historic/mkswap.8

   1 .\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu)
   2 .\" May be distributed under the GNU General Public License
   3 .\" Modified with suggestions from Linus, Mon Feb  1 21:40:49 1993
   4 .\" Modified with patches from Kai, Wed Jun 22 21:54:56 1994
   5 .\" Patches from jaggy@purplet.demon.co.uk (Mike Jagdis), Wed Feb 8 1995
   6 .\" Added comments from Nick Holloway, Sat Feb 11 1995, faith@cs.unc.edu
   7 .\" "
   8 .TH MKSWAP 8 "8 February 1995" "Linux 1.0" "Linux Programmer's Manual"
   9 .SH NAME
  10 mkswap \- set up a Linux swap device
  11 .SH SYNOPSIS
  12 .B "mkswap [ \-c ]"
  13 .IB device  " [" size-in-blocks "]"
  14 .SH DESCRIPTION
  15 .B mkswap
  16 sets up a Linux swap area on a device (usually a disk partition).
  17
  18 The
  19 .I device
  20 is usually of the following form:
  21
  22 .nf
  23 .RS
  24 /dev/hda[1-8]
  25 /dev/hdb[1-8]
  26 /dev/sda[1-8]
  27 /dev/sdb[1-8]
  28 .RE
  29 .fi
  30
  31 The
  32 .I size-in-blocks
  33 parameter is the desired size of the file system, in blocks.  This
  34 information is determined automatically by mkswap if it is omitted.  Block
  35 counts are rounded down to pages of 4 kB each.  Only block counts equal to
  36 or greater than 40 and equal to or less than 131072 are allowed.  Block
  37 counts greater than 130752 are (silently) rounded down to 130752.
  38
  39 As Nick Holloway explains, the actual maximum for each swap file/partition
  40 is:
  41 .RS
  42 (4096 - 10) * 8 * 4096 = 133890048 bytes = 130752 blocks =  127.6875 Mb
  43 .RE
  44 This is because a single page is used to hold the swap bitmap at the
  45 start of the partition, where each bit is a single 4K page.  The reason
  46 for the -10, is that the signature is "SWAP-SPACE" -- 10 characters.
  47
  48 .B mkswap
  49 can also set up swap files, although the file has to be created first.  A
  50 sequence of commands similar to the following is reasonable for this
  51 purpose:
  52
  53 .nf
  54 .RS
  55 # dd if=/dev/zero of=swapfile bs=1024 count=8192
  56 # mkswap swapfile 8192
  57 # sync
  58 # swapon swapfile
  59 .RE
  60 .fi
  61
  62 Note that the regular file has to be created before running
  63 .B mkswap
  64 on the file, and that the file must not contain any holes (so, using
  65 .BR cp (1)
  66 to create the file is not acceptable).
  67
  68 .SH OPTIONS
  69 .TP
  70 .B \-c
  71 Check the device for bad blocks before creating the file system.  If any
  72 are found, the count is printed.  This option is meant to be used for swap
  73 partitions
  74 .BR only ,
  75 and should
  76 .B not
  77 be used for regular files!  To make sure that regular files do not contain
  78 bad blocks, the partition that contains the regular file should have been
  79 created with
  80 .BR "mkfs -c" .
  81 .SH "SEE ALSO"
  82 .BR fsck (8),
  83 .BR mkfs (8),
  84 .BR fdisk (8)
  85 .SH AUTHOR
  86 Linus Torvalds (torvalds@cs.helsinki.fi)