mkswap(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | WARNING | OPTIONS | ENVIRONMENT | NOTES | SEE ALSO | AVAILABILITY | COLOPHON

MKSWAP(8)                 System Administration                MKSWAP(8)

NAME         top

       mkswap - set up a Linux swap area

SYNOPSIS         top

       mkswap [options] device [size]

DESCRIPTION         top

       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         top

       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         top

       -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.

       --lock[=mode]
              Use exclusive BSD lock for device or file it operates.
              The optional argument mode can be yes, no (or 1 and 0) or
              nonblock.  If the mode argument is omitted, it defaults to
              "yes".  This option overwrites environment variable
              $LOCK_BLOCK_DEVICE.  The default is not to use any lock at
              all, but it's recommended to avoid collisions with udevd
              or other tools.

       -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).)

       --verbose
              Verbose execution.  With this option mkswap will output
              more details about detected problems during swap area set
              up.

       -h, --help
              Display help text and exit.

       -V, --version
              Display version information and exit.

ENVIRONMENT         top

       LIBBLKID_DEBUG=all
              enables libblkid debug output.

       LOCK_BLOCK_DEVICE=<mode>
              use exclusive BSD lock.  The mode is "1" or "0".  See
              --lock for more details.

NOTES         top

       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).

SEE ALSO         top

       fdisk(8), swapon(8)

AVAILABILITY         top

       The mkswap command is part of the util-linux package and is
       available from
       https://www.kernel.org/pub/linux/utils/util-linux/.

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found
       at ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you
       have a bug report for this manual page, send it to
       util-linux@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2020-12-18.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-12-17.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

util-linux                     March 2009                      MKSWAP(8)

Pages that refer to this page: swapon(2)crypttab(5)swaplabel(8)swapon(8)