How to Check Memory and I/O with vmstat on Linux CentOS 5/CentOS 6/RHEL 5/RHEL 6 server – System Performance

vmstat command is a utility that will provides interesting information abaout processes, memory, i/O and CPU activity. When you run vmstat utility command without any arguments, you will see the output as below. This post will guide you on how to check memory and I/O with vmstat on Linux CentOS 5/CentOS 6/RHEL 5/RHEL 6 server to optimize the linux system performance.

[root@rhel6 ~]# 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      0 888252  28976  63004    5    0     0    11   15   18  0  0 99  0  0

Below are the description of above vmstat output :
1. The procs fields show the number of processes
– Waiting for run time (r)
-Blocked (b)
-Swapped out (w)

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2. The memory fields show the kilobytes of swap memory,free memory, buffered memory and Cached memory

3. The swap fields show the kilobytes per second of memory
-Swapped in from disk (si)
-Swapped out to disk (so)

4. The io fields show the number of blocks per second
-Sent to block devices (bi)
-Received from block devices (bo)

5. The system shows the number of
-Interrupts per second (in)
-Context switches per second (cs)

6. The cpu field shows the percentage of total CPU time as
-User time (us)
-System time (sy)
-Idle (id) time

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To prints the vmstat version, run this command :

[root@rhel6 ~]# vmstat -V
procps version 3.2.8

We can let the vmstat to run automatically by execute this command :

[root@rhel6 ~]# vmstat 

Where nsec is the number of seconds you want it to wait before another update.

To run vmstat on every 10 seconds :

[root@rhel6 ~]# vmstat 10
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 888072  29088  63004    4    0     0    11   14   18  0  0 99  0  0
 0  0      0 888064  29088  63004    0    0     0     0   12   15  0  0 100  0  0
 0  0      0 888064  29088  63004    0    0     0     0   13   16  0  0 100  0  0

Other vmstat usage as below :

usage: vmstat [-V] [-n] [delay [count]]
              -V prints version.
              -n causes the headers not to be reprinted regularly.
              -a print inactive/active page stats.
              -d prints disk statistics
              -D prints disk table
              -p prints disk partition statistics
              -s prints vm table
              -m prints slabinfo
              -t add timestamp to output
              -S unit size
              delay is the delay between updates in seconds.
              unit size k:1000 K:1024 m:1000000 M:1048576 (default is K)
              count is the number of updates.

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