NAME [Toc] [Back]
swapinfo - system paging space information
SYNOPSIS [Toc] [Back]
DESCRIPTION [Toc] [Back]
swapinfo prints information about device and file system paging space.
(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
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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.
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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"
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
Paging Allocation [Toc] [Back]
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
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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
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) [Toc] [Back]
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:
Options [Toc] [Back]
swapinfo recognizes the following options:
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-m Display the AVAIL, USED, FREE, LIMIT, and RESERVE values in
Mbytes instead of Kbytes, rounding off to the nearest whole
Mbyte (multiples of 1024^2). 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
-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
-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 [Toc] [Back]
swapinfo returns 0 if it completes successfully (including if any
warnings are issued), or 1 if it reports any errors.
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DIAGNOSTICS [Toc] [Back]
swapinfo prints messages to standard error if it has any problems.
EXAMPLES [Toc] [Back]
List all file system paging areas with a totals line:
WARNINGS [Toc] [Back]
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
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 [Toc] [Back]
swapinfo was developed by HP.
SEE ALSO [Toc] [Back]
lvlnboot(1M), lvrmboot(1M), swapon(1M), swapon(2), fstab(4).
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