1MKSWAP(8)                    System Administration                   MKSWAP(8)
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NAME

6       mkswap - set up a Linux swap area
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SYNOPSIS

9       mkswap [options] device [size]
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DESCRIPTION

12       mkswap sets up a Linux swap area on a device or in a file.
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14       The  device  argument  will usually be a disk partition (something like
15       /dev/sdb7) but can also be a file.  The Linux kernel does not  look  at
16       partition  IDs,  but  many installation scripts will assume that parti‐
17       tions of hex type 82 (LINUX_SWAP) are  meant  to  be  swap  partitions.
18       (Warning:  Solaris  also  uses  this type.  Be careful not to kill your
19       Solaris partitions.)
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21       The size parameter is superfluous but retained for  backwards  compati‐
22       bility.   (It  specifies the desired size of the swap area in 1024-byte
23       blocks.  mkswap will use the entire partition or file if it is omitted.
24       Specifying it is unwise – a typo may destroy your disk.)
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26       After  creating  the  swap  area,  you need the swapon command to start
27       using it.  Usually swap areas are listed in /etc/fstab so that they can
28       be  taken  into  use  at  boot time by a swapon -a command in some boot
29       script.
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WARNING

33       The swap header does not touch the first block.  A boot loader or  disk
34       label can be there, but it is not a recommended setup.  The recommended
35       setup is to use a separate partition for a Linux swap area.
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37       mkswap, like many others mkfs-like utils, erases  the  first  partition
38       block to make any previous filesystem invisible.
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40       However,  mkswap  refuses  to  erase the first block on a device with a
41       disk label (SUN, BSD, ...).
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OPTIONS

45       -c, --check
46              Check the device (if it is a block device) for bad blocks before
47              creating  the swap area.  If any bad blocks are found, the count
48              is printed.
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50       -f, --force
51              Go ahead even if the command is stupid.  This  allows  the  cre‐
52              ation  of  a  swap  area  larger  than  the file or partition it
53              resides on.
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55              Also, without this option, mkswap will refuse to erase the first
56              block on a device with a partition table.
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58       -L, --label label
59              Specify a label for the device, to allow swapon by label.
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61       -p, --pagesize size
62              Specify the page size (in bytes) to use.  This option is usually
63              unnecessary; mkswap reads the size from the kernel.
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65       -U, --uuid UUID
66              Specify the UUID to use.  The default is to generate a UUID.
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68       -v, --swapversion 1
69              Specify the  swap-space  version.   (This  option  is  currently
70              pointless,  as  the  old -v 0 option has become obsolete and now
71              only -v 1 is supported.  The kernel has not supported  v0  swap-
72              space  format  since  2.5.22 (June 2002).  The new version v1 is
73              supported since 2.1.117 (August 1998).)
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75       -h, --help
76              Display help text and exit.
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78       -V, --version
79              Display version information and exit.
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NOTES

83       The maximum useful size of a swap area depends on the architecture  and
84       the kernel version.
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86       The  maximum  number  of  the pages that is possible to address by swap
87       area header is 4294967295 (32-bit unsigned int).  The  remaining  space
88       on the swap device is ignored.
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90       Presently, Linux allows 32 swap areas.  The areas in use can be seen in
91       the file /proc/swaps
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93       mkswap refuses areas smaller than 10 pages.
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95       If you don't know the page size that your machine uses, you may be able
96       to  look  it up with "cat /proc/cpuinfo" (or you may not – the contents
97       of this file depend on architecture and kernel version).
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99       To set up a swap file, it is necessary to create that file before  ini‐
100       tializing it with mkswap, e.g. using a command like
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102              # dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024))
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104       to create 8GiB swapfile.
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106       Please  read  notes from swapon(8) about the swap file use restrictions
107       (holes, preallocation and copy-on-write issues).
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ENVIRONMENT

111       LIBBLKID_DEBUG=all
112              enables libblkid debug output.
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SEE ALSO

116       fdisk(8), swapon(8)
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AVAILABILITY

119       The mkswap command is part of the util-linux package and  is  available
120       from https://www.kernel.org/pub/linux/utils/util-linux/.
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124util-linux                        March 2009                         MKSWAP(8)
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