MKSWAP manpage

Search topic Section

MKSWAP(8)		     System Administration		     MKSWAP(8)

       mkswap - set up a Linux swap area

       mkswap [options] 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  IDs,	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.)

       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 a 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  partition
       block to make any previous filesystem invisible.

       However,	 mkswap	 refuses  to  erase the first block on a device with a
       disk label (SUN, BSD, ...).

       -c, --check
	      Check the device (if it is a block device) for bad blocks before
	      creating	the swap area.	If any bad blocks are found, the count
	      is printed.

       -f, --force
	      Go ahead even if the command is stupid.  This  allows  the  cre-
	      ation  of	 a  swap  area	larger	than  the file or partition it
	      resides on.

	      Also, without this option, mkswap will refuse to erase the first
	      block on a device with a partition table.

       -L, --label label
	      Specify a label for the device, to allow swapon by label.

       -p, --pagesize size
	      Specify the page size (in bytes) to use.	This option is usually
	      unnecessary; mkswap reads the size from the kernel.

       -U, --uuid UUID
	      Specify the UUID to use.	The default is to generate a UUID.

       -v, --swapversion 1
	      Specify the  swap-space  version.	  (This	 option	 is  currently
	      pointless,  as  the  old -v 0 option has become obsolete and now
	      only -v 1 is supported.  The kernel has not supported  v0	 swap-
	      space  format  since  2.5.22 (June 2002).	 The new version v1 is
	      supported since 2.1.117 (August 1998).)

       -h, --help
	      Display help text and exit.

       -V, --version
	      Display version information and exit.

       The maximum useful size of a swap area depends on the architecture  and
       the kernel version.

       The  maximum  number  of	 the pages that is possible to address by swap
       area header is 4294967295 (32-bit unsigned int).	 The  remaining	 space
       on the swap device is ignored.

       Presently, Linux allows 32 swap areas.  The areas in use can be seen in
       the file /proc/swaps

       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 set up 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=1MiB count=$((8*1024))

       to create 8GiB swapfile.

       Please  read  notes from swapon(8) about the swap file use restrictions
       (holes, preallocation and copy-on-write issues).

	      enables libblkid debug output.

       fdisk(8), swapon(8)

       The mkswap command is part of the util-linux package and	 is  available
       from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux			  March 2009			     MKSWAP(8)