swapinfo(1M)

NAME

swapinfo — system paging space information

SYNOPSIS

/usr/sbin/swapinfo [-mtadfnrMqws]

DESCRIPTION

swapinfo prints information about device and file system paging space. swapinfo also prints information about primary paging device for next boot.

(Note: the term `swap' refers to an obsolete implementation of virtual memory; HP-UX actually implements virtual memory by way of paging rather than swapping. This command and others retain names derived from `swap' for historical reasons.)

By default, swapinfo prints to standard output a two line header as shown here, followed by one line per paging area:

        Kb      Kb      Kb      PCT     START/  Kb 
TYPE    AVAIL   USED    FREE    USED    LIMIT   RESERVE PRI     NAME 

The fields are:

TYPE

One of:

dev: Paging space residing on a mass storage device, either taking up the entire device or, if the device contains a file system, taking up the space between the end of the file system and the end of the device. This space is exclusively reserved for paging, and even if it is not being used for paging, it cannot be used for any other purpose. Device paging areas typically provide the fastest paging.
fs: Dynamic paging space available from a file system. When this space is needed, the system creates files in the file system and uses them as paging space. File system paging is typically slower than device paging, but allows the space to be used for other things (user files) when not needed for paging.
localfs: File system paging space (see fs above) on a file system residing on a local disk.
network: File system paging space (see fs above) on a file system residing on another machine. This file system would have been mounted on the local machine via NFS.
reserve: Paging space on reserve. This is the amount of paging space that could be needed by processes that are currently running, but that has not yet been allocated from one of the above paging areas. See "Paging Allocation" below.
memory: Memory paging area (also known as pseudo-swap). This is the amount of system memory that can be used to hold pages in the event that all of the above paging areas are used up. See "Paging Allocation" below. This line appears only if memory paging is enabled.

Kb AVAIL

The total available space from the paging area, in blocks of 1024 bytes (rounded to nearest whole block if necessary), including any paging space already in use.

For file system paging areas the value is not necessarily constant. It is the current space allocated for paging (even if not currently used), plus the free blocks available on the file system to ordinary users, minus RESERVE (but never less than zero). AVAIL is never more than LIMIT if LIMIT is non-zero. Since paging space is allocated in large chunks, AVAIL is rounded down to the nearest full allocation chunk.

For the memory paging area this value is also not necessarily constant, because it reflects allocation of memory by the kernel as well as by processes that might need to be paged.

Kb USED

The current number of 1-Kbyte blocks used for paging in the paging area. For the memory paging area, this count also includes memory used for other purposes and thus unavailable for paging.

Kb FREE

The amount of space that can be used for future paging. Usually this is the difference between Kb AVAIL and Kb USED. There could be a difference if some portion of a device paging area is unusable, perhaps because the size of the paging area is not a multiple of the allocation chunk size, or because the tunable parameter swchunk is not set high enough.

PCT USED

The percentage of capacity in use, based on Kb USED divided by Kb AVAIL; 100% if Kb AVAIL is zero.

START/LIMIT

For device paging areas, START is the block address on the mass storage device of the start of the paging area. The value is normally 0 for devices dedicated to paging, or the end of the file system for devices containing both a file system and paging space.

For file system paging areas, LIMIT is the maximum number of 1-Kbyte blocks that will be used for paging, the same as the limit value given to swapon. A file system LIMIT value of none means there is no fixed limit; all space is available except that used for files, less the blocks represented by minfree (see tunefs(1M)) plus RESERVE.

RESERVE

For device paging areas, this value is always ``—''. For file system paging areas, this value is the number of 1-Kbyte blocks reserved for file system use by ordinary users, the same as the reserve value given to swapon.

PRI

The same as the priority value given to swapon. This value indicates the order in which space is taken from the devices and file systems used for paging. Space is taken from areas with lower priority values first. priority can have a value between 0 and 10. See "Paging Allocation" below.

NAME

For device paging areas, the block special file name whose major and minor numbers match the device's ID. The swapinfo command searches the /dev tree to find device names. If no matching block special file is found, swapinfo prints the device ID (major and minor values), for example, 28,0x15000.

For file system swap areas, NAME is the name of a directory on the file system in which the paging files are stored.

When used with -s option, swapinfo also prints to standard output a three line header as shown here, followed by one line for the primary paging area configured for next boot:

             Kb        Kb 
TYPE      START    LENGTH    NAME 

The fields are:

TYPE

swapon(1M) can configure primary paging area for next boot on a storage device only.

dev: The paging space configured for next boot resides on a mass storage device, either taking up the entire device or, if the device contains a file system, taking up the space between the end of the file system and the end of the device.

Kb START

Kb LENGTH

LENGTH is the maximum number of blocks that will be used for paging. This is same as the value given to swapon(1M) when configuring primary paging area for next boot.

NAME

The block special file name whose major and minor numbers match the device's ID. The swapinfo command searches the /dev tree to find device names. If no matching block special file is found, swapinfo prints the device ID (major and minor values), for example, 28,0x15000.

Paging Allocation

Paging areas are enabled at boot time (for device paging areas configured into the kernel) or by the swapon command (see swapon(1M)), often invoked by /sbin/init.d/swap_start during system initialization based on the contents of /etc/fstab. When a paging area is enabled, some portion of that area is allocated for paging space. For device paging areas, the entire device is allocated, less any leftover fraction of an allocation chunk. (The size of an allocation chunk is controlled by the tunable parameter swchunk, and is typically 2 MB.) For file system paging areas, the minimum value given to swapon (rounded up to the nearest allocation chunk) is allocated.

When a process is created, or requests additional space, space is reserved for it by increasing the space shown on the reserve line above. When paging activity actually occurs, space is used in one of the paging areas (the one with the lowest priority number that has free space available, already allocated), and that space will be shown as used in that area.

The sum of the space used in all of the paging areas, plus the amount of space reserved, can never exceed the total amount allocated in all of the paging areas. If a request for more memory occurs which would cause this to happen, the system tries several options:

1.: The system tries to increase the total space available by allocating more space in file system paging areas.
2.: If all file system paging areas are completely allocated and the request is still not satisfied, the system will try to use memory paging as described on the memory line above. (Memory paging is controlled by the tunable parameter swapmem_on, which defaults to 1 (on). If this parameter is turned off, the memory line will not appear.)
3.: If memory paging also cannot satisfy the request, because it is full or turned off, the request is denied.

Several implications of this procedure are noteworthy for understanding the output of swapinfo:

Paging space will not be allocated in a file system paging area (except for the minimum specified when the area is first enabled) until all device paging space has been reserved, even if the file system paging area has a lower priority value.
When paging space is allocated to a file system paging area, that space becomes unavailable for user files, even if there is no paging activity to it.
Requests for more paging space will fail when they cannot be satisfied by reserving device, file system, or memory paging, even if some of the reserved paging space is not yet in use. Thus it is possible for requests for more paging space to be denied when some, or even all, of the paging areas show zero usage — space in those areas is completely reserved.
System available memory is shared between the paging subsystem and kernel memory allocators. Thus, the system may show memory paging usage before all available disk paging space is completely reserved or fully allocated.

Logical Volume Manager (LVM)

The swapinfo command displays swap logical volume if the system was installed with LVM. To modify swap logical volume, refer to the LVM commands and manpages for lvlnboot and lvrmboot. For example, to remove a swap logical volume, run the following LVM command:

lvrmboot -s

Options

swapinfo recognizes the following options:

-s

In addition to printing information about device and file system paging space that are currently in use, swapinfo will also print information about primary paging area configured for next boot using swapon(1M).

If the primary paging area for next boot has not been configured using swapon(1M), swapinfo -s will not be able to display any information. In this case swapinfo -s will display the error message - "Primary swap for next boot was not set using swapctl()"

-m

Display the AVAIL, USED, FREE, START, LIMIT, and RESERVE values in Mbytes instead of Kbytes, rounding off to the nearest whole Mbyte (multiples of 1024²). The output header format changes from Kb to Mb accordingly.

-t

Add a totals line with a TYPE of total. This line totals only the paging information displayed above it, not all paging areas; this line might be misleading if a subset of -dfrM is specified.

-a

Show all device paging areas, including those configured into the kernel but currently disabled. (These are normally omitted.) The word disabled appears after the NAME, and the Kb AVAIL, Kb USED, and Kb FREE values are 0. The -a option is ignored unless the -d option is present or is true by default.

-d

Print information about device paging areas only. This modifies the output header appropriately.

-f

Print information about file system paging areas only. This modifies the output header appropriately.

-n

Categorize file system paging area information into localfs areas and network areas, instead of calling them both fs areas.

-r

Print information about reserved paging space only.

-M

Print information about memory paging space only.

The -d, -f, -n, -r and -M options can be combined. The default is -dfnrM.

-q

Quiet mode. Print only a total "Kb AVAIL" value (with the -m option, Mb AVAIL); that is, the total paging space available on the system (device, file system, reserve, or memory paging space only if -d, -f, -r, or -M is specified), for possible use by programs that want a quick total. If -q is specified, the -t and -a options are ignored.

-w

Print a warning about each device paging area that contains wasted space; that is, any device paging area whose allocated size is less than its total size. This option is effective only if -d is also specified or true by default.

RETURN VALUE

swapinfo returns 0 if it completes successfully (including if any warnings are issued), or 1 if it reports any errors.

DIAGNOSTICS

swapinfo prints messages to standard error if it has any problems.

EXAMPLES

List all file system paging areas with a totals line:

swapinfo -ft 

WARNINGS

swapinfo needs kernel access for some information. If the user does not have appropriate privileges for kernel access, swapinfo will print a warning and assume that the defaults for that information have not been changed.

Users of swapinfo must not rely on the exact field widths and spacing of its output, as these will vary depending on the system, the release of HP-UX, and the data to be displayed.

The information in this manual page about paging allocation and other implementation details may change without warning; users should not rely on the accuracy of this information.

AUTHOR

swapinfo was developed by HP.