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  (32-bit
       unsigned int).  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

              # dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024))

       to create 8GiB swapfile.

       Please  read notes from swapon(8) about the swap file use restrictions (holes, preallocation and copy-on-
       write issues).

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/.