Understanding VMSTAT Output - Explained

Posted by Parthiban Ponnusamy

vmstat is a nice tool, to analyze the Linux / UNIX server performance.



 procs            memory                        swap        io       system    cpu
 r  b   swpd   free   buff  cache         si   so    bi    bo     in    cs       us sy id wa
 2  5 375912  19548  17556 477472    0    1     0     0      1     1        1  0  0  1
 0  4 375912  18700  17556 478264    0    0  1044   0     774  1329   8  1   0  91
 0  5 375912  17664  17556 479168    0    0  1160   0     764  1110   8  1   0  91
 1  8 375912  15836  17568 479796    0    0  1144   840  751  1622  16 7   0  78
 0  7 375912  19340  17576 480224    0    0  1224   148  587  1958  17 18  0  65
 2  0 375912  18288  17588 481036    0    0   812    0     845  1732  18 3  21  59
 0  2 375912  15868  17588 481528    0    0  1012   0     588   941   4   1  5   90 



Proc: 
-------
r: How many processes are waiting for CPU time.
b: Wait Queue - Process which are waiting for I/O (disk, network, user 
    input,etc..) 


Memory: 
-----------
swpd: shows how many blocks are swapped out to disk (paged). Total Virtual  
          memory usage. 
            
Note: you can see the swap area configured in server using "cat proc/swaps"


free: Idle Memory 
buff: Memory used as buffers, like before/after I/O operations
cache: Memory used as cache by the Operating System


Swap: 
---------
si: How many blocks per second the operating system is swapping in. i.e 
    Memory swapped in from the disk (Read from swap area to Memory)
so: How many blocks per second the operating system is swaped Out. i.e 
     Memory swapped to the disk (Written to swap area and cleared from 
     Memory)


In Ideal condition, We like to see si and so at 0 most of the time, and we definitely don’t like to see more than 10 blocks per second.


IO: 
------
bi: Blocks received from block device - Read (like a hard disk) 
bo: Blocks sent to a block device - Write


System: 
-------------
in: The number of interrupts per second, including the clock. 
cs: The number of context switches per second. 


CPU: 
--------
us: percentage of cpu used for running non-kernel code. (user time, including 
     nice time) 
sy: percentage of cpu used for running kernel code. (system time - network, IO 
     interrupts, etc) 
id: cpu idle time in percentage.
wa: percentage of time spent by cpu for waiting to IO.




If you used to monitor this data, you can understand how is your server doing during peak usage times. 


Note: the memory, swap, and I/O statistics are in blocks, not in bytes. In Linux, blocks are usually 1,024 bytes (1 KB).

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I'm Parthiban, An UNIX System Admin by Profession. I'm Experienced in Linux/Unix System Administration and Scripting. I have done lot of work on the infrastructure Mgmt side in Linux, UNIX and Windows system administration, Hardware, Storage and Data center. I'm blogging since 2008.
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