SWAPCTL(8)						    BSD System Manager's Manual 						SWAPCTL(8)

NAME

     swapctl, swapon -- system swap management tool

SYNOPSIS

     swapctl -A [-f | -o] [-n] [-p priority] [-t blk|noblk|auto]
     swapctl -D dumpdev|none
     swapctl -U [-n] [-t blk|noblk|auto]
     swapctl -a [-p priority] path
     swapctl -c -p priority path
     swapctl -d path
     swapctl -l | -s [-k | -m | -g | -h]
     swapctl -q
     swapctl -z
     swapon -a [-t blk|noblk]
     swapon path

DESCRIPTION

     The swapctl program adds, removes, lists, and prioritizes swap devices and files for the system.  The swapon program acts the same as the
     swapctl program as if called with the -a option, except if swapon itself is called with -a in which case swapon acts as swapctl with the -A
     option.

     The following options are available:

     -A      This option causes swapctl to read the /etc/fstab file for devices and files with a ``sw'' or ``dp'' type, and adds all ``sw'' type
	     entries as swap devices and sets the last ``dp'' type entry as the dump device.  If no swap devices are configured, swapctl will exit
	     with an error code.  If used together with -t auto this option will not read /etc/fstab but query the kernel for all swap partitions
	     on local hard disks.

     -a      The -a option requires that a path also be in the argument list.  The path is added to the kernel's list of swap devices using the
	     swapctl(2) system call.  When using the swapon form of this command, the -a option is treated the same as the -A option, for back-
	     wards compatibility.

     -c      The -c option changes the priority of the listed swap device or file.

     -D      The -D option requires that a dumpdev also be in the argument list.  The kernel dump device is set to dumpdev.  The word ``none'' can
	     be used instead of a dumpdev to disable the currently set dump device.  This change is made via the swapctl(2) system call.  The dump
	     device is used when the system crashes to write a current snapshot of real memory, to be saved later with savecore(8) at system
	     reboot, and analyzed to determine the problem.

     -d      The -d option removes the listed path from the kernel's list of swap devices or files.

     -f      Used in combination with the -A command and -t auto flag this option makes swapctl use the first discovered swap device to also
	     become the dump device.  The -f option is mutually exclusive with the -o option.

     -g      The -g option uses (1024 * 1024 * 1024) byte blocks instead of the default 512 byte.

     -h      The -h option uses humanize_number(3) to display the sizes.

     -k      The -k option uses 1024 byte blocks instead of the default 512 byte.

     -l      The -l option lists the current swap devices and files, and their usage statistics.

     -m      The -m option uses (1024 * 1024) byte blocks instead of the default 512 byte.

     -n      Used with the -A or -U command, the -n option makes swapctl print the action it would take, but not actually change any swap or dump
	     devices.

     -o      Similar to the -f flag, this ``Dump Only'' option makes swapctl find the first swap device and configure it as dump device.  No swap
	     device is changed.  This option needs to be used in combination with -A -t auto and is mutually exclusive with -f.

     -p      The -p option sets the priority of swap devices or files to the priority argument.  This works with the -a, -c, and -l options.

     -q      Query /etc/fstab, checking for any defined swap or dump devices.  If any are found, swapctl returns with an exit status of 0, if none
	     are found the exit status will be 1.

     -s      The -s option displays a single line summary of current swap statistics.

     -t      This flag modifies the function of the -A and -U options.	The -t option allows the type of device to add to be specified.  An argu-
	     ment of blk causes all block devices in /etc/fstab to be added.  An argument of noblk causes all non-block devices in /etc/fstab to
	     be added.	An argument of auto causes all swap partitions on local hard disks to be used.	This option is useful in early system
	     startup, where swapping may be needed before all file systems are available, such as during disk checks of large file systems.

     -U      This option causes swapctl to read the /etc/fstab file for devices and files with a ``sw'' type, and remove all these entries as swap
	     devices.  If no swap devices are unconfigured, swapctl will exit with an error code.  If used together with -t auto this option will
	     not read /etc/fstab but unconfigure all local swap partitions.

     -z      The -z option displays the current dump device.

SWAP PRIORITY

     The NetBSD swap system allows different swap devices and files to be assigned different priorities, to allow the faster resources to be used
     first.  Swap devices at the same priority are used in a round-robin fashion until there is no more space available at this priority, when the
     next priority level will be used.	The default priority is 0, the highest.  This value can be any valid integer, with higher values receiving
     less priority.

SWAP OPTIONS

     When parsing the /etc/fstab file for swap devices, the following options are recognized:

     priority=N      This option sets the priority of the specified swap device to N.
     nfsmntpt=/path  This option is useful for swapping to NFS files.  It specifies the local mount point to mount an NFS filesystem.  The mount
		     point must exist as a directory.  Typically, once this mount has succeeded, the file to be used for swapping on will be
		     available under this point mount.	For example:

		     server:/export/swap/client none swap sw,nfsmntpt=/swap

EXIT STATUS

     If the requested operation was successful, the swapctl utility exits with status 0.  If an error occurred, the exit status is 1.

     The -A and -U operations (add or remove swap devices listed in fstab(5)) return an exit status of 2 to report that no suitable swap devices
     were found.

     The -z operation (query dump device) and -l (list swap partitions) return an exit status of 1 if no dump device or swap partition has been
     configured.  If any swap partition is available or a dump device is set, the respective query returns 0.

SEE ALSO

     swapctl(2), fstab(5), mount_nfs(8)

HISTORY

     The swapctl program was first made available in NetBSD 1.3.  The original swapon program, provided for backwards compatibility, appeared in
     4.0BSD.

AUTHORS

     The swapctl program was written by Matthew R. Green <mrg@eterna.com.au>.

CAVEATS

     Using the automatic swap partition detection done by the -A -t auto option may be dangereous.  Depending on the on-disk partitioning scheme
     used, the type of a partition may not be accurately recognizable as a swap partition.  The autodetection might recognize and use partitions
     on removable media like USB sticks.  An easy way to test the autoconfiguration is to use swapctl with the -n option.

BUGS

     If no swap information is specified in /etc/fstab, the system startup scripts (see rc(8)) will configure no swap space and your machine will
     behave very badly if (more likely when) it runs out of real memory.

     Local and remote swap files cannot be configured until after the file systems they reside on are mounted read/write.  The system startup
     scripts need to fsck(8) all local file systems before this can happen.  This process requires substantial amounts of memory on some systems.
     If you configure no local block swap devices on a machine that has local file systems to check and rely only on swap files, the machine will
     have no swap space at all during system fsck(8) and may run out of real memory, causing fsck to abnormally exit and startup scripts to fail.

BSD
								   June 1, 2011 							       BSD