Linux calculates real available memory

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The free command shows the usage statistics for the physical memory and swap partitions in the Linux system.

Available memory = Free + buffers + Cached

First behavior physical memory usage statistics:

Title	Description
Total	Total Physical Memory Total=used+free
Used	Amount of memory used, including reference usage +buffer+cached
Free	Total Free Memory
Shared	Total Shared memory
Buffers	Cache consumed by block devices
Cached	Cache for normal file data consumption
Available	Current total available memory, without virtual memory

In the second row-/+ Buffers/cache only two columns used and free have values, which are the adjustment values of the physical memory

Title	Description
Used	Memory used (used) minus buffer and cached, that is, the total amount of memory that the app is using
Free	Free memory plus buffer and cached memory, which is the total amount of available memory

Third act Exchange partition usage statistics

Title	Description
Total	Total Swap partition memory
Used	Swap partition memory in use
Free	Idle swap partition memory

In the above indicators, we need to note that under these circumstances, the system is normal, do not need to worry about

Idle memory free close to 0
0 using memory used close to total
Available memory (Free+buffers/cache) accounted for more than 20% of total
Swap partition memory swap has not changed
The following situation indicates that the memory is too low, need attention!

Available memory (Free+buffers/cache) is too low, close to 0
Swap partition memory consumption swap used increased or fluctuating
DMESG | grep Oom-killer shows a outofmemory-killer is running

Common parameters
-b/k/m/g display results in bytes/kilobytes/megabytes/gigabytes units
-H output statistical results in a human-readable manner
-T use this option to display more than one row of statistics that is titled Total
-O Suppress buffer adjustment values for the second row
-S automatically refreshes results every few seconds
-C with-s used to control the number of refresh results
-L display statistical details of high and low memory
-A shows available memory
-V Show version number

Linux calculates real available memory