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

NAME
     swapctl, swapon - system swap management tool

SYNOPSIS
     swapctl -A [-p priority] [-t blk|noblk]
     swapctl -a [-p priority] path
     swapctl -c -p priority path
     swapctl -d path
     swapctl -l | -s [-k]
     swapon -a | path

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

     Note: The initial swap device (root disk, partition b) is handled auto-
     matically by the kernel and does not need to be added to /etc/fstab or
     added via swapctl.  It will show up as "swap_device" in the output dis-
     played with the -l flag.

     The options are as follows:

     -A      This option causes swapctl to read the /etc/fstab file for de-
             vices and files with an ``sw'' type, and adds all these entries
             as swap devices.  If no swap devices are configured, swapctl will
             exit with an error code.

     -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 com-
             mand, the -a option is treated the same as the -A option, for
             backwards compatibility.

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

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

     -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.

     -p priority
             The -p option sets the priority of swap devices or files to the
             priority argument.

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

     -t blk|noblk
             This flag modifies the function of the -A option.  The -t option
             allows the type of device to add to be specified.  An argument of
             blk causes all block devices in /etc/fstab to be added.  An argu-
             ment of noblk causes all non-block devices in /etc/fstab to be
             added.  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.

     The swapctl utility exits 0 on success, and >0 if an error occurs.

SWAP OPTIONS
     When parsing the /etc/fstab file for swap devices, lines such as the fol-
     lowing specify additional swap devices:

           /dev/sd1b none swap sw 0 0

     Additional flags include:

     priority=N      Swap devices and files may be assigned different priori-
                     ties, to allow 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 pri-
                     ority.
     nfsmntpt=/path  This option is useful for swapping to NFS files.  It
                     specifies the local mount point to mount an NFS filesys-
                     tem.  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

SEE ALSO
     swapctl(2), vnd(4), fstab(5), mount_nfs(8), mount_vnd(8)

HISTORY
     The swapctl program was originally developed in NetBSD 1.3.  It was port-
     ed to OpenBSD 2.6 by Tobias Weingartner.  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>.

BUGS
     Local and remote swap files cannot be configured until 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 one config-
     ures 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.

OpenBSD 4.7                      July 17, 2007                               2
