mkswap
Hurricane Electric Internet Services
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)
Hurricane Electric Internet Services
Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.