I have read What do the "buff/cache" and "avail mem" fields in top mean? and https://askubuntu.com/questions/770108/what-do-the-changes-in-free-output-from-14-04-to-16-04-mean. But still have questions.
$ free -h
total used free shared buff/cache available
Mem: 7.7G 5.3G 268M 620M 2.1G 1.5G
Swap: 14G 874M 14G
Does "used" already include "shared"?
Can "available" be determined from other columns?
Why does "available" not equal to sum of "free" and "buff/cache"?
I thought that "buff/cache" is actually available to be used by starting a new process, so why is "available" smaller than "buff/cache"?
What columns does "total - used" (2.4G) consist of? Why isn't it the same as "available"?
Thanks.