.\" Copyright 1998 Andries E. Brouwer (aeb@cwi.nl)
.\"
.\" May be distributed under the GNU General Public License
-.\" Rewritten for 2.1.117, aeb, 981010.
.\"
.TH MKSWAP 8 "March 2009" "util-linux" "System Administration"
.SH NAME
mkswap \- set up a Linux swap area
.SH SYNOPSIS
.B mkswap
-.RB [ options ]
-.IR device
-.RB [ size ]
+[options]
+.I device
+.RI [ size ]
.SH DESCRIPTION
.B mkswap
sets up a Linux swap area on a device or in a file.
(It specifies the desired size of the swap area in 1024-byte blocks.
.B mkswap
will use the entire partition or file if it is omitted.
-Specifying it is unwise -- a typo may destroy your disk.)
+Specifying it is unwise \(en a typo may destroy your disk.)
After creating the swap area, you need the
.B swapon
command to start using it. Usually swap areas are listed in
.I /etc/fstab
so that they can be taken into use at boot time by a
-.B swapon -a
+.B swapon \-a
command in some boot script.
.SH WARNING
can be there, but it is not a recommended setup. The recommended setup is to
use a separate partition for a Linux swap area.
-.B mkswap, like many others mkfs-like utils, erases the first block to remove
-.B old on-disk filesystems.
+.BR mkswap ,
+like many others mkfs-like utils,
+.B erases the first partition block to make any previous filesystem invisible.
+However,
.B mkswap
refuses to erase the first block on a device with a disk
-label (SUN, BSD, ...) or on a whole disk (e.g. /dev/sda).
+label (SUN, BSD, \&...\&).
.SH OPTIONS
.TP
.BR \-c , " \-\-check"
Check the device (if it is a block device) for bad blocks
before creating the swap area.
-If any are found, the count is printed.
+If any bad blocks are found, the count is printed.
.TP
.BR \-f , " \-\-force"
-Force -- go ahead even if the command is stupid.
+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.
-Without this option,
+Also, without this option,
.B mkswap
-will refuse to erase the first block on a device with a partition table or on
-a whole disk (e.g. /dev/sda).
+will refuse to erase the first block on a device with a partition table.
.TP
-.BR \-L , " \-\-label" \ device-label
-Specify a label, to allow
+.BR \-L , " \-\-label " \fIlabel\fR
+Specify a \fIlabel\fR for the device, to allow
.B swapon
by label.
.TP
-.BR \-p , " \-\-pagesize" \ SIZE
-Specify the page size (in bytes) to use. This option is usually unnecessary,
+.BR \-p , " \-\-pagesize " \fIsize\fR
+Specify the page \fIsize\fR (in bytes) to use. This option is usually unnecessary;
.B mkswap
reads the size from the kernel.
.TP
-.BR \-U , " \-\-uuid" \ UUID
-Specify the uuid to use. The default is to generate a UUID.
+.BR \-U , " \-\-uuid " \fIUUID\fR
+Specify the \fIUUID\fR to use. The default is to generate a UUID.
.TP
-.BR \-v , " \-\-swapversion" \ 1
-Specify the swap-space version. 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 (Jun 2002).
-The new version v1 is supported since 2.1.117 (Aug 1998).
+.BR \-v , " \-\-swapversion 1"
+Specify the swap-space version. (This option is currently pointless, as the old
+.B \-v 0
+option has become obsolete and now only
+.B \-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).)
.TP
-.BR \-V , " \-\-version"
-Output version information and exit.
.BR \-h , " \-\-help"
-Output help screen and exit.
+Display help text and exit.
+.TP
+.BR \-V , " \-\-version"
+Display version information and exit.
.SH NOTES
The maximum useful size of a swap area depends on the architecture and
the kernel version.
-It is roughly 2GiB on i386, PPC, m68k and ARM, 1GiB on sparc, 512MiB on mips,
-128GiB on alpha, and 3TiB on sparc64. For kernels after 2.3.3 (May 1999) there is no
-such limitation.
-Note that before version 2.1.117 the kernel allocated one byte for each page,
-while it now allocates two bytes, so that taking into use a swap area of 2 GiB
-might require 2 MiB of kernel memory.
+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 (this was 8 before Linux 2.4.10 (Sep 2001)).
+Presently, Linux allows 32 swap areas.
The areas in use can be seen in the file
.I /proc/swaps
-(since 2.1.25 (Sep 1997)).
.B 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 --
+able to look it up with "cat /proc/cpuinfo" (or you may not \(en
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
.BR mkswap ,
-e.g. using a command like
+e.g.\& using a command like
.nf
.RS
-# dd if=/dev/zero of=swapfile bs=1024 count=65536
+# dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024))
.RE
.fi
-Note that a swap file must not contain any holes (so, using
-.BR cp (1)
-to create the file is not acceptable).
+to create 8GiB swapfile.
+
+Please read notes from
+.BR swapon (8)
+about
+.B the swap file use restrictions
+(holes, preallocation and copy-on-write issues).
+.SH ENVIRONMENT
+.IP LIBBLKID_DEBUG=all
+enables libblkid debug output.
.SH "SEE ALSO"
.BR fdisk (8),
.BR swapon (8)
.SH AVAILABILITY
The mkswap command is part of the util-linux package and is available from
-ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
+https://www.kernel.org/pub/linux/utils/util-linux/.
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