Ubuntu – What can be harmed by incorrect power off, and what can be checked

an other option (I used myself) can be to edit the hdparm configuration file:

/etc/hdparm.conf

In there you find a commented line like this:

#apm = 255

Just delete the # to uncomment so that the hd power management will be disabled by default.

In my case I did it because my laptop disk was turned off and on several times in short time intervals. By the way I discovered that it is the BIOS that is doing that and not hdparm policies and the likes... It happens when I am on battery though.

When you have a laptop that can run on battery, in default interactive mode (launching with sudo powertop) on the overview tab, the first column shows estimated power consumption in mW (milliwatts) or µW (microwatts)

The units in the usage column are ms/s (milliseconds per second) and µs/s (microseconds per second) which show how much time per second the processor is spending on those tasks (so they can't be converted to watts)

PowerTOP 2.8      Overview   Idle stats   Frequency stats   Device stats   Tunables                                     

The battery reports a discharge rate of 3.51 W
The estimated remaining time is 9 hours, 32 minutes

Summary: 1017.3 wakeups/second,  7.0 GPU ops/seconds, 0.0 VFS ops/sec and 3.8% CPU use

Power est.              Usage       Events/s    Category       Description
  1.97 W     50.0%                      Device         Display backlight
  980 mW      3.5 pkts/s                Device         Network interface: wlan0 (brcmfmac_sdio)
  100 mW    100.0%                      Device         radio:hci0
 43.3 mW      1.1 ms/s     559.1        Interrupt      [1] timer(softirq)
 22.6 mW      0.8 ms/s     290.8        Timer          intel_pstate_timer_func
 10.8 mW     15.3 ms/s      31.5        Process        /usr/lib/firefox/firefox
 9.62 mW    433.2 µs/s      14.6        Process        marco
 3.79 mW      6.9 ms/s      0.00        Interrupt      [7] sched(softirq)
 2.22 mW    204.1 µs/s      27.6        Interrupt      [6] tasklet(softirq)
 2.01 mW      3.6 ms/s      0.05        Process        [khugepaged]
 1.72 mW    459.2 µs/s      19.2        Process        /usr/lib/mate-panel/wnck-applet
 1.27 mW      2.2 ms/s       0.9        Process        /usr/lib/xorg/Xorg -nolisten tcp :1 vt1 -keeptty -auth /tmp/serverauth.JdmwHkcqKp
 1.12 mW      1.0 ms/s       3.4        Process        mate-terminal
 819 µW       0.7 ms/s       5.5        Process        [mmcqd/0]

The man page for powertop seems to suggest that power usage (the first column) is only available while running on battery. However, I find that this is not the case - it always shows me that column on my Ubuntu machine, which is a laptop with a healthy battery

However @edwinksl very helpfully pointed out that 'a minimum of 270 measurements are needed' running on battery only to give power usage estimates. This is for calibration.

Therefore, it seems that you need to run powertop on battery only for some time before it can give power consumption statistics.

If running on a desktop machine or laptop with no battery of course, this information would never become available. I've tried it with a battery-less laptop (running Arch), and there's no sign of the power usage column.

One more caveat from the user guide - /var/cache/powertop must be empty for power consumption estimates to show.