mkswap(8) — Linux manual page


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

       After creating the swap area, you need the swapon(8) 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

       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.

       -q, --quiet
           Suppress output and warning messages.

       -L, --label label
           Specify a label for the device, to allow swapon(8) by label.

           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
           systemd-udevd(8) 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.
           The format of the UUID is a series of hex digits separated by
           hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16".
           The UUID parameter may also be one of the following:

               clear the filesystem UUID

               generate a new randomly-generated UUID

               generate a new time-based UUID

       -e, --endianness ENDIANNESS
           Specify the ENDIANNESS to use, valid arguments are native,
           little or big. The default is native.

       -o, --offset offset
           Specify the offset to write the swap area to.

       -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 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
           Print version and exit.

ENVIRONMENT         top

           enables libblkid debug output.

           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 can
       look it up with getconf PAGESIZE.

       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)

REPORTING BUGS         top

       For bug reports, use the issue tracker at

AVAILABILITY         top

       The mkswap command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <>. This page
       is part of the util-linux (a random collection of Linux
       utilities) project. Information about the project can be found at
       ⟨⟩. If you have
       a bug report for this manual page, send it to This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2023-12-22. (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-14.) If you discover
       any rendering problems in this HTML version of the page, or you
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       send a mail to

util-linux 2.39.594-1e0ad      2023-07-19                      MKSWAP(8)

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