SWAP(1M)SWAP(1M)NAMEswap - swap administrative interface
SYNOPSIS
/usr/sbin/swap -a swapname [swaplow] [swaplen]
/usr/sbin/swap -d swapname [swaplow]
/usr/sbin/swap -l [-h | -k]
/usr/sbin/swap -s [-h]
DESCRIPTION
The swap utility provides a method of adding, deleting, and monitoring
the system swap areas used by the memory manager.
OPTIONS
The following options are supported:
-a swapname [swaplow] [swaplen]
Add the specified swap area. This option can only be used by the
superuser or by one who has assumed the Primary Administrator role.
swapname is the name of the swap area or regular file. For example,
on system running a UFS root file system, specify a slice, such as
/dev/dsk/c0t0d0s1, or a regular file for a swap area. On a system
running a ZFS file system, specify a ZFS volume, such as
/dev/zvol/dsk/rpool/swap, for a swap area. Using a regular file for
swap is not supported on a ZFS file system. In addition, you cannot
use the same ZFS volume for both the swap area and a dump device
when the system is running a ZFS root file system.
swaplow is the offset in 512-byte blocks into the file where the
swap area should begin. swaplen is the desired length of the swap
area in 512-byte blocks. The value of swaplen can not be less than
16. For example, if n blocks are specified, then (n-1) blocks would
be the actual swap length. swaplen must be at least one page in
length. The size of a page of memory can be determined by using the
pagesize command. See pagesize(1). Since the first page of a swap
file is automatically skipped, and a swap file needs to be at least
one page in length, the minimum size should be a multiple of 2
pagesize bytes. The size of a page of memory is machine-dependent.
swaplow + swaplen must be less than or equal to the size of the
swap file. If swaplen is not specified, an area will be added
starting at swaplow and extending to the end of the designated
file. If neither swaplow nor swaplen are specified, the whole file
will be used except for the first page. Swap areas are normally
added automatically during system startup by the /sbin/swapadd
script. This script adds all swap areas which have been specified
in the /etc/vfstab file; for the syntax of these specifications,
see vfstab(4).
To use an NFS or local file system swapname, you should first cre‐
ate a file using mkfile(1M). A local file system swap file can now
be added to the running system by just running the swap-a command.
For NFS mounted swap files, the server needs to export the file. Do
this by performing the following steps:
1. Add the following line to /etc/dfs/dfstab:
share -F nfs -o \
rw=clientname,root=clientname path-to-swap-file
2. Run shareall(1M).
3. Have the client add the following line to /etc/vfstab:
server:path-to-swap-file - local-path-to-swap-file nfs \
--- local-path-to-swap-file --swap---
4. Have the client run mount:
# mount local-path-to-swap-file
5. The client can then run swap-a to add the swap space:
# swap-a local-path-to-swap-file
-d swapname
Delete the specified swap area. This option can only be used by the
super-user. swapname is the name of the swap file: for example,
/dev/dsk/c0t0d0s1 or a regular file. swaplow is the offset in
512-byte blocks into the swap area to be deleted. If swaplow is not
specified, the area will be deleted starting at the second page.
When the command completes, swap blocks can no longer be allocated
from this area and all swap blocks previously in use in this swap
area have been moved to other swap areas.
-h
All sizes are scaled to a human readable format. Scaling is done by
repetitively dividing by 1024.
-k
Write the files sizes in units of 1024 bytes.
-l
List the status of all the swap areas. The output has five columns:
path
The path name for the swap area.
dev
The major/minor device number in decimal if it is a block spe‐
cial device; zeroes otherwise.
swaplo
The swaplow value for the area in 512-byte blocks.
blocks
The swaplen value for the area in 512-byte blocks.
free
The number of 512-byte blocks in this area that are not cur‐
rently allocated.
The list does not include swap space in the form of physical memory
because this space is not associated with a particular swap area.
If swap-l is run while swapname is in the process of being deleted
(by swap-d), the string INDEL will appear in a sixth column of the
swap stats.
-s
Print summary information about total swap space usage and avail‐
ability:
allocated
The total amount of swap space in bytes currently allocated for
use as backing store.
reserved
The total amount of swap space in bytes not currently allo‐
cated, but claimed by memory mappings for possible future use.
used
The total amount of swap space in bytes that is either allo‐
cated or reserved.
available
The total swap space in bytes that is currently available for
future reservation and allocation.
These numbers include swap space from all configured swap areas as
listed by the -l option, as well swap space in the form of physical
memory.
USAGE
On the 32-bit operating system, only the first 2 Gbytes -1 are used for
swap devices greater than or equal to 2 Gbytes in size. On the 64-bit
operating system, a block device larger than 2 Gbytes can be fully uti‐
lized for swap up to 2^63 −1 bytes.
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables
that affect the execution of swap: LC_CTYPE and LC_MESSAGE.
SEE ALSOpagesize(1), mkfile(1M), shareall(1M), getpagesize(3C), vfstab(4),
attributes(5), largefile(5)NOTES
For information about setting up a swap area with ZFS, see the ZFS
Administration Guide.
WARNINGS
No check is done to determine if a swap area being added overlaps with
an existing file system.
Apr 11, 2008 SWAP(1M)
