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vmstat(1)
NAME
vmstat - Displays virtual memory statistics
SYNOPSIS
vmstat interval [count]
vmstat [-f|-M|-P|-s]
The vmstat command displays system statistics for virtual memory,
processes, trap, and CPU activity.
OPTIONS
-f Displays only statistics about the number of forks since system startup
(see the fork() call).
-M Displays information about memory usage by buckets. This information
can be used for kernel debugging.
-P Displays the following accumulated statistics about physical memory
use:
Total Physical Memory
Number of megabytes of installed memory, and the equivalent page
value.
Physical Memory Clusters
How physical memory is clustered. The starting and ending page
frames (pfn) and where the memory is utilized (pal, os, and
*nvram).
Physical Memory Use
A breakdown of memory usage by os, the starting and ending page
frames, type of usage such as unixtable, or bss and the total
physical memory in use.
Managed Pages Break Down
A snapshot of where managed physical memory resided when the vmstat
command executed. The display shows the number of pages in the
free queue, active and inactive pages, wired pages and unified
buffer cache (ubc) pages.
WIRED Pages Break Down
A further breakdown of physical pages that are wired in memory.
The display typically shows:
·
vm and ubc wired pages
·
meta data, malloc, and contig pages
·
user, kernel, and free ptepages.
-s Displays the following accumulated statistics along with the page size:
active pages
Total number of pages that are currently in use but can be used for
paging.
inactive pages
Total number of VM pages that are allocated but are most likely to
be used for paging.
free pages
Total number of unreferenced (clean) pages that are available for
use.
wire pages
Total number of pages that are currently in use and cannot be used
for paging (not a real list).
virtual memory page faults
Number of address translation faults that have occurred.
copy-on-write page faults
Number of copy-on-write page faults, which occur if the requested
page is shared by a parent process and one or more child processes
(using the fork function) and if one of the processes needs to
modify the page. In this case, VM loads a new address into the
translation buffer and copies the contents of the requested page
into the new address for modification by the process.
zero file page faults
Number of zero-filled-on-demand page faults, which occur if VM
cannot find the page in the internal data structures and if the
requested page is new and has never been referenced. In this case,
VM initializes a physical page (the contents of the page are zeroed
out) and loads the address into the page table.
reattaches from reclaim list
Number of pages that have been faulted while on the inactive list.
pages paged in
Number of requests for pages from a pager.
pages paged out
Number of pages that have been paged out.
task and thread context switches
Number of task and thread context switches per second.
device interrupts
Number of nonclock device interrupts per second.
system calls
Number of system calls called per second.
DESCRIPTION
If you specify interval, vmstat displays the statistics listed below every
interval seconds. The first report is for all time since a reboot, and
each subsequent report is for the last interval only. If you specify count
after interval, count specifies the number of reports. For example, vmstat
1 10 produces 10 reports at 1-second intervals. You cannot specify count
without interval, since the first numeric argument to vmstat is always
assumed to be interval.
At any time, system memory can be in use by the kernel in kseg, wired
(pages that are currently in use and cannot be used for paging), on the
active list (pages that are currently in use but can be used for paging),
on the inactive list (pages that are allocated but are most likely to be
used for paging), on the free list (pages that are clean and available for
use), or used by the Unified Buffer Cache (UBC). The vmstat command does
not report on the memory in kseg and memory used by the UBC.
The following values are displayed:
Process information:
r Number of threads that are running or are runnable.
w Number of threads waiting interruptibly.
u Number of threads waiting uninterruptibly.
Virtual memory information:
act Total number of pages on the active list, the inactive list (pages that
are allocated but are most likely to be used for paging), and the
Unified Buffer Cache (UBC) least recently used (LRU) list.
free
Total number of pages that are clean and available for use.
wire
Total number of pages that are currently in use and cannot be used for
paging (not a real list).
fault
Number of address translation faults that have occurred.
cow Number of copy-on-write page faults, which occur if the requested page
is shared by a parent process and one or more child processes (using
the fork function) and if one of the processes needs to modify the
page. In this case, VM loads a new address into the translation buffer
and copies the contents of the requested page into the new address for
modification by the process.
zero
Number of zero-filled-on-demand page faults, which occur if VM cannot
find the page in the internal data structures and if the requested page
is new and has never been referenced. In this case, VM initializes a
physical page (the contents of the page are zeroed out) and loads the
address into the page table.
react
Number of pages that have been faulted while on the inactive list.
pin Number of requests for pages from a pager.
pout
Number of pages that have been paged out.
Interrupt information:
in Number of nonclock device interrupts per second.
sy Number of system calls called per second.
cs Number of task and thread context switches per second.
CPU information:
us Percentage of user time for normal and priority processes.
sy Percentage of system time.
id Percentage of idle time.
Specify -f to display fork statistics only. Specify -s for a single
display of accumulated statistics, as well as page size.
SEE ALSO
Commands: iostat(1)