Q. How can I find out Linux Resource utilization using vmstat command? How do I get information about high disk I/O and memory usage?
A. 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. Please note that Linux vmstat does not count itself as a running process.
Here is an output of vmstat command from my enterprise grade system:
$ vmstat -S MOutput:
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
3 0 0 1963 607 2359 0 0 0 0 0 1 32 0 68 0Where,
- The fist line is nothing but six different categories. The second line gives more information about each category. This second line gives all data you need.
- -S M: vmstat lets you choose units (k, K, m, M) default is K (1024 bytes) in the default mode. I am using M since this system has over 4 GB memory. Without -M option it will use K as unit
$ vmstatOutput:
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
3 0 0 2485120 621952 2415368 0 0 0 0 0 1 32 0 68 0
Field Description For Vm Mode
(a) procs is the process-related fields are:
- r: The number of processes waiting for run time.
- b: The number of processes in uninterruptible sleep.
(b) memory is the memory-related fields are:
- 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.
(c) swap is swap-related fields are:
- si: Amount of memory swapped in from disk (/s).
- so: Amount of memory swapped to disk (/s).
(d) io is the I/O-related fields are:
- bi: Blocks received from a block device (blocks/s).
- bo: Blocks sent to a block device (blocks/s).
(e) system is the system-related fields are:
- in: The number of interrupts per second, including the clock.
- cs: The number of context switches per second.
(f) cpu is the CPU-related fields are:
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.
As you see the first output produced gives averages data since the last reboot. Additional reports give information on a sampling period of length delay. You need to sample data using delays i.e. collect data by setting intervals. For example collect data every 2 seconds (or collect data every 2 second 5 times only):
$ vmstat -S M 2OR
$ vmstat -S M 2 5Output:
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
3 0 0 1756 607 2359 0 0 0 0 0 1 32 0 68 0
3 0 0 1756 607 2359 0 0 0 0 1018 65 38 0 62 0
3 0 0 1756 607 2359 0 0 0 0 1011 64 37 0 63 0
3 0 0 1756 607 2359 0 0 0 20 1018 72 37 0 63 0
3 0 0 1756 607 2359 0 0 0 0 1012 64 37 0 62 0
3 0 0 1756 607 2359 0 0 0 0 1011 65 38 0 63 0
3 0 0 1995 607 2359 0 0 0 0 1012 62 35 2 63 0
3 0 0 1731 607 2359 0 0 0 0 1012 64 34 3 62 0
3 0 0 1731 607 2359 0 0 0 0 1013 72 38 0 62 0
3 0 0 1731 607 2359 0 0 0 0 1013 63 37 0 63 0This is what most system administrators do to identify system bottlenecks. I hope all of you find vmstat data is concise and easy to read.