Power management

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:

Console

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

https://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-tools^AUR

• libsmbios — Library and tools for interacting with Dell SMBIOS tables.

https://github.com/dell/libsmbios || libsmbios

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

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

• systemd — A system and service manager.

https://freedesktop.org/wiki/Software/systemd/ || systemd

• TLP — Advanced power management for Linux.

https://linrunner.de/tlp || tlp

Graphical

• batterymon-clone — Simple battery monitor tray icon.

https://github.com/jareksed/batterymon-clone || batterymon-clone^AUR

• batsignal — Lightweight battery monitor that uses libnotify to warn of low battery levels.

https://github.com/electrickite/batsignal || batsignal^AUR

• cbatticon — Lightweight and fast battery icon that sits in your system tray.

https://github.com/valr/cbatticon || cbatticon

• GNOME Power Statistics — System power information and statistics for GNOME.

https://gitlab.gnome.org/GNOME/gnome-power-manager || gnome-power-manager

• KDE Power Devil — Power management module for Plasma.

https://invent.kde.org/plasma/powerdevil || powerdevil

• LXQt Power Management — Power management module for LXQt.

https://github.com/lxqt/lxqt-powermanagement || lxqt-powermanagement

• MATE Power Management — Power management tool for MATE.

https://github.com/mate-desktop/mate-power-manager || mate-power-manager

• MATE Power Statistics — System power information and statistics for MATE.

https://github.com/mate-desktop/mate-power-manager || mate-power-manager

• powerkit — Desktop independent power manager.

https://github.com/rodlie/powerkit || powerkit^AUR

• Xfce Power Manager — Power manager for Xfce.

https://docs.xfce.org/xfce/xfce4-power-manager/start || xfce4-power-manager

• vattery — Battery monitoring application written in Vala that will display the status of a laptop battery in a system tray.

https://www.jezra.net/projects/vattery.html || vattery^AUR

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, suspend-then-hibernate, 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
HandleLidSwitchExternalPower	Triggered when the lid is closed if the system is connected to external power.	action set for HandleLidSwitch

To apply any changes, signal systemd-logind with HUP:

# systemctl kill -s HUP systemd-logind

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 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 to suspend to RAM or hibernate using the kernel's native suspend/resume functionality. There are also mechanisms to add hooks to customize pre- and post-suspend actions.

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.

There are also two modes combining suspend and hibernate:

• systemctl hybrid-sleep suspends the system both to RAM and disk, so a complete power loss does not result in lost data. This mode is also called suspend to both.
• systemctl suspend-then-hibernate initially suspends the system to RAM and if it is not interrupted within the delay specified by HibernateDelaySec in systemd-sleep.conf(5), then the system will be woken using an RTC alarm and hibernated.

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.

Hybrid-sleep on suspend or hibernation request

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 and the linux kernel documentation on power states.

Sleep hooks

Suspend/resume service files

Service files can be hooked into suspend.target, hibernate.target, sleep.target, hybrid-sleep.target and suspend-then-hibernate.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
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
ExecStart=/usr/local/bin/ssh-connect.sh

[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-suspend.service

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

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

[Install]
WantedBy=sleep.target

/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

Tip: 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.

Generic service template

In this example, we create a template service which we can then use to hook any existing systemd service to power events:[1]

/etc/systemd/system/sleep@.service

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

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=-/usr/bin/systemctl stop %i
ExecStop=-/usr/bin/systemctl start %i

[Install]
WantedBy=sleep.target

Then enable an instance of this template by specifying the basename of an existing systemd service after the @, i.e., sleep@service-file-basename.service. See systemd.unit(5) § DESCRIPTION for more details on templates.

Tip: Templates are not limited to systemd services and can be used with other programs/ See [2] for some examples.

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 journalctl:

# journalctl -b -u systemd-suspend.service

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. [3] This delay was made configurable with systemd v220:[4]

/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. [5] 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 [6] :

# 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 systemd-udevd.service, reload rules by running udevadm trigger as root, and restart systemd-logind.service.

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

PC will not wake from sleep on B550I motherboards

On some motherboards with B550i chipsets (i.e, Gigabyte Technology Co., Ltd. Default string B550I AORUS PRO AX), the system will not completely enter the sleep state or come out of it. Symptoms include the system entering sleep and the monitor turning off while internal LEDs on the motherboard or the power LED stay on. Subsequently, the system will not come back from this state and require a hard power off. If you have similar issues with AMD, first make sure your system is fully updated and check whether the AMD microcode package is installed.

Next, check the following:

$ cat /proc/acpi/wakeup

You will see something like this:

Device	S-state	  Status   Sysfs node
GP12	  S4	*enabled   pci:0000:00:07.1
GP13	  S4	*enabled   pci:0000:00:08.1
XHC0	  S4	*enabled   pci:0000:0b:00.3
GP30	  S4	*disabled
GP31	  S4	*disabled
PS2K	  S3	*disabled
GPP0	  S4	*enabled   pci:0000:00:01.1
GPP8	  S4	*enabled   pci:0000:00:03.1
PTXH	  S4	*enabled   pci:0000:05:00.0
PT20	  S4	*disabled
PT24	  S4	*disabled
PT26	  S4	*disabled
PT27	  S4	*disabled
PT28	  S4	*enabled   pci:0000:06:08.0
PT29	  S4	*enabled   pci:0000:06:09.0

Notice the line starting with GPP0. If that is enabled, you can run the following command:

# echo GPP0 > /proc/acpi/wakeup

Now test by running systemctl suspend and let the system go to sleep. Then try to wake the system after a few seconds. If it works, you can make the workaround permanent. Create a unit file:

/etc/systemd/system/toggle.ggp0.to.fix.suspend.issue.service

[Unit]
Description="Disable GGP0 to fix suspend issue"

[Service]
ExecStart=/bin/sh -c "/bin/echo GPP0 > /proc/acpi/wakeup"

[Install]
WantedBy=multi-user.target

Reload the systemd manager and start/enable the newly created unit.

Power saving

Note: See Laptop#Power management for power management specific to laptops, such as battery monitoring. See also pages specific to your CPU and GPU (e.g., Ryzen, AMDGPU).

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.

Processors with Intel HWP (Intel Hardware P-state) support

The available energy preferences of a HWP supported processor are default performance balance_performance balance_power power.

This can be validated by running

$ cat /sys/devices/system/cpu/cpufreq/policy?/energy_performance_available_preferences

To conserve more energy, you can configuration by creating the following file:

/etc/tmpfiles.d/energy_performance_preference.conf

w /sys/devices/system/cpu/cpufreq/policy?/energy_performance_preference - - - - balance_power

See the systemd-tmpfiles(8) and tmpfiles.d(5) man pages for details.

Audio

Kernel

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).

PulseAudio

By default, PulseAudio suspends any audio sources that have become idle for too long. When using an external USB microphone, recordings may start with a pop sound. As a workaround, comment out the following line in /etc/pulse/default.pa:

load-module module-suspend-on-idle

Afterwards, restart PulseAudio with systemctl restart --user pulseaudio.

Backlight

See Backlight.

Bluetooth

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 configurations 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

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 the Wake-on-LAN#udev rule to disable the feature for all ethernet interfaces. To enable powersaving with iw on all wireless interfaces:

/etc/udev/rules.d/81-wifi-powersave.rules

ACTION=="add", SUBSYSTEM=="net", KERNEL=="wl*", RUN+="/usr/bin/iw dev $name set power_save on"

The name of the configuration file is important. With the use of persistent device names in systemd, the above network rule, named lexicographically after 80-net-setup-link.rules, is applied after the device is renamed with a persistent name e.g. wlan0 renamed wlp3s0. Be aware that the RUN command is executed after all rules have been processed and must anyway use the persistent name, available in $name for the matched device.

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 them persistent can be achieved by adding the lines below to the /etc/modprobe.d/iwlwifi.conf file:

options iwlwifi power_save=1

This option will probably increase your median latency:

options iwlwifi uapsd_disable=0

On kernels < 5.4 you can use this option, but it will probably decrease your maximum throughput:

options iwlwifi d0i3_disable=0

Depending on your wireless card one of these two options will apply.

options iwlmvm power_scheme=3

options iwldvm force_cam=0

You can check which one is relevant by checking which of these modules is running using

# lsmod | grep '^iwl.vm'

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 [7]:

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, run dmesg | grep ASPM as root. If so, consult the Wiki article specific to your hardware.

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

# echo powersave > /sys/module/pcie_aspm/parameters/policy

By default it looks like this:

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

[default] performance powersave powersupersave

PCI Runtime Power Management

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

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

The rule above powers all unused devices down, but some devices will not wake up again. To allow runtime power management only for devices that are known to work, use simple matching against vendor and device IDs (use lspci -nn to get these values):

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

# whitelist for pci autosuspend
SUBSYSTEM=="pci", ATTR{vendor}=="0x1234", ATTR{device}=="0x1234", ATTR{power/control}="auto"

Alternatively, to blacklist devices that are not working with PCI runtime power management and enable it for all other devices:

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

# blacklist for pci runtime power management
SUBSYSTEM=="pci", ATTR{vendor}=="0x1234", ATTR{device}=="0x1234", ATTR{power/control}="on", GOTO="pci_pm_end"

SUBSYSTEM=="pci", ATTR{power/control}="auto"
LABEL="pci_pm_end"

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 built-in kernel module. To set the delay to 5 seconds instead of the default 2 seconds, add the following kernel parameter for your bootloader.

usbcore.autosuspend=5

Similarly to power/control, the delay time can be fine-tuned per device by setting the power/autosuspend attribute. This means, alternatively, autosuspend can be disabled by setting power/autosuspend to -1 (i.e., never autosuspend):

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

ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="05c6", ATTR{idProduct}=="9205", ATTR{power/autosuspend}="-1"

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

SATA Active Link Power Management

Warning: SATA Active Link Power Management can lead to data loss on some devices. Do not enable this setting unless you have frequent backups.

Since Linux 4.15 there is a new setting called med_power_with_dipm that matches the behaviour of Windows IRST driver settings and should not cause data loss with recent SSD/HDD drives. The power saving can be significant, ranging from 1.0 to 1.5 Watts (when idle). It will become a default setting for Intel based laptops in Linux 4.16 [8].

The current setting can be read from /sys/class/scsi_host/host*/link_power_management_policy as follows:

$ cat /sys/class/scsi_host/host*/link_power_management_policy

Available ALPM settings

Setting	Description	Power saving
max_performance	current default	None
medium_power	-	~1.0 Watts
med_power_with_dipm	recommended setting	~1.5 Watts
min_power	WARNING: possible data loss	~1.5 Watts

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

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

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.

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

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-git^AUR
• powersave
• throttle, from indicator-powersave^AUR

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