SWAPCTL(8) FreeBSD 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.
The options are as follows:
-A This option causes swapctl to read the /etc/fstab file for
devices 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
command, 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
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 available,
such as during disk checks of large file systems.
SWAP OPTIONS
Lines such as the following specify swap devices in /etc/fstab:
/dev/sd1b none swap sw
d48d0e3fc1c39531.k none swap sw
The initial swap device (root disk, partition b) need not appear in
/etc/fstab, though it is not an error for it to do so.
Additional flags include:
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.
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 mount point. For example:
server:/export/swap/client none swap sw,nfsmntpt=/swap
EXIT STATUS
The swapctl utility exits 0 on success, and >0 if an error occurs.
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
ported 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 <
[email protected]>.
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
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 fsck(8) and may run out of real memory,
causing fsck to abnormally exit and startup scripts to fail.
FreeBSD 14.1-RELEASE-p8 July 9, 2024 FreeBSD 14.1-RELEASE-p8