Section: System Administration (8)
Updated: March 2009
mkswap - set up a Linux swap area
sets up a Linux swap area on a device or in a file.
argument will usually be a disk partition (something like
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.)
parameter is superfluous but retained for backwards compatibility.
(It specifies the desired size of the swap area in 1024-byte blocks.
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
command to start using it. Usually swap areas are listed in
so that they can be taken into use at boot time by a
command in some boot script.
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.
like many others mkfs-like utils,
erases the first partition block to make any previous filesystem invisible.
refuses to erase the first block on a device with a disk
label (SUN, BSD, ...).
- -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,
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
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 $LOCK_BLOCK_DEVICE. The default is not to use any
lock at all, but it's recommended to avoid collisions with udevd or other
- -p, --pagesize size
Specify the page size (in bytes) to use. This option is usually unnecessary;
reads the size from the kernel.
- -U, --uuid UUID
Specify the UUID to use. The default is to generate a UUID.
- -v, --swapversion 1
Specify the swap-space version. (This option is currently pointless, as the old
option has become obsolete and now only
The kernel has not supported v0 swap-space format since 2.5.22 (June 2002).
The new version v1 is supported since 2.1.117 (August 1998).)
- -h, --help
Display help text and exit.
- -V, --version
Display version information and exit.
enables libblkid debug output.
use exclusive BSD lock. The mode is "1" or "0". See --lock for more details.
The maximum useful size of a swap area depends on the architecture and
the kernel version.
The maximum number of the pages that is possible to address by swap area header
is 4294967295 (32-bit unsigned int). The remaining space on the swap device is ignored.
Presently, Linux allows 32 swap areas.
The areas in use can be seen in the file
refuses areas smaller than 10 pages.
If you don't know the page size that your machine uses, you may be
able to look it up with "cat /proc/cpuinfo" (or you may not -
the contents of this file depend on architecture and kernel version).
To set up a swap file, it is necessary to create that file before
initializing it with
e.g. using a command like
- # dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024))
to create 8GiB swapfile.
Please read notes from
the swap file use restrictions
(holes, preallocation and copy-on-write issues).
The mkswap command is part of the util-linux package and is available from