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
       https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux                                         March 2009                                          MKSWAP(8)