Check Linux System’s Performance by vmstat command

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Vmstat command collects and reports data about system's memory, paging, block IO, kernel threads, swap and processor utilization in real time. It is used to determine the root cause of linux system performance and memory use related issues. It reports virtual memory statistics.

[machindra@desktop03]~% vmstat procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----  r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa  0  0    208  83508 253692 2206428    0    0     0    14    0     1  8  3 89  0 [machindra@desktop03]~%

Difference between top and vmstat command:

 Field descriptions of vmstat command's output:

 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)

Click to  know more about: when and where not to use shell script

   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, shown as zero.

Vmstat command examples:

·         Get vmstat five reports after 2 seconds interval as follows:

[machindra@desktop03]~% vmstat 2 5 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----  r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa  0  0    208  83308 253692 2206428    0    0     0    14    0     1  8  3 89  0  0  0    208  83308 253692 2206428    0    0     0     0 1017    36  0  0 100  0  0  0    208  83308 253692 2206428    0    0     0     6 1017    43  0  0 100  0  0  0    208  83372 253692 2206428    0    0     0    22 1018    43  0  0 100  0  0  0    208  83372 253692 2206428    0    0     0     0 1024    40  0  0 100  0 [machindra@desktop03]~%

·         Get size in kilobytes. Use –S for unit size and 1 1 for getting 1 report after 1 second. You can use  M instead of k, to get size in Mega Bytes.

[machindra@desktop03]~% vmstat -S k 1 1 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----  r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa  0  0    212  85315 259780 2259382    0    0     0    14    0     1  8  3 89  0 [machindra@desktop03]~%

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