VMSTAT(1) General Commands Manual VMSTAT(1)

vmstat — report virtual memory statistics

vmstat [-CefHiLlmstUvW] [-c count] [-h hashname] [-M core] [-N system] [-n diskcount] [-u histname] [-w wait] [disks]

vmstat reports certain kernel statistics kept about process, virtual memory, disk, trap, and CPU activity. If vmstat is invoked without any options, it displays the summary of statistics since boot and exits. This is also referred to as the first line of vmstat.

The options are as follows:

Report on kernel memory caches. Combine with the -m option to see information about memory pools that back the caches.
count
Repeat the display count times. The first display is for the time since a reboot and each subsequent report is for the time period since the last display. If no wait interval is specified, the default is 1 second.
Report the values of system event counters.
Report fork statistics.
Report all hash table statistics.
hashname
Report hash table statistics for hashname.
Report the values of system interrupt counters.
List all the hashes supported for -h and -H.
List the UVM histories being maintained by the kernel.
core
Extract values associated with the name list from the specified core instead of the default /dev/mem.
Report on the list of the kernel memory pools and their usage.
system
Extract the name list from the specified system instead of the default /netbsd.
diskcount
Display up to diskcount disks in the standard output, instead of the default 2.
Display the contents of the uvmexp structure. This contains various paging event and memory status counters.
Display the contents of the vmtotal structure. This includes information about processes and virtual memory.

The process part shows the number of processes in the following states:

ru
on the run queue
dw
in disk I/O wait
pw
waiting for paging
sl
sleeping

The virtual memory section shows:

total-v
Total virtual memory
active-v
Active virtual memory in use
active-r
Active real memory in use
vm-sh
Shared virtual memory
avm-sh
Active shared virtual memory
rm-sh
Shared real memory
arm-sh
Active shared real memory
free
Free memory

All memory values are shown in number of pages.

Dump all UVM histories.
histname
Dump the specified UVM history.
Print more verbose information. When used with the -i, -e, or -m options prints out all counters, not just those with non-zero values.
Print more verbose information about kernel memory pools.
wait
Pause wait seconds between each display. If no repeat count is specified, the default is infinity. The vmstat command will accept and honor a negative number of wait seconds.

By default, vmstat displays the following information:

procs
Information about the numbers of processes in various states.

r
in run queue
b
blocked for resources (i/o, paging, etc.)
memory
Information about the usage of virtual and real memory. Virtual pages (reported in units of 1024 bytes) are considered active if they belong to processes which are running or have run in the last 20 seconds.

avm
active virtual pages
fre
size of the free list
page
Information about page faults and paging activity. These are averaged every five seconds, and given in units per second.

flt
total page faults
re
page reclaims (simulating reference bits)
pi
pages paged in
po
pages paged out
fr
pages freed per second
sr
pages scanned by clock algorithm, per-second
disks
Disk transfers per second. Typically paging will be split across the available drives. The header of the field is the first character of the disk name and the unit number. If more than four disk drives are configured in the system, vmstat displays only the first four drives. To force vmstat to display specific drives, their names may be supplied on the command line.
faults
Trap/interrupt rate averages per second over last 5 seconds.

in
device interrupts per interval (including clock interrupts)
sy
system calls per interval
cs
CPU context switch rate (switches/interval)
cpu
Breakdown of percentage usage of CPU time.

us
user time for normal and low priority processes
sy
system time
id
CPU idle

/netbsd
default kernel namelist
/dev/mem
default memory file

The command “vmstat -w 5” will print what the system is doing every five seconds; this is a good choice of printing interval since this is how often some of the statistics are sampled in the system. Others vary every second and running the output for a while will make it apparent which are recomputed every second.

fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), iostat(8), pstat(8), kernhist(9)

The -c, -n, and -w options are only available with the default output.

The -l, -U, and -u options are useful only if the system was compiled with support for UVM history.

MOUSE February 1, 2022 VMSTAT(1)