Changing power settings

in elementary OS

The #elementary channel on Freenode got an interesting question today:

How can one change the Suspend / Turn off screen settings to interval smaller than 5 minutes ie. turn off screen after 1 minute and suspend the laptop after 2 minutes when idle?

Despite spending a lot of time working on elementary OS I don't know the answer, so I start with the power menu.

Power settings

⌘+Space opens the elementary applications menu:

This menu controls all the power settings for the desktop. It's part of a set of elementary components called Switchboard. I'm looking for an option here to turn the screen after 1 minute.

No such option. I dig deeper and try to find out how Switchboard manages power settings and see if that leads me to a workaround.

Use the source

Every piece of the elementary OS desktop is free software, which means its source code is available for the community to study, change, and re-use. I don't know how the Switchboard power menu works, so I'm going to study the source code to find out.

Finding the source code for power settings

The elementary project has a page on GitHub where I can search for components:

Scrolling down, there's a search box for repositories. I try typing "power" to see what comes up:

This is the repository where the source code for the power settings is stored. I browse a few files in the repository, looking for the key phrase "Turn off display" which is found in the settings menu:

Now I know there's a component called screen_timeout which we manipulate when we touch the control with that label. But what does it actually do to change the power settings when we select a different option?

Understanding the power settings method of action

I search for "screen_timeout" and scan through the results until I see one that says "connect," suggesting that this is where the settings panel connects to another component that takes action to change settings. The name of this component is dpms_helper.

Back to the elementary GitHub organization! Now I'm looking for the dpms helper to dig further.

This repository has the source code for dpms-helper, the tool that I found out Switchboard uses to act on our power settings preferences. How does it work? I search around in its source code and soon find that it's executing another program called xset:

How can we use xset to achieve the desired goal of turning our screen off after a short time-interval? Now that I know what to look for, let's see what the system manual has to say:

Solutions & recap

I set out to find out how to set short intervals for power management: 1 minute before turning off the screen, and 2 minutes before suspending. The search took me through:

• The applications menu and power settings menu

• The elementary project's GitHub repositories

• Source code for Switchboard and dpms-helper

• The system manual

After researching the method of action, I can answer the original question like so:

# power settings: standby after 2 minutes, never suspend,
# and screen off after 1 minute.

# `xset dpms` takes arguments in seconds, in that order.

standby_seconds=$(((2*60)))
screen_off_seconds=$(((1*60)))

xset dpms $standby_seconds 0 $screen_off_seconds

Even better using dpms-helper

The above solution works, but it has two shortcomings:

1. It doesn't put our settings anywhere that other applications (like Switchboard) can find out about them

2. It uses a lower-level tool, xset, instead of a standard platform tool.

I'd like to find another solution that leverages the elementary technology better. In the dpms-helper source code, I find this:

standby_time=$(gsettings get io.elementary.dpms standby-time | cut -d" " -f2)

suspend_time=$(gsettings get io.elementary.dpms suspend-time | cut -d" " -f2)

off_time=$(gsettings get io.elementary.dpms off-time | cut -d" " -f2)

It gets the time values for these options from GSettings, a configuration management tool that comes with GNOME. We can use gsettings set to change the time values and then run dpms-helper:

# power settings: standby after 2 minutes, never suspend,
# and screen off after 1 minute.

# gsettings for these take time in seconds

gsettings set io.elementary.dpms standby-time $(((2*60)))
gsettings set io.elementary.dpms off-time $(((1*60)))

io.elementary.dpms-helper

This solution leaves the configuration in GSettings so other apps can find and respect those values.

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