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NAME | SYNOPSIS | DESCRIPTION | WARNING | OPTIONS | ENVIRONMENT | NOTES | SEE ALSO | AVAILABILITY | COLOPHON |
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MKSWAP(8) System Administration MKSWAP(8)
mkswap - set up a Linux swap area
mkswap [options] device [size]
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.
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, ...).
-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
$LOCK_BLOCK_DEVICE. The default is not to use any lock at
all, but it's recommended to avoid collisions with udevd
or other tools.
-p, --pagesize size
Specify the page size (in bytes) to use. This option is
usually unnecessary; mkswap reads the size from the
kernel.
-U, --uuid UUID
Specify the UUID to use. The default is to generate a
UUID.
-v, --swapversion 1
Specify the swap-space version. (This option is currently
pointless, as the old -v 0 option has become obsolete and
now only -v 1 is supported. The kernel has not supported
v0 swap-space format since 2.5.22 (June 2002). The new
version v1 is supported since 2.1.117 (August 1998).)
--verbose
Verbose execution. With this option mkswap will output
more details about detected problems during swap area set
up.
-h, --help
Display help text and exit.
-V, --version
Display version information and exit.
LIBBLKID_DEBUG=all
enables libblkid debug output.
LOCK_BLOCK_DEVICE=<mode>
use exclusive BSD lock. The mode is "1" or "0". See
--lock for more details.
The maximum useful size of a swap area depends on the
architecture and the kernel version.
The maximum number of the pages that is possible to address by
swap area header is 4294967295 (32-bit unsigned int). The
remaining space on the swap device is ignored.
Presently, Linux allows 32 swap areas. The areas in use can be
seen in the file /proc/swaps
mkswap refuses areas smaller than 10 pages.
If you don't know the page size that your machine uses, you may
be able to look it up with "cat /proc/cpuinfo" (or you may not –
the contents of this file depend on architecture and kernel
version).
To set up a swap file, it is necessary to create that file before
initializing it with mkswap, e.g. using a command like
# dd if=/dev/zero of=swapfile bs=1MiB count=$((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).
fdisk(8), swapon(8)
The mkswap command is part of the util-linux package and is
available from
https://www.kernel.org/pub/linux/utils/util-linux/.
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)
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