How to check memory usage in Linux?

Input: top

RESSHR##S##% CPU%MEM

##PID	Process ID
USER	Process Owner
PR	The priority level of the process, the smaller it is, the priority it will be executed
Ninice	##Value
##VIRT ##Virtual virtual space occupied by the process Memory
Physical memory occupied by the process
Shared memory used by the process
The status of the process. S means sleeping, R means running, Z means zombie state, N means the priority value of the process is negative
CPU usage occupied by the process
	Percentage of physical memory and total memory used by the process
TIME+	The total CPU time occupied by the process after it is started, that is, the accumulated value of the CPU usage time.
##COMMAND	Process Start command name

Input: free

Free##Shared

##Total

Total physical memory size.

##Used

##Already How big to use.

##Available how many.

More The total amount of memory shared by processes.

##Buffers/cached

The size of the disk cache.

The third line (-/+ buffers/cached):

##Used	How big has it been used.
Free	##Available how many.

##The fourth line

swap:

#Total##UsedFree

Total size of physical memory.
##Already How big to use.
##Available how many.	Difference:

used/ in the second line (mem) The difference between free and used/free in the third line (-/+ buffers/cache)

The difference between these two lies in the perspective of use. The first line is from the OS ( From the perspective of the operating system), because for the OS (operating system), buffers/cached are all used, so its available memory is 434884KB and the used memory is 3489800KB,

The third line refers to the

application perspective

. For the application, buffers/cached is equal to available, because buffer/cached is to improve the performance of file reading. When the application When the program needs to use memory, buffer/cached will be recycled quickly.

So from the perspective of the application, available memory = free +buffers+cached.

As in the above example: 434884 + 36436 + 421856 = 893176 ##-/+ Calculation of the number of buffers/cache memory:

-The number of memory in buffers/cache: used - buffers - cached

The value of used: 3489800 - 36436 - 421856 = 3031508

+The number of memory in buffers/cache: free + buffers + cached

The value of free: 434884 + 36436 + 421856 = 893176

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