Provided by: mount_2.20.1-1ubuntu3_i386 bug


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


       Get info:
            swapon -s [-h] [-V]

            swapon [-d] [-f] [-p priority] [-v] specialfile...
            swapoff [-v] specialfile...

       Enable/disable all:
            swapon -a [-e] [-f] [-v]
            swapoff -a [-v]


       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
              Discard  freed  swap  pages  before they are reused, if the swap
              device supports the discard or trim operation.  This may improve
              performance  on some Solid State Devices, but often it does not.
              The /etc/fstab mount option discard may be also used  to  enable
              discard flag.

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

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

       -h, --help
              Provide help.

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

       -p, --priority priority
              Specify the priority of the swap device.  priority  is  a  value
              between  0  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

       -s, --summary
              Display  swap  usage  summary  by  device.  Equivalent  to  "cat
              /proc/swaps".  Not available before Linux 2.1.25.

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

       -v, --verbose
              Be verbose.

       -V, --version
              Display version.


       You  should not use swapon on a file with holes.  Swap over NFS may not

       swapon automatically detects and rewrites 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.

       swapon may not work correctly when using a swap file with some versions
       of btrfs.  This is due to the swap file implementation  in  the  kernel
       expecting  to  be  able  to  write  to  the  file directly, without the
       assistance of the file system.  Since btrfs  is  a  copy-on-write  file
       system,  the file location may not be static and corruption can result.
       Btrfs actively disallows the use  of  files  on  its  file  systems  by
       refusing  to  map  the  file.  This  can  be  seen in the system log as
       "swapon: swapfile has holes." One possible workaround  is  to  map  the
       file to a loopback device. This will allow the file system to determine
       the mapping properly but may come with a performance impact.


       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