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 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, ...).

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.

   -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.

   The  maximum  number  of  the pages that is possible to address by swap
   area header is 4294967295 (UINT_MAX).  The remaining space on the  swap
   device is ignored.

   Presently, Linux allows 32 swap areas.  The areas in use can be seen in
   the file /proc/swaps

   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

          # fallocate --length 8GiB swapfile

   Note  that  a  swap  file  must  not contain any holes.  Using cp(1) to
   create the file is not acceptable.  Neither is use of  fallocate(1)  on
   file  systems  that support preallocated files, such as XFS or ext4, or
   on copy-on-write filesystems like btrfs.   It  is  recommended  to  use
   dd(1)  and  /dev/zero in these cases.  Please read notes from swapon(8)
   before adding a swap file to copy-on-write filesystems.

ENVIRONMENT

   LIBBLKID_DEBUG=all
          enables libblkid debug output.

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/.

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