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VMSTAT output explanation

Tags: pagingswap memoryvmstat

Published on: October 6, 2014 by George K.

VMSTAT output explanation

Scenario:

VMSTAT

vmstat command reports information about processes, memory, paging, block IO, traps, and cpu activity. However, a real advantage of vmstat command output – is to the point and (concise) easy to read/understand. The output of vmstat command use to help identify system bottlenecks. The details related with each field in the output is given in the man pages and hence I just try to explain the result. For more detailed explanation refer the man pages. vmstat output explained here with an example

A sample vmstat output would look like this.


# vmstat -S M 1 10

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------

r   b  swpd  free   buff   cache    si  so   bi   bo    in    cs   us   sy   id   wa    st

6  0   1      905   462    15205    0    0   59   116     0      0   49   6   44  1      0

4  0   1    955     462    15206    0    0   212  0    2479  11962   23    4  72  1      0

4  1   1   1033     462    15206    0    0   72  2560  2479  4638  21  3   76    0      0

6  3  1   1045      462    15206    0    0   804  812  2760  8050  32  4   61    3      0

Ideally r/b values under “procs” block with close to 0 or 0 itself. If one or value counter values are constantly reporting high values, it means that system may not have sufficient CPU or Memory or I/O bandwidth.

If value of swpd under swap is too high and it keeps changing, the it means that system is running short of memory.

The data under “io” indicates the flow of data to and from the disks. This shows how much disk activity is going on, which does not necessarily indicate some problem(obviously data has to go to disk in order to be persistent). If we see some large number under “proc” and then “b” column (processes being blocked) and high I/O, the issue could be a I/O contention.

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Category : Linux, Troubleshooting

George K.

George K.

George started his career in web hosting and Linux technical support in the year 2004 and is with SupportSages since 2009. He has keen interest in server optimizations, custom security solutions, hacked server recovery, cyber forensic and high availability fail over system design and implementation. George loves long drives and is passionate about art and literature.

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