diskimage configuration file

Configuration file for diskimage


The diskimage utility requires a configuration file that specifies the disk image layout and content.

For the full grammar of the configuration file, see Grammar.”

The configuration file has these parts:
  • disk configuration—(Required unless the output file is a disk device) A description of disk-wide parameters.
  • partition definitions—(Optional) Any number of partition descriptions. The partition descriptions specify the partitions to create, as well as the contents and characteristics (attributes) of each partition.

The diskimage utility also supports short type names for some GUID partitions.

The configuration file uses a specific syntax. The following general rules apply:
  • Line breaks and spaces can occur anywhere, except in literals or tokens.
  • Whitespaces used in a string literal in double quotes ("") are interpreted as part of that string.
  • A line feed (LF) character indicates the end of a line. Carriage return characters (CR) are silently ignored and aren't interpreted as the end of line.
  • A hash (#) character indicates the beginning of a comment. Comments can begin anywhere and always extend to the end of the line.
  • Numeric values can be specified as decimal, octal, or hexadecimal. Optionally, numeric values can use these suffix values to indicate a factor:
    • k or K to represent kilo (1024)
    • m or M to represent mega (10242)
    • g or G to represent giga (10243)
    • t or T to represent tera (10244)
    • p or P to represent peta (10245)


The contents of the diskimage configuration file must conform to the following grammar, which is defined using a BNF-like notation.

# Configuration file
config_file : disk_cfg* partn_def*

# Disk configuration
disk_cfg : '[' disk_attr+ ']'

# Disk attributes
disk_attr : 'cylinders' '=' uint
          | 'heads' '=' uint
          | 'sectors_per_track' '=' uint
          | 'sector_size' '=' uint
          | 'num_sectors' '=' uint
          | 'align' '=' uint
          | 'start_at_cylinder' '=' uint
# Partition definition            
partn_def : primary_partn_def
          | extended_partn_def
          | logical_partn_def
# Primary partition definition            
primary_partn_def : 
      '[' 'partition' '=' partn_idx ppartn_attr* ']'  [partn_file]

# Extended partition definition  
extended_partn_def : 
     '[' 'extended' '=' partn_idx epartn_attr* ']'

# Logical partition definition  
logical_partn_def : 
     '[' 'logical' lpartn_attr* ']'  [partn_file]
# Partition index  
partn_idx : uint

# The primary partition attributes  
ppartn_attr : boot_attr
            | type_attr
            | type_guid_attr
            | nsec_attr
            | name_attr
            | required_attr
            | noblock_attr
            | fssize_attr

# The extended partition attributes  
epartn_attr : nsec_attr

# The logical partition attributes  
lpartn_attr : boot_attr
            | type_attr
            | nsec_attr
            | esec_attr
            | fssize_attr

# The boot attribute
boot_attr : 'boot' '=' bool

# The type attribute
type_attr : 'type' '=' uint

# The type_guid attribute
type_guid_attr : 'type_guid' '=' type_guid_name
               | 'type_guid' '=' type_guid_guid

# The num_sectors attribute
nsec_attr : 'num_sectors' '=' uint

# The ebr_sectors attribute
esec_attr : 'ebr_sectors' '=' uint

# The fssize attribute
fssize_attr : 'fssize' '=' uint

# The name attribute
name_attr : 'name' '=' gpt_partn_name

# The 'required' attribute
required_attr : 'required' '=' bool

# The noblock attribute
noblock_attr : 'noblock' '=' bool

# Partition file
partn_file : string

# GUID name
type_guid_name : string

type_guid_guid : guid

# The boolean definition
bool : 'true'
     | 'false'

# Unsigned integer 
uint : '0' odigit* sfx?
     | '0x' xdigit+ sfx?
     | [1-9] ddigit* sfx?

# Octal digits
odigit : [0-7]

# Decimal digits
ddigit : [0-9]

# Hexadecimal digits
xdigit : [0-9a-fA-F]

# Factors that can be used with integers 
sfx : [kKmMgGtTpP]

# String values must be enclosed within double quotes ("")            
string : '"' [^"]* '"'

guid : 
'{' xdigit{8} '-' xdigit{4} '-' xdigit{4} '-' xdigit{4} '-' xdigit{12} '}'

Disk configuration

Unless the diskimage output goes to a disk device, you must specify a disk configuration in the configuration file. The disk configuration is made up of disk attributes, most of which describe the disk's geometry. All disk attribute definitions must be enclosed in square brackets ([]). A single pair of brackets can contain one or more attribute definitions; multiple attribute definitions within a pair of brackets must be separated by whitespace.

Disk attributes

The diskimage command supports the following disk attributes:
(Required) The number of cylinders on the disk. The value must be in the range 1–4294967295 (i.e., 232 - 1) for MBR disks or 1–18446744073709551615 (i.e., 264 - 1) for GPT disks.
(Required) The number of heads on the disk. The value must be in the range 1–255.
(Required) The number of sectors on each track. The value must be in the range 1–63.
(Optional) The number of bytes per sector. The value must be one of 512, 1024, 2048, or 4096. If not specified, a default value of 512 is used.
(Optional) The total number of sectors on the disk. This is usually calculated from the values for cylinders, heads, and sectors_per_track. If the number of sectors that the device reports isn't the product of these three, you must explicity specify the total sector count to generate correct GPT disk images.
  • For MBR, the value must be in the range 1–8589934590 (i.e., 233 - 2), but we recommend a maximum of 4294967295 (i.e., 232 - 1). If you use a value that's greater than the recommended one, diskimage gives you a warning.
  • For GPT disks, the value must be in the range 1–18446744073709551615 (i.e., 264 - 1)
(Optional) The sector count for partition alignment. Every partition is adjusted such that its first sector number is an integral multiple of this value. The value must be in the range 1–4294967295 (232 - 1) for MBR disks or 1–18446744073709551615 (264 - 1) for GPT disks. By default, the number of sectors per cylinder is used (i.e., each partition begins on a cylinder boundary).
(Optional) The cylinder at which the first partition begins. The value must be in the range 0–4294967294 (i.e., 232 - 2) for MBR disks or 0–18446744073709551614 (i.e., 264 - 2) for GPT disks. The default is 0 (zero).
Note: The first few sectors of the disk are always reserved for partition table metadata. For MBR disks, the first track is reserved (= sectors_per_track sectors); for GPT disks, 2 + ((num_partitions * 128 + sector_size - 1) / sector_size) sectors are reserved. The first partition begins at the next multiple of the alignment unit size.

Partition configuration

In the partition configuration, you can specify the following kinds of partitions: primary, extended, and logical. These partition definitions must comply with the following conditions:

You can declare primary, extended, and logical partitions using the following syntax (for the complete configuration file syntax, see Grammar):

primary_partn_def : '[' 'partition' '=' partn_idx ppartn_attr* ']' [partn_file]

extended_partn_def : '[' 'extended' '=' partn_idx epartn_attr* ']'

logical_partn_def : '[' 'logical' lpartn_attr* ']' [partn_file]



A unique value in the range 1–4 for MBR disks or 1–number for GPT disks (where there are number partitions).
ppartn_attr, epartn_attr, lpartn_attr
The partition attributes that apply for primary, extended, and logical partitions, respectively. For details, see Grammar.”
The pathname of the file containing the filesystem image for the partition. The pathname must be enclosed in double quotes (""), and can't exceed the host's maximum pathname length. The file size must not exceed the partition size. For filesystems that are not Power-Safe filesystems, the image file can be smaller than the partition (although a warning is issued). If no pathname is specified, an empty partition is created. In this case, the num_sectors attribute must be specified.

Partition Attributes

The following partition attributes are supported by diskimage:

(Optional) Specifies whether the partition should be marked as bootable. A boolean value is used, where true indicates that the partition is bootable and false indicates that it isn't. The default value is false.
(Required; MBR only) Specifies the partition type. The value must be in the range 1–255 and should match the type of the filesystem in the partition image file. Frequently used types include 11/12 (DOS FAT32) and 177/178/179 (Power-Safe filesystem). For more information about partitions and a list of partition IDs, refer to http://en.wikipedia.org/wiki/Partition_type.
(Required; GPT only) Specifies the GUID partition type. Either a short type name enclosed in double quotes (""), or a GUID enclosed in curly braces of the form {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}. For more information on GPT disks and GUID partition types, refer to Partition information and http://en.wikipedia.org/wiki/GUID_Partition_Table.
(Optional) Specifies the number of sectors to allocate for the partition. The value must be in the range 1–4294967295 (i.e., 232 - 1) for MBR disks, or 1–18446744073709551615 (i.e., 264 - 1) for GPT disks. If this attribute isn't specified, it's set to the smallest number of sectors required for the partition’s filesystem image.
(Optional; MBR, logical partitions only) Specifies the number of sectors to be reserved in front of the logical partition. At least one sector is required for the EBR (Extended Boot Record) associated with the partition. The value must be in the range 1–4294967295 (i.e., 232 - 1). If this attribute isn't specified, exactly one track is reserved. For more information, see the sectors_per_track disk attribute.
(Optional) Specifies the size of the filesystem. The value must be in the range 0–264 - 1 (i.e., 1.844674407 × 1019); the default is 0.

The fssize attribute is currently useful only for Power-Safe (fs-qnx6.so) filesystems. You must use it to indicate to diskimage what the true size of the filesystem is in cases where the Power-Safe filesystem has extra data appended to the filesystem image. Examples of such special filesystems include Merkle-verified filesystems.

(Optional; GPT only) Specifies an arbitrary name for the partition. The name must be enclosed in double quotes ("") and be between 1 and 35 characters in length. If this attribute isn't specified, a default name of the form type.N is created, where type is the type_guid short name and N is a sequential number for this type. The string is expected to be UTF-8 encoded.
(Optional; GPT only) Specifies whether the "Required Partition" attribute bit is set for this GUID partition (true for set; false otherwise). For more information about partition attribute bits, refer to the UEFI specification 2.4B, 5.3.3, "GPT Partition Entry Array", Table 20.
(Optional; GPT only) Specifies whether the "No Block I/O Protocol" attribute bit is set for this GUID partition (true for set; false otherwise). For more information about partition attribute bits, refer to the UEFI specification 2.4B, 5.3.3, "GPT Partition Entry Array", Table 20.

Using extended and logical partitions

If you want to use logical partitions, you must also define exactly one extended partition. It can be defined explicitly or created automatically by diskimage. The extended partition acts as a primary partition and serves as a container for the logical partitions. Within the extended partition, the logical partitions are laid out in the order in which they appear in the configuration file.

The total combined size of all logical partitions (including any overhead) must be less than or equal to the size of the extended partition. When calculating the space required for the extended partition, be aware that each logical partition is preceeded by an Extended Boot Record (EBR), which is exactly one sector in size, and some optional padding sectors:

Figure 1. Extended boot record, padding, and logical partition

By default, the ebr_sectors option is set to the disk's number of sectors per track (i.e., exactly one track). The ebr_sectors value includes the EBR as well as any padding sectors. We recommend that you use the default value of one track.

To illustrate this calculation, consider the following example:
Note: In the following example, the specified partitions intentionally don't add up to fill the disk.
Target disk geometry
16 cylinders
32 heads
32 sectors per track
One primary type 11 (DOS FAT32), bootable, 4096 sectors
One extended partition with:
  • 1 logical type 179 (Power-Safe filesystem), 2048 sectors
  • 1 logical type 178 (Power-Safe filesystem), 6144 sectors

To calculate the extended partition, use the following formula:

  <sectors_per_track>	/* First logical EBR  */
+ <logical-type-179>	 /* First logical data */
+ <sectors_per_track>	/* Second logical EBR  */
+ <logical-type-178>	 /* Second logical data */
= ext_sectors

For the example, these are the values to use in the formula:

    32    /* sectors_per_track */
+ 2048    /* First logical data */
+   32    /* sectors_per_track  */
+ 6144    /* Second logical data */
= 8256    /* size of extended partition sectors */

To define the configuration specified in the previous example, the configuration file would be:

[cylinders=16 heads=32 sectors_per_track=32]
[partition=1 boot=true  type= 11 num_sectors=4096] "fat.img"
[extended=2                      num_sectors=8256]
[logical     boot=false type=179 num_sectors=2048] "qnx-179.img"
[logical     boot=false type=178 num_sectors=6144] "qnx-178.img"

However, if you assume the three filesystem images are full-sized, you can use a simplified syntax by taking advantage of default behavior:

[cylinders=16 heads=32 sectors_per_track=32]
[partition=1 boot=true type=11] "fat.img"
[logical type=179] "qnx-179.img"
[logical type=178] "qnx-178.img"

Supported short type names for GUID partitions

The following tables list the GUID partition types for which diskimage has a defined short type name. You can use any of the listed types in a partition declaration by specifying the string in the “Type Name” column as the value of the type_guid partition attribute. For types not listed, you must specify the full GUID.


Type Name GUID Description
unused 00000000-0000-0000-0000-000000000000 Unused entry
mbr 024DEE41-33E7-11D3-9D69-0008C781F39F Nested MBR
bios 21686148-6449-6E6F-744E-656564454649 BIOS Boot
gpfs 37AFFC90-EF7D-4E96-91C3-2D7AE055B174 IBM General Parallel File System (GPFS)
lenovo BFBFAFE7-A34F-448A-9A5B-6213EB736C22 Lenovo Boot Partition
efi C12A7328-F81F-11D2-BA4B-00A0C93EC93B EFI System Partition (ESP)
iffs D3BFE2DE-3DAF-11DF-BA40-E3A556D89593 Intel Fast Flash (iFFS) Partition (Intel Rapid Start)
sony F4019732-066E-4E12-8273-346C5641494F Sony Boot Partition


Type Name GUID Description
qnx6 CEF5A9AD-73BC-4601-89F3-CDEEEEE321A1 Power-Safe filesystem (fs-qnx6.so)


Type Name GUID Description
ldmm 5808C8AA-7E8F-42E0-85D2-E1E90434CFB3 Logical Disk Manager (LDM) Metadata
ldmd AF9B60A0-1431-4F62-BC68-3311714A69AD Logical Disk Manager Data
msrec DE94BBA4-06D1-4D40-A16A-BFD50179D6AC Windows Recovery Environment
mswin E3C9E316-0B5C-4DB8-817D-F92DF00215AE Microsoft Reserved Partition (MSR)
strgsp E75CAF8F-F680-4CEE-AFA3-B001E56EFC2D Storage Spaces Partition
ms EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 Microsoft File System

Apple (Mac OS X)

Type Name GUID Description
aboot 426F6F74-0000-11AA-AA11-00306543ECAC Apple Boot Partition
hfs 48465300-0000-11AA-AA11-00306543ECAC Apple HFS/HFS+
albl 4C616265-6C00-11AA-AA11-00306543ECAC Apple Label Partition (Disklabel)
araid 52414944-0000-11AA-AA11-00306543ECAC Apple RAID Partition
aoraid 52414944-5F4F-11AA-AA11-00306543ECAC Apple RAID Partition, offline
atvr 5265636F-7665-11AA-AA11-00306543ECAC Apple TV Recovery Partition
acs 53746F72-6167-11AA-AA11-00306543ECAC Apple Core Storage (Lion FileVault) Partition
aufs 55465300-0000-11AA-AA11-00306543ECAC Apple UFS
azfs 6A898CC3-1DD2-11B2-99A6-080020736631 Apple ZFS


Type Name GUID Description
cedm 45B0969E-9B03-4F30-B4C6-5EC00CEFF106 Ceph dm-crypt Encrypted Journal
cejour 45B0969E-9B03-4F30-B4C6-B4B80CEFF106 Ceph Journal
ceosd 4FBD7E29-9D25-41B8-AFD0-062C0CEFF05D Ceph OSD
cedmosd 4FBD7E29-9D25-41B8-AFD0-5EC00CEFF05D Ceph dm-crypt OSD


Type Name GUID Description
chrsrvd 2E0A753D-9E48-43B0-8337-B15192CB1B5E ChromeOS Future Use
chroot 3CB8E202-3B7E-47DD-8A3C-7FF2A13CFCEC ChromeOS Rootfs
chkrnl FE3A2A5D-4F32-41A7-B725-ACCC3285A309 ChromeOS Kernel


Type Name GUID Description
fbdata 516E7CB4-6ECF-11D6-8FF8-00022D09712B FreeBSD Data Partition
fbswap 516E7CB5-6ECF-11D6-8FF8-00022D09712B FreeBSD Swap Partition
fbufs 516E7CB6-6ECF-11D6-8FF8-00022D09712B FreeBSD Unix File System (UFS)
fblvm 516E7CB8-6ECF-11D6-8FF8-00022D09712B FreeBSD-LVM (Vinum) Volume Manager Partition
fbzfs 516E7CBA-6ECF-11D6-8FF8-00022D09712B FreeBSD ZFS Partition
fbboot 83BD6B9D-7F41-11DC-BE0B-001560B84F0F FreeBSD Boot Partition


Type Name GUID Description
hbfs 42465331-3BA3-10F1-802A-4861696B7521 Haiku BFS


Type Name GUID Description
hpuxlvm 75894C1E-3AEB-11D3-B7C1-7B03A0000000 HP-UX-LVM Data Partition
hpuxsvc E2A1E728-32E3-11D6-A682-7B03A0000000 HP-UX Service Partition


Type Name GUID Description
lnxswap 0657FD6D-A4AB-43C4-84E5-0933C84B4F4F Linux Swap Partition
lnxdata 0FC63DAF-8483-4772-8E79-3D69D8477DE4 Linux Filesystem Data
lnxsrv 3B8F8425-20E0-4F3B-907F-1A25A76F98E8 Linux /srv (server data)
dmcrypt 7FFEC5C9-2D00-49B7-8941-3EA10A5586B7 Plain dm-crypt Partition
lnxrsrv 8DA63339-0007-60C0-C436-083AC8230908 Linux Reserved
lnxhome 933AC7E1-2EB4-4F13-B844-0E14E2AEF915 Linux /home Partition (systemd)
lnxraid A19D880F-05FC-4D3B-A006-743F0F84911E Linux RAID Partition
lnxluks CA7D7CCB-63ED-4C53-861C-1742536059CC Linux LUKS Partition
lnxlvm E6D6D379-F507-44C2-A23C-238F2A3DF928 Linux Logical Volume Manager (LVM)


Type Name GUID Description
mbufs 0394EF8B-237E-11E1-B4B3-E89A8F7FC3A7 Unix File System (UFS) Partition
mbdata 85D5E45A-237C-11E1-B4B3-E89A8F7FC3A7 Data Partition
mbswap 85D5E45B-237C-11E1-B4B3-E89A8F7FC3A7 Swap Partition
mbvin 85D5E45C-237C-11E1-B4B3-E89A8F7FC3A7 Vinum volume manager Partition
mbzfs 85D5E45D-237C-11E1-B4B3-E89A8F7FC3A7 ZFS Partition
mbboot 85D5E45E-237C-11E1-B4B3-E89A8F7FC3A7 Boot Partition


Type Name GUID Description
nbcat 2DB519C4-B10F-11DC-B99B-0019D1879648 Concatenated Partition
nbcrypt 2DB519EC-B10F-11DC-B99B-0019D1879648 Encrypted Partition
nbswap 49F48D32-B10E-11DC-B99B-0019D1879648 Swap Partition
nbffs 49F48D5A-B10E-11DC-B99B-0019D1879648 FFS Partition
nblfs 49F48D82-B10E-11DC-B99B-0019D1879648 LFS Partition
nbraid 49F48DAA-B10E-11DC-B99B-0019D1879648 RAID Partition


Type Name GUID Description
obdata 824CC7A0-36A8-11E3-890A-952519AD3F61 OpenBSD Data Partition


Type Name GUID Description
sboot 6A82CB45-1DD2-11B2-99A6-080020736631 Boot Partition
sroot 6A85CF4D-1DD2-11B2-99A6-080020736631 Root Partition
sswap 6A87C46F-1DD2-11B2-99A6-080020736631 Swap Partition
susr 6A898CC3-1DD2-11B2-99A6-080020736631 /usr Partition
sbkup 6A8B642B-1DD2-11B2-99A6-080020736631 Backup Partition
srsvd 6A8D2AC7-1DD2-11B2-99A6-080020736631 Reserved Partition
svar 6A8EF2E9-1DD2-11B2-99A6-080020736631 /var Partition
shome 6A90BA39-1DD2-11B2-99A6-080020736631 /home Partition
altsctr 6A9283A5-1DD2-11B2-99A6-080020736631 Alternate sector (EFI_ALTSCTR)
srsvd1 6A945A3B-1DD2-11B2-99A6-080020736631 Reserved Partition 1
srsvd2 6A96237F-1DD2-11B2-99A6-080020736631 Reserved Partition 2
srsvd3 6A9630D1-1DD2-11B2-99A6-080020736631 Reserved Partition 3
srsvd4 6A980767-1DD2-11B2-99A6-080020736631 Reserved Partition 4


Configuration file for three primary partitions

The following is a sample configuration for a disk with three primary partitions—one DOS FAT32 filesystem and two Power-Safe filesystems—intended for a disk geometry of 974/255/63 (cylinders/heads/sectors). The configuration file expects the filesystem images to reside in the directory ../fsi.

] "../fsi/fat32.fsi"

# First Power-Safe filesystem, >2GB, bootable
] "../fsi/qnx6-1.fsi"

# Second Power-Safe filesystem
] "../fsi/qnx6-2.fsi"

Configuration file for three primary and two logical partitions

The configuration below is for a disk with three primary and two logical partitions. The primary partitions are a DOS FAT32 filesystem and a Power-Safe filesystem, plus an empty partition reserved for another Power-Safe filesystem. Both logical partitions are Power-Safe filesystems. The extended partition uses slot 3 in the MBR. The resulting image is intended for a disk geometry of 4096/64/32 (cylinders/heads/sectors), which could represent an eMMC. The configuration file expects the filesystem images to reside in the directory ../fsi.
[cylinders=4096 heads=64 sectors_per_track=32]

# DOS FAT32 (~480MB)
[partition=1 type=11 num_sectors=963837] "../fsi/fat32.fsi"

# Primary Power-Safe filesystem, >2GB, bootable
[partition=2 boot=true type=179 num_sectors=4273290] "../fsi/qnx6-1.fsi"


# Reserved for Power-Safe filesystem
[partition=4 type=178 num_sectors=65536]

# Power-Safe filesystem (~500MB)
[logical type=178 num_sectors=1060290] "../fsi/qnx6-2.fsi"

# Power-Safe filesystem (~500MB)
[logical type=177 num_sectors=1060290] "../fsi/qnx6-3.fsi"

Configuration file for a GPT disk with two partitions

This example is for a GPT disk with two partitions–one DOS FAT32 named "dos" and one Power-Safe filesystem named "qnx". This configuration is intended for a disk geometry of 65536/32/16 (cylinders/heads/sectors). Partitions are aligned to multiples of 1MB. Use the first and the last entry of the partition table. The configuration file expects the filesystem images to reside in the directory ../fsi.
[cylinders=64k heads=32 sectors_per_track=16]
# At 512 bytes/sector, 2k sectors give 1MB
] "../fsi/fat32.fsi"
# Power-Safe filesystem, bootable
] "../fsi/qnx6.fsi"