mkswap

MKSWAP(8)                    System Administration                   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 parti-
       tions of hex type 82 (LINUX_SWAP) are  meant  to  be  swap  partitions.
       (Warning: Solaris also uses this type.  Be careful not to kill your So-
       laris partitions.)

       The size parameter is superfluous but retained for  backwards  compati-
       bility.   (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 us-
       ing 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  cre-
              ation  of  a  swap area larger than the file or partition it re-
              sides 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  ini-
       tializing 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/.

util-linux                        March 2009                         MKSWAP(8)