Ubuntu - Disable Sleep or Suspend Mode

 I have a small Ubuntu 18.04 system (should work on 16.04) that is running headless and appears to be going to sleep on me.  

I found references to changing the settings for a laptop when the lid was closed, but this isn't a laptop and so I didn't believe that would be the cause of my system sleeping.   If simply pressed the power button quickly, the system responded to ping/ssh, etc and I could see that the system showed it had been up for several days (since my last known reboot).  

I also ran the command below and saw that it "reached target Sleep"

me@ubuntu:~$systemctl status sleep.target

● sleep.target - Sleep

     Loaded: loaded (/lib/systemd/system/sleep.target; static; vendor preset: enabled)

     Active: inactive (dead) since Sun 2022-07-10 22:47:44 UTC; 17min ago

       Docs: man:systemd.special(7)

Jul 10 17:16:33 ubuntu systemd[1]: Reached target Sleep.

Jul 10 22:47:44 ubuntu systemd[1]: Stopped target Sleep.

To disable Suspend mode, I ran the following command:

sudo systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target

To re-enable it run:

sudo systemctl unmask sleep.target suspend.target hibernate.target hybrid-sleep.target

For good measure, I also changed the Power Mangement Settings (which can also be done in the GUI if you are running one). 

Power Management Settings (without a GUI)

gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout '0' && gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-battery-timeout '0'