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           mkswap [-c] [-f] [-p PSZ] [-L label] [-U uuid] device [size]


           mkswap sets up a Linux swap area on a device or in a file.
           The  device  argument  will usually be a disk partition (something like
           /dev/sdb7) but can also be a file.  The Linux kernel does not  look  at
           partition  Id's,  but many installation scripts will assume that parti-
           tions of hex type 82 (LINUX_SWAP) are  meant  to  be  swap  partitions.
           (Warning:  Solaris  also  uses  this  type. Be careful not to kill your
           Solaris partitions.)
           The size parameter is superfluous but retained for  backwards  compati-
           bility.   (It  specifies the desired size of the swap area in 1024-byte
           blocks.  mkswap will use the entire partition or file if it is omitted.
           Specifying it is unwise - a typo may destroy your disk.)
           The  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 mkswap gets it wrong.
           The symptom is that a subsequent swapon fails because no swap signature
           is found. Typical values for PSZ are 4096 or 8192.
           After  creating  the  swap  area,  you need the swapon command to start
           using it. Usually swap areas are listed in /etc/fstab so that they  can
           be  taken  into  use  at  boot time by a swapon -a command in some boot


           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 use a separate partition for a Linux swap area.
           mkswap like many others mkfs-like  utils  erases  the  first  block  to
           remove old on-disk filesystems.
           mkswap  refuses  to erase the first block on a device with a disk label
           (SUN, BSD, ...) or on whole disk (e.g. /dev/sda).


           -c     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.
           -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 mkswap will refuse to erase the first  block
                  on  a  device  with  a  partition  table  or on whole disk (e.g.
           -U uuid
                  Specify the uuid to use. The default is to generate UUIDs.


           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 ker-
           nels 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.
           Presently, Linux allows 32 swap areas (this was 8 before Linux 2.4.10).
           The areas in use can be seen in the file /proc/swaps (since 2.1.25).
           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 -  the  contents
           of this file depend on architecture and kernel version).
           To  setup  a swap file, it is necessary to create that file before ini-
           tializing it with mkswap, e.g. using a command like
                  # dd if=/dev/zero of=swapfile bs=1024 count=65536
           Note that a swap file must not contain any holes (so,  using  cp(1)  to
           create the file is not acceptable).


           fdisk(8), swapon(8)


           The  mkswap  command is part of the util-linux-ng package and is avail-
           able from

    Linux 13 March 2009 MKSWAP(8)


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