MKSWAP(8)					       System Administration						 MKSWAP(8)



NAME
       mkswap - set up a Linux swap area

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 partitions 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 compatibility.	(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 set‐
       up.  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 creation 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.

       -p, --pagesize size
	      Specify the page size (in bytes) to use.	This option is usually unnecessary; mkswap reads the size from the kernel.

       -U, --uuid UUID
	      Specify the UUID to use.	The default is to generate a UUID.

       -v, --swapversion 1
	      Specify the swap-space version.  (This option is currently pointless, as the old -v 0 option has become obsolete and
	      now only -v 1 is supported.  The kernel has not supported v0 swap-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 initializing 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)