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/.