Power Management: Difference between revisions

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-{{expansion}}
+This article covers configurations related to power management in terms of energy saving modes of various devices and components.
-== Suspend ==
+== Configuration ==
+=== Hard drives ===
+Following snippet configures [[Udev]] rules which automatically run the program <code>hdparm</code> to enable power saving modes for hard disks, especially rotational drives mapped to <code>/dev/sd*</code>.<syntaxhighlight lang="nix">
+services.udev.extraRules =
+  let
+    mkRule = as: lib.concatStringsSep ", " as;
+    mkRules = rs: lib.concatStringsSep "\n" rs;
+  in mkRules ([( mkRule [
+    ''ACTION=="add|change"''
+    ''SUBSYSTEM=="block"''
+    ''KERNEL=="sd[a-z]"''
+    ''ATTR{queue/rotational}=="1"''
+    ''RUN+="${pkgs.hdparm}/bin/hdparm -B 90 -S 41 /dev/%k"''
+  ])]);
+</syntaxhighlight>The <code>hdparm</code> parameters <code>-B</code> and <code>-S</code> define power saving modes and in case of <code>-S</code> the standby (spindown) timeout. The number 41 means therefore: Turn off the motor after 205 = 41*5 seconds.
 === Suspend hooks ===
 NixOS provides the {{nixos:option|powerManagement.resumeCommands}} option which defines commands that are added to a global script that will be executed after resuming.
@@ Line 27: / Line 41: @@
 </syntaxhighlight>
-=== Troubleshooting ===
+=== Hibernation ===
+Hibernation requires a configured swap device. See [https://nixos.org/manual/nixos/stable/#ch-installation installation instructions] on how to create a swap partition.
+Please note that <code>resumeDevice</code> must match the output of  <code>swapon -s</code> especially if you're dealing with mapped volumes (LUKS, logical volumes, logical volumes under LUKS, etc.). If you're using a swapfile, you must also [https://search.nixos.org/options?channel=unstable&show=boot.resumeDevice&from=0&size=50&sort=relevance&type=packages&query=resume+offset specify the offset to it.]
+Therefore, an example configuration could look like this:<syntaxhighlight lang="nix">
+/*
+  I'm hibernating into a logical volume that's also under LUKS. Pretty cool, right?
+*/
+swapDevices = [
+  {
+    device = "/dev/VG/SWAP";
+  }
+];
+boot.resumeDevice = "/dev/dm-7";
+</syntaxhighlight>Derived from a system with the following output from <code>swapon -s</code> :<syntaxhighlight>
+Filename                                Type            Size           Used             Priority
+/dev/dm-7                               partition       67108860       00
+/dev/zram0                              partition       32881148       032767
+</syntaxhighlight>
+Test and use hibernation with the following command:<syntaxhighlight lang="nix">
+systemctl hibernate
+</syntaxhighlight>
+== Tips and tricks ==
+=== Go into hibernate after specific suspend time ===
+Using following configuration, your system will go from suspend into hibernate after 1 hour:<syntaxhighlight lang="nix">
+systemd.sleep.extraConfig = ''
+  HibernateDelaySec=1h
+'';
+</syntaxhighlight>
+Or, to disable suspend entirely, consider a configuration like this:
+<syntaxhighlight lang="nix">
+systemd.sleep.extraConfig = ''
+  AllowSuspend=no
+  AllowHibernation=no
+  AllowHybridSleep=no
+  AllowSuspendThenHibernate=no
+'';
+</syntaxhighlight>
+== Troubleshooting ==
 ==== System immediately wakes up from suspend ====
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 * {{manual:nixos|sec=#sec-rebooting|chapter=Chapter 23. Rebooting and Shutting Down}}
+[[Category:Configuration]]