swapctl(8) - NetBSD Manual Pages

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


NAME

     swapctl, swapon - system swap management tool


SYNOPSIS

     swapctl -A [-p priority] [-t blk|noblk]
     swapctl -D dumpdev
     swapctl -U [-t blk|noblk]
     swapctl -a [-p priority] path
     swapctl -c -p priority path
     swapctl -d path
     swapctl -l | -s [-k]
     swapctl -z
     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 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 de-
             vices and files with a ``sw'' and ``dp'' type, and adds all these
             entries as swap devices, or for a dump device in the case of a
             ``dp'' type.  If no swap devices are configured, swapctl will ex-
             it with an error code.

     -D      The -D option requires that a dumpdev also be in the argument
             list.  The kernel dump device is set to dumpdev.  This changed is
             made via the swapctl(2) system call.  The dump device is used
             when the system crashes to write a current snapshot of real memo-
             ry, to be saved later with savecore(8) at system reboot, and ana-
             lyzed to determine the problem.

     -U      This option causes swapctl to read the /etc/fstab file for de-
             vices 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.

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

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

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

     -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.

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

     -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 ar-
             gument 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.  This option is useful in early system startup,
             where swapping may be needed before all file systems are avail-
             able, such as during disk checks of large file systems.

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


SWAP PRIORITY

     The NetBSD swap system allows different swap devices and files to be as-
     signed different priorities, to allow the faster resources to be used
     first.  Swap devices at the same priority are used in a round-robin fash-
     ion until there is no more space available at this priority, when the
     next priority level will be used.  The default priority is 0, the high-
     est.  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 de-
                     vice to N.
     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), 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>.


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 memo-
     ry, causing fsck to abnormally exit and startup scripts to fail.

NetBSD 1.6.1                     March 5, 2000                               2