sbin/swapctl/swapctl.8

.\"	$OpenBSD: swapctl.8,v 1.36 2021/08/24 13:15:07 jmc Exp $
.\"	$NetBSD: swapctl.8,v 1.14 1998/05/22 18:27:52 msaitoh Exp $
.\"
.\" Copyright (c) 1997 Matthew R. Green
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.Dd $Mdocdate: August 24 2021 $
.Dt SWAPCTL 8
.Os
.Sh NAME
.Nm swapctl ,
.Nm swapon
.Nd system swap management tool
.Sh SYNOPSIS
.Nm swapctl
.Fl A
.Op Fl p Ar priority
.Op Fl t Cm blk | noblk
.Nm swapctl
.Fl a
.Op Fl p Ar priority
.Ar path
.Nm swapctl
.Fl c
.Fl p Ar priority
.Ar path
.Nm swapctl
.Fl d
.Ar path
.Nm swapctl
.Op Oo Fl l Oc | Fl s
.Op Fl k
.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
.Ic swapctl -a ,
except if
.Nm swapon
itself is called with
.Fl a ,
in which case
it acts as
.Ic swapctl -A .
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl A
This option causes
.Nm
to read the
.Pa /etc/fstab
file for devices and files with an
.Dq sw
type, and adds all these entries
as swap devices.
If no swap devices are configured,
.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 Ar path
The
.Fl d
option removes the listed
.Ar path
from the kernel's list of swap devices or files.
.It Fl k
The
.Fl k
option uses 1024 byte blocks instead of the default 512 byte.
.It Fl l
The
.Fl l
option lists the current swap devices and files, and their usage statistics.
.It Fl p Ar priority
The
.Fl p
option sets the priority of swap devices or files to the
.Ar priority
argument.
.It Fl s
The
.Fl s
option displays a single line summary of current swap statistics.
.It Fl t Cm blk | noblk
This flag modifies the function of the
.Fl A
option.
The
.Fl t
option allows the type of device to add to be specified.
An argument of
.Cm blk
causes all block devices in
.Pa /etc/fstab
to be added.
An argument of
.Cm 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.
.El
.Sh SWAP OPTIONS
Lines such as the following
specify swap devices in
.Pa /etc/fstab :
.Bd -literal -offset indent
/dev/sd1b none swap sw
d48d0e3fc1c39531.k none swap sw
.Ed
.Pp
The initial swap device (root disk, partition b) need not appear in
.Pa /etc/fstab ,
though it is not an error for it to do so.
.Pp
Additional flags include:
.Pp
.Bl -tag -width nfsmntpt=/path -compact
.It priority=N
Swap devices and files may be assigned different priorities,
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 priority.
.It nfsmntpt=/path
This option is useful for swapping to NFS files.
It specifies the local mount point to mount an NFS filesystem.
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 EXIT STATUS
.Ex -std swapctl
.Sh SEE ALSO
.Xr swapctl 2 ,
.Xr vnd 4 ,
.Xr fstab 5 ,
.Xr mount_nfs 8 ,
.Xr mount_vnd 8
.Sh HISTORY
The
.Nm
program was originally developed in
.Nx 1.3 .
It was ported to
.Ox 2.6
by Tobias Weingartner.
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 Mt mrg@eterna.com.au .
.Sh 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
.Xr fsck 8
all local file systems before this can happen.
This process requires substantial amounts of memory on some systems.
If one configures 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.