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 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 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/.