Provided by: util-linux_2.17.2-0ubuntu1_i386 bug

NAME

       mkswap - set up a Linux swap area

SYNOPSIS

       mkswap [-c] [-f] [-p PSZ] [-L label] [-U uuid] 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   Id’s,  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.)

       The  PSZ  parameter specifies the page size to use. It is almost always
       unnecessary (even unwise) to specify it, but certain old libc  versions
       lie  about  the page size, so it is possible that mkswap gets it wrong.
       The symptom is that a subsequent swapon fails because no swap signature
       is found. Typical values for PSZ are 4096 or 8192.

       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 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  block  to
       remove old on-disk filesystems.

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

OPTIONS

       -c     Check the device (if it is a block device) for bad blocks before
              creating the swap area.  If any 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.

              Without this option mkswap will refuse to erase the first  block
              on  a  device  with  a  partition  table  or on whole disk (e.g.
              /dec/sda).

       -p PSZ Specify the page size to use.

       -L label
              Specify a label, to allow swapon by label.  (Only for new  style
              swap areas.)

       -v0, -v1
              Specify  the  swap  space version. This option is deprecated and
              -v1 is supported only.

              The kernel has not supported v0 swap space format since  2.5.22.
              The new version v1 is supported since 2.1.117.

       -U uuid
              Specify the uuid to use. The default is to generate UUIDs.

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,  ARM,  1GiB
       on  sparc,  512MiB  on  mips,  128GiB on alpha and 3TiB on sparc64. For
       kernels after 2.3.3 there is no such limitation.

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

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

       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  setup  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-ng  package  and is
       available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.