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 technique:

$ 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

• USER
• PID
• %CPU
• %MEM
• VSZ -- Virtual Memory Size, in Kb
• RSS -- Resident Set Size, in Kb
• TTY
• STAT
• START
• TIME
• COMMAND e.g. /usr/bin/dotnet /opt/webapps/example.com/app/example.dll

Quickly explanations:

• Virtual Memory Size is how much the operating system has been told to set aside for the process, but probably is not all in use.
• Resident Set Size is how much is residing in memory that this app can access... the trick though is that there might be resources counted in there that are used by multiple apps. So, killing one app won't necessarily free this much memory.
• ...and read more here: ps output - Difference between VSZ vs RSS memory usage - Linux Tutorials - Learn Linux Configuration

Machine information

Related --

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

sudo lshw

Meaning: "list hardware"

Gives a lot of output.

External Resources

• Linux Ate My Ram
• ps output - Difference between VSZ vs RSS memory usage - Linux Tutorials - Learn Linux Configuration
• explainshell.com for ps aux --sort=-%mem | head

See also

• Supervisor... it keeps your app running! - see how much supervisor is using