fdisk
manipulate disk partition table
see also :
cfdisk - sfdisk - mkfs - parted - partprobe
Synopsis
fdisk
[-uc] [-b sectorsize]
[-C cyls] [-H heads]
[-S sects] device
fdisk
-l [-u] [device...]
fdisk
-s partition...
fdisk
-v
fdisk
-h
add an example, a script, a trick and tips
examples
source
How to recover data from a USB-connected hard disk that shows no partition?
If the data is truly valuable, then the only real
solution is to ship it to a professional data recovery expert.
This process is expensive, and cannot guarantee that you'll be
able to get the data back.
The important question to ask here is: If your data was so
valuable, why do you not have a backup of it?
source
Is my OCZ SSD aligned correctly?
The default alignment in order to fully ensure compatibility with
both 4K sectors and SSD cell boundaries (typically 128 or 256 or
512K) would be 1MByte into the disk.
2048 (sectors) * 512 = 1048576 (or exactly 1MByte)
So to me your disk looks to be properly aligned, both with your
flash-erase cell size and the page write size.
Remember that sector counts start at 0, so while it claims to be
at sector 2048 the actual sector your partition is starting at is
the 2049th sector of the disk, which places it in the first
sector after the first two NAND-flash cells and likewise that
sector is also the first sector past the 256th 4KByte "page".
source
Re-reading the partition table failed with error 22: invalid argument
You should boot the system from the gparted live cd and use it to
make the changes. That would tell you if it is your OS or
hardware.
source
How to create NTFS partition in Linux to install Windows 7 from USB?
Is there a reason why you can't use Linux to delete all of the
partitions. Boot Win 7 Installation from USB Drive, and then
install normally? With no partitions, the Win 7 installer will
allow you to create a new partition and automatically format it
to NTFS plus a 100MB System Partition.
source
What is the "the dos compatibility flag" in fdisk?
source
Partitioning a disk with already existing partitions
You should be able to use fdisk to add an extended partition with
no trouble. I've done so a number of times in Ubuntu as well as
in several other ancient distros. But I prefer the graphical
program GParted. It's available as a live CD if you don't have X
installed.
source
Update udev after fdisk run
You could try one of the options to udevadm,
for example
$ udevadm control --reload-rules
Although you're not actually changing udev rules in this case,
the reload operation might force udev to refresh its knowledge of
devices and partitions.
source
What does sfdisk do, and how does it compare to fdisk or parted?
sfdisk reads lines of the form
<start> <size> <id> <bootable>
<c,h,s> <c,h,s>
where each line fills one partition descriptor.
... When a field is absent or empty, a default value is used.
So this sets up a new partition, starting at 0 and ending at the
default of size.
The default value of size is as much as possible (until next
partition or end-of-disk).
source
fdisk / sfdisk not saving partitions on USB drive
source
fdisk (Linux) partitioning RAID 0
I don't think you have a problem.
If your partitioning tool is seeing the RAID array properly, the
RAIDness of the disk being partitioned doesn't matter.
I have heard that the actual layout of a modern disk is nothing
like what is reported in the partitioning tool - so what is seen
as a cylinder boundary in the partitioning tool probably isn't
one anyway. The warning is just there for historical reasons.
The reason for the warning stems from the fact that MS-DOS (I
think, but may be wrong - it hasn't been very relevant for ages)
needed partitions that started and ended on a cylinder boundary.
Windows carried on the tradition of making sure that partitions
started ended on a cylinder boundary for no reason, externally
created partitions that didn't end on the boundary worked ok.
source
real number of sectors on HDD
CHS is a very old way to address sectors on a hard drive and
usually limits the total number of sectors addressable to numbers
divisible by the Cylinder and Head count. So in this case it will
be a number divisible by 63 * 255 or 16065. The sectors on the
drive in excess of the closest such number won't be used.
source
What is the equivalent of the Linux command "sudo fdisk -l" in MacOS?
You can use the 'diskutil' tool for that:
% diskutil list
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_CoreStorage 499.2 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS Macintosh HD *498.9 GB disk1
source
What does the output of fdisk mean?
I am guessing that the sectors 1-31 are reserved for boot
information and partition table info. The partition /dev/sdb1
starts at block/sector 32 and goes to 249854. It is a logical
partition on the physical disk.
The 124911+ is giving you the count of blocks between 32 and
249854.
About Disk Geometry here is what man fdsik
says
about it:
If possible, fdisk will obtain the disk geometry automatically.
This is not necessarily the physical disk geometry (indeed,
modern disks do not really have anything like a physical
geometry, certainly not something that can be described in
simplistic Cylinders/Heads/Sectors form), but it is the disk
geometry that MS-DOS uses for the partition table.
Usually all goes well by default, and there are no problems if
Linux is the only system on the disk. However, if the disk has to
be shared with other operating systems, it is often a good idea
to let an fdisk from another operating system make at least one
partition. When Linux boots it looks at the partition table, and
tries to deduce what (fake) geometry is required for good
cooperation with other systems.
description
fdisk
(in the first form of invocation) is a menu-driven program
for creation and manipulation of partition tables. It
understands DOS-type partition tables and BSD- or SUN-type
disklabels.
fdisk
does not understand GUID partition tables (GPTs) and it is
not designed for large partitions. In these cases, use the
more advanced GNU parted(8).
fdisk
does not use DOS-compatible mode and cylinders as display
units by default. The old deprecated DOS behavior can be
enabled with the ’-c=dos -u=cylinders’
command-line options.
Hard disks can
be divided into one or more logical disks called
partitions. This division is recorded in the
partition table, found in sector 0 of the disk. (In
the BSD world one talks about ’disk slices’ and
a ’disklabel’.)
Linux needs at
least one partition, namely for its root file system. It can
use swap files and/or swap partitions, but the latter are
more efficient. So, usually one will want a second Linux
partition dedicated as swap partition. On Intel-compatible
hardware, the BIOS that boots the system can often only
access the first 1024 cylinders of the disk. For this reason
people with large disks often create a third partition, just
a few MB large, typically mounted on /boot, to store
the kernel image and a few auxiliary files needed at boot
time, so as to make sure that this stuff is accessible to
the BIOS. There may be reasons of security, ease of
administration and backup, or testing, to use more than the
minimum number of partitions.
options
-b
sectorsize
Specify the sector size of the
disk. Valid values are 512, 1024, 2048 or 4096. (Recent
kernels know the sector size. Use this only on old kernels
or to override the kernel’s ideas.) Since
util-linux-2.17, fdisk differentiates between logical and
physical sector size. This option changes both sector sizes
to sectorsize.
-c[=mode]
Specify the compatiblity mode,
’dos’ or ’nondos’. The default is
non-DOS mode. For backward compatibility, it is possible to
use the option without the <mode> argument -- then the
default is used. Note that the optional <mode>
argument cannot be separated from the -c option by a space,
the correct form is for example ’-c=dos’.
-C cyls
Specify the number of cylinders
of the disk. I have no idea why anybody would want to do
so.
-H
heads
Specify the number of heads of
the disk. (Not the physical number, of course, but the
number used for partition tables.) Reasonable values are 255
and 16.
-S
sects
Specify the number of sectors
per track of the disk. (Not the physical number, of course,
but the number used for partition tables.) A reasonable
value is 63.
-h
Print help and then exit.
-l
List the partition tables for the specified devices and
then exit. If no devices are given, those mentioned in
/proc/partitions (if that exists) are used.
-s
partition...
Print the size (in blocks) of
each given partition.
-u[=unit]
When listing partition tables,
show sizes in ’sectors’ or in
’cylinders’. The default is to show sizes in
sectors. For backward compatibility, it is possible to use
the option without the <units> argument -- then the
default is used. Note that the optional <unit>
argument cannot be separated from the -u option by a space,
the correct form is for example
’-u=cylinders’.
-v
Print version number of fdisk program and
exit.
availability
The fdisk command is part of the util-linux package and is
available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
devices
The device is usually /dev/sda, /dev/sdb or so. A device
name refers to the entire disk. Old systems without libata (a
library used inside the Linux kernel to support ATA host
controllers and devices) make a difference between IDE and SCSI
disks. In such cases the device name will be /dev/hd* (IDE) or
/dev/sd* (SCSI).
The partition is a device name followed by a partition
number. For example, /dev/sda1 is the first partition on the
first hard disk in the system. See also Linux kernel
documentation (the Documentation/devices.txt file).
disk labels
A BSD/SUN-type disklabel can describe 8 partitions, the third of
which should be a ’whole disk’ partition. Do not start a
partition that actually uses its first sector (like a swap
partition) at cylinder 0, since that will destroy the disklabel.
An IRIX/SGI-type disklabel can describe 16 partitions, the
eleventh of which should be an entire ’volume’ partition, while
the ninth should be labeled ’volume header’. The volume header
will also cover the partition table, i.e., it starts at block
zero and extends by default over five cylinders. The remaining
space in the volume header may be used by header directory
entries. No partitions may overlap with the volume header. Also
do not change its type or make some filesystem on it, since you
will lose the partition table. Use this type of label only when
working with Linux on IRIX/SGI machines or IRIX/SGI disks under
Linux.
A DOS-type partition table can describe an unlimited number of
partitions. In sector 0 there is room for the description of 4
partitions (called ’primary’). One of these may be an extended
partition; this is a box holding logical partitions, with
descriptors found in a linked list of sectors, each preceding the
corresponding logical partitions. The four primary partitions,
present or not, get numbers 1-4. Logical partitions start
numbering from 5.
In a DOS-type partition table the starting offset and the size of
each partition is stored in two ways: as an absolute number of
sectors (given in 32 bits), and as a Cylinders/Heads/Sectors
triple (given in 10+8+6 bits). The former is OK -- with 512-byte
sectors this will work up to 2 TB. The latter has two problems.
First, these C/H/S fields can be filled only when the number of
heads and the number of sectors per track are known. And second,
even if we know what these numbers should be, the 24 bits that
are available do not suffice. DOS uses C/H/S only, Windows uses
both, Linux never uses C/H/S.
If possible, fdisk will obtain the disk geometry
automatically. This is not necessarily the physical disk geometry
(indeed, modern disks do not really have anything like a physical
geometry, certainly not something that can be described in
simplistic Cylinders/Heads/Sectors form), but it is the disk
geometry that MS-DOS uses for the partition table.
Usually all goes well by default, and there are no problems if
Linux is the only system on the disk. However, if the disk has to
be shared with other operating systems, it is often a good idea
to let an fdisk from another operating system make at least one
partition. When Linux boots it looks at the partition table, and
tries to deduce what (fake) geometry is required for good
cooperation with other systems.
Whenever a partition table is printed out, a consistency check is
performed on the partition table entries. This check verifies
that the physical and logical start and end points are identical,
and that each partition starts and ends on a cylinder boundary
(except for the first partition).
Some versions of MS-DOS create a first partition which does not
begin on a cylinder boundary, but on sector 2 of the first
cylinder. Partitions beginning in cylinder 1 cannot begin on a
cylinder boundary, but this is unlikely to cause difficulty
unless you have OS/2 on your machine.
A sync() and an ioctl(BLKRRPART) (reread partition table from
disk) are performed before exiting when the partition table has
been updated. Long ago it used to be necessary to reboot after
the use of fdisk. I do not think this is the case anymore --
indeed, rebooting too quickly might cause loss of not-yet-written
data. Note that both the kernel and the disk hardware may buffer
data.
dos 6 x warning
The DOS 6.x FORMAT command looks for some information in the
first sector of the data area of the partition, and treats this
information as more reliable than the information in the
partition table. DOS FORMAT expects DOS FDISK to clear the first
512 bytes of the data area of a partition whenever a size change
occurs. DOS FORMAT will look at this extra information even if
the /U flag is given -- we consider this a bug in DOS FORMAT and
DOS FDISK.
The bottom line is that if you use cfdisk or fdisk to change the
size of a DOS partition table entry, then you must also use
dd to zero the first 512 bytes of that partition before
using DOS FORMAT to format the partition. For example, if you
were using cfdisk to make a DOS partition table entry for
/dev/sda1, then (after exiting fdisk or cfdisk and rebooting
Linux so that the partition table information is valid) you would
use the command "dd if=/dev/zero of=/dev/sda1 bs=512 count=1" to
zero the first 512 bytes of the partition.
BE EXTREMELY CAREFUL if you use the dd command,
since a small typo can make all of the data on your disk useless.
For best results, you should always use an OS-specific partition
table program. For example, you should make DOS partitions with
the DOS FDISK program and Linux partitions with the Linux fdisk
or Linux cfdisk program.
bugs
There are
several *fdisk programs around. Each has its problems and
strengths. Try them in the order cfdisk,
fdisk, sfdisk. (Indeed, cfdisk is a
beautiful program that has strict requirements on the
partition tables it accepts, and produces high quality
partition tables. Use it if you can. fdisk is a buggy
program that does fuzzy things - usually it happens to
produce reasonable results. Its single advantage is that it
has some support for BSD disk labels and other non-DOS
partition tables. Avoid it if you can. sfdisk is for
hackers only -- the user interface is terrible, but it is
more correct than fdisk and more powerful than both fdisk
and cfdisk. Moreover, it can be used noninteractively.)
These days
there also is parted. The cfdisk interface is nicer,
but parted does much more: it not only resizes partitions,
but also the filesystems that live in them.
The
IRIX/SGI-type disklabel is currently not supported by the
kernel. Moreover, IRIX/SGI header directories are not fully
supported yet.
The option
’dump partition table to file’ is missing.
see also
cfdisk ,
sfdisk , mkfs , parted ,
partprobe , kpartx