Disable Server Sleep Mode (Ubuntu)

Check Sleep Mode:

systemctl status sleep.target
systemctl status suspend.target
systemctl status hibernate.target
systemctl status hybrid-sleep.target

Disable Server Sleep Mode (Ubuntu):

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

Check status (if sleep mode inactive):

# systemctl status sleep.target
● sleep.target
     Loaded: masked (Reason: Unit sleep.target is masked.)
     Active: inactive (dead)

# systemctl status suspend.target
● suspend.target
     Loaded: masked (Reason: Unit suspend.target is masked.)
     Active: inactive (dead)

# systemctl status hibernate.target
● hibernate.target
     Loaded: masked (Reason: Unit hibernate.target is masked.)
     Active: inactive (dead)

# systemctl status hybrid-sleep.target
● hybrid-sleep.target
     Loaded: masked (Reason: Unit hybrid-sleep.target is masked.)
     Active: inactive (dead)

Output, if they are active would look like:

○ sleep.target - Sleep
     Loaded: loaded (/usr/lib/systemd/system/sleep.target; static)
     Active: inactive (dead)
       Docs: man:systemd.special(7)
○ suspend.target - Suspend
     Loaded: loaded (/usr/lib/systemd/system/suspend.target; static)
     Active: inactive (dead)
       Docs: man:systemd.special(7)
○ hibernate.target - System Hibernation
     Loaded: loaded (/usr/lib/systemd/system/hibernate.target; static)
     Active: inactive (dead)
       Docs: man:systemd.special(7)
○ hybrid-sleep.target - Hybrid Suspend+Hibernate
     Loaded: loaded (/usr/lib/systemd/system/hybrid-sleep.target; static)
     Active: inactive (dead)
       Docs: man:systemd.special(7)