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)
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
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.
