swapon,  swapoff  -  enable/disable  devices  and  files for paging and


   swapon [options] [specialfile...]
   swapoff [-va] [specialfile...]


   swapon is used to specify devices on which paging and swapping  are  to
   take place.

   The  device or file used is given by the specialfile parameter.  It may
   be of the form -L label or -U uuid to indicate a  device  by  label  or

   Calls  to  swapon  normally occur in the system boot scripts making all
   swap devices available, so that the paging  and  swapping  activity  is
   interleaved across several devices and files.

   swapoff disables swapping on the specified devices and files.  When the
   -a flag is given, swapping is disabled on all known  swap  devices  and
   files (as found in /proc/swaps or /etc/fstab).


   -a, --all
          All devices marked as ``swap'' in /etc/fstab are made available,
          except for those with the ``noauto'' option.  Devices  that  are
          already being used as swap are silently skipped.

   -d, --discard[=policy]
          Enable  swap  discards,  if the swap backing device supports the
          discard or trim operation.  This may improve performance on some
          Solid  State  Devices, but often it does not.  The option allows
          one to select  between  two  available  swap  discard  policies:
          --discard=once  to  perform  a single-time discard operation for
          the  whole  swap  area  at   swapon;   or   --discard=pages   to
          asynchronously   discard   freed  swap  pages  before  they  are
          available for reuse.  If no  policy  is  selected,  the  default
          behavior  is to enable both discard types.  The /etc/fstab mount
          options discard, discard=once, or discard=pages may also be used
          to enable discard flags.

   -e, --ifexists
          Silently  skip  devices that do not exist.  The /etc/fstab mount
          option nofail may also be used to skip non-existing device.

   -f, --fixpgsz
          Reinitialize (exec mkswap) the swap space if its page size  does
          not  match  that  of  the  current  running  kernel.   mkswap(2)
          initializes the whole device and does not check for bad blocks.

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

   -L label
          Use the partition that has  the  specified  label.   (For  this,
          access to /proc/partitions is needed.)

   -o, --options opts
          Specify  swap  options  by  an  fstab-compatible comma-separated
          string.  For example:

                 swapon -o pri=1,discard=pages,nofail /dev/sda2

          The opts string  is  evaluated  last  and  overrides  all  other
          command line options.

   -p, --priority priority
          Specify  the  priority  of the swap device.  priority is a value
          between -1 and 32767.  Higher numbers indicate higher  priority.
          See  swapon(2)  for  a full description of swap priorities.  Add
          pri=value to the option field of /etc/fstab for use with  swapon
          -a.  When no priority is defined, it defaults to -1.

   -s, --summary
          Display  swap  usage  summary  by  device.   Equivalent  to "cat
          /proc/swaps".  Not available before Linux 2.1.25.   This  output
          format  is  DEPRECATED  in favour of --show that provides better
          control on output data.

          Display a definable table of swap areas.  See the --help  output
          for a list of available columns.

          Do not print headings when displaying --show output.

   --raw  Display --show output without aligning table columns.

          Display  swap size in bytes in --show output instead of in user-
          friendly units.

   -U uuid
          Use the partition that has the specified uuid.

   -v, --verbose
          Be verbose.

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


   You should not use swapon on a file with holes.  This can  be  seen  in
   the system log as

          swapon: swapfile has holes.

   The  swap file implementation in the kernel expects to be able to write
   to the file directly, without the assistance of the  filesystem.   This
   is  a problem on preallocated files (e.g.  fallocate(1)) on filesystems
   like XFS or ext4, and on copy-on-write filesystems like btrfs.

   It is recommended to use dd(1) and /dev/zero to avoid holes on XFS  and

   swapon may not work correctly when using a swap file with some versions
   of btrfs.  This is due to btrfs being a copy-on-write  filesystem:  the
   file  location  may  not  be  static  and corruption can result.  Btrfs
   actively disallows the use of swap files on its filesystems by refusing
   to map the file.

   One  possible  workaround is to map the swap file to a loopback device.
   This will allow the filesystem to determine the  mapping  properly  but
   may come with a performance impact.

   Swap over NFS may not work.

   swapon  automatically  detects and rewrites a swap space signature with
   old software suspend data (e.g S1SUSPEND, S2SUSPEND, ...). The  problem
   is that if we don't do it, then we get data corruption the next time an
   attempt at unsuspending is made.


          enables libmount debug output.

          enables libblkid debug output.


   swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8)


   /dev/sd??  standard paging devices
   /etc/fstab ascii filesystem description table


   The swapon command appeared in 4.0BSD.


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


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.