swapctl,
swapon —
system swap management tool
swapctl |
-A
[-p
priority
]
[-t
blk |
noblk
] |
swapctl |
-a
[-p
priority
]
path |
swapctl |
-c
-p
priority
path |
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.
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 point mount. For example:
server:/export/swap/client none swap sw,nfsmntpt=/swap
The
swapctl utility exits 0 on
success, and >0 if an error occurs.
swapctl(2),
vnd(4),
fstab(5),
mount_nfs(8),
mount_vnd(8)
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.
The
swapctl program was written by
Matthew R. Green
<
mrg@eterna.com.au>.
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.
![[OpenBSD]](/openbsd.gif){kind=small}