1MKSWAP(8) System Administration MKSWAP(8)
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6 mkswap - set up a Linux swap area
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9 mkswap [options] device [size]
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12 mkswap sets up a Linux swap area on a device or in a file.
13 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
17 partitions 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.)
20 The size parameter is superfluous but retained for backwards
22 compatibility. (It specifies the desired size of the swap area in
23 1024-byte blocks. mkswap will use the entire partition or file if it is
24 omitted. Specifying it is unwise - a typo may destroy your disk.)
25 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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32 The swap header does not touch the first block. A boot loader or disk
33 label can be there, but it is not a recommended setup. The recommended
34 setup is to use a separate partition for a Linux swap area.
35 mkswap, like many others mkfs-like utils, erases the first partition
37 block to make any previous filesystem invisible.
38 However, mkswap refuses to erase the first block on a device with a
40 disk label (SUN, BSD, ...).
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43 -c, --check
44 Check the device (if it is a block device) for bad blocks before
45 creating the swap area. If any bad blocks are found, the count is
46 printed.
47 -f, --force
49 Go ahead even if the command is stupid. This allows the creation of
50 a swap area larger than the file or partition it resides on.
51 Also, without this option, mkswap will refuse to erase the first
53 block on a device with a partition table.
54 -L, --label label
56 Specify a label for the device, to allow swapon by label.
57 --lock[=mode]
59 Use exclusive BSD lock for device or file it operates. The optional
60 argument mode can be yes, no (or 1 and 0) or nonblock. If the mode
61 argument is omitted, it defaults to "yes". This option overwrites
62 environment variable $LOCK_BLOCK_DEVICE. The default is not to use
63 any lock at all, but it’s recommended to avoid collisions with
64 udevd or other tools.
65 -p, --pagesize size
67 Specify the page size (in bytes) to use. This option is usually
68 unnecessary; mkswap reads the size from the kernel.
69 -U, --uuid UUID
71 Specify the UUID to use. The default is to generate a UUID.
72 -v, --swapversion 1
74 Specify the swap-space version. (This option is currently
75 pointless, as the old -v 0 option has become obsolete and now only
76 -v 1 is supported. The kernel has not supported v0 swap-space
77 format since 2.5.22 (June 2002). The new version v1 is supported
78 since 2.1.117 (August 1998).)
79 --verbose
81 Verbose execution. With this option mkswap will output more details
82 about detected problems during swap area set up.
83 -h, --help
85 Display help text and exit.
86 -V, --version
88 Display version information and exit.
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91 LIBBLKID_DEBUG=all
92 enables libblkid debug output.
93 LOCK_BLOCK_DEVICE=<mode>
95 use exclusive BSD lock. The mode is "1" or "0". See --lock for more
96 details.
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99 The maximum useful size of a swap area depends on the architecture and
100 the kernel version.
101 The maximum number of the pages that is possible to address by swap
103 area header is 4294967295 (32-bit unsigned int). The remaining space on
104 the swap device is ignored.
105 Presently, Linux allows 32 swap areas. The areas in use can be seen in
107 the file /proc/swaps.
108 mkswap refuses areas smaller than 10 pages.
110 If you don’t know the page size that your machine uses, you may be able
112 to look it up with cat /proc/cpuinfo (or you may not - the contents of
113 this file depend on architecture and kernel version).
114 To set up a swap file, it is necessary to create that file before
116 initializing it with mkswap, e.g. using a command like
117 # dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024))
119 to create 8GiB swapfile.
121 Please read notes from swapon(8) about the swap file use restrictions
123 (holes, preallocation and copy-on-write issues).
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126 fdisk(8), swapon(8)
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129 For bug reports, use the issue tracker at
130 https://github.com/karelzak/util-linux/issues.
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133 The mkswap command is part of the util-linux package which can be
134 downloaded from Linux Kernel Archive
135 <https://www.kernel.org/pub/linux/utils/util-linux/>.
136util-linux 2.37.2 2021-06-02 MKSWAP(8)