Talk:Power management

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Suspend/resume service files

I have the slight suspicion that the service files posted in the section Power Management#Suspend/resume service files might not work. Has anybody tried them or is actually using them?
-- jakobh 03:12, 10 May 2013 (UTC)

(Mod: the section was moved from systemd into Power Management, so I moved this post too, fixed link along the way. -- Lahwaacz (talk) 10:24, 21 August 2013 (UTC))

Sleep hooks

Where is the exact difference between Suspend/resume service files approach and Hooks in /usr/lib/systemd/system-sleep?

Is the latter obsolete?

-- Orschiro 07:33, 17 January 2014

From systemd-sleep(8):
"Note that scripts or binaries dropped in /usr/lib/systemd/system-sleep/ are intended for local use only and should be considered hacks."
It's always preferred to use service files, they are much more flexible in handling the dependencies etc.
-- Lahwaacz (talk) 23:52, 31 January 2014 (UTC)

Delayed hibernation service

I have found that the service file given in this section does not work. My laptop hibernates immediately after resuming from suspend. I have also found that the older version of this service found in the forum post does indeed work perfectly. Does anyone know why this is? Aouellette (talk) 16:16, 30 May 2015 (UTC)

Resume file does not work after resuming from hibernation

The systemd unit User resume actions presented on this page only worked for me after resuming from sleep, not from hibernate. After adding hibernate.target to the After and WantedBy lines it works both ways. However this is the first time I've done anything with such service files so I ain't sure if this is the optimal way. Can anyone confirm?

—This unsigned comment is by PhilippD (talk) 18:30, 12 October 2015‎. Please sign your posts with ~~~~!

Actually, the suspend@.service in Power_management#Suspend.2Fresume_service_files binds to sleep.target, but resume@.service binds to suspend.target. They are not synonyms, systemd triggers suspend.target and sleep.target when the system is suspended to RAM, and hibernate.target and sleep.target when it is suspended to disk. This way you can bind your service to either one or both suspend methods using just a single target. -- Lahwaacz (talk) 19:17, 12 October 2015 (UTC)

Bluetooth rfkill

Systemd now provides systemd-rkfill.service. If you use rfkill block to disable bluetooth, systemd-rfkill.service will remember this and restore this state on next boot -- robtaylor (talk) Wed 18 May 16:10:05 BST 2016

A "sensible value" for the laptop mode

The vast amount of specific information carried in this part, I find it a bit surprising. It seems "A sensible value for the laptop mode 'knob' is 5 seconds." could be heard in the mouth of a politician kicking the ball into touch.

From Documentation/laptops/laptop-mode.txt:

> The value of the laptop_mode knob determines the time between the occurrence of disk I/O and when the flush is triggered. A sensible value for the knob is 5 seconds. Setting the knob to 0 disables laptop mode.

So "5 (seconds)" is related to the virtual memory subsystem (in direct relation to vm.dirty_writeback_centisecs). Then "0" turns laptop mode off, aha. It'd be cool to know *what* is laptop_mode is in the first place: Is it the whole vm configuration settings that are described in the docs? I believe not, as e.g. the conf files are not to be seen in present Arch (nor in other distros I know of).

A few things changed a bit since the Documentation/laptops/laptop-mode.txt was last edited, in 2004. I've searched extensively which part of it might still be up to date, without success so far. TLP has many if not most of the settings the doc explains. And so looks as an evolution of laptop_mode. Would a guru or someone with knowledge about that be kind enough to specify the effect of vm.laptop_mode? kozaki (talk) 23:33, 1 September 2016 (UTC)

The effect of the vm.laptop_mode is described in the kernel docs in "The Details" section. The scripts that the docs talk about are probably Laptop Mode Tools nowadays. They are needed only to switch settings based on the current power source (and as a "bonus" they integrate most of the things in the Power_management#Power_saving section), but I bet the kernel settings are mostly the same as in 2004. -- Lahwaacz (talk) 08:41, 2 September 2016 (UTC)
I now see that, thank you Lahwaacz. Now as we may increase flush time to disk (to, say, ten minutes) via vm.dirty_writeback_centisecs, delaying the flush up to five seconds via the vm.laptop_mode knob doesn't make much sense regarding the disk power-savings... But it may help the cpu staying idle longer. Hence, whether set via laptop-mode-tools, tlp or proper self-made udev rules. I.e. vm.laptop_mode and vm.dirty_* together help delaying and grouping system's activity as a whole, allowing for longer power-saving efficient idle times. Please correct me if I'm wrong. kozaki (talk) 19:37, 4 September 2016 (UTC)
True, but the delay via vm.laptop_mode makes sense also for other reasons. Let's say vm.dirty_writeback_centisecs is set to something like 10 minutes and the disk is spun down due to inactivity and stays like that for e.g. 8 minutes, when it spins up due to user activity. Flushing all the cummulated dirty pages to the disk immediately might delay the request which caused the disk to spin up, so it's better to wait couple of seconds until there is chance that small high-priority requests have been serviced. Also, it might take couple of seconds to spin up the disk. -- Lahwaacz (talk) 20:14, 4 September 2016 (UTC)