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diff --git a/fdisks/fdisk.8 b/fdisks/fdisk.8 new file mode 100644 index 0000000..3c53473 --- /dev/null +++ b/fdisks/fdisk.8 @@ -0,0 +1,288 @@ +.\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu) +.\" Copyright 1998 Andries E. Brouwer (aeb@cwi.nl) +.\" Copyright 2012 Davidlohr Bueso <dave@gnu.org> +.\" May be distributed under the GNU General Public License +.TH FDISK 8 "June 2012" "util-linux" "System Administration" +.SH NAME +fdisk \- manipulate disk partition table +.SH SYNOPSIS +.B fdisk +.RB [ \-uc ] +.RB [ \-b +.IR sectorsize ] +.RB [ \-C +.IR cyls ] +.RB [ \-H +.IR heads ] +.RB [ \-S +.IR sects ] +.I device +.sp +.B fdisk \-l +.RB [ \-u ] +.RI [ device ...] +.sp +.B fdisk \-s +.IR partition ... +.sp +.B fdisk \-v +.sp +.B fdisk \-h +.SH DESCRIPTION +.B 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. + +.B fdisk +does not understand GUID partition tables (GPTs) and it is not designed +for large partitions. In these cases, use the more advanced GNU +.BR parted (8). + +.B 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 +.IR partitions . +This division is recorded in the +.IR "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 +.IR /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. + +.SH DEVICES +The +.I 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 +.I 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). + +.SH 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, +.B 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. + +.SH "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 +.B 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. + +.B BE EXTREMELY CAREFUL +if you use the +.B 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. + +.SH OPTIONS +.TP +.BI "\-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 +.IB sectorsize . +.TP +.BI "\-c"[=mode] +Specify the compatibility 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'. This option is DEPRECATED. +.TP +.BI "\-C " cyls +Specify the number of cylinders of the disk. +I have no idea why anybody would want to do so. This option is DEPRECATED. +.TP +.BI "\-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. This option is DEPRECATED. +.TP +.BI "\-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. This option is DEPRECATED. +.TP +.BI \-h +Print help and then exit. +.TP +.B \-l +List the partition tables for the specified devices and then exit. +If no devices are given, those mentioned in +.I /proc/partitions +(if that exists) are used. +.TP +.BI "\-s " partition... +Print the size (in blocks) of each given partition. +.TP +.BI "\-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'. +.TP +.B \-v +Print version number of +.B fdisk +program and exit. +.SH BUGS +There are several *fdisk programs around. +Each has its problems and strengths. +Try them in the order +.BR cfdisk , +.BR fdisk , +.BR sfdisk . +(Indeed, +.B 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. +.B 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. +.B 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.) +.PP +There also is +.BR parted +which supports many types of different partition table formats. +.PP +The IRIX/SGI-type disklabel is currently not supported by the kernel. +Moreover, IRIX/SGI header directories are not fully supported yet. +.PP +The option `dump partition table to file' is missing. +.\" .SH AUTHORS +.\" A. V. Le Blanc (LeBlanc@mcc.ac.uk) +.\" Bernhard Fastenrath (fasten@informatik.uni-bonn.de) +.\" Jakub Jelinek (jj@sunsite.mff.cuni.cz) +.\" Andreas Neuper (ANeuper@GUUG.de) +.\" and many others. + +.SH ENVIRONMENT +.IP FDISK_DEBUG=0xffff +enables debug output + +.SH "SEE ALSO" +.BR cfdisk (8), +.BR sfdisk (8), +.BR mkfs (8), +.BR parted (8), +.BR partprobe (8), +.BR kpartx (8) +.SH AVAILABILITY +The fdisk command is part of the util-linux package and is available from +ftp://ftp.kernel.org/pub/linux/utils/util-linux/. |