readme.fdisk

Util-linux 软件包包含许多工具。其中比较重要的是加载、卸载、格式化、分区和管理硬盘驱动器

     
        Device Boot  Begin   Start     End  Blocks   Id  System
     /dev/hda1   *       1      17   20059   10021+   1  DOS 12-bit FAT
     /dev/hda2       71060   71060   83044    5992+   5  Extended
     /dev/hda3   *   20060   20060   71059   25500   83  Linux native
     /dev/hda5       71061   71061   79559    4249+  82  Linux swap
     /dev/hda6       79985   80001   83044    1522    1  DOS 12-bit FAT

The start of data in both DOS partitions is 16 sectors after the
beginning of the partition: this is one reason why you should use DOS's
own `FDISK' to create DOS partitions.  Changing the units to sectors
also affects the way in which the new partition command asks for the
beginning and end of a new partition.

*Warning*: it is dangerous to create a new partition when the
display/entry units are sectors.

The Verify command is useful because

  1. It warns you if anything is wrong.  *Always* do a Verify command
     to check your work before writing any changes to disk.

  2. It reports how many unallocated sectors there are on the disk.

The Quit command is also useful.  `fdisk' does not actually change
any data on your disk unless you give a Write command.  If you are
unhappy about any changes you may have made, give the Quit command, and
your disk will remain as it was before you ran `fdisk'.  You can also
interrupt `fdisk' with `CTRL-C'.


Deleting and adding partitions
------------------------------

Deleting a partition is simple.  Give the Delete command by typing
`d'.  `fdisk' asks:

     Partition number (1-6): _

Once you get this far, you must either delete a partition or
interrupt the program with `CTRL-C' (or whatever your current interrupt
character is).  Note:

  1. You may delete a nonexistent partition.  You will get a warning
     message.

  2. You may delete an extended partition.  This has the side effect of
     deleting all partitions greater than or equal to 5.

  3. You may delete a logical partition.  In that case, all partitions
     above it are renumbered at once.  For example, if you delete
     partition 5, then partition 6 becomes known as partition 5, and
     partition 7 as partition 6.

Adding a partition is just a bit more complicated.  Give the New
command by typing `n'.  `fdisk' allows you to

  1. Create a primary partition, if there is a free slot in the primary
     partition table.

  2. Create an extended partition if there is a free slot in the
     primary partition table, and if there is no extended partition.

  3. Create a logical partition if an extended partition exists.

If more than one of these actions is possible, you will be asked to
select Primary, Extended, or Logical, depending on what is currently
permissible.  Before you create a primary or an extended partition, you
are asked what slot it is to have in the table (1-4).

You may not add a primary or an extended partition if the selected
slot in the primary partition table is already occupied: in that case
you simply return to the main menu.  You are not allowed to add a new
primary partition unless there are sectors available outside the
extended partition.  You are not allowed to add a new logical partition
unless there are sectors available inside the extended partition.

If space is available, you are prompted for the first cylinder:

     First cylinder ([237]-977): _

The limits are the lowest and the highest cylinders in which sectors
are available in the appropriate part of the disk.  The square-bracketed
number is what you'll get if you simply press enter.  Not all numbers in
this range are necessarily available: they may fall inside an existing
partition.  If you select a cylinder which is already in use, you are
told off and prompted again for the first cylinder.  After selecting the
first cylinder, you are prompted again:

     Last cylinder or +size or +sizeM or +sizeK (237-[836]): _

The limits are the cylinder you have chosen as the first cylinder,
and the highest cylinder which contains a legitimate upper boundary for
the new partition.  The square-bracketed number is what you'll get if
you simply press enter. In other words, all numbers in the given range are
legitimate, unlike those in the first range of cylinders.  You may also
specify the size of a partition in megabytes, kilobytes, or in the
current units (cylinders or sectors).  A plus sign `+' indicates that
your answer is a size rather than a boundary, and the suffix `m' or `k'
(upper or lower case) indicates that the size is not given in units of
sectors or cyliners, but in megabytes or kilobytes respectively.  Thus
possible answers to the last cylinder request above are

700
     Make cylinder 700 the last cylinder in the partition.

+300
     Make cylinder 237 + 300 = 537 the last cylinder in the partition.

+15m
     Make the partition at least 15 megabytes in size.

+12500k
     Make the partition at least 12,500 kilobytes in size.

If you specify a size which is too large or an end which is out of
range, fdisk complains and repeats the prompt.

Adding or deleting partitions has no effect unless you subsequently
give the Write command.  Please remember to give the Verify command
first, just before giving the Write command: this is a safety
precaution.  After giving the Write command, you will see this message:

     The partition table has been altered!
     Calling ioctl() to re-read partition table.
     Syncing disks.

If there are no further messages, the kernel has successfully copied
the information from the partition table into its own internal table.
But sometimes you will see a message like this one:

     Re-read table failed with error 16: Device or resource busy.
     Reboot your system to ensure the partition table is updated.

In this case, depending on what you have changed in the partition
table, it may be dangerous to continue working without rebooting,
since you may lose or corrupt your data.


Here are some important things to note:

  1. Before you reboot, you *may* run `fdisk' again, either to manage
     another disk, or to make additional changes to the same disk, or
     just to check that the changes have been made as you expected.
     This is true even after you receive the message warning you to
     reboot.

  2. It is not a good idea to run any of the programs `mkfs', `mkswap',
     `mount', or `swapon' if you have received the warning message but
     have not rebooted.  In this case it is dangerous to run any program,
     but these in particular may cause serious damage to the data on your
     disk, including the partition tables themselves.


Active flags and system types
-----------------------------

The active flag is a bit in the partition table entry which marks a
partition as bootable.  This is important to some primary boot sector
programs, which will not boot from an unflagged partition.  Other such
programs do not allow more than one partition to be flagged.  Some,
like LILO, ignore the flags completely.  I prefer to flag all bootable
partitions as active so that they stand out on the menu which `fdisk'
lists.  Fdisk prints a star after the name of a partition's device file
if its active flag is set.

The Active command changes, or toggles, a partition's active flag.
Give the Active command, and select a partition by number.  If it was
marked inactive, it will be flagged as active; if it was flagged as
active, it will be marked inactive.  You may set the active flag on an
extended or logical partition, though the meaning of such a flag is by
no means clear.  This can be used to install LILO as a secondary boot
loader to boot a Linux which lives on a second hard disk.

The Type command changes the ID number which describes what type a
partition is.  `fdisk' currently recognises 30 system IDs, in the sense
that it prints a string for each of them, but it allows you to change
any system ID to any other, with the following exceptions: you may not
change any partition to or from the type Extended, and you may not
change a partition whose type is Empty (0) to any other type.  You may,
however, change the type of any data partition to 0, which is
equivalent to deleting it.

The new system ID or type code is a hexadecimal number.  There are
two ways of listing the numbers which `fdisk' recognises: use the List
command, which prints the list, or use the Type command, which, when it
prompts you for the code, says

     Hex code (type L to list codes): _

where the upper case `L' is used for clarity.  The codes printed are:
Some of these numbers are a trifle uncertain.  By default `fdisk' uses
a type of 83.  It used to use 81, the type code used by the MINIX
`fdisk'.  It seemed prudent to change the default since (a) many Linux
`minix' file systems are no longer compatible with MINIX, (b) the ext2
file system, a native Linux file system, is fairly stable, as is the
Xia file system, and (c) the number 81 causes problems with DR-DOS.
Linux does not usually care what values you use for type codes, but
other systems, in particular DOS, OS/2, and DR-DOS, may.

The value of 82 for Linux swap partitions is my own invention, and
is intended to give some recognisable distinction to the partitions
when the values are displayed in hexadecimal.

New active flags and new system type codes are not written to the
disk until you exit from `fdisk' with the Write command, as described
above, in the section on deleting and adding partitions.


Extra commands for experts
--------------------------

The eXtra command `x' puts `fdisk' into `expert' mode, in which a
slightly different set of commands is available.  The Active, Delete,
List, New, Type, Verify, and `eXpert' commands are not available in
expert mode.  The commands Write and Quit are available as in ordinary
mode, the Print command is available, but produces output in a slightly
different format, and of course the Menu command prints the expert
menu.  There are several new commands.

  1. The Return command brings you back to the main menu.

  2. The Extended command prints the list of table entries which point
     to other tables.  Ordinary users do not need this information.
     The data is shown as it is stored.  The same format is used for
     the expert Print command.

  3. The dangerous Begin command allows you to move the start of data
     in a partition away from its beginning.  Other systems create
     partitions with this format, and it is sometimes useful to be able
     to reproduce it.

  4. The slightly dangerous Cylinders command allows you to change the
     available number of cylinders.  For SCSI disk owners, note that we
     require not the actual number of physical cylinders, but the
     number of logical cylinders used by DOS and other operating
     systems.

  5. The extremely dangerous Heads and Sectors commands allow you to
     change the number of heads and sectors.  It should not be
     necessary to use these commands unless you have a SCSI disk, whose
     geometry Linux is not always able to determine.  SCSI disk owners
     note that we need not the actual number of heads or of sectors per
     track, but the number believed to exist by DOS and other operating
     systems.  *Warning*: If you set either of these numbers to a bad
     value, you may lose all data on your disk.

Always, after giving any of the commands Begin, Cylinder, Heads, or
Sectors, you should Return to the main menu and give the Verify command.


Warnings for `fdisk' users
--------------------------

In general, you should not use this `fdisk' program to create
partitions for other operating systems, only for Linux.  Nor should you
use `fdisk' commands from other operating systems to create partitions
for Linux.

DR-DOS 5.0 and 6.0 are reported to have difficulties with partition
ID codes of 80 or more.  The Linux `fdisk' used to set the system type
of new partitions to hexadecimal 81.  DR-DOS seems to confuse this with
hexadecimal 1, a DOS code.  The values 82 for swap and 83 for file
systems should not cause problems with DR-DOS.  If they do, you may use
the `fdisk' command `t' to change the system code of any Linux
partitions to some number less than hexadecimal 80; I suggest 42 and 43
for the moment.

Partitioning a hard disk may destroy data which is on that disk if you
are not careful.  Go slowly, write down a description of the partition
tables before you changed them, and always verify before you write.

Most operating systems and utilities expect that all partitions begin and
end at cylinder boundaries.  This version of `fdisk' does so by default,
but you can use it to create partitions which begin or end anywhere.
This does not normally affect Linux, but it is very dangerous, as other
operating systems (including DOS) may try to `correct' the partition
boundaries.

It is dangerous to create a new partition when the display/entry
units are sectors.

The Verify command warns you if anything is wrong.  *Always* give a
Verify command before writing any changes to disk.

If you set the disk geometry (tracks per cylinder, or sectors per
track) to an incorrect value, you may lose all data on your disk.

Do create BSD/SUN and/or IRIX/SGI disk labels only when you are sure
that you want them.  Both features are intended to allow you READing
those labels and prevent unintentional formatting of these disks.