mkswap


SYNOPSIS
       mkswap [options] device [size]

DESCRIPTION
       mkswap sets up a Linux swap area on a device or in a file.

       The  device  argument  will usually be a disk partition (something like
       /dev/sdb7) but can also be a file.  The Linux kernel does not  look  at
       partition  IDs,  but  many installation scripts will assume that parti-
       tions of hex type 82 (LINUX_SWAP) are  meant  to  be  swap  partitions.
       (Warning:  Solaris  also  uses  this type.  Be careful not to kill your
       Solaris partitions.)

       The size parameter is superfluous but retained for  backwards  compati-
       bility.   (It  specifies the desired size of the swap area in 1024-byte
       blocks.  mkswap will use the entire partition or file if it is omitted.
       Specifying it is unwise -- a typo may destroy your disk.)

       After  creating  the  swap  area,  you need the swapon command to start
       using it.  Usually swap areas are listed in /etc/fstab so that they can
       be  taken  into  use  at  boot time by a swapon -a command in some boot
       script.


WARNING
       The swap header does not touch the first block.  A boot loader or  disk
       label can be there, but it is not a recommended setup.  The recommended
       setup is to use a separate partition for a Linux swap area.

       mkswap, like many others mkfs-like utils, erases  the  first  partition
       block to make any previous filesystem invisible.

       However,  mkswap  refuses  to  erase the first block on a device with a
       disk label (SUN, BSD, ...) and on a whole disk (e.g. /dev/sda).


OPTIONS
       -c, --check
              Check the device (if it is a block device) for bad blocks before
              creating  the swap area.  If any bad blocks are found, the count
              is printed.

       -f, --force
              Go ahead even if the command is stupid.  This  allows  the  cre-
              ation  of  a  swap  area  larger  than  the file or partition it
              resides on.

              Also, without this option, mkswap will refuse to erase the first
              block  on  a  device  with a partition table and on a whole disk
              (e.g. /dev/sda).

       -L, --label label
              Specify a label for the device, to allow swapon by label.
              space format since 2.5.22 (June 2002).  The new  version  v1  is
              supported since 2.1.117 (August 1998).)

       -h, --help
              Display help text and exit.

       -V, --version
              Display version information and exit.


NOTES
       The  maximum useful size of a swap area depends on the architecture and
       the kernel version.  It is roughly 2GiB on i386,  PPC,  m68k  and  ARM,
       1GiB  on  sparc,  512MiB on mips, 128GiB on alpha, and 3TiB on sparc64.
       For kernels after 2.3.3 (May 1999) there is no such limitation.

       Note that before version 2.1.117 the kernel allocated one byte for each
       page,  while it now allocates two bytes, so that taking into use a swap
       area of 2 GiB might require 2 MiB of kernel memory.

       Presently, Linux allows 32 swap areas (this was 8 before  Linux  2.4.10
       (Sep  2001)).   The  areas  in  use can be seen in the file /proc/swaps
       (since 2.1.25 (Sep 1997)).

       mkswap refuses areas smaller than 10 pages.

       If you don't know the page size that your machine uses, you may be able
       to  look it up with "cat /proc/cpuinfo" (or you may not -- the contents
       of this file depend on architecture and kernel version).

       To set up a swap file, it is necessary to create that file before  ini-
       tializing it with mkswap, e.g. using a command like

              # dd if=/dev/zero of=swapfile bs=1024 count=65536

       Note  that  a  swap file must not contain any holes (so, using cp(1) to
       create the file is not acceptable).



SEE ALSO
       fdisk(8), swapon(8)

AVAILABILITY
       The mkswap command is part of the util-linux package and  is  available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.



util-linux                        March 2009                         MKSWAP(8)
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