Alter Ubuntu desktop configuration using gsettings utility. I will use it to change the number of seconds the desktop computer needs to be inactive before it goes to sleep.
List available schemas and look for ones related to the power subsystem.
$ gsettings list-schemas | grep power
org.gnome.power-manager org.gnome.settings-daemon.plugins.power
Alternatively, list schemas, keys, and values to look for power-related ones.
$ gsettings list-recursively | grep "\\.power"
org.gnome.power-manager info-stats-type 'power' org.gnome.power-manager info-history-type 'power' org.gnome.power-manager info-stats-graph-points true org.gnome.power-manager info-page-number 0 org.gnome.power-manager info-stats-graph-smooth true org.gnome.power-manager info-history-graph-points true org.gnome.power-manager info-last-device '' org.gnome.power-manager info-history-time 21600 org.gnome.power-manager info-history-graph-smooth true org.gnome.settings-daemon.plugins.power lid-close-ac-action 'suspend' org.gnome.settings-daemon.plugins.power time-critical 300 org.gnome.settings-daemon.plugins.power power-button-action 'interactive' org.gnome.settings-daemon.plugins.power lid-close-suspend-with-external-monitor false org.gnome.settings-daemon.plugins.power button-hibernate 'hibernate' org.gnome.settings-daemon.plugins.power idle-dim true org.gnome.settings-daemon.plugins.power button-power 'interactive' org.gnome.settings-daemon.plugins.power lid-close-battery-action 'suspend' org.gnome.settings-daemon.plugins.power priority 0 org.gnome.settings-daemon.plugins.power idle-brightness 30 org.gnome.settings-daemon.plugins.power active true org.gnome.settings-daemon.plugins.power critical-battery-action 'suspend' org.gnome.settings-daemon.plugins.power button-suspend 'suspend' org.gnome.settings-daemon.plugins.power button-sleep 'suspend' org.gnome.settings-daemon.plugins.power percentage-critical 3 org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 900 org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type 'suspend' org.gnome.settings-daemon.plugins.power ambient-enabled true org.gnome.settings-daemon.plugins.power notify-perhaps-recall true org.gnome.settings-daemon.plugins.power percentage-low 10 org.gnome.settings-daemon.plugins.power percentage-action 2 org.gnome.settings-daemon.plugins.power sleep-inactive-battery-type 'suspend' org.gnome.settings-daemon.plugins.power time-low 1200 org.gnome.settings-daemon.plugins.power sleep-inactive-battery-timeout 1200 org.gnome.settings-daemon.plugins.power time-action 120 org.gnome.settings-daemon.plugins.power use-time-for-policy true
List keys in a specific schema.
$ gsettings list-keys org.gnome.settings-daemon.plugins.power
lid-close-ac-action time-critical power-button-action lid-close-suspend-with-external-monitor button-hibernate idle-dim button-power lid-close-battery-action priority idle-brightness active critical-battery-action button-suspend button-sleep percentage-critical sleep-inactive-ac-timeout sleep-inactive-ac-type ambient-enabled notify-perhaps-recall percentage-low percentage-action sleep-inactive-battery-type time-low sleep-inactive-battery-timeout time-action use-time-for-policy
List keys and values in a specific schema.
$ gsettings list-recursively org.gnome.settings-daemon.plugins.power
org.gnome.settings-daemon.plugins.power lid-close-ac-action 'suspend' org.gnome.settings-daemon.plugins.power time-critical 300 org.gnome.settings-daemon.plugins.power power-button-action 'interactive' org.gnome.settings-daemon.plugins.power lid-close-suspend-with-external-monitor false org.gnome.settings-daemon.plugins.power button-hibernate 'hibernate' org.gnome.settings-daemon.plugins.power idle-dim true org.gnome.settings-daemon.plugins.power button-power 'interactive' org.gnome.settings-daemon.plugins.power lid-close-battery-action 'suspend' org.gnome.settings-daemon.plugins.power priority 0 org.gnome.settings-daemon.plugins.power idle-brightness 30 org.gnome.settings-daemon.plugins.power active true org.gnome.settings-daemon.plugins.power critical-battery-action 'suspend' org.gnome.settings-daemon.plugins.power button-suspend 'suspend' org.gnome.settings-daemon.plugins.power button-sleep 'suspend' org.gnome.settings-daemon.plugins.power percentage-critical 3 org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 3600 org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type 'suspend' org.gnome.settings-daemon.plugins.power ambient-enabled true org.gnome.settings-daemon.plugins.power notify-perhaps-recall true org.gnome.settings-daemon.plugins.power percentage-low 10 org.gnome.settings-daemon.plugins.power percentage-action 2 org.gnome.settings-daemon.plugins.power sleep-inactive-battery-type 'suspend' org.gnome.settings-daemon.plugins.power time-low 1200 org.gnome.settings-daemon.plugins.power sleep-inactive-battery-timeout 1200 org.gnome.settings-daemon.plugins.power time-action 120 org.gnome.settings-daemon.plugins.power use-time-for-policy true
Get a description of a specific key.
$ gsettings describe org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout
The amount of time in seconds the computer on AC power needs to be inactive before it goes to sleep. A value of 0 means never.
$ gsettings describe org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type
The type of sleeping that should be performed when the computer is inactive.
Get the possible values for a specific key.
$ gsettings range org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout
type i
$ gsettings range org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type
enum 'blank' 'suspend' 'shutdown' 'hibernate' 'interactive' 'nothing' 'logout'
Check if a specific key is writable.
$ gsettings writable org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout
true
Alter the value of a specific key.
$ gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 3600
Read the value of a specific key.
$ gsettings get org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout
3600