vmstat – Virtual Memory Statistics. The vmstat command in Linux is utilized to display virtual memory statistics. It reports details about processes, memory, paging, block IO, traps, and CPU activity. This command proves beneficial for recognizing potential performance bottlenecks and diagnosing system-related issues.
Syntax:
The syntax for using vmstat command in Linux is as follows:
vmstat [options] [delay [count]]
- vmstat: Command used to view virtual memory statistics.
- [options]: Optional flags that modify the behavior of the vmstat command.
- [delay]: The delay between updates in seconds. If specified without count, vmstat will continuously display statistics with the specified delay.
- [count]: The number of times the statistics will be displayed before the command exits.
Usage Examples:
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: Enables the display of active/inactive memory information for kernels 2.5.41 or later.
- -f: Displays the total number of forks since boot, including fork, vfork, and clone system calls. Each process is represented by one or more tasks, depending on thread usage. This display does not repeat.
- -t: Adds timestamps to the output.
- -m: Displays slabinfo information.
- -n: Suppresses the repeating header and only displays it once.
- -s: Displays a table of various event counters and memory statistics. This display does not repeat.
- delay: Specifies the delay in seconds between updates. If no delay is specified, only one report is printed with the average values since boot.
- count: Specifies the number of updates. If no count is specified and delay is defined, count defaults to infinity.
- -d: Reports disk statistics (requires kernel 2.5.70 or later).
- -w: Enlarges field width for displaying large memory sizes.
- -p: Followed by a partition name, displays detailed statistics for that partition (requires kernel 2.5.70 or later).
- -S: Followed by k, K, m, or M, switches the output units between 1000, 1024, 1000000, or 1048576 bytes.
- -V: Displays version information.
vmstat Command Examples:
Example 1: Simple example along-with field descriptions
The vmstat command provides valuable insights into system performance, offering detailed statistics about various aspects of the system, such as memory, swap, I/O, CPU, and more.
$ 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.
Example 2: To execute every 2 seconds for 10 times
Executing the vmstat command with a specific interval and count provides an automated way to monitor system statistics:
$ 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 ..
This command will run vmstat every 2 seconds for 10 times, providing periodic updates on system statistics without the need for manual interruption.
Example 3: Grep Memory Overview Using vmstat
The following command combines vmstat, -s, and grep to extract an overview of memory usage:
$ vmstat -s -S M | grep mem
This command extracts and displays essential memory statistics in megabytes.
5965 M total memory 5136 M used memory 3580 M active memory 1176 M inactive memory 829 M free memory 474 M buffer memory
Example 4: Display active and inactive memory
The -a option with vmstat displays active and inactive memory information:
$ 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
This command showcases the active and inactive memory along with other system statistics.
Example 5: Display number of forks since last boot
Use the -f option to display the count of forks (including fork, vfork, and clone system calls) since the last boot:
$ vmstat -f 81651975 forks
This command provides the total count of fork system calls made by the system since the last boot.
Example 6: Display timestamp
When monitoring memory usage repeatedly with vmstat, including a timestamp along with each line item can be beneficial. Using the -t option enables displaying the timestamp, as demonstrated 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
Example 7: Display slab info
To showcase slabinfo details, utilize the -m option with vmstat:
$ 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 ...
Example 8: Display statistics in a table format
Instead of the default record format, the -s option allows displaying the vmstat output in a table format:
$ 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 ..
Example 9: Display disk statistics
To view disk statistics, utilize the -d option with vmstat. This provides information regarding disk reads, writes, and I/O:
$ 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
Example 10: Changing width of output
$ 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
Example 11: Display statistics for a partition
To view disk I/O statistics for a specific disk partition, use the -p option followed by the partition name:
$ vmstat -p sdb1 sdb1 reads read sectors writes requested writes 501423248 2345417917 419221612 2661885948
Example 12: Display in MB
To display memory information in megabytes instead of kilobytes, use the -S m option:
$ 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
These options enhance the vmstat command’s capabilities, providing more specific and formatted insights into various system statistics.
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