.\" 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 "13 March 2009" "Linux" "Linux Programmer's Manual"
+.TH MKSWAP 8 "March 2009" "util-linux" "System Administration"
.SH NAME
mkswap \- set up a Linux swap area
.SH SYNOPSIS
.B mkswap
-.RB [ \-c ]
-.RB [ \-f ]
-.RB [ \-p
-.IR PSZ ]
-.RB [ \-L
-.IR label ]
-.RB [ \-U
-.IR uuid ]
+[options]
.I device
.RI [ size ]
.SH DESCRIPTION
argument will usually be a disk partition (something like
.IR /dev/sdb7 )
but can also be a file.
-The Linux kernel does not look at partition Id's, but
+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.
-(\fBWarning: Solaris also uses this type. Be careful not to kill
+(\fBWarning: Solaris also uses this type. Be careful not to kill
your Solaris partitions.\fP)
The
(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.)
-
-The
-.I PSZ
-parameter specifies the page size to use. It is almost always
-unnecessary (even unwise) to specify it, but certain old libc
-versions lie about the page size, so it is possible that
-.B mkswap
-gets it wrong. The symptom is that a subsequent
-.B swapon
-fails because no swap signature is found. Typical values for
-.I PSZ
-are 4096 or 8192.
+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
+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
-The swap header does not touch the first block. A boot loader or disk label
-can be there, but it is not recommended setup. The recommended setup is to
+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.
-.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 whole disk (e.g. /dev/sda).
+label (SUN, BSD, \&...\&).
.SH OPTIONS
.TP
-.B \-c
+.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
-.B \-f
-Force - go ahead even if the command is stupid.
+.BR \-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.
-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
-whole disk (e.g. /dec/sda).
+will refuse to erase the first block on a device with a partition table.
+.TP
+.BR \-L , " \-\-label " \fIlabel\fR
+Specify a \fIlabel\fR for the device, to allow
+.B swapon
+by label.
.TP
-.BI \-p \ PSZ
-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 kernel.
+reads the size from the kernel.
.TP
-.BI \-L \ label
-Specify a label, to allow swapon by label.
-(Only for new style swap areas.)
+.BR \-U , " \-\-uuid " \fIUUID\fR
+Specify the \fIUUID\fR to use. The default is to generate a UUID.
.TP
-.BR \-v0 , \ \-v1
-Specify the swap space version. This option is deprecated and \-v1 is
-supported only.
-
-The kernel has not supported v0 swap space format since 2.5.22. The new version
-v1 is supported since 2.1.117.
-
+.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
-.BI \-U \ uuid
-Specify the uuid to use. The default is to generate UUIDs.
+.BR \-h , " \-\-help"
+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, ARM, 1GiB on sparc, 512MiB on mips,
-128GiB on alpha and 3TiB on sparc64. For kernels after 2.3.3 there is no
-such limitation.
-Note that before 2.1.117 the kernel allocated one byte for each page,
-while it now allocates two bytes, so that taking a swap area of 2 GiB
-in use 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).
+Presently, Linux allows 32 swap areas.
The areas in use can be seen in the file
.I /proc/swaps
-(since 2.1.25).
.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 setup a swap file, it is necessary to create that file before
+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-ng package and is available from
-ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
+The mkswap command is part of the util-linux package and is available from
+https://www.kernel.org/pub/linux/utils/util-linux/.
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