swapon(8)						      System Manager's Manual							 swapon(8)

NAME

       swapon - Specifies additional disk partitions for paging and swapping

SYNOPSIS

       /sbin/swapon [-asv] [-s special-device] [-v special-device]

DESCRIPTION

       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 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 flags can override the partition specifications in the /etc/sysconfigtab file.

       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 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  cre-
       ated  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 parameter in /etc/sysconfigtab.  If	it
       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.

FLAGS

       Installs  all  paging  partitions specified in the /etc/sysconfigtab file.  Displays swap space utilization.  For each swap partition, this
       flag displays the total amount of allocated swap space, the amount of swap space that is being used, and the amount  of	free  swap  space.
       Generates verbose output.

NOTES

       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 for information on crash dumps.

EXAMPLES

       The following example shows a swap device entry in an /etc/sysconfigtab file: vm:
	   swapdevice=/dev/disk/dsk0b,/dev/disk/dsk1b

       The following command adds the /dev/disk/dsk0b block device file as swap space: swapon /dev/disk/dsk0b

ERRORS

       You may receive the following messages when using the swapon command: special-device or an overlapping partition is open.  Quitting...

	      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.  spe-
	      cial-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]

	      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.

	      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]

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

       The  following  examples  illustrate  these  messages:  Adding  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.	 Adding  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.  Adding 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...  Adding 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

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

RELATED INFORMATION

       Functions:  swapon(2), savecore(8)

       System Administration delim off

																	 swapon(8)