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System Administration Guide: Devices and File Systems
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Monitoring Swap Resources

The /usr/sbin/swap command is used to manage swap areas. Two options, -l and -s, display information about swap resources.

Use the swap -l command to identify a system's swap areas. Activated swap devices or files are listed under the swapfile column.

# swap -l
swapfile             dev  swaplo blocks   free
/dev/dsk/c0t0d0s1   136,1      16 1638608 1600528

Use the swap -s command to monitor swap resources.

# swap -s
total: 57416k bytes allocated + 10480k reserved = 67896k used, 
833128k available

The used value plus the available value equals the total swap space on the system, which includes a portion of physical memory and swap devices (or files).

You can use the amount of available and used swap space (in the swap -s output) as a way to monitor swap space usage over time. If a system's performance is good, use swap -s to determine how much swap space is available. When the performance of a system slows down, check the amount of available swap space to determine if it has decreased. Then you can identify what changes to the system might have caused swap space usage to increase.

When using this command, keep in mind that the amount of physical memory available for swap usage changes dynamically as the kernel and user processes lock down and release physical memory.


Note - The swap -l command displays swap space in 512-byte blocks. The swap -s command displays swap space in 1024-byte blocks. If you add up the blocks from swap -l and convert them to Kbytes, the result is less than used + available (in the swap -s output). The reason is that swap -l does not include physical memory in its calculation of swap space.


The output from the swap -s command is summarized in the following table.

Table 21-1 Output of the swap -s Command

Keyword

Description

bytes allocated

The total amount of swap space in 1024-byte blocks that is currently allocated as backing store (disk-backed swap space).

reserved

The total amount of swap space in 1024-byte blocks that is not currently allocated, but claimed by memory for possible future use.

used

The total amount of swap space in 1024-byte blocks that is either allocated or reserved.

available

The total amount of swap space in 1024-byte blocks that is currently available for future reservation and allocation.

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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire