This tutorial explains Linux “vmstat” command, options and its usage with examples.
Description:
vmstat command is used to report virtual memory statistics. vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.
Synopsis:
vmstat [-a] [-n] [-t] [-S unit] [delay [ count]]
vmstat [-s] [-n] [-S unit]
vmstat [-m] [-n] [delay [ count]]
vmstat [-d] [-n] [delay [ count]]
vmstat [-p disk partition] [-n] [delay [ count]]
vmstat [-f]
vmstat [-V]
OPTIONS:
-a
switch displays active/inactive memory, given a 2.5.41 kernel or better.
-f
switch displays the number of forks since boot. This includes the fork, vfork, and clone system calls, and is equivalent to the total number of tasks created. Each process is represented by one or more tasks, depending on thread usage. This display does not repeat.
-t
switch adds timestamp to the output.
-m
switch displays slabinfo.
-n
switch causes the header to be displayed only once rather than periodically.
-s
switch displays a table of various event counters and memory statistics. This display does not repeat.
delay
delay between updates in seconds. If no delay is specified, only one report is printed with the average values since boot.
count
number of updates. If no count is specified and delay is defined, count defaults to infinity.
-d
reports disk statistics (2.5.70 or above required)
-w
enlarges field width for big memory sizes
-p
followed by some partition name for detailed statistics (2.5.70 or above required)
-S
followed by k or K or m or M switches outputs between 1000, 1024, 1000000, or 1048576 bytes
-V
switch results in displaying version information.
Examples:
1. Simple example along-with field descriptions
$ vmstat procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 305416 260688 29160 2356920 2 2 4 1 0 0 6 1 92 2 0
Field Description For Vm Mode
Procs
r: The number of processes waiting for run time.
b: The number of processes in uninterruptible sleep.
Memory
swpd: the amount of virtual memory used.
free: the amount of idle memory.
buff: the amount of memory used as buffers.
cache: the amount of memory used as cache.
inact: the amount of inactive memory. (-a option)
active: the amount of active memory. (-a option)
Swap
si: Amount of memory swapped in from disk (/s).
so: Amount of memory swapped to disk (/s).
IO
bi: Blocks received from a block device (blocks/s).
bo: Blocks sent to a block device (blocks/s).
System
in: The number of interrupts per second, including the clock.
cs: The number of context switches per second.
CPU
These are percentages of total CPU time.
us: Time spent running non-kernel code. (user time, including nice time)
sy: Time spent running kernel code. (system time)
id: Time spent idle. Prior to Linux 2.5.41, this includes IO-wait time.
wa: Time spent waiting for IO. Prior to Linux 2.5.41, included in idle.
st: Time stolen from a virtual machine. Prior to Linux 2.6.11, unknown.
2. To execute every 2 seconds for 10 times, do the following. You don’t need to press Ctrl-C in this case. After executing 10 times, it will stop automatically.
$ vmstat 2 10 procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 1 0 0 537144 182736 6789320 0 0 0 0 1 1 0 0 100 0 0 0 0 0 537004 182736 6789320 0 0 0 0 50 32 0 0 100 0 0 ..
3. Using vmstat, this next command will grep the memory and give a good overview of the memory used in the computer.
$ vmstat -s -S M | grep mem 5965 M total memory 5136 M used memory 3580 M active memory 1176 M inactive memory 829 M free memory 474 M buffer memory
4. Display active and inactive memory
By default vmstat doesn’t display this information. Use option -a, to display active and inactive memory information as shown below.
$ vmstat -a procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free inact active si so bi bo in cs us sy id wa st 0 0 305416 253820 1052680 2688928 2 2 4 1 0 0 6 1 92 2 0
4. Display number of forks since last boot
This displays all the fork system calls made by the system since the last boot. This displays all fork, vfork, and clone system call counts.
$ vmstat -f 81651975 forks
5. Display timestamp
When you use vmstat to monitor the memory usage repeately, it would be nice to see the timestap along with every line item. Use option -t to display the time stamp as shown below.
$ vmstat -t 1 100 procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ ---timestamp--- r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 0 3608728 148368 3898200 0 0 0 0 1 1 0 0 100 0 0 2011-07-09 21:16:28 PDT 0 0 0 3608728 148368 3898200 0 0 0 0 60 15 0 0 100 0 0 2011-07-09 21:16:29 PDT 0 0 0 3608712 148368 3898200 0 0 0 0 32 28 0 0 100 0 0 2011-07-09 21:16:30 PDT
6. Display slab info
Use option -m, to display the slab info as shown below.
$ vmstat -m Cache Num Total Size Pages fib6_nodes 5 113 32 113 ip6_dst_cache 4 15 256 15 ndisc_cache 1 15 256 15 RAWv6 7 10 768 5 UDPv6 0 0 640 6 tw_sock_TCPv6 0 0 128 30 ...
7. Display statistics in a table format
Instead of displays the values in the record format, you can display the output of vmstat in table format using option -s as shown below.
$ vmstat -s 4149928 total memory 3864824 used memory 2606664 active memory 1098180 inactive memory 285104 free memory 19264 buffer memory 2326692 swap cache 4192956 total swap 274872 used swap 3918084 free swap 1032454000 non-nice user cpu ticks 14568 nice user cpu ticks 89482270 system cpu ticks 16674327143 idle cpu ticks 368965706 IO-wait cpu ticks 1180468 IRQ cpu ticks ..
8. Display disk statistics
Use option -d to display the disk statistics as shown below. This displays the reads, writes, and I/O statistics of the disk.
$ vmstat -d disk- ------------reads------------ ------------writes----------- -----IO------ total merged sectors ms total merged sectors ms cur sec sda 153189971 69093708 2719150864 737822879 329617713 157559204 3965687592 4068577985 0 1102243 sdb 501426305 97099356 2345472425 731613156 419220973 533565961 2661869460 1825174087 0 1510434 sdc 884213459 22078974 513390701 452540172 127474901 8993357 2411187300 2133226954 0 1569758
9. Changing width of output
The default output without increasing the width is shown below.
$ vmstat 1 3 procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 0 3608688 148368 3898204 0 0 0 0 1 1 0 0 100 0 0 0 0 0 3608804 148368 3898204 0 0 0 0 72 30 0 0 100 0 0 0 0 0 3608804 148368 3898204 0 0 0 0 60 27 0 0 100 0 0
Use option -w to increase the width of the output columns as shown below. This give better readability.
$ vmstat -w 1 3 procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu------- r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 0 3608712 148368 3898204 0 0 0 0 1 1 0 0 100 0 0 0 0 0 3608712 148368 3898204 0 0 0 0 93 23 0 0 100 0 0 0 0 0 3608696 148368 3898204 0 0 0 0 35 34 0 0 100 0 0
10. Display statistics for a partition
To display the disk I/O statistics of a specific disk partition use option -p as shown below.
$ vmstat -p sdb1 sdb1 reads read sectors writes requested writes 501423248 2345417917 419221612 2661885948
11. Display in MB
By default vmstat displays the memory information in kb. To disply in MB, use the option “-S m” as shown below.
$ vmstat -S m procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 281 288 19 2386 0 0 4 1 0 0 6 1 92 2 0
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