Power management - ArchWiki

# Power management

From ArchWiki

Related articles

- Power management/Suspend and hibernate
- Display Power Management Signaling
- CPU frequency scaling
- Hybrid graphics
- Kernel modules
- sysctl
- udev

Power management is a feature that turns off the power or switches system's components to a low-power state when inactive.

In Arch Linux, power management consists of two main parts:

1. Configuration of the Linux kernel, which interacts with the hardware.
   - Kernel parameters
   - Kernel modules
   - udev rules
2. Configuration of userspace tools, which interact with the kernel and react to its events. Many userspace tools also allow to modify kernel configuration in a "user-friendly" way. See #Userspace tools for the options.

## Userspace tools

Using these tools can replace setting a lot of settings by hand. Only run one of these tools to avoid possible conflicts as they all work more or less similarly. Have a look at the power management category to get an overview on what power management options exist in Arch Linux.

These are the more popular scripts and tools designed to help power saving:

- aclidswitch — Simple Power Management tool to define custom lid, brightness and low battery actions depending on the laptop's AC state.

  https://github.com/orschiro/aclidswitch || aclidswitch-gitAUR

- acpid — A daemon for delivering ACPI power management events with netlink support.

  http://sourceforge.net/projects/acpid2/ || acpid

- Laptop Mode Tools — Utility to configure laptop power saving settings, considered by many to be the de facto utility for power saving though may take a bit of configuration.

  https://github.com/rickysarraf/laptop-mode-tools || laptop-mode-toolsAUR

- powertop — A tool to diagnose issues with power consumption and power management to help set power saving settings.

  https://01.org/powertop/ || powertop

- systemd
- TLP — Advanced power management for Linux.

  http://linrunner.de/tlp || tlp

## Power management with systemd

### ACPI events

systemd handles some power-related ACPI events, whose actions can be configured in `/etc/systemd/logind.conf` or `/etc/systemd/logind.conf.d/*.conf` — see logind.conf(5). On systems with no dedicated power manager, this may replace the acpid daemon which is usually used to react to these ACPI events.

The specified action for each event can be one of `ignore`, `poweroff`, `reboot`, `halt`, `suspend`, `hibernate`, `hybrid-sleep`, `lock` or `kexec`. In case of hibernation and suspension, they must be properly set up. If an event is not configured, systemd will use a default action.

Event handler | Description | Default action
--- | --- | ---
`HandlePowerKey` | Triggered when the power key/button is pressed. | `poweroff`
`HandleSuspendKey` | Triggered when the suspend key/button is pressed. | `suspend`
`HandleHibernateKey` | Triggered when the hibernate key/button is pressed. | `hibernate`
`HandleLidSwitch` | Triggered when the lid is closed, except in the cases below. | `suspend`
`HandleLidSwitchDocked` | Triggered when the lid is closed if the system is inserted in a docking station, or more than one display is connected. | `ignore`

To apply any changes, restart the `systemd-logind` daemon (be warned that this will terminate all login sessions that might still be open).

Note: systemd cannot handle AC and Battery ACPI events, so if you use Laptop Mode Tools or other similar tools acpid is still required.

#### Power managers

Some desktop environments include power managers which inhibit (temporarily turn off) some or all of the systemd ACPI settings. If such a power manager is running, then the actions for ACPI events can be configured in the power manager alone. Changes to `/etc/systemd/logind.conf` or `/etc/systemd/logind.conf.d/*.conf` need be made only if you wish to configure behaviour for a particular event that is not inhibited by the power manager.

Note that if the power manager does not inhibit systemd for the appropriate events you can end up with a situation where systemd suspends your system and then when the system is woken up the other power manager suspends it again. As of December 2016, the power managers of KDE, GNOME, Xfce and MATE issue the necessary inhibited commands. If the inhibited commands are not being issued, such as when using acpid or others to handle ACPI events, set the `Handle` options to `ignore`. See also systemd-inhibit(1).

#### xss-lock

xss-lock-gitAUR subscribes to the systemd-events `suspend`, `hibernate`, `lock-session`, and `unlock-session` with appropriate actions (run locker and wait for user to unlock or kill locker). xss-lock also reacts to DPMS events and runs or kills the locker in response.

Start xss-lock in your autostart, for example

    xss-lock -- i3lock -n -i background_image.png &

### Suspend and hibernate

systemd provides commands for suspend to RAM, hibernate and a hybrid suspend using the kernel's native suspend/resume functionality. There are also mechanisms to add hooks to customize pre- and post-suspend actions.

Note: systemd can also use other suspend backends (such as Uswsusp), in addition to the default kernel backend, in order to put the computer to sleep or hibernate. See Uswsusp#With systemd for an example.

`systemctl suspend` should work out of the box, for `systemctl hibernate` to work on your system you need to follow the instructions at Suspend and hibernate#Hibernation.

#### Hybrid sleep

`systemctl hybrid-sleep` both hibernates and suspends at the same time. This combines some of the benefits and drawbacks of suspension and hibernation. This is useful in case a computer were to suddenly lose power (AC disconnection or battery depletion) since upon powerup it will resume from hibernation. If there is no power loss, then it will resume from suspension, which is much faster than resuming from hibernation. However, since "hybrid-sleep" has to dump memory to swap in order for hibernation to work, it is slower to enter sleep than a plain `systemctl suspend`. An alternative is a delayed hibernation service file.

#### Always do hybrid-sleep instead of suspend or hibernation

It is possible to configure systemd to always do a hybrid-sleep even on a suspend or hibernation request.

The default suspend and hibernation action can be configured in the `/etc/systemd/sleep.conf` file. To set both actions to hybrid-sleep:

    /etc/systemd/sleep.conf

    [Sleep]
    # suspend=hybrid-sleep
    SuspendMode=suspend
    SuspendState=disk
    # hibernate=hybrid-sleep
    HibernateMode=suspend
    HibernateState=disk

See the sleep.conf.d(5) manual page for details.

### Sleep hooks

#### Suspend/resume service files

Service files can be hooked into suspend.target, hibernate.target and sleep.target to execute actions before or after suspend/hibernate. Separate files should be created for user actions and root/system actions. Enable the `suspend@user` and `resume@user` services to have them started at boot. Examples:

    /etc/systemd/system/suspend@.service

    [Unit]
    Description=User suspend actions
    Before=sleep.target

    [Service]
    User=%I
    Type=forking
    Environment=DISPLAY=:0
    ExecStartPre= -/usr/bin/pkill -u %u unison ; /usr/local/bin/music.sh stop ; /usr/bin/mysql -e 'slave stop'
    ExecStart=/usr/bin/sflock
    ExecStartPost=/usr/bin/sleep 1

    [Install]
    WantedBy=sleep.target

    /etc/systemd/system/resume@.service

    [Unit]
    Description=User resume actions
    After=suspend.target

    [Service]
    User=%I
    Type=simple
    ExecStartPre=/usr/local/bin/ssh-connect.sh
    ExecStart=/usr/bin/mysql -e 'slave start'

    [Install]
    WantedBy=suspend.target

Note: As screen lockers may return before the screen is "locked", the screen may flash on resuming from suspend. Adding a small delay via `ExecStartPost=/usr/bin/sleep 1` helps prevent this.

For root/system actions (enable the `root-resume` and `root-suspend` services to have them started at boot):

    /etc/systemd/system/root-resume.service

    [Unit]
    Description=Local system resume actions
    After=suspend.target

    [Service]
    Type=simple
    ExecStart=/usr/bin/systemctl restart mnt-media.automount

    [Install]
    WantedBy=suspend.target

    /etc/systemd/system/root-suspend.service

    [Unit]
    Description=Local system suspend actions
    Before=sleep.target

    [Service]
    Type=simple
    ExecStart=-/usr/bin/pkill sshfs

    [Install]
    WantedBy=sleep.target

A couple of handy hints about these service files (more in systemd.service(5)):

- If `Type=oneshot` then you can use multiple `ExecStart=` lines. Otherwise only one `ExecStart` line is allowed. You can add more commands with either `ExecStartPre` or by separating commands with a semicolon (see the first example above; note the spaces before and after the semicolon, as they are required).
- A command prefixed with `-` will cause a non-zero exit status to be ignored and treated as a successful command.
- The best place to find errors when troubleshooting these service files is of course with journalctl.

#### Combined Suspend/resume service file

With the combined suspend/resume service file, a single hook does all the work for different phases (sleep/resume) and for different targets (suspend/hibernate/hybrid-sleep).

Example and explanation:

    /etc/systemd/system/wicd-sleep.service

    [Unit]
    Description=Wicd sleep hook
    Before=sleep.target
    StopWhenUnneeded=yes

    [Service]
    Type=oneshot
    RemainAfterExit=yes
    ExecStart=-/usr/share/wicd/daemon/suspend.py
    ExecStop=-/usr/share/wicd/daemon/autoconnect.py

    [Install]
    WantedBy=sleep.target

- `RemainAfterExit=yes`: After started, the service is considered active until it is explicitly stopped.
- `StopWhenUnneeded=yes`: When active, the service will be stopped if no other active service requires it. In this specific example, it will be stopped after sleep.target is stopped.
- Because sleep.target is pulled in by suspend.target, hibernate.target and hybrid-sleep.target and because sleep.target itself is a StopWhenUnneeded service, the hook is guaranteed to start/stop properly for different tasks.

#### Delayed hibernation service file

An alternative approach is delayed hibernation. This makes use of sleep hooks to suspend as usual but sets a timer to wake up later to perform hibernation. Here, entering sleep is faster than `systemctl hybrid-sleep` since no hibernation is performed initially. However, unlike "hybrid-sleep", at this point there is no protection against power loss via hibernation while in suspension. This caveat makes this approach more suitable for laptops than desktops. Since hibernation is delayed, the laptop battery is only used during suspension and to trigger the eventual hibernation. This uses less power over the long-term than a "hybrid-sleep" which will remain suspended until the battery is drained. Note that if your laptop has a spinning hard disk, when it wakes up from suspend in order to hibernate, you may not want to be moving or carrying the laptop for these few seconds. Delayed hibernation may be desirable both to reduce power use as well as for security reasons (e.g. when using full disk encryption). An example script is located here. See also this post for an updated systemd sleep hook.

A slightly updated version of the service is:

    /etc/systemd/system/suspend-to-hibernate.service

    [Unit]
    Description=Delayed hibernation trigger
    Documentation=https://bbs.archlinux.org/viewtopic.php?pid=1420279#p1420279
    Documentation=https://wiki.archlinux.org/index.php/Power_management
    Conflicts=hibernate.target hybrid-sleep.target
    Before=sleep.target
    StopWhenUnneeded=true

    [Service]
    Type=oneshot
    RemainAfterExit=yes
    Environment="WAKEALARM=/sys/class/rtc/rtc0/wakealarm"
    Environment="SLEEPLENGTH=+2hour"
    ExecStart=-/usr/bin/sh -c 'echo -n "alarm set for "; date +%%s -d$SLEEPLENGTH | tee $WAKEALARM'
    ExecStop=-/usr/bin/sh -c '\
      alarm=$(cat $WAKEALARM); \
      now=$(date +%%s); \
      if [ -z "$alarm" ] || [ "$now" -ge "$alarm" ]; then \
         echo "hibernate triggered"; \
         systemctl hibernate; \
      else \
         echo "normal wakeup"; \
      fi; \
      echo 0 > $WAKEALARM; \
    '

    [Install]
    WantedBy=sleep.target

The `Before` and `Conflicts` options ensure it only is run for suspension and not hibernation--otherwise the service will run twice if delayed hibernation is triggered. The `WantedBy` and `StopWhenUnneeded` options are so it is started before sleep and stops upon resume. (Note that the `suspend.target` and `hibernate.target` targets do not stop when unneeded, but `sleep.target` does). Enable the service.

#### Hooks in /usr/lib/systemd/system-sleep

systemd runs all executables in `/usr/lib/systemd/system-sleep/`, passing two arguments to each of them:

- Argument 1: either `pre` or `post`, depending on whether the machine is going to sleep or waking up
- Argument 2: `suspend`, `hibernate` or `hybrid-sleep`, depending on which is being invoked

systemd will run these scripts concurrently and not one after another.

The output of any custom script will be logged by systemd-suspend.service, systemd-hibernate.service or systemd-hybrid-sleep.service. You can see its output in systemd's journal:

    # journalctl -b -u systemd-suspend

Note: You can also use sleep.target, suspend.target, hibernate.target or hybrid-sleep.target to hook units into the sleep state logic instead of using custom scripts.

An example of a custom sleep script:

    /usr/lib/systemd/system-sleep/example.sh

    #!/bin/sh
    case $1/$2 in
      pre/*)
        echo "Going to $2..."
        ;;
      post/*)
        echo "Waking up from $2..."
        ;;
    esac

Do not forget to make your script executable:

    # chmod a+x /usr/lib/systemd/system-sleep/example.sh

See systemd.special(7) and systemd-sleep(8) for more details.

### Troubleshooting

#### Delayed lid switch action

When performing lid switches in short succession, logind will delay the suspend action for up to 90s to detect possible docks. [1] This delay was made configurable with systemd v220:[2]

    /etc/systemd/logind.conf

    ...
    HoldoffTimeoutSec=30s
    ...

#### Suspend from corresponding laptop Fn key not working

If, regardless of the setting in logind.conf, the sleep button does not work (pressing it does not even produce a message in syslog), then logind is probably not watching the keyboard device. [3] Do:

    # journalctl | grep "Watching system buttons"

You might see something like this:

    May 25 21:28:19 vmarch.lan systemd-logind[210]: Watching system buttons on /dev/input/event2 (Power Button)
    May 25 21:28:19 vmarch.lan systemd-logind[210]: Watching system buttons on /dev/input/event3 (Sleep Button)
    May 25 21:28:19 vmarch.lan systemd-logind[210]: Watching system buttons on /dev/input/event4 (Video Bus)

Notice no keyboard device. Now obtain ATTRS{name} for the parent keyboard device [4] :

    # udevadm info -a /dev/input/by-path/*-kbd
    ...
    KERNEL=="event0"
    ...
    ATTRS{name}=="AT Translated Set 2 keyboard"

Now write a custom udev rule to add the "power-switch" tag:

    /etc/udev/rules.d/70-power-switch-my.rules

    ACTION=="remove", GOTO="power_switch_my_end"
    SUBSYSTEM=="input", KERNEL=="event*", ATTRS{name}=="AT Translated Set 2 keyboard", TAG+="power-switch"
    LABEL="power_switch_my_end"

Restart services and reload rules:

    # systemctl restart systemd-udevd
    # udevadm trigger
    # systemctl restart systemd-logind

Now you should see "Watching system buttons on /dev/input/event0" in syslog

## Power saving

Note: See Laptop#Power management for power management specific to laptops, such as battery monitoring.

This section is a reference for creating custom scripts and power saving settings such as by udev rules. Make sure that the settings are not managed by some other utility to avoid conflicts.

Almost all of the features listed here are worth using whether or not the computer is on AC or battery power. Most have negligible performance impact and are just not enabled by default because of commonly broken hardware/drivers. Reducing power usage means reducing heat, which can even lead to higher performance on a modern Intel or AMD CPU, thanks to dynamic overclocking.

### Audio

By default, audio power saving is turned off by most drivers. It can be enabled by setting the `power_save` parameter; a time (in seconds) to go into idle mode. To idle the audio card after one second, create the following file for Intel soundcards.

    /etc/modprobe.d/audio_powersave.conf

    options snd_hda_intel power_save=1

Alternatively, use the following for ac97:

    options snd_ac97_codec power_save=1

Note:

- To retrieve the manufacturer and the corresponding kernel driver which is used for your sound card, run `lspci -k`.
- Toggling the audio card's power state can cause a popping sound or noticeable latency on some broken hardware.

It is also possible to further reduce the audio power requirements by disabling the HDMI audio output, which can done by blacklisting the appropriate kernel modules (e.g. `snd_hda_codec_hdmi` in case of Intel hardware).

### Backlight

See Backlight.

### Bluetooth

This article or section needs expansion.

Reason: The device should likely be disabled with hciconfig first. (Discuss in Talk:Power management#)

To disable bluetooth completely, blacklist the `btusb` and `bluetooth` modules.

To turn off bluetooth only temporarily, use rfkill:

    # rfkill block bluetooth

Or with udev rule:

    /etc/udev/rules.d/50-bluetooth.rules

    # disable bluetooth
    SUBSYSTEM=="rfkill", ATTR{type}=="bluetooth", ATTR{state}="0"

### Web camera

If you will not use integrated web camera then blacklist the `uvcvideo` module.

### Kernel parameters

This section uses configs in `/etc/sysctl.d/`, which is "a drop-in directory for kernel sysctl parameters." See The New Configuration Files and more specifically sysctl.d(5) for more information.

#### Disabling NMI watchdog

This article or section needs expansion.

Reason: This or `nowatchdog` as can be seen in Improving performance#Watchdogs (Discuss in Talk:Power management#)

The NMI watchdog is a debugging feature to catch hardware hangs that cause a kernel panic. On some systems it can generate a lot of interrupts, causing a noticeable increase in power usage:

    /etc/sysctl.d/disable_watchdog.conf

    kernel.nmi_watchdog = 0

or add `nmi_watchdog=0` to the kernel line to disable it completely from early boot.

#### Writeback Time

Increasing the virtual memory dirty writeback time helps to aggregate disk I/O together, thus reducing spanned disk writes, and increasing power saving. To set the value to 60 seconds (default is 5 seconds):

    /etc/sysctl.d/dirty.conf

    vm.dirty_writeback_centisecs = 6000

To do the same for journal commits on supported filesystems (e.g. ext4, btrfs...), use `commit=60` as a option in fstab.

Note that this value is modified as a side effect of the Laptop Mode setting below. See also sysctl#Virtual memory for other parameters affecting I/O performance and power saving.

#### Laptop Mode

See the kernel documentation on the laptop mode 'knob.' "A sensible value for the knob is 5 seconds."

    /etc/sysctl.d/laptop.conf

    vm.laptop_mode = 5

Note: This setting is mainly relevant to spinning-disk drives.

### Network interfaces

Wake-on-LAN can be a useful feature, but if you are not making use of it then it is simply draining extra power waiting for a magic packet while in suspend. You can adapt a udev rule to disable the feature for all Ethernet interfaces.

To enable powersaving with iw on all wireless interfaces:

    /etc/udev/rules.d/70-wifi-powersave.rules

    ACTION=="add", SUBSYSTEM=="net", KERNEL=="wlan*", RUN+="/usr/bin/iw dev %k set power_save on"

In this example, `%k` is a specifier for the kernel name of the matched device. For example, if it finds that the rule is applicable to `wlan0`, the `%k` specifier will be replaced with `wlan0`. To apply the rules to only a particular interface, just replace the pattern `eth*` and specifier `%k` with the desired interface name. For more information, see Writing udev rules.

Note: In this case, the name of the configuration file is important. Due to the introduction of persistent device names via `80-net-setup-link.rules` in systemd, it is important that the network powersave rules are named lexicographically before `80-net-setup-link.rules` so that they are applied before the devices are named e.g. `enp2s0`. However, be advised that commands ran with `RUN` are executed after all rules have been processed -- in which case the naming of the rules file is irrelevant and the persistent device names should be used (the persistent device name can be referenced by replacing `%k` with `$name`).

#### Intel wireless cards (iwlwifi)

Additional power saving functions of Intel wireless cards with `iwlwifi` driver can be enabled by passing the correct parameters to the kernel module. Making it persistent can be achieved by adding the line below to `/etc/modprobe.d/iwlwifi.conf` file:

     options iwlwifi power_save=1 d0i3_disable=0 uapsd_disable=0
     options iwldvm force_cam=0

Keep in mind that these power saving options are experimental and can cause an unstable system.

### Bus power management

#### Active State Power Management

If the computer is believed not to support ASPM it will be disabled on boot:

    # lspci -vv | grep ASPM.*abled\;

ASPM is handled by the BIOS, if ASPM is disabled it will be because ref:

1. The BIOS disabled it for some reason (for conflicts?).
2. PCIE requires ASPM but L0s are optional (so L0s might be disabled and only L1 enabled).
3. The BIOS might not have been programmed for it.
4. The BIOS is buggy.

If believing the computer has support for ASPM it can be forced on for the kernel to handle with the `pcie_aspm=force` kernel parameter.

Warning:

- Forcing on ASPM can cause a freeze/panic, so make sure you have a way to undo the option if it does not work.
- On systems that do not support it forcing on ASPM can even increase power consumption.
- This forces ASPM in kernel while it can still remain disabled in hardware and not work. To check whether this is the case the `dmesg | grep ASPM` command can be used and if that is the case, hardware-specific Wiki article should be consulted.

To adjust to `powersave` do (the following command will not work unless enabled):

    echo powersave | tee /sys/module/pcie_aspm/parameters/policy

By default it looks like this:

    $ cat /sys/module/pcie_aspm/parameters/policy

    [default] performance powersave

#### PCI Runtime Power Management

    /etc/udev/rules.d/pci_pm.rules

    ACTION=="add", SUBSYSTEM=="pci", ATTR{power/control}="auto"

#### USB autosuspend

The Linux kernel can automatically suspend USB devices when they are not in use. This can sometimes save quite a bit of power, however some USB devices are not compatible with USB power saving and start to misbehave (common for USB mice/keyboards). udev rules based on whitelist or blacklist filtering can help to mitigate the problem.

The most simple and likely useless example is enabling autosuspend for all USB devices:

    /etc/udev/rules.d/50-usb_power_save.rules

    ACTION=="add", SUBSYSTEM=="usb", TEST=="power/control", ATTR{power/control}="auto"

To allow autosuspend only for devices that are known to work, use simple matching against vendor and product IDs (use lsusb to get these values):

    /etc/udev/rules.d/50-usb_power_save.rules

    # whitelist for usb autosuspend
    ACTION=="add", SUBSYSTEM=="usb", TEST=="power/control", ATTR{idVendor}=="05c6", ATTR{idProduct}=="9205", ATTR{power/control}="auto"

Alternatively, to blacklist devices that are not working with USB autosuspend and enable it for all other devices:

    /etc/udev/rules.d/50-usb_power_save.rules

    # blacklist for usb autosuspend
    ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="05c6", ATTR{idProduct}=="9205", GOTO="power_usb_rules_end"

    ACTION=="add", SUBSYSTEM=="usb", TEST=="power/control", ATTR{power/control}="auto"
    LABEL="power_usb_rules_end"

The default autosuspend idle delay time is controlled by the `autosuspend` parameter of the `usbcore` kernel module. To set the delay to 5 seconds instead of the default 2 seconds:

    /etc/modprobe.d/usb-autosuspend.conf

    options usbcore autosuspend=5

Similarly to `power/control`, the delay time can be fine-tuned per device by setting the `power/autosuspend` attribute.

See the Linux kernel documentation for more information on USB power management.

#### SATA Active Link Power Management

Note: This adds latency when accessing a drive that has been idle, so it is one of the few settings that may be worth toggling based on whether you are on AC power.

    /etc/udev/rules.d/hd_power_save.rules

    ACTION=="add", SUBSYSTEM=="scsi_host", KERNEL=="host*", ATTR{link_power_management_policy}="min_power"

Warning: SATA Active Link Power Management can lead to data loss on some devices. For example, the Lenovo T440s is known to suffer from this problem. Do not enable this setting unless you have frequent backups.

### Hard disk drive

See hdparm#Power management configuration for drive parameters that can be set.

Power saving is not effective when too many programs are frequently writing to the disk. Tracking all programs, and how and when they write to disk is the way to limit disk usage. Use iotop to see which programs use the disk frequently. See Improving performance#Storage devices for other tips.

Also little things like setting the noatime option can help. If enough RAM is available, consider disabling or limiting swappiness as it has the possibility to limit a good number of disk writes.

### CD-ROM or DVD drive

See Udisks#Devices do not remain unmounted (udisks).

## Tools and scripts

This article or section needs language, wiki syntax or style improvements.

Reason: Merged from Power saving, needs reorganization to fit into this page. (Discuss in Talk:Power management#)

### Using a script and an udev rule

Since systemd users can suspend and hibernate through `systemctl suspend` or `systemctl hibernate` and handle acpi events with `/etc/systemd/logind.conf`, it might be interesting to remove pm-utils and acpid. There is just one thing systemd cannot do (as of systemd-204): power management depending on whether the system is running on AC or battery. To fill this gap, you can create a single udev rule that runs a script when the AC adapter is plugged and unplugged:

    /etc/udev/rules.d/powersave.rules

    SUBSYSTEM=="power_supply", ATTR{online}=="0", RUN+="/path/to/your/script true"
    SUBSYSTEM=="power_supply", ATTR{online}=="1", RUN+="/path/to/your/script false"

Note: You can use the same script that pm-powersave uses. You just have to make it executable and place it somewhere else (for example `/usr/local/bin/`).

Examples of powersave scripts:

- ftw, package: ftw-gitAUR
- powersave
- throttle, from indicator-powersaveAUR

The above udev rule should work as expected, but if your power settings are not updated after a suspend or hibernate cycle, you should add a script in `/usr/lib/systemd/system-sleep/` with the following contents:

    /usr/lib/systemd/system-sleep/00powersave

    #!/bin/sh

    case $1 in
        pre) /path/to/your/script false ;;
        post)
    	if cat /sys/class/power_supply/AC0/online | grep 0 > /dev/null 2>&1
    	then
        		/path/to/your/script true
    	else
        		/path/to/your/script false
    	fi
        ;;
    esac
    exit 0

Do not forget to make it executable!

Note: Be aware that AC0 may be different for your laptop, change it if that is the case.

### Print power settings

This script prints power settings and a variety of other properties for USB and PCI devices. Note that root permissions are needed to see all settings.

    #!/bin/bash

    for i in $(find /sys/devices -name "bMaxPower")
    do
    	busdir=${i%/*}
    	busnum=$(<$busdir/busnum)
    	devnum=$(<$busdir/devnum)
    	title=$(lsusb -s $busnum:$devnum)

    	printf "\n\n+++ %s\n  -%s\n" "$title" "$busdir"

    	for ff in $(find $busdir/power -type f ! -empty 2>/dev/null)
    	do
    		v=$(cat $ff 2>/dev/null|tr -d "\n")
    		[[ ${#v} -gt 0 ]] && echo -e " ${ff##*/}=$v";
    		v=;
    	done | sort -g;
    done;

    printf "\n\n\n+++ %s\n" "Kernel Modules"
    for mod in $(lspci -k | sed -n '/in use:/s,^.*: ,,p' | sort -u)
    do
    	echo "+ $mod";
    	systool -v -m $mod 2> /dev/null | sed -n "/Parameters:/,/^$/p";
    done

## See also

- ThinkWiki:How to reduce power consumption
- How to get longer battery life on Linux

Category:

- Power management

Hidden categories:

- Pages or sections flagged with Template:Expansion
- Pages or sections flagged with Template:Style