NetBSD/sbin/swapctl/swapctl.8

.\"	$NetBSD: swapctl.8,v 1.27 2003/12/20 11:22:25 mrg Exp $
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.\" Copyright (c) 1997 Matthew R. Green
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.Dd March 5, 2000
.Dt SWAPCTL 8
.Os
.Sh NAME
.Nm swapctl ,
.Nm swapon
.Nd system swap management tool
.Sh SYNOPSIS
.Nm
.Fl A
.Op Fl p Ar priority
.Op Fl t Ar blk|noblk
.Nm
.Fl D Ar dumpdev
.Nm
.Fl U
.Op Fl t Ar blk|noblk
.Nm
.Fl a
.Op Fl p Ar priority
.Ar path
.Nm
.Fl c
.Fl p Ar priority
.Ar path
.Nm
.Fl d
.Ar path
.Nm
.Fl l | Fl s
.Op Fl k
.Op Fl h
.Nm
.Fl z
.Nm swapon
.Fl a | Ar path
.Sh DESCRIPTION
The
.Nm
program adds, removes,
lists and prioritizes swap devices and files for the system.
The
.Nm swapon
program acts the same as the
.Nm
program, as if called with the
.Fl a
option, except if
.Nm swapon
itself is called with
.Fl a
in which case,
.Nm swapon
acts as
.Nm
with the
.Fl A
option.
.Pp
The following options are available:
.Bl -tag -width 123456
.It Fl A
This option causes
.Nm
to read the
.Pa /etc/fstab
file for devices and files with a
.Dq sw
and
.Dq dp
type, and adds all these entries
as swap devices, or for a dump device in the case of a
.Dq dp
type.
If no swap devices are configured,
.Nm
will exit with an error code.
.It Fl D
The
.Fl D
option requires that a
.Ar dumpdev
also be in the argument list.
The kernel dump device is set to
.Ar dumpdev .
This changed is made via the
.Xr 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
.Xr savecore 8
at system reboot, and analyzed to determine the problem.
.It Fl U
This option causes
.Nm
to read the
.Pa /etc/fstab
file for devices and files with a
.Dq sw
type, and remove all these entries as swap devices.
If no swap devices are unconfigured,
.Nm
will exit with an error code.
.It Fl a
The
.Fl a
option requires that a
.Ar path
also be in the argument list.
The
.Ar path
is added to the kernel's list of swap devices using the
.Xr swapctl 2
system call.
When using the
.Nm swapon
form of this command, the
.Fl a
option is treated the same as the
.Fl A
option, for backwards compatibility.
.It Fl c
The
.Fl c
option changes the priority of the listed swap device or file.
.It Fl d
The
.Fl d
option removes the listed
.Ar path
from the kernel's list of swap devices or files.
.It Fl l
The
.Fl l
option lists the current swap devices and files, and their usage statistics.
.It Fl s
The
.Fl s
option displays a single line summary of current swap statistics.
.It Fl p
The
.Fl p
option sets the priority of swap devices or files to the
.Ar priority
argument.
This works with the
.\" .Fl d ,
.Fl a ,
.Fl c ,
and
.Fl l
options.
.It Fl k
The
.Fl k
option uses 1024 byte blocks instead of the default 512 byte.
.It Fl h
The
.Fl h
option uses
.Xr humanize_number 3
to display the sizes.
.It Fl t
This flag modifies the function of the
.Fl A
and
.Fl U
options.
The
.Fl t
option allows the type of device to add to be specified.
An argument of
.Ar blk
causes all block devices in
.Pa /etc/fstab
to be added.
An argument of
.Ar noblk
causes all non-block devices in
.Pa /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.
.It Fl z
The
.Fl z
option displays the current dump device.
.El
.Sh SWAP PRIORITY
The
.Nx
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.
.Sh SWAP OPTIONS
When parsing the
.Pa /etc/fstab
file for swap devices, the following options are recognized:
.Pp
.Bl -tag -width nfsmntpt=/path -compact
.It priority=N
This option sets the priority of the specified swap device to N.
.It 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:
.Bd -literal
server:/export/swap/client none swap sw,nfsmntpt=/swap
.Ed
.El
.Sh SEE ALSO
.Xr swapctl 2 ,
.Xr fstab 5 ,
.Xr mount_nfs 8
.Sh HISTORY
The
.Nm
program was first made available in
.Nx 1.3 .
The original
.Nm swapon
program, provided for backwards compatibility, appeared in
.Bx 4.0 .
.Sh AUTHORS
The
.Nm
program was written by
.An Matthew R. Green Aq mrg@eterna.com.au .
.Sh BUGS
If no swap information is specified in
.Pa /etc/fstab ,
the system startup scripts (see
.Xr rc 8 )
will configure no swap space and your machine will behave very badly
if (more likely when) it runs out of real memory.
.Pp
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
.Xr 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
.Xr fsck 8
and may run out of real memory, causing fsck to abnormally exit and
startup scripts to fail.