swap(1M)

Synopsis

Description

Command options

-a

This option can only be used by a privileged user.

Add the specified swap area. swapname is the name of the block special partition, for example, /dev/dsk/*, where the value of * is machine dependent, or a regular file. swaplow is the offset in 512-byte blocks into the partition where the swap area should begin.

swaplow gives the starting offset of the portion of the file to be used as swap (in 512 byte block units).

swaplen gives the length of the file to be used as swap (in 512 byte block units). The maximum allowable swaplen is 8388608 512-byte blocks, or 4GB (4 gigabytes).

If both swaplow and swaplen are omitted, then the entire device or file is used for swap space. If a single number is specified on the command line, then it is taken to mean swaplen. In this case swaplow defaults to 0 (the beginning of the file). If two numbers are specified on the command line, then the first is used as swaplow and the second is used as swaplen.

The actual area used by the operating system may be slightly smaller due to filesystem page-size rounding.

-c

This option can only be used by a privileged user.

Configure the swap area by adding all the devices and files listed in filename as swap devices. If no filename option is given, /etc/swaptab is used as the input file.

-d

This option can only be used by a privileged user.

Delete the specified swap area. swapname is the name of block special partition, for example, /dev/dsk/*, where the value of * is machine dependent, or a regular file.

swaplow is the offset in 512-byte blocks into the partition specifying the beginning of the swap area to be deleted. If swaplow is omitted, an offset of zero is assumed. While the delete operation is in process, the swap area is marked as ``INDEL'' (in the process of being deleted). A concurrently executed swap -l command could observe the INDEL state and report it at the end of the line listing the swap area. The system will not allocate any new blocks from the area, and will try to free swap blocks from it. The area will remain in use until all blocks from it are freed. When the swap command completes, the deletion is also complete.

-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 special device; zeros 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 free 512-byte blocks in the area. This number does not include physical memory allocated to swapping. If the swap area is being deleted, the word INDEL will be printed to the right of this number.

-s

Print the following information about total swap space usage:

allocated

The amount of swap space (in 512-byte blocks) allocated to private pages.

reserved

The amount of swap space (in 512-bytes blocks) not currently allocated, but claimed by memory mappings that have not yet created private pages, or have created them but have not swapped them out.

used

The total amount of swap space, in 512-byte blocks, that is either allocated or reserved.

available

The total swap space, in 512-byte blocks, that is currently available for future reservation and allocation. This number includes physical swap memory that is available (that is, the total swap memory less the amount currently in use).

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NOTE: The sum of used and available will be larger than the sum of the swap slices because main memory may be used as effective swap space.

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Usage

   #swapname               offset(in blocks)       size(in blocks)
   /dev/swap               0                       -
   /dev/dsk/c0b0t1d0s2     0                       -
   /dev/dsk/c0b0t2d0s2     0                       -
   /dev/dsk/c0b0t3d0s2     0                       -
   /dev/dsk/c0b0t4d0s2     0                       -
   /dev/dsk/c0b0t5d0s3     0                       -
   /dev/dsk/c0b0t6d0s2     0                       -

For good performance, construct the swap space out of disk slices rather than files. When multiple disk slices are used, they should be equal in size, and placed on separate disks. See disksetup(1M) for information on configuring disk slices. Should you wish to change the slice structure on a disk following setup, you can use prtvtoc(1M) and edvtoc(1M).

If you have licensed the VERITAS advanced Volume Manager product, an alternative to using many slices for swap might be to use a Volume Manager based ``volume''. For example:

   #swapname               offset(in blocks)       size(in blocks)
   /dev/vx/dsk/swapvol                63,1       0 881280 811128

It may not always be possible to find an extra slice to solve a swap problem. In that case, a file can be used. To use a regular file as swap space, you need to create a file as big as the intended swap space. It is not enough to simply create a zero-length file; it must be as large as the intended swap space.

To do this, you can use the dd(1M) command, as shown in the following example (which creates 1GB of swap space):

   dd if=/dev/null of=/swapfile oseek=1024 bs=1024k

Then add the following line to /etc/swaptab:

   /swapfile 0 -

Then issue this command:

   swap -c

The system will use the new swap file following the next reboot, because swap -c is run from /etc/inittab at system start time.

Examples

Diagnostics

   SC_REMOVE failed

References

Notices

No check is done to see if a swap area being added overlaps with an existing filesystem.

Files in general are not recommended for use as swap storage (disk slices or Volume Manager volumes are preferred). Should use of a file be needed, disk based file systems are preferred over NFS. Failure to follow these recommendations can result in poor performance or system instability.