x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
MKSWAP(8) System Administration MKSWAP(8)
NAME
mkswap - set up a Linux swap area
SYNOPSIS
mkswap [options] device [size]
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 parti-
tions 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 compati-
bility. (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
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, --force
Go ahead even if the command is stupid. This allows the cre-
ation 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.
-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).)
-h, --help
Display help text and exit.
-V, --version
Display version information and exit.
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 (UINT_MAX). 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 ini-
tializing it with mkswap, e.g. using a command like
# fallocate --length 8GiB swapfile
Note that a swap file must not contain any holes (so, using cp(1) to
create the file is not acceptable).
ENVIRONMENT
LIBBLKID_DEBUG=0xffff
enables debug output.
SEE ALSO
fdisk(8), swapon(8)
AVAILABILITY
The mkswap command is part of the util-linux package and is available
from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
util-linux March 2009 MKSWAP(8)
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