mkswap manpage

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MKSWAP(8)		     System Administration		     MKSWAP(8)

       mkswap - set up a Linux swap area

       mkswap [options] device [size]

       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

       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, ...).

       -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.

       -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.

       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

	      # fallocate --length 8GiB swapfile

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

	      enables debug output.

       fdisk(8), swapon(8)

       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)