Ubuntu – How to set the system to suspend when inactive to a longer amount of time

What you need to do is set up your power management preferences for the gdm user. To do this from the command line use this command to make the preferences window show up when you log out or switch user:

sudo cp /usr/share/applications/gnome-power-preferences.desktop /usr/share/gdm/autostart/LoginWindow/

Now log out, restart or switch user and you should get the power management preferences window. (I did, I just tested this)

Once you've set up your preferences how you like them, log back in and remove the auto start desktop file:

sudo rm /usr/share/gdm/autostart/LoginWindow/gnome-power-preferences.desktop

Seeing as your managing a lab, you will want to know how to duplicate these settings for all the comptuers on your network without busting a sweat all day. Simply sync the /var/lib/gdm/.gconf directory to your other computers (I have automated scripts to do this on my network, you might too)

You can run this trick with a bunch of different configuration apps, look at what's auto starting, in the directory above, to see what kind of services are available. It is possible to change the theme and wallpaper this way too, but you can use gdm2setup, a third party app to do some of that.

Until Ubuntu 14.10 (Upstart-based)

Have a look at pm-action(8) and search for /etc/pm/sleep.d in section “FILES”. If one of these scripts returns with a non-zero exit status, suspension is prevented.

Updated instructions for clarity:

1. So create a file /etc/pm/sleep.d/05_ssh_keepawake.

2. Put a shebang (#!/bin/sh) and the code mentioned in the question in this file.

3. Set execute permissions on it:

   chmod +x /etc/pm/sleep.d/05_ssh_keepawake
   

Since Ubuntu 15.04 (systemd-based)

systemd doesn’t use pm-utils to manage its power state hooks but has its own infrastructure to the same end. Sleep inhibitor checkers are no longer executed on sleep but must be set by the action that inhibits sleep (see 1).

As such you’d have to add commands to the SSH session log-in and log-out that registers a sleep inhibitor with systemd (e. g. via systemd-inhibit(1)) and later releases the inhibitor. If somebody knows how to hook into SSH log-in and log-out, I’d welcome a comment or edit so that we could work out the relevant steps and commands.

The following section is work in progress – Only use it when you know what you’re doing!

You might be able to write a systemd unit /etc/systemd/system/ssh-inhibt-sleep.service that makes itself a dependency of sleep.target using the RequiredBy option. If your new unit fails (with a non-zero exit status from its invoked process), it will make sleep.target and thus the subsequent sleep action.

[Unit]
Description=Check for running SSH sessions and, if any, inhibit sleep
Before=sleep.target

[Service]
Type=oneshot
ExecStart=/bin/sh -c '! who | grep -qv "\(:0\)"'

[Install]
RequiredBy=sleep.target

As always you need to activate systemd units for them to take effect:

sudo systemctl enable ssh-inhibt-sleep.service

For more info see systemd.unit(5) and systemd.service(5).