Search notes:

Shell command: free

free reports the amount of free and used physical memory and swap space.
free: grep /proc/meminfo 'MemFree\|SwapFree' (Sometimes slightly different. Because of delay between executing commands?)
shared: used by tmpfs
grep Shmem /proc/meminfo
cache: page cache and slabs.
grep '^Cached:\|Slab /proc/meminfo
buffers: used for kernel buffers
grep Buffers /proc/meminfo
available: An estimation on how much memory a new process might allocate.
grep MemAvailable /proc/meminfo
total: cat /proc/meminfo | grep MemInfo
total = used + free + buffers + cache

Actual free memory

Since cache (and also buffers?) are used to speed up hard disk access, the actual free memory calculates as
free + cache + buffers

Determine size in megabyes

-m: megabytes 
free -m

-w: wide

-w is the wide option: the buff/cache column is shown separately as buffers and cache. 
free -w

See also

Displaying swap space
/proc/meminfo
memory
Shell commands

Index

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