mkswap 2.23.2
Usage:
mkswap [options] device [size]
Options:
-c, --check check bad blocks before creating the swap area
-f, --force allow swap size area be larger than device
-p, --pagesize SIZE specify page size in bytes
-L, --label LABEL specify label
-v, --swapversion NUM specify swap-space version number
-U, --uuid UUID specify the uuid to use
-V, --version output version information and exit
-h, --help display this help and exit
mkswap manual (CentOS 7)
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 parti‐
tion 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.
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 cre‐
ating 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.
-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 sup‐
ported. 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 (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 initializ‐
ing 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).
ENVIRONMENT
LIBBLKID_DEBUG=all
enables libblkid debug output.
SEE ALSO
fdisk(8), swapon(8)
AVAILABILITY
The mkswap command is part of the util-linux package and is available from
https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux March 2009 MKSWAP(8)
mkswap manual (CentOS 9)
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
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.
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 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 $LOCK_BLOCK_DEVICE. The default is not to use
any lock at all, but it’s recommended to avoid collisions with
udevd or other tools.
-p, --pagesize size
Specify the page size (in bytes) to use. This option is usually
unnecessary; mkswap reads the size from the kernel.
-U, --uuid UUID
Specify the UUID to use. The default is to generate a UUID.
-v, --swapversion 1
Specify the swap-space version. (This option is currently
pointless, as the old -v 0 option has become obsolete and now only
-v 1 is supported. The kernel has not supported v0 swap-space
format since 2.5.22 (June 2002). The new version v1 is supported
since 2.1.117 (August 1998).)
--verbose
Verbose execution. With this option mkswap will output more details
about detected problems during swap area set up.
-h, --help
Display help text and exit.
-V, --version
Display version information and exit.
ENVIRONMENT
LIBBLKID_DEBUG=all
enables libblkid debug output.
LOCK_BLOCK_DEVICE=<mode>
use exclusive BSD lock. The mode is "1" or "0". See --lock for more
details.
NOTES
The maximum useful size of a swap area depends on the architecture and
the kernel version.
The maximum number of the pages that is possible to address by swap
area header is 4294967295 (32-bit unsigned int). The remaining space on
the swap device is ignored.
Presently, Linux allows 32 swap areas. The areas in use can be seen in
the file /proc/swaps.
mkswap refuses areas smaller than 10 pages.
If you don’t know the page size that your machine uses, you may be able
to look it up with cat /proc/cpuinfo (or you may not - the contents of
this file depend on architecture and kernel version).
To set up a swap file, it is necessary to create that file before
initializing it with mkswap, e.g. using a command like
# dd if=/dev/zero of=swapfile bs=1MiB count=$((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).
SEE ALSO
fdisk(8), swapon(8)
REPORTING BUGS
For bug reports, use the issue tracker at
https://github.com/karelzak/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 2.37.4 2022-02-14 MKSWAP(8)