MKSWAP(8)		     System Administration		     MKSWAP(8)

NAME
       mkswap - set up a Linux swap area

SYNOPSIS
       mkswap [options] device [blocks]

       mkswap [options] --size size --file file

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 blocks 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(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
       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, --file
	   Create a swap file with the appropriate file permissions and
	   populated blocks on disk.

       -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.

       --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
	   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
	       clear the filesystem UUID

	   random
	       generate a new randomly-generated UUID

	   time
	       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.

       -s, --size size
	   Specify the size of the created swap file in bytes and may be
	   followed by a multiplicative suffix: KiB (=1024), MiB (=1024*1024),
	   and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is
	   optional, e.g., "K" has the same meaning as "KiB"). If the file
	   exists and is larger than size, it will be truncated to this size.
	   This option only makes sense when used with --file.

       -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 and exit.

ENVIRONMENT
       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
       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.

       Aside from mkswap --file, it is also possible to create the swapfile
       manually before initializing it with mkswap, e.g. using a command like

       Since version 2.41, mkswap --file sets the nocow attribute for newly
       created files to support swapfiles on Btrfs.

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

       to create 8GiB swapfile.

       In such a case, please read notes from swapon(8) about the swap file
       use restrictions (holes, preallocation and copy-on-write issues).

SEE ALSO
       fdisk(8), swapon(8)

REPORTING BUGS
       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY
       The mkswap command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.41.2		  2025-09-22			     MKSWAP(8)