https://askubuntu.com/questions/399992/how-to-open-system-monitor-easily

snap install gnome-system-monitor

GNOME System Monitor

Run the system monitor from Terminal by typing: gnome-system-monitor

Alternatively, run this command by pressing ALT+F2 (or Super, also known as “Windows key”) and typing gnome-system-monitor

Keyboard shortcut

You can add a custom keyboard command using the following steps:

1. Go to System Settings
2. Click Keyboard
3. Open the Shortcuts tab
4. Click the “+” symbol near the bottom of the window
5. Give your command a title. E.g. System Monitor
6. In the Command field, enter gnome-system-monitor
7. Click Apply
8. Click Disabled on your newly created shortcut
9. Enter the key combination you want for your shortcut. E.g. Ctrl+Alt+M