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swapon(1M)							    swapon(1M)

NAME
       swapon - enable device or file system for paging

SYNOPSIS
   Form 1: Enable all defined swap areas
       type]...

   Form 2: Enable paging on specified block devices (for the current boot)
       priority] device ...

   Form 3: Define the primary paging device (for subsequent boots)
       start] length] device

   Form	 4: Unconfigure a previously set primary paging device (for subsequent
       boots)
       device

   Form 5: Enable file system swap (preferred form)
       min] limit] reserve] priority] directory ...

   Form 6: Enable file system swap (obsolescent form)
       directory [min limit reserve priority]

DESCRIPTION
       The command enables devices or file systems on which paging is to  take
       place.	command	 also  configures primary paging device for next boot.
       (NOTE: the term `swap' refers to an obsolete implementation of  virtual
       memory;	HP-UX  actually	 implements  virtual  memory  by way of paging
       rather than swapping.  This command and	others	retain	names  derived
       from `swap' for historical reasons.)

       By  enabling  a	device for paging, the device can be accessed directly
       (without going through the file system) during paging activity.	When a
       file system is enabled for paging, the device(s) on which the file sys‐
       tem resides are accessed indirectly through the file system.  There are
       advantages  and disadvantages to both type of paging.  Keep the follow‐
       ing tradeoffs in mind when enabling devices or file systems for paging.

       Paging directly to a device  is	significantly  faster  than  doing  so
       through	the  file  system.   However,  the space on the device that is
       allocated to paging cannot be used for anything else, even if it is not
       being actively used for paging.

       Paging  through	a file system, while slower, provides a more efficient
       use of the space on the device.	Space that is not being used for  pag‐
       ing  in this case can be used by the file system.  Paging across a net‐
       work to a remote machine is always file system paging.

       The system begins by paging on only a single device so  that  only  one
       disk  is	 required  at  bootstrap time.	Calls to normally occur in the
       system startup script making all paging space  available	 so  that  the
       paging activity is interleaved across several disks.

       Normally, the option is given (see Form 1 of causing all devices marked
       as and all file systems marked as in the file to be made	 available  to
       the paging system.  By using the fields in (special_file_name or direc‐
       tory; see fstab(4)), the system determines which block device  or  file
       system  to  use.	  The  special_file_name specified for each entry must
       specify a block special file.  The directory specified for  each	 entry
       must specify a directory within the file system to be enabled.

       In  Form	 2,  the  option enables specific block devices to be used for
       paging for the current boot.  The device arguments must	specify	 block
       special files.  If more than one device is given, any options specified
       will be applied to all devices.

       In Form 3, the option configures the block device to  be	 used  as  the
       primary paging area for subsequent boots.

       In  either  Form	 2 or Form 3, if a file system exists on the specified
       block device and neither an nor option is specified, fails and an error
       message is given.  This prevents a file system from being inadvertently
       destroyed.  To request paging in the space between the end of the  file
       system  and the end of the device, use To force paging to a device con‐
       taining a file system (destroying the file system), the option  can  be
       used.  Use with extreme caution!

       In  either  Form	 2  or Form 3, an attempt to enable paging to a device
       will fail and a warning message will be issued if determines  that  the
       device is being used by the command to retrieve system dump information
       (see savecrash(1M)).  The option can be used to forcibly enable	paging
       to  devices being used by the command; however, this may overwrite sys‐
       tem dump information contained on the device.

       In Form 4, the option unconfigures the block device that was previously
       defined as the primary paging area for subsequent boots (see option).

       The  last  two  forms  of provide methods for enabling file systems for
       paging.	Form 5 is the preferred method.	 Form  6  is  obsolescent  and
       provided	 only for backward compatibility.  The directory name in these
       forms specifies a directory on the file system that is  to  be  enabled
       for  paging.  A directory named is created at the root of the specified
       file system (unless the file system's name ends with All	 paging	 files
       are created within this directory.  The optional arguments to the sixth
       form have the same meaning as the arguments to the options in  Form  5.
       Note  that,  in Form 6, if any of the optional arguments are specified,
       all must be specified.  In Form 5, if more than one directory is given,
       any options specified will be applied to all directories.

       After a file system has been enabled for paging, the optional arguments
       can be modified by subsequent commands.

   Options
       recognizes the following options and arguments:

	      Cause all devices marked as
			     and all file systems marked as in the file to  be
			     made available to the paging system.  The options
			     field in entries is read by and must contain ele‐
			     ments formatted as follows:

			     See the	    option for the value of min.

			     See the	    option  for	 the  value  of limit.
					    (File system paging areas only.)

			     See the	    option for the value  of  reserve.
					    (File system paging areas only.)

			     See the	    option  for the value of priority.
					    (File system paging areas only.)

			     See the	    option for	the  meaning  of  this
					    option.    (Device	 paging	 areas
					    only.)

			     See fstab(4) for an example entry.

	      Use space after the end of the file system on the block device
			     for paging.  An error message is returned	if  no
			     file  system is found on the device.  This option
			     cannot be used with the option.  Do  not  confuse
			     this  with	 paging to a file system.  This option
			     is for use with a disk that has both a file  sys‐
			     tem and dedicated paging space on it.

	      Force the	     device to be enabled, which will destroy the file
			     system on it.  Use with  extreme  caution.	  Nor‐
			     mally,  if	 a file system exists on the device to
			     be enabled, fails and displays an error  message.
			     This option cannot be used with the option.

	      limit	     specifies	the maximum space the paging system is
			     allowed to take from the disk, provided space  is
			     available	that is not reserved for exclusive use
			     by the  file  system.   The  value	 of  limit  is
			     rounded up so that it is a multiple of the paging
			     allocation chunk size, which is set with the ker‐
			     nel    tunable    parameter    (see   swchunk(5),
			     kctune(1M), and swapinfo(1M)).  See  The  default
			     value  for	 limit	is  0,	indicating there is no
			     limit to the amount of file system space the pag‐
			     ing system can use.

			     limit  can	 be  specified in decimal (no prefix),
			     octal prefix), or hexadecimal prefix).  It may be
			     specified	 in   units   of   kilobytes  suffix),
			     megabytes suffix), or file system blocks (no suf‐
			     fix).   (A	 kilobyte is 1024 bytes; a megabyte is
			     1024 kilobytes; the size of a file	 system	 block
			     is	 determined by the administrator when the file
			     system is created.)

	      When configuring the primary paging device for next boot,
			     length specifies the  maximum  number  of	blocks
			     that  will	 be  used for paging.  The default for
			     length is to  the	end-of-device.	 can  only  be
			     specified	when  defining	primary swap space for
			     subsequent boots; therefore, must be used in con‐
			     junction with the option.

	      min	     indicates	the  space the paging system will ini‐
			     tially take from the file system.	The  value  of
			     min is rounded up so that it is a multiple of the
			     paging allocation chunk size, which is  set  with
			     the  kernel  tunable  parameter  (see swchunk(5),
			     kctune(1M), and swapinfo(1M)).  The default value
			     for min is 0, indicating no paging space is to be
			     allocated initially.  min can be specified in the
			     same forms as limit, above.

	      priority	     indicates	the order in which space is taken from
			     the file systems and  devices  used  for  paging.
			     Space is taken from the systems with lower prior‐
			     ity numbers  first.   Under  most	circumstances,
			     space  is	taken  from device paging areas before
			     file system paging areas, regardless of priority.
			     See  "Paging Allocation" in swapinfo(1M) for more
			     information.  priority can have a value from 0 to
			     10 and has a default value of 1.

	      reserve	     specifies	the  space,  in	 addition to the space
			     currently occupied by the file  system,  that  is
			     reserved  for  file  system  use  only, making it
			     unavailable to the paging system.	This  reserved
			     space  is	in  addition to the minimum free space
			     specified by the administrator when the file sys‐
			     tem  was  created.	  See  The  default  value for
			     reserve is 0 indicating that no file system space
			     is	 reserved  for	file system use only.  reserve
			     can be specified in  the  same  forms  as	limit,
			     above.

	      Unconfigure the primary paging device that was previously set
			     (with  the option) as the primary paging area for
			     subsequent boots.

	      Configure the primary paging device for the next
			     and subsequent boots.  See also the and options.

	      When configuring the primary paging device for subsequent boots,
			     start specifies the block address on  the	device
			     where  the	 paging	 area will begin.  The default
			     value for start is 0 indicating that  the	device
			     is	 dedicated  to	paging.	  A starting block can
			     only be  specified	 when  defining	 primary  swap
			     space  for	 subsequent  boots; therefore, must be
			     used in conjunction with the option.

	      Restrict the type of the paging area.
			     If the option is omitted, all of the paging areas
			     defined in are made available.  type can have one
			     of the following values:

			     Device paging areas.

			     File system paging areas.

			     Paging areas defined on the local system.

			     Paging areas defined on remote systems.

	      Unlock block device files which are being used by the
			     command.  Normally, will not enable paging	 on  a
			     device if it is being used by command to retrieve
			     system dump information.  The list of devices  in
			     use  is maintained in the file This option forces
			     the device to be enabled, which may overwrite any
			     system  dump information contained on the device.
			     This option should be used with extreme caution.

RETURN VALUE
       returns one of the following values:

	      Successful completion.
	      An error condition occurred.

EXAMPLES
       The first two examples enable paging to the file system containing  the
       directory.   The	 maximum number of file system blocks available to the
       paging system is set to 5000, the number of file system blocks reserved
       for file system use only is set to 10000, and the priority is set to 2.
       The number of file system blocks initially taken by the	paging	system
       defaults to 0 in the first example, and is set to 0 in the second exam‐
       ple.  On a file system with the default 8kB block size, these  examples
       allocate approximately 40MB of file system paging.

       This  example enables paging to two block devices and sets the priority
       of both devices to 0.

       This example enables paging to a block device, using  the  space	 after
       the  end of the file system for paging and letting the priority default
       to 1.

       This example enables paging to a block device, forcing paging even if a
       file system exists on the device.

       This example defines the primary paging device for the next boot, using
       the space after the end of the file system to the end of the device for
       paging.

       This example defines the primary paging device for the next boot, using
       8192Kb of the device for paging, starting 1024Kb from the start of  the
       device.

WARNINGS
       On systems running VxVM 3.5, the swap volumes to be configured for sys‐
       tem crash dumps should be created with the usage	 type  as  during  the
       creation	 of the swap volume.  Not doing so will cause dump corruption.
       You could use the option of vxassist(1M) to do the same.

       Once file system blocks have been allocated for paging space, the  file
       system cannot be unmounted unless the system is rebooted.

       If any paging area becomes unavailable while the system is running, for
       example if a network failure occurs while paging to  a  remote  system,
       the system will immediately halt.

       The  file system block size used by the and options varies between file
       systems, and is defined by the system administrator  at	the  time  the
       file system is created.	The command can be used to determine the block
       size for a particular file system (see dumpfs(1M)).

       When using the and options, the reserve space specified by  the	option
       takes precedence over the option.  Thus, if:

	      D		= Total disk space available to ordinary users
	      R		= Reserve space specified by the option
	      limit	= Paging space limit specified by the option
	      L		= Space currently available to the paging system
	      F		= Space currently occupied by the file system

       the following relationships hold:

	      F + R + limit < D	  In normal operation

	      L = 0		  If F + R >= D

	      0 <= L <= limit	  If F + R + limit >= D

FILES
       Normal paging devices
       File system table
       List of devices being used by	  command

AUTHOR
       was developed by HP and the University of California, Berkeley.

SEE ALSO
       kctune(1M),   savecrash(1M),  swapinfo(1M),  vxassist(1M),  swapctl(2),
       swapon(2), fstab(4), swchunk(5).

								    swapon(1M)
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