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swapon(8)

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NAME    [Toc]    [Back]

       swapon  -  Specifies additional disk partitions for paging
       and swapping

SYNOPSIS    [Toc]    [Back]

       /sbin/swapon [-a  | -v  | -p   |  -s   |  -d   |  -F]  [-D
       device] [-l size] [-h size]  filename

OPTIONS    [Toc]    [Back]

       Installs   all   paging   partitions   specified   in  the
       /etc/sysconfigtab file.  Generates verbose output.  Specifies
  the  filename  given in the command is the preferred
       paging device.  Displays swap space utilization.  For each
       swap  partition,  this option displays the total amount of
       allocated swap space, the amount of  swap  space  that  is
       being  used,  and the amount of free swap space.  Sets the
       first specified swap device as  the  system  dump  device,
       providing  the  system dump device was not previously set.
       Force the use of the specified swap device, even if either
       of the following conditions are true: You specified a partition
 that is currently in use (that  is,  the  partition
       contains  a valid file system).  The device contains other
       file partitions that are currently in use.

              If you do not specify the -F option and the  partition
  is in use, the swapon command displays a partition
 check warning message. It then gives you  an
              opportunity   to   override  the  partition  check.
              Explicitly sets the system dump device  to  be  the
              specified  device,  even  if the system dump device
              was previously set.  Specifies the low water  mark.
              Specifies the high water mark.

OPERANDS    [Toc]    [Back]

       Specifies the device special file name.

DESCRIPTION    [Toc]    [Back]

       The swapon command is used to specify additional disk partitions
 for paging and swapping. A paging partition  is  a
       block  special device. (Tru64 UNIX does not currently support
 paging and swapping to a regular  file.   All  paging
       and  swapping  areas  must be block special devices.)  The
       swapon command uses a priority default of 4 for block special
 devices. Calls to swapon normally occur in the system
       multiuser state initialization.

       When you make more swap space available  with  the  swapon
       command,  the additional swap space is available until the
       system is rebooted.  To make additional swap space  permanent,
  you  must  specify  the  swap  device  entry in the
       /etc/sysconfigtab file.

       The swapon command  options  can  override  the  partition
       specifications  in the /etc/sysconfigtab file. You must be
       superuser or have the mount command authorization  to  run
       the  swapon  command.  System administrators and operators
       (users with the sysadmin and operator  command  authorizations,
  respectively)  usually  are  given  mount  command
       authorization. See dop(8)  for  information  about  giving
       certain  users  authorization to issue privileged commands
       without knowing the root password.

       You can use Logical  Storage  Manager  (LSM)  volumes  for
       additional  swap space.  For high system availability, you
       can mirror the LSM volumes. The  Logical  Storage  Manager
       manual  describes how to use the swapon command to configure
 an LSM mirrored volume as additional swap space.

       There are two strategies for swap space allocation:  immediate
  mode and deferred or over-commitment mode.  The two
       strategies differ in the point in time at which swap space
       is  allocated.   If  immediate mode is used, swap space is
       allocated when modifiable virtual address  space  is  created.
   If  deferred mode is used, swap space is not allocated
 until the system needs to write a  modified  virtual
       page  to  swap  space.  Immediate mode is the default swap
       space allocation strategy.

       Immediate mode is more  conservative  than  deferred  mode
       because each modifiable virtual page is assigned a page of
       swap space when it is created.  If you use  the  immediate
       mode  of  swap  space allocation, you must allocate a swap
       space that is at least as large as  the  total  amount  of
       modifiable  virtual  address space that will be created on
       your system.  Immediate mode requires  significantly  more
       swap  space  than deferred mode because it guarantees that
       there will be enough swap space if every  modifiable  virtual
 page is modified.

       If you use the deferred mode of swap space allocation, you
       must estimate the total amount of  virtual  address  space
       that  will  be both created and modified, and compare that
       total amount with the size of your system's physical  memory.
   If  this  total  amount is greater than the size of
       physical memory, the swap space must be  large  enough  to
       hold  the modified virtual pages that do not fit into your
       physical memory. If your system's workload is complex  and
       you  are unable to estimate the appropriate amount of swap
       space by using this mode, you should first use the default
       amount  of swap space and adjust the swap space as needed.

       To determine which swap space  allocation  mode  is  being
       used,  check the setting of the vm-swap-eager attribute in
       /etc/sysconfigtab. If this value is either  not  specified
       or  set  to 1, the system uses immediate swap mode.  If it
       is set to 0 (zero), the system uses deferred mode.

NOTES    [Toc]    [Back]

       There is no way to stop paging and swapping  on  a  partition.
   It  is  therefore not possible to use swap devices
       that can be dismounted during system operation.

       Swap space is also used during a system  crash  dump.   In
       planning  your  swap space allocation you should also consider
 your crash dump requirements.  See the System Administration
 manual for information on crash dumps.

ERRORS    [Toc]    [Back]

       special-device  or an overlapping partition is open. Quitting...



              Explanation:

              This message indicates that you tried to add a partition
  as a swap device that is actively in use by
              UFS, AdvFS, swap, or LSM.

              User Action:

              Specify a different swap device.  special-device is
              marked  in use for fstype in the disklabel.  If you
              continue  with  the  operation  you  can   possibly
              destroy existing data. CONTINUE? [y/n]

              Explanation:

              This message indicates that you tried to use a partition
 as a swap device that is  not  currently  in
              active  use  but  is  marked  for  use  in the disk
              label's partition map.  For example, the  partition
              may be part of an LSM volume or an AdvFS domain.

              User Action:

              Specify  a  different  swap  device or override the
              warning.

              If you know that the  partition  you  specified  to
              swapon does not contain any data, you can choose to
              override the warning. In this case, the  fstype  in
              the disk label will be modified to swap.

              Note  that  you can use the disklabel -s command to
              set the fstype in the disk label to unused for partitions
  that  do  not  contain any valid data. See
              disklabel(8) for  more  information.   Partition(s)
              which  overlap  special-device are marked in use If
              you continue with the operation  you  can  possibly
              destroy existing data. CONTINUE? [y/n]

              Explanation:

              This message indicates that the partition you specified
 is not marked for use, but other, overlapping
              partitions on the disk are marked for use.

              User Action:

              Specify  a  different  swap  device or override the
              warning.

              If you override this warning,  the  fstype  in  the
              disk's  label  will be modified.  The partition you
              specified to swapon will be marked as in use  as  a
              swap  device and all overlapping partitions will be
              marked UNUSED.

EXAMPLES    [Toc]    [Back]

       Entering the swapon comand with no parameters displays the
       following  help  message: # swapon usage: swapon [-avpsdF]
       [-D device] [-l size] [-h  size]  filename  The  following
       example  shows a swap device entry in an /etc/sysconfigtab
       file:

              vm:
                  swapdevice=/dev/disk/dsk0b,/dev/disk/dsk1b  The
              following  example  adds  the /dev/disk/dsk0b block
              device file as swap space: # swapon /dev/disk/dsk0b
              The following example tries to add a partition that
              is  marked  for   use   as   a   swap   device:   #
              /usr/sbin/swapon /dev/disk/dsk11g

              /dev/disk/dsk11g  disk is marked in use for LSMpubl
              in the disklabel.  If you continue with the  operation
  you can possibly destroy existing data.  CONTINUE?
 [y/n]

              Partition g of disk dsk11 is part of a disk  marked
              for  use  by LSM. If LSM is not actively using this
              partition and the partition does  not  contain  any
              data,  you  may  want  to override this warning, by
              answering y.  In this case,  partition  g  will  be
              marked  as  swap  in the disk label.  The following
              example tries to add a partition as a  swap  device
              whose  overlapping partitions are marked for use: #
              /usr/sbin/swapon /dev/disk/dsk11c

              Partition(s)  which  overlap  /dev/disk/dsk11c  are
              marked  in use.  If you continue with the operation
              you can possibly destroy existing data.   CONTINUE?
              [y/n]

              If  you  answer yes, partition c on disk dsk11 will
              be marked swap in the disk label and all partitions
              that  overlap c will be marked UNUSED.  The following
 example tries to add a partition that  is  currently
  in use as a swap device: # /usr/sbin/swapon
              /dev/disk/dsk11g

              /dev/disk/dsk11g or  an  overlapping  partition  is
              open.   Quitting...  The following example tries to
              add a partition that does not have a disk label  as
              a swap device: # /usr/sbin/swapon /dev/disk/dsk11c

              The  disklabel  for /dev/disk/dsk11c does not exist
              or is corrupted.  Quitting...

              See disklabel(8) for information  on  installing  a
              disk label on a disk.

FILES    [Toc]    [Back]

       Specifies  the  command path.  Specifies information about
       file systems and swap devices.

SEE ALSO    [Toc]    [Back]

      
      
       Commands: dop(8), savecore(8)

       Functions: swapon(2)

       Others: sys_attrs(5), sys_attrs_vm(5)

       System Administration

       Logical Storage Manager

       Security



                                                        swapon(8)
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