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SWAPON(8)                  Linux Programmer's Manual                 SWAPON(8)

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

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

            swapon [-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 uuid.

       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 oper-
              ation for the whole swap area at swapon; or --discard=pages to discard freed
              swap  pages  before  they  are  reused,  while  swapping.   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 be also
              used to enable discard flags.

       -e, --ifexists
              Silently skip devices that do not exist.

       -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 -a.

       -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 work.

       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(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-ng package and is available from

Linux 1.x                      25 September 1995                     SWAPON(8)

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