How to Disable Automatic Sleep and Suspend on Debian 12 Production Servers

When running Debian 12 (Bookworm) on home servers, lab nodes, or production workstations with desktop environments installed, power-saving defaults can cause the system to automatically suspend or sleep after periods of user inactivity (no keyboard or mouse movement). This disconnects SSH sessions and halts background services.

Method 1: Configure GDM3 Greeter Power Settings (Desktop / GDM3)

For systems running the GNOME Display Manager (GDM3), edit the greeter defaults configuration:

sudo nano /etc/gdm3/greeter.dconf-defaults

Uncomment or add the following directives under [org/gnome/settings-daemon/plugins/power] to set inactive timeout actions to blank instead of suspend:

[org/gnome/settings-daemon/plugins/power]
sleep-inactive-ac-type='blank'
sleep-inactive-battery-type='blank'

Method 2: Mask Systemd Sleep Targets (Recommended for Headless / Servers)

To completely prohibit the Linux kernel and systemd from entering sleep, suspend, or hibernation at any time, mask the respective systemd targets:

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

Verification: Check system sleep state with systemctl status sleep.target. If masked, the target points to /dev/null, ensuring 24/7 server uptime without unexpected idle shutdowns.