# gpart
[](https://travis-ci.org/baruch/gpart)
Gpart is a small tool which tries to guess what partitions
are on a PC type, MBR-partitioned hard disk in case the
primary partition table was damaged.
Gpart works by scanning through the device (or file) given on
the command line on a sector basis. Each guessing module is
asked if it thinks a filesystem it knows about could start at
a given sector. Several filesystem guessing modules are built
in.
Consult the manual page for command line options and usage.
## Installation
See file *INSTALL*.
## Currently recognized partitions/filesystems types
Modname | Typ | Description
:--------|:----:|:------------
fat | 0x01 | Primary DOS with 12 bit FAT
| 0x04 | Primary DOS with 16 bit FAT (<= 32MB)
| 0x06 | Primary 'big' DOS (> 32MB)
| 0x0B | DOS or Windows 95 with 32 bit FAT
| 0x0C | DOS or Windows 95 with 32 bit FAT, LBA
ntfs | 0x07 | OS/2 HPFS, NTFS, QNX or Advanced UNIX
hpfs | 0x07 | OS/2 HPFS, NTFS, QNX or Advanced UNIX
ext2 | 0x83 | Linux ext2 filesystem
lswap | 0x82 | Linux swap
bsddl | 0xA5 | FreeBSD/NetBSD/386BSD
s86dl | 0x82 | Solaris/x86 disklabel
minix | 0x80 | Minix V1
| 0x81 | Minix V2
reiserfs | 0x83 | ReiserFS filesystem
hmlvm | 0xFE | Linux LVM physical volumes
qnx4 | 0x4F | QNX 4.x
beos | 0xEB | BeOS fs
xfs | 0x83 | SGI XFS filesystem
## Guessing modules
Each guessing module must provide three functions callable from
gpart:
int xxx_init(disk_desc *d,g_module *m)
> Initialisation function. Will be called before a scan.
> It should return the minimum number of bytes it wants
> to receive for a test. The module should set the
> description of the filesystem/partition type it handles
> in `g_module.m_desc`. If the filesystem/partition type
> included a partition table like first sector (like the
> \*BSD disklabels do), the flag `m_hasptbl` should be set.
> Another flag is `m_notinext` which means the tested type
> cannot reside in a logical partition.
int xxx_term(disk_desc *d)
> Termination/cleanup function, called after the scanning
> of the device has been done.
int xxx_gfun(disk_desc *d,g_module *m)
> The actual guessing function, called from within the
> scan loop. It should test the plausibility of the
> given sectors, and return its guess in `m->m_guess` (a
> probability between 0 and 1). See existing modules
> for examples.
>
> The given file descriptor `d->d_fd` can be used for seeking
> and reading (see e.g. *gm_ext2.c* which tries to read
> the first spare superblock). If a module is convinced
> that it has found a filesystem/partition start it should
> fill in the assumed begin and size of the partition.
>
> The test performed should not be too pedantic, for
> instance it should not be relied upon that the file-
> system is clean/was properly unmounted. On the other
> hand too much tolerance leads to misguided guesses,
> so a golden middle way must be found.
## Output explanation
Here is a sample `gpart -v` run on my first IDE hard disk
(comments in block-quotes):
dev(/dev/hda) mss(512) chs(1232/255/63)(LBA) #s(19792080) size(9664mb)
> `mss` is the medium sector size, `chs` the geometry retrieved
> from the OS (or from the command line), `#s` is the total
> sector count.
Primary partition(1)
type: 006(0x06)(Primary 'big' DOS (> 32MB)) (BOOT)
size: 502mb #s(1028097) s(63-1028159)
chs: (0/1/1)-(63/254/63)d (0/1/1)-(63/254/63)r
hex: 80 01 01 00 06 FE 3F 3F 3F 00 00 00 01 B0 0F 00
> `size`: the size of the partition in megabytes, number of
> sectors and the sector range.
> `chs`: the partition table chs range (`d`) and the real one
> (`r`). If the number of cylinders is less than 1024, both
> are identical.
> `hex`: the hexadecimal representation of the partition entry
> as found in the partition table.
...
Begin scan...
Possible partition(DOS FAT), size(502mb), offset(0mb)
type: 006(0x06)(Primary 'big' DOS (> 32MB))
size: 502mb #s(1028097) s(63-1028159)
chs: (0/1/1)-(63/254/63)d (0/1/1)-(63/254/63)r
hex: 00 01 01 00 06 FE 3F 3F 3F 00 00 00 01 B0 0F 00
Possible extended partition at offset(502mb)
Possible partition(Linux ext2), size(31mb), offset(502mb)
type: 131(0x83)(Linux ext2 filesystem)
size: 31mb #s(64196) s(1028223-1092418)
chs: (64/1/1)-(67/254/62)d (64/1/1)-(67/254/62)r
hex: 00 01 01 40 83 FE 3E 43 7F B0 0F 00 C4 FA 00 00
Possible partition(Linux swap), size(125mb), offset(533mb)
type: 130(0x82)(Linux swap or Solaris/x86)
size: 125mb #s(256976) s(1092483-1349458)
chs: (68/1/1)-(83/254/62)d (68/1/1)-(83/254/62)r
hex: 00 01 01 44 82 FE 3E 53 83 AB 10 00 D0 EB 03 00
> During the scan phase all found partitions are listed by
> their real type names. The Linux swap partition above is
> recognized as Linux swap but will get the 0x82 partition
> identifier which can be both a Solaris disklabel or a
> Linux swap partition.
>
> When examining the hex values of the first primary partition
> it can be seen that they are identical to the values of the
> actual partition table (good guess) except for the first
> value (0x80 vs. 0x00). This entry denotes the partition
> 'boot' flag which cannot be guessed.
...
End scan.
Checking partitions...
Partition(Primary 'big' DOS (> 32MB)): primary
Partition(Linux ext2 filesystem): logical
Partition(Linux swap or Solaris/x86): logical
Partition(Linux LVM physical volume): logical
Partition(Linux ext2 filesystem): logical
Partition(DOS or Windows 95 with 32 bit FAT, LBA): logical
Partition(FreeBSD/NetBSD/386BSD): primary
Partition(Linux LVM physical volume): primary
Ok.
> During the scan phase gpart gathers a simple list of possible
> partitions, the check phase now tries to decide if found
> extended partitions seem consistent, if partitions do not
> overlap etc. Overlapping partitions are silently discarded,
> all remaining ones are given an attribute 'primary', 'logical',
> 'orphaned' or 'invalid'. If gpart is called like `gpart -vv ...`,
> it also tells why it thinks a partition guess is invalid.
>
> If any inconsistencies are found, gpart prints the number
> of remaining inconsistencies, otherwise it says 'Ok.'
Guessed primary partition table:
Primary partition(1)
type: 006(0x06)(Primary 'big' DOS (> 32MB))
size: 502mb #s(1028097) s(63-1028159)
chs: (0/1/1)-(63/254/63)d (0/1/1)-(63/254/63)r
hex: 00 01 01 00 06 FE 3F 3F 3F 00 00 00 01 B0 0F 00
Primary partition(2)
type: 005(0x05)(Extended DOS)
size: 6157mb #s(12611025) s(1028160-13639184)
chs: (64/0/1)-(848/254/63)d (64/0/1)-(848/254/63)r
hex: 00 00 01 40 05 FE FF 50 40 B0 0F 00 D1 6D C0 00
Primary partition(3)
type: 165(0xA5)(FreeBSD/NetBSD/386BSD)
size: 1396mb #s(2859570) s(13639185-16498754)
chs: (849/0/1)-(1023/254/63)d (849/0/1)-(1026/254/63)r
hex: 00 00 C1 51 A5 FE FF FF 11 1E D0 00 32 A2 2B 00
Primary partition(4)
type: 254(0xFE)(Linux LVM physical volume)
size: 1608mb #s(3293325) s(16498755-19792079)
chs: (1023/254/63)-(1023/254/63)d (1027/0/1)-(1231/254/63)r
hex: 00 FE FF FF FE FE FF FF 43 C0 FB 00 8D 40 32 00
> This is a resulting primary partition table. Note that
> the logical partition guesses were only used to create
> the extended partition entry. Up to now gpart cannot
> reconstruct a damaged logical partition chain itself.
>
> If a guessed primary partition table should be written to
> some file or device the user must specify (via the `-W`
> option) which partition gets the active (bootable) one.
## Author
gpart README, Aug 1999, Michail Brzitwa <mb@ichabod.han.de>
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