'free' command shows available ram less than buff/cache!

Question

I have a laptop running ubuntu 16.04 with 4gb ram. I've been using it for about a month now and recently I noticed that the system slows down a lot even with only 3-4 apps running. This is the output of free -m with a terminal and gedit open.

       total        used        free      shared      buff/cache   available
Mem:    3872         797         842        1971            2232         848
Swap:   4015         141        3874

You can see that the available memory is less than cached memory. Shouldn't cached memory be included in available memory? The problem is, when I open some other application, the cached memory size increases instead of giving space to the new app! Here's the output of 'free -m' after opening firefox, document viewer and vscode.

              total        used        free      shared  buff/cache   available
Mem:           3872        1391         145        1923        2335         299
Swap:          4015         250        3765

sudo sync; echo 3>'/proc/sys/vm/drop_cache' doesn't help much.

              total        used        free      shared  buff/cache   available
Mem:           3872        1368         239        1923        2265         324
Swap:          4015         256        3759

It turns out I can't even open 5 applications on Ubuntu simultaneously. It seems like the 2265mb memory has just leaked out. It's more than half of my physical ram! What can I do about it?

Answer 1

If you want to calculate your free memory try this

(it will print it in MB's)

make a script in bash add these

mem1=$( free | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $8 }' | awk '{ total = $1 / 1024 ; print total }' | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $1}' )
mem2c=$( free | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $10}' | awk '{ total = $1 / 1024 ; print total }' | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $1}' )
mem3=$( free | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $9}' | awk '{ total = $1 / 1024 ; print total }' | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $1}' )
mem2f=$( free | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $12}' | awk '{ total = $1 / 1024 ; print total }' | sed 'N;s/\n/ /;N;s/\n/ /' | awk '{ print $1}')
mem2=$(awk "BEGIN {print $mem2c+$mem2f; exit}")

then just do this

echo "$mem1 / $mem3 / $mem2"

source: my own code :)

https://github.com/ppigmans/Tool-box