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<!DOCTYPE html>
<html>
<!-- This is an automatically generated file. Do not edit.
t
Title: mkswap
Author: [see the "AUTHOR(S)" section]
Generator: Asciidoctor 2.0.20
Date: 2024-05-01
Manual: System Administration
Source: util-linux 2.40.1
Language: English
-->
<head>
<meta charset="utf-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<link rel="stylesheet" href="mandoc.css" type="text/css" media="all"/>
<title>MKSWAP(8)</title>
</head>
<body>
<table class="head">
<tr>
<td class="head-ltitle">MKSWAP(8)</td>
<td class="head-vol">System Administration</td>
<td class="head-rtitle">MKSWAP(8)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp">mkswap - set up a Linux swap area</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><b>mkswap</b> [options] <i>device</i> [<i>blocks</i>]</p>
<p class="Pp"><b>mkswap</b> [options] --size <i>size</i> --file <i>file</i></p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp"><b>mkswap</b> sets up a Linux swap area on a device or in a
file.</p>
<p class="Pp">The <i>device</i> argument will usually be a disk partition
(something like <i>/dev/sdb7</i>) 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.
(<b>Warning: Solaris also uses this type. Be careful not to kill your
Solaris partitions.</b>)</p>
<p class="Pp">The <i>blocks</i> parameter is superfluous but retained for
backwards compatibility. (It specifies the desired size of the swap area in
1024-byte blocks. <b>mkswap</b> will use the entire partition or file if it
is omitted. Specifying it is unwise - a typo may destroy your disk.)</p>
<p class="Pp">After creating the swap area, you need the <b>swapon</b>(8)
command to start using it. Usually swap areas are listed in
<i>/etc/fstab</i> so that they can be taken into use at boot time by a
<b>swapon -a</b> command in some boot script.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="WARNING"><a class="permalink" href="#WARNING">WARNING</a></h1>
<p class="Pp">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.</p>
<p class="Pp"><b>mkswap</b>, like many others mkfs-like utils, <b>erases the
first partition block to make any previous filesystem invisible.</b></p>
<p class="Pp">However, <b>mkswap</b> refuses to erase the first block on a
device with a disk label (SUN, BSD, ...).</p>
</section>
<section class="Sh">
<h1 class="Sh" id="OPTIONS"><a class="permalink" href="#OPTIONS">OPTIONS</a></h1>
<p class="Pp"><b>-c</b>, <b>--check</b></p>
<div class="Bd-indent">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.</div>
<p class="Pp"><b>-F</b>, <b>--file</b></p>
<div class="Bd-indent">Create a swap file with the appropriate file permissions
and populated blocks on disk.</div>
<p class="Pp"><b>-f</b>, <b>--force</b></p>
<div class="Bd-indent">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.
<p class="Pp">Also, without this option, <b>mkswap</b> will refuse to erase the
first block on a device with a partition table.</p>
</div>
<p class="Pp"><b>-q</b>, <b>--quiet</b></p>
<div class="Bd-indent">Suppress output and warning messages.</div>
<p class="Pp"><b>-L</b>, <b>--label</b> <i>label</i></p>
<div class="Bd-indent">Specify a <i>label</i> for the device, to allow
<b>swapon</b>(8) by label.</div>
<p class="Pp"><b>--lock</b>[=<i>mode</i>]</p>
<div class="Bd-indent">Use exclusive BSD lock for device or file it operates.
The optional argument <i>mode</i> can be <b>yes</b>, <b>no</b> (or 1 and 0) or
<b>nonblock</b>. If the <i>mode</i> argument is omitted, it defaults to
<b>yes</b>. This option overwrites environment variable
<b>$LOCK_BLOCK_DEVICE</b>. The default is not to use any lock at all, but
it’s recommended to avoid collisions with <b>systemd-udevd</b>(8) or
other tools.</div>
<p class="Pp"><b>-p</b>, <b>--pagesize</b> <i>size</i></p>
<div class="Bd-indent">Specify the page <i>size</i> (in bytes) to use. This
option is usually unnecessary; <b>mkswap</b> reads the size from the
kernel.</div>
<p class="Pp"><b>-U</b>, <b>--uuid</b> <i>UUID</i></p>
<div class="Bd-indent">Specify the <i>UUID</i> to use. The default is to
generate a UUID. The format of the UUID is a series of hex digits separated by
hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUID
parameter may also be one of the following:
<p class="Pp"><b>clear</b></p>
<div class="Bd-indent">clear the filesystem UUID</div>
<p class="Pp"><b>random</b></p>
<div class="Bd-indent">generate a new randomly-generated UUID</div>
<p class="Pp"><b>time</b></p>
<div class="Bd-indent">generate a new time-based UUID</div>
</div>
<p class="Pp"><b>-e</b>, <b>--endianness</b> <i>ENDIANNESS</i></p>
<div class="Bd-indent">Specify the <i>ENDIANNESS</i> to use, valid arguments are
<b>native</b>, <b>little</b> or <b>big</b>. The default is
<b>native</b>.</div>
<p class="Pp"><b>-o</b>, <b>--offset</b> <i>offset</i></p>
<div class="Bd-indent">Specify the <i>offset</i> to write the swap area
to.</div>
<p class="Pp"><b>-s</b>, <b>--size</b> <i>size</i></p>
<div class="Bd-indent">Specify the size of the created swap file in bytes and
may be followed by a multiplicative suffix: KiB (=1024), MiB (=1024*1024), and
so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional,
e.g., "K" has the same meaning as "KiB"). If the file
exists and is larger than <i>size</i>, it will be truncated to this size. This
option only makes sense when used with <b>--file</b>.</div>
<p class="Pp"><b>-v</b>, <b>--swapversion 1</b></p>
<div class="Bd-indent">Specify the swap-space version. (This option is currently
pointless, as the old <b>-v 0</b> option has become obsolete and now only
<b>-v 1</b> 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).)</div>
<p class="Pp"><b>--verbose</b></p>
<div class="Bd-indent">Verbose execution. With this option <b>mkswap</b> will
output more details about detected problems during swap area set up.</div>
<p class="Pp"><b>-h</b>, <b>--help</b></p>
<div class="Bd-indent">Display help text and exit.</div>
<p class="Pp"><b>-V</b>, <b>--version</b></p>
<div class="Bd-indent">Print version and exit.</div>
</section>
<section class="Sh">
<h1 class="Sh" id="ENVIRONMENT"><a class="permalink" href="#ENVIRONMENT">ENVIRONMENT</a></h1>
<p class="Pp">LIBBLKID_DEBUG=all</p>
<div class="Bd-indent">enables libblkid debug output.</div>
<p class="Pp">LOCK_BLOCK_DEVICE=<mode></p>
<div class="Bd-indent">use exclusive BSD lock. The mode is "1" or
"0". See <b>--lock</b> for more details.</div>
</section>
<section class="Sh">
<h1 class="Sh" id="NOTES"><a class="permalink" href="#NOTES">NOTES</a></h1>
<p class="Pp">The maximum useful size of a swap area depends on the architecture
and the kernel version.</p>
<p class="Pp">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.</p>
<p class="Pp">Presently, Linux allows 32 swap areas. The areas in use can be
seen in the file <i>/proc/swaps</i>.</p>
<p class="Pp"><b>mkswap</b> refuses areas smaller than 10 pages.</p>
<p class="Pp">If you don’t know the page size that your machine uses, you
can look it up with <b>getconf PAGESIZE</b>.</p>
<p class="Pp">To set up a swap file, it is necessary to create that file before
initializing it with <b>mkswap</b>, e.g. using a command like</p>
<p class="Pp"></p>
<div class="Bd-indent">
<pre># dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024))</pre>
</div>
<p class="Pp">to create 8GiB swapfile.</p>
<p class="Pp">Please read notes from <b>swapon</b>(8) about <b>the swap file use
restrictions</b> (holes, preallocation and copy-on-write issues).</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><b>fdisk</b>(8), <b>swapon</b>(8)</p>
</section>
<section class="Sh">
<h1 class="Sh" id="REPORTING_BUGS"><a class="permalink" href="#REPORTING_BUGS">REPORTING
BUGS</a></h1>
<p class="Pp">For bug reports, use the issue tracker at <i></i>
<https://github.com/util-linux/util-linux/issues>.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="AVAILABILITY"><a class="permalink" href="#AVAILABILITY">AVAILABILITY</a></h1>
<p class="Pp">The <b>mkswap</b> command is part of the util-linux package which
can be downloaded from <i>Linux Kernel Archive</i>
<https://www.kernel.org/pub/linux/utils/util-linux/>.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">2024-05-01</td>
<td class="foot-os">util-linux 2.40.1</td>
</tr>
</table>
</body>
</html>