Linux常用命令之vmstat

1.vmstat

vmstat是Virtual Meomory Statistics（虚拟内存统计）的缩写，可用来纪录 processes, memory, paging, block IO, traps, 与 cpu activity

[root@raclinux1 ~]# vmstat –help
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
-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.

其中红色部分是新选项，2.5.70及以上内核适用

2.举例：

[ oracle @raclinux1 ~]$ vmstat 3
procs —————–memory—————swap– —–io—- –system– —-cpu—-
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 0 1672 29032 108664 0 0 66 16 1012 259 2 7 87 3
0 0 0 1672 29040 108664 0 0 0 11 930 199 1 4 95 0
0 0 0 1676 29040 108664 0 0 0 39 949 202 1 3 96 0
0 0 0 1680 29048 108664 0 0 0 4 937 199 1 3 96 0
0 0 0 1680 29048 108664 0 0 0 25 932 198 1 4 95 0
0 0 0 1680 29056 108664 0 0 0 4 944 206 1 3 96 0
0 0 0 1680 29056 108664 0 0 0 0 932 198 1 3 96 0
0 0 0 1680 29064 108664 0 0 0 4 935 196 1 3 96 0
0 0 0 1680 29064 108664 0 0 0 0 941 198 1 3 96 0
0 0 0 1680 29072 108664 0 0 0 4 949 202 1 2 96 0
0 0 0 1680 29072 108664 0 0 0 0 938 196 1 3 96 0

其中：

Procs
r: The number of processes 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 context switches per second.

CPU
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.

3.解读：

A.CPU问题：

下面几列需要被察看，以确定cpu是否有问题

Processes in the run queue (procs r)
User time (cpu us)
System time (cpu sy)
Idle time (cpu id)

问题情况:
1.) 如果processes in run queue (procs r)的数量远大于系统中cpu的数量，将会使系统便慢。
2.) 如果这个数量是cpu的4倍的话，说明系统正面临cpu能力短缺,这将使系统运行速度大幅度降低
3.) 如果cpu的idle时间经常为0的话，或者系统占用时间(cpu sy)是用户占用时间(cpu us)两辈的话，系统面临缺少cpu资源

解决方案 :
解决这些情况，涉及到调整应用程序，使其能更有效的使用cpu，同时增加cpu的能力或数量

B.内存问题：

主要查看页导入的数值（swap中的si），如果该值比较大就要考虑内存，大概方法如下：

1).最简单的，加大RAM
2).改小SGA，使得对RAM需求减少
3).减少RAM的需求（如：减少PGA）

4.新参数：

1）.vmstat -D 显示磁盘信息(只能一次性，delay参数无效）

[ oracle @raclinux1 ~]$ vmstat -D
25 disks
6 partitions
17577 total reads
4140 merged reads

587320 read sectors
248149 milli reading
6889 writes
13672 merged writes
164444 written sectors
167353 milli writing
0 inprogress IO
178 milli spent IO

2）.vmstat -d 查看磁盘统计信息

[ oracle @raclinux1 ~]$ vmstat -d | grep -v ram
disk- ————reads———— ————writes———– —–IO——
total merged sectors ms total merged sectors ms cur sec
hdc 13 88 680 249 0 0 0 0 0 0
sda 17396 2644 580819 243635 6983 13749 165836 167797 0 178
sdb 46 657 1185 1808 0 0 0 0 0 0
sdc 53 420 1436 1667 6 4 56 7 0 1
sdd 24 132 1248 348 0 0 0 0 0 0
disk- ————reads———— ————writes———– —–IO——
total merged sectors ms total merged sectors ms cur sec
sde 36 135 1368 288 0 0 0 0 0 0
sdf 9 64 584 154 0 0 0 0 0 0
fd0 0 0 0 0 0 0 0 0 0 0
md0 0 0 0 0 0 0 0 0 0 0

3）.vmstat -s （一次性，delay参数无效）

[ oracle @raclinux1 ~]$ vmstat -s
256044 total memory
254428 used memory
153584 active memory
70960 inactive memory
1616 free memory
33976 buffer memory
104140 swap cache
1044184 total swap
0 used swap
1044184 free swap
13214 non-nice user cpu ticks
3759 nice user cpu ticks
43122 system cpu ticks
827934 idle cpu ticks
14246 IO-wait cpu ticks
98 IRQ cpu ticks
27960 softirq cpu ticks
293660 pages paged in
83714 pages paged out
0 pages swapped in
0 pages swapped out
9369649 interrupts
2217323 CPU context switches
1143195570 boot time
29804 forks