mkswap

NAME

       mkswap - set up a Linux swap device

SYNOPSIS

       mkswap [ -c ] device [size-in-blocks]

DESCRIPTION

       mkswap  sets  up  a Linux swap area on a device (usually a
       disk partition).

       The device is usually of the following form:

              /dev/hda[1-8]
              /dev/hdb[1-8]
              /dev/sda[1-8]
              /dev/sdb[1-8]

       The size-in-blocks parameter is the desired  size  of  the
       file  system,  in  blocks.  This information is determined
       automatically by mkswap if it is  omitted.   Block  counts
       are rounded down to pages of 4 kB each.  Only block counts
       equal to or greater than 40 and  equal  to  or  less  than
       131072  are allowed.  Block counts greater than 130752 are
       (silently) rounded down to 130752.

       As Nick Holloway explains, the  actual  maximum  for  each
       swap file/partition is:
              (4096  -  10) * 8 * 4096 = 133890048 bytes = 130752
              blocks =  127.6875 Mb
       This is because a single page is used  to  hold  the  swap
       bitmap  at the start of the partition, where each bit is a
       single 4K page.  The reason for the -10, is that the  sig-
       nature is "SWAP-SPACE" -- 10 characters.

       mkswap  can  also set up swap files, although the file has
       to be created first.  A sequence of  commands  similar  to
       the following is reasonable for this purpose:

              # dd if=/dev/zero of=swapfile bs=1024 count=8192
              # mkswap swapfile 8192
              # sync
              # swapon swapfile

       Note  that  the regular file has to be created before run-
       ning mkswap on the file, and that the file must  not  con-
       tain  any holes (so, using cp(1) to create the file is not
       acceptable).

OPTIONS

       -c     Check the device for bad blocks before creating the
              file  system.   If  any  are  found,  the  count is
              printed.  This option is meant to be used for  swap
              partitions only, and should not be used for regular
              files!  To make sure that regular files do not con-
              tain  bad  blocks,  the partition that contains the
              regular file should have been created with mkfs -c.

SEE ALSO

       fsck(8), mkfs(8), fdisk(8)

AUTHOR

       Linus Torvalds (torvalds@cs.helsinki.fi)