146 lines
4.1 KiB
Groff
146 lines
4.1 KiB
Groff
.\" Copyright 1998 Andries E. Brouwer (aeb@cwi.nl)
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.\"
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.\" May be distributed under the GNU General Public License
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.\" Rewritten for 2.1.117, aeb, 981010.
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.\"
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.TH MKSWAP 8 "March 2009" "util-linux" "System Administration"
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.SH NAME
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mkswap \- set up a Linux swap area
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.SH SYNOPSIS
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.B mkswap
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.RI [ options ]
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.I device
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.RI [ size ]
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.SH DESCRIPTION
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.B mkswap
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sets up a Linux swap area on a device or in a file.
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The
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.I device
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argument will usually be a disk partition (something like
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.IR /dev/sdb7 )
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but can also be a file.
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The Linux kernel does not look at partition IDs, but
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many installation scripts will assume that partitions
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of hex type 82 (LINUX_SWAP) are meant to be swap partitions.
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(\fBWarning: Solaris also uses this type. Be careful not to kill
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your Solaris partitions.\fP)
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The
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.I size
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parameter is superfluous but retained for backwards compatibility.
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(It specifies the desired size of the swap area in 1024-byte blocks.
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.B mkswap
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will use the entire partition or file if it is omitted.
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Specifying it is unwise \(en a typo may destroy your disk.)
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After creating the swap area, you need the
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.B swapon
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command to start using it. Usually swap areas are listed in
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.I /etc/fstab
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so that they can be taken into use at boot time by a
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.B swapon \-a
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command in some boot script.
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.SH WARNING
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The swap header does not touch the first block. A boot loader or disk label
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can be there, but it is not a recommended setup. The recommended setup is to
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use a separate partition for a Linux swap area.
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.BR mkswap ,
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like many others mkfs-like utils,
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.B erases the first partition block to make any previous filesystem invisible.
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However,
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.B mkswap
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refuses to erase the first block on a device with a disk
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label (SUN, BSD, \&...\&).
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.SH OPTIONS
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.TP
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.BR \-c , " \-\-check"
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Check the device (if it is a block device) for bad blocks
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before creating the swap area.
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If any bad blocks are found, the count is printed.
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.TP
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.BR \-f , " \-\-force"
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Go ahead even if the command is stupid.
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This allows the creation of a swap area larger than the file
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or partition it resides on.
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Also, without this option,
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.B mkswap
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will refuse to erase the first block on a device with a partition table.
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.TP
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.BR \-L , " \-\-label " \fIlabel\fR
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Specify a \fIlabel\fR for the device, to allow
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.B swapon
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by label.
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.TP
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.BR \-p , " \-\-pagesize " \fIsize\fR
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Specify the page \fIsize\fR (in bytes) to use. This option is usually unnecessary;
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.B mkswap
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reads the size from the kernel.
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.TP
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.BR \-U , " \-\-uuid " \fIUUID\fR
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Specify the \fIUUID\fR to use. The default is to generate a UUID.
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.TP
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.BR \-v , " \-\-swapversion 1"
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Specify the swap-space version. (This option is currently pointless, as the old
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.B \-v 0
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option has become obsolete and now only
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.B \-v 1
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is supported.
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The kernel has not supported v0 swap-space format since 2.5.22 (June 2002).
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The new version v1 is supported since 2.1.117 (August 1998).)
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.TP
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.BR \-h , " \-\-help"
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Display help text and exit.
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.TP
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.BR \-V , " \-\-version"
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Display version information and exit.
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.SH NOTES
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The maximum useful size of a swap area depends on the architecture and
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the kernel version.
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The maximum number of the pages that is possible to address by swap area header
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is 4294967295 (UINT_MAX). The remaining space on the swap device is ignored.
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Presently, Linux allows 32 swap areas.
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The areas in use can be seen in the file
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.I /proc/swaps
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.B mkswap
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refuses areas smaller than 10 pages.
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If you don't know the page size that your machine uses, you may be
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able to look it up with "cat /proc/cpuinfo" (or you may not \(en
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the contents of this file depend on architecture and kernel version).
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To set up a swap file, it is necessary to create that file before
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initializing it with
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.BR mkswap ,
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e.g.\& using a command like
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.nf
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.RS
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# fallocate \-\-length 8GiB swapfile
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.RE
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.fi
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Note that a swap file must not contain any holes (so, using
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.BR cp (1)
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to create the file is not acceptable).
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.SH ENVIRONMENT
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.IP LIBBLKID_DEBUG=all
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enables libblkid debug output.
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.SH "SEE ALSO"
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.BR fdisk (8),
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.BR swapon (8)
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.SH AVAILABILITY
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The mkswap command is part of the util-linux package and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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