Ubuntu Vmstat Command Explained

The Vmstat command is the most common Linux/unix monitoring tool that can show the status of a server at a given time interval, including server CPU utilization, memory usage, virtual memory exchange, IO Read and write situations. This command is I see Linux/unix favorite commands, one is Linux/unix support, two is compared to top, I can see the whole machine CPU, memory, IO usage, rather than just see the CPU usage and memory utilization of each process (using the scene is not the same).

The use of the general Vmstat tool is done by two numeric parameters, the first parameter is the number of time intervals sampled, the unit is seconds, the second parameter is the number of samples, such as:

[Email protected]:~# vmstat 2 1
procs-----------Memory-------------Swap-------io-----system------CPU----
R  B   swpd   free   buff  cache   si   so    bi    bo   in   CS US sy ID WA
1  0      0 3498472 315836 3819540    0    0     0     1    2    0  0  0 +  0

2 indicates that the server state is collected every two seconds, and 1 means that it is collected only once.

In fact, in the application process, we will be monitoring for a period of time, do not want to monitor the direct end of Vmstat, such as:

 [email protected]:~# vmstat 2  
  procs-----------Memory-------------Swap-------io-----system------CPU---- 
  R b swpd free buff cache si so bi bo in CS us sy ID WA  
  1 0 0 3499840 315836 3819660 0 0 0 1 2 0 0 0 0  
  0 0 0 3499584 315836 3819660 0 0 0 0 + 158 0 0 + 0  
  0 0 0 3499708 315836 3819660 0 0 0 2 162 0 0 + 0  
  0 0 0 3499708 315836 3819660 0 0 0, Bayi 151 0 0 0  
  1 0 0 3499732 315836 3819660 0 0 0 2 154 0 0 0  

This means that Vmstat collects data every 2 seconds and collects it until I have finished the program, and I have collected 5 data and I have finished the program.

Well, the command is complete, now the actual combat to explain the meaning of each parameter.

R means running the queue (that is, how many processes are really allocated to the CPU), the server I am testing is currently idle, there is no program running, when this value exceeds the number of CPUs, there will be a CPU bottleneck. This is also related to top of the load, the general load over 3 is relatively high, more than 5 is high, more than 10 is not normal, the state of the server is very dangerous. The load on top is similar to the run queue per second. If the running queue is too large, it means that your CPU is busy, which generally results in high CPU usage.

b represents the blocking process, which is not much to say, the process is blocked, you understand.

swpd Virtual memory has been used size, if greater than 0, indicates that your machine is out of physical memory, if not the cause of program memory leaks, then you should upgrade the memory or the memory-consuming task to other machines.

Free physical memory size, my machine memory total 8G, the remaining 3415M.

Buff Linux/unix system is used to store, directory inside what content, permissions, etc. of the cache, I machine about more than 300 m

the cache cache is used directly to memorize the files we open, to buffer the files, I have about 300 m of this machine (this is the smart place of Linux/unix, the spare part of the physical memory to do the file and directory cache, is to improve the performance of the program execution, When the program uses memory, buffer/cached is quickly used. )

Si reads the size of the virtual memory from disk every second, if this value is greater than 0, it means that the physical memory is not enough or the memory leaks, to find out the memory process. My machine has plenty of memory and everything is fine.

so per second the virtual memory is written to the size of the disk, if this value is greater than 0, ibid.

The number of blocks received per second by BI block devices, where the block device refers to all the disks and other block devices on the system, the default block size is 1024byte, I have no IO operation on this machine, so it has been 0, but I have been working on copying large amounts of data (2-3T) The machine has seen can reach 140000/s, disk write speed of almost 140M per second

The number of blocks that Bo block devices send per second, such as when we read a file, the Bo will be greater than 0. Bi and Bo are generally close to 0, otherwise the IO is too frequent and needs to be adjusted.

in CPU interrupts per second, including time interrupts

CS per second, such as the number of context switches, such as we call the system function, the context switch, the thread of the switch, but also the process context switch, the smaller the value of the better, too big, to consider the number of threads or processes, such as in Apache and Nginx Web server , we generally do performance testing will carry out thousands of concurrent or even tens of thousands of concurrent testing, the process of selecting a Web server can be the peak of the process or the thread has been down, pressure measurement, until CS to a relatively small value, the process and the number of threads is a more appropriate value. System calls are also, each time the system function is called, our code will enter the kernel space, resulting in context switching, this is very resource-intensive, but also try to avoid frequent calls to system functions. Too many context switches means that most of your CPU is wasted in context switching, resulting in less time for the CPU to do serious work, and the CPU not being fully utilized, is undesirable.

US user CPU time, I used to do encryption and decryption very frequently on the server, you can see us approaching 100,r running queue reached 80 (the machine is doing a stress test, poor performance).

sy System CPU time, if too high, indicates a long system call time, for example, the IO operation is frequent.

ID Idle CPU time, in general, ID + US + sy = 100, generally I think ID is idle CPU usage, US is the user CPU usage, SY is the system CPU utilization.

wt waits for IO CPU time.

Ext.: http://www.cnblogs.com/ggjucheng/archive/2012/01/05/2312625.html

FIELD DESCRIPTION for VM MODE
Procs
R:the Number of runnable processes (running or waiting for run time).
B:the number of processes in uninterruptible sleep.

Memory
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.
Inact:the amount of inactive memory. (-a option)
Active:the amount of active memory. (-a option)

Swap
Si:amount of memory swapped in from disk (/s).
So:amount of memory swapped to disk (/s).

Io
Bi:blocks received from a block device (BLOCKS/S).
Bo:blocks sent to a block device (BLOCKS/S).

System
In:the number of interrupts per second, including the clock.
Cs:the number of the context switches per second.

Cpu
These is 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, included in idle.
St:time stolen from a virtual machine. Prior to Linux 2.6.11, unknown.

Ubuntu Vmstat Command Explained