatten image Flatten a read-only (or compressed) UDIF disk image into a single-fork file. By default, metadata will be stored both as XML (for the kernel's use) and in an embedded resource fork (for OS X 10.1 and earlier). Common options: -srcimagekey, -encryption, and -stdinpass. Since images are created "flat" by default, flatten is only required if the UDIF has previously been unflattened. Other options: -noxml don't embed XML data for in-kernel attachment. The image will never attach in-kernel. -norsrcfork don't embed resource fork data. The image will not attach on OS X versions prior to OS X 10.2. fsid image Print information about file systems on a given disk image. Per DEVICE SPECIAL FILES, image can be a /dev entry corresponding to a disk. More detailed information is presented for HFS file systems. Common options: -encryption, -stdinpass, -srcimagekey, and -shadow and related. mountvol dev_name mount the filesystem in dev_name using Disk Arbitration (similar to diskutil(8)'s mount). XML output is available from -plist. Note that mountvol (rather than mount, though it often works in OS X 10.5 and later) is the correct way to remount a volume after it has been unmounted by unmount. Prior to OS X 10.5, mount/attach would treat a /dev entry as a disk image to be attached (creating another /dev entry). That behavior was undesirable. unmount volume [-force] unmount a mounted volume without detaching any associated image. Volume is a /dev entry or mountpoint. NOTE: unmount does NOT detach any disk image associated with the volume. Images are attached and detached; volumes are mounted and unmounted. 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 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 filesystems 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 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 min- inum valid value or space remaining on the underlying file system, an error will be returned and the partition will not be resized. min automatically determines the smallest possible size. Other options: -imageonly only resize the image file, not the partition(s) and filesystems inside of it. -partitiononly only resize a partition / filesystem in the image, not the image. -partitiononly will fail if the new size won't fit inside the image. On APM, shrinking a partition results in an explicit Apple_Free entry taking up the remaining space in the image. -partitionNumber partitionNumber specifies which partition to resize (UDIF only -- see HISTORY below). partitionNumber is 0-based, but, per hdiutil pmap, partition 0 is the partition map itself. -growonly only allow the image to grow -shrinkonly only allow the image to shrink -nofinalgap allow resize to entirely eliminate the trailing free partition in an APM map. Restoring such images to very old hardware may interfere with 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 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 filesys- tems, 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 oth- ers. Only one of -segmentCount or -segmentSize will be honored. Segmenting read/write (UDRW) images is not sup- ported (as of OS X 10.3). -firstSegmentSize segment_size Specify the first segment size in sectors in the same form as for -segmentSize. Used for multi-CD restores. -restricted Make restricted segments for use in multi-CD restores. -ov overwrite any existing files. pmap [options] image display the partition map of an image or device. By default, this report includes 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. -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 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+ 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 Attaching an image on a web server to the system, with any writes going to a local file: hdiutil attach -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/Moby ditto /Applications/ /Volumes/Moby 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. 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 ENVIRONMENT
The following environment variables affect hdiutil and DiskImages: com_apple_hdid_verbose enable -verbose behavior for attach. com_apple_hdid_debug enable -debug behavior for attach. com_apple_hdid_nokernel similar to -nokernel but works even with, for example, create -attach. com_apple_hdid_kernel attempt to attach in-kernel first (like attach -kernel). In OS X 10.4.x, in-kernel was the default behavior for UDRW and SPARSE images. On OS X 10.5, these and other kernel-compatible 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 sup- port 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 modi- fying 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-sensi- cal (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. [EAGAIN] Resource temporarily unavailable. As of 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 par- ticular file access mode prevented the operation. USING PERSISTENT SPARSE IMAGES
As of OS X 10.5, a more reliable, efficient, and scalable sparse format, UDSB (SPARSEBUNDLE), is recommended for persistent sparse images as long as a backing bundle (directory) is acceptable. OS X 10.5 also introduced F_FULLFSYNC over AFP (on client and server), allowing proper journal flushes for HFS+J-bearing images. Critical data should never be stored in sparse disk images on file servers that don't support F_FULLFSYNC. SPARSE (UDSP) images and shadow files were designed for intermediate use when creating other images (e.g. UDZO) when final image sizes are unknown. As of OS X 10.3.2, partially-updated SPARSE images are properly handled and are thus safe for persistent storage. SPARSE images are not recommended for persistent storage on versions of OS X earlier than 10.3.2 and should be avoided in favor of SPARSEBUNDLE images or UDRW images and resize. If more space is needed than is referenced by the hosted filesystem, hdiutil resize or diskutil(8) resize can help to grow or shrink the filesystem in an image. compact reclaims unused space in sparse images. Though they request that hosted HFS+ filesystems use a special "front first" allocation 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. 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. OS X'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). When owners are ignored, the system dynamically substitutes the current user's identify for any owners recorded in the filesystem. When creating new files, a special UID and GID of _unknown are recorded on the disk. Even if a filesystem is later mounted with on-disk owners honored, files with stored UID or GID of _unknown will continue to substitute the current user's credentials any time the given file is accessed. The net result is that shared volumes behave as expected even when connected to systems where their on-disk owners are honored. On modern OS X systems, root (UID 0) can "see through" the _unknown 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 respected on that volume. In contrast, non-root users will see themselves any time owners are ignored (either via mount -o noowners or stored _unknown): mary running ls -l will see that mary owns any owners-ignored filesystems objects while joe running ls -l on the same objects will see that joe owns them. 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 owners are ignored for that file. Because anyone accessing an owners-ignored file is treated as the owner, everyone is effectively the owner. 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 filesys- tem in the future. COMPATIBILITY
The DiskImages framework supports a variety of flat-file and dual-fork image formats, including read/write, read-only, and read-only com- pressed (which are decompressed in small chunks as I/O requests are made). It automatically decodes AppleSingle and MacBinary file formats and 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. OS X 10.0 supported the disk images of Disk Copy 6 on Mac OS 9. OS X 10.1 added sparse, encrypted, and zlib-compressed images. These images will not be recognized on OS X 10.0 (or will attach read/write, possibly allowing for their destruction). As the sparse, shadow, and encrypted formats have evolved, switches have been added to facilitate the creation of images that are compatible with older OS 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 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 "compressed" format became UDZO (breaking compatibility with 10.0). OS X 10.4 introduced bzip2 compression in the UDBZ format which provides smaller images (especially when combined with makehybrid) at the expense of backwards compatibility. In OS X 10.4.7, the resource forks previously embedded in UDIF images were abandoned entirely to avoid metadata length limitations imposed by resource fork structures. As a result, UDIF images created on 10.4.7 and later will not, by default, be recognized by either OS X 10.1 or OS X 10.0. flatten can be used to customize the type of metadata stored in the image. OS X 10.5 introduced sparse bundle images which compact quickly but are not recognized by previous OS versions. OS X 10.6 removed support for attaching SPARSEBUNDLE images from network file servers that don't support F_FULLFSYNC. OS X 10.7 removed double-click support for images using legacy metadata; these can be rehabilitated using flatten and unflatten, or simply convert. 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 OS X rec- ognizes the filesystems. They can also be burned with hdiutil burn. WHAT'S NEW 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 OS X 10.6, pmap was rewritten to use MediaKit's latest reporting routines so that it can properly support GPT partition maps. Also -debug now implies -verbose for all verbs. OS X 10.5 changed the behavior of attach when run on an existing image or /dev node: if the image was attached but no volume was mounted, the volume would be mounted. Prior systems would return the /dev without mounting the volume. This change effectively removes the ability to create a second /dev node from an existing one. SEE ALSO
authopen(1), diskutil(8), ditto(8), ioreg(8), drutil(1), msdos.util(8), hfs.util(8), diskarbitrationd(8), /System/Library/CoreServices/ OS X
16 Aug 2013 OS X
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