How much memory is free?

A common way...

$ top

(And the newer and prettier htop)

Also

$ free -m
              total        used        free      shared  buff/cache   available
Mem:            488         228          23          11         236         217
Swap:             0           0           0

The figure under "available" is how much is "Free and available"

i.e. what humans usually mean when they say "free"

To watch it as it changes...

$ watch -n 5 free -m

This will refresh every 5 seconds.

Another techinique:

$ cat /proc/meminfo | grep MemAvailable

MemAvailable:     223336 kB

And similarly:

$ watch -n 5 'cat /proc/meminfo | grep MemAvailable'

How much are particular apps using?

Sort the current processes by memory usage

ps aux --sort=-%mem | head

Note, see also explain shell for this command

Columns of ps aux

Quickly explanations:

Machine information

Related --

To see a lot of specific info about your machine...

$ sudo lshw

Meaning: "list hardware"

External Resources

See also