How do I make my laptop sleep when it reaches some low battery threshold?

Question

I'm using Ubuntu, but I have i3 as my window manager instead of a desktop environment.

When my battery reaches 0%, the computer will just abruptly shut down, no warning or anything.

Is there a simple script or configuration I can set up so that it goes to sleep at, say 4% battery?

Solution 1

Here's a small script that checks for the battery level and calls a custom command, here pm-hibernate, in case the battery level is below a certain threshold.

#!/bin/sh

###########################################################################
#
# Usage: system-low-battery
#
# Checks if the battery level is low. If “low_threshold” is exceeded
# a system notification is displayed, if “critical_threshold” is exceeded
# a popup window is displayed as well. If “OK” is pressed, the system
# shuts down after “timeout” seconds. If “Cancel” is pressed the script
# does nothing.
#
# This script is supposed to be called from a cron job.
#
###########################################################################

# This is required because the script is invoked by cron. Dbus information
# is stored in a file by the following script when a user logs in. Connect
# it to your autostart mechanism of choice.
#
# #!/bin/sh
# touch $HOME/.dbus/Xdbus
# chmod 600 $HOME/.dbus/Xdbus
# env | grep DBUS_SESSION_BUS_ADDRESS > $HOME/.dbus/Xdbus
# echo 'export DBUS_SESSION_BUS_ADDRESS' >> $HOME/.dbus/Xdbus
# exit 0
#
if [ -r ~/.dbus/Xdbus ]; then
  source ~/.dbus/Xdbus
fi

low_threshold=10
critical_threshold=4
timeout=59
shutdown_cmd='/usr/sbin/pm-hibernate'

level=$(cat /sys/devices/platform/smapi/BAT0/remaining_percent)
state=$(cat /sys/devices/platform/smapi/BAT0/state)

if [ x"$state" != x'discharging' ]; then
  exit 0
fi

do_shutdown() {
  sleep $timeout && kill $zenity_pid 2>/dev/null

  if [ x"$state" != x'discharging' ]; then
    exit 0
  else
    $shutdown_cmd
  fi
}

if [ "$level" -gt $critical_threshold ] && [ "$level" -lt $low_threshold ]; then
  notify-send "Battery level is low: $level%"
fi

if [ "$level" -lt $critical_threshold ]; then

  notify-send -u critical -t 20000 "Battery level is low: $level%" \
    'The system is going to shut down in 1 minute.'

  DISPLAY=:0 zenity --question --ok-label 'OK' --cancel-label 'Cancel' \
    --text "Battery level is low: $level%.\n\n The system is going to shut down in 1 minute." &
  zenity_pid=$!

  do_shutdown &
  shutdown_pid=$!

  trap 'kill $shutdown_pid' 1

  if ! wait $zenity_pid; then
    kill $shutdown_pid 2>/dev/null
  fi

fi

exit 0

It's a very simple script, but I think you get the idea and can easily adapt it to your needs. The path to the battery level might be different on your system. A little more portable would probably be to use something like acpi | cut -f2 -d, to obtain the battery level. This script can be scheduled by cron to run every minute. Edit your crontab with crontab -e and add the script:

*/1 * * * * /home/me/usr/bin/low-battery-shutdown

Another solution would be to install a desktop environment like Gnome or Xfce (and change your window manager to i3). Both mentioned destop environments feature power management daemons which take care of powering off the computer. But I assume you deliberately don't use them and are seeking for a more minimalistic solution.

Solution 2

As of Debian ≥ 10 (and comparably recent Linux systems), you can just create a file /etc/cron.d/check-battery that contains:

* * * * * root [ "$(cat /sys/class/power_supply/BAT0/status)" != Discharging -o "$(cat /sys/class/power_supply/BAT0/capacity)" -gt 30 ] || systemctl suspend

This will suspend your system whenever the battery level reaches 30%.

Of course, feel free to replace the final suspend with hybrid-sleep, hibernate, poweroff or whatever fits your needs.

No external tools are required, not even the acpi package. This is based on the idea of Matija Nalis' answer, but adjusted to the year 2022.

Solution 3

Instead of hacking your own scripts and if you are using Ubuntu as the tag suggests, you could just install the upower package. It should be available on all Debian derivatives including Ubuntu. By default it comes with a configuration in /etc/UPower/UPower.conf which activates hybrid sleep once the battery level reaches critical values. The default for the critical level is 2%.

For users of other distributions, the relevant entries for /etc/UPower/UPower.conf are:

PercentageAction=2
CriticalPowerAction=HybridSleep

You can also use TimeAction together with UsePercentageForPolicy=false to let the action be carried out once only the specified time is left:

TimeAction=120

The valid values for CriticalPowerAction are PowerOff, Hibernate and HybridSleep. If HybridSleep is set but not available, Hibernate will be used. If Hibernate is set but not available, PowerOff will be used.

The advantage of HybridSleep is, that in addition to writing out memory into your swap area, it then suspends the system. Suspend will still consume some battery but if you come back before the battery ran out, you can much more quickly resume from a suspended system than from a hibernated one. In case the battery does run out before you get back to a power socket, you can resume the system from hibernation once you have power again.

Solution 4

The currently accepted answer is great, but a little bit outdated for Ubuntu 16.04:

• The commands to get battery status have changed.
• The environment variables required for notify-send to work have changed.
• The script given there no longer works from user cron as hibernate requires root.
• systemctl hibernate is preferred over pm-hibernate.

So, here is the script I use:

#!/usr/bin/env bash

# Notifies the user if the battery is low.
# Executes some command (like hibernate) on critical battery.
# This script is supposed to be called from a cron job.
# If you change this script's name/path, don't forget to update it in crontab !!

level=$(cat /sys/class/power_supply/BAT1/capacity)
status=$(cat /sys/class/power_supply/BAT1/status)

# Exit if not discharging
if [ "${status}" != "Discharging" ]; then
  exit 0
fi

# Source the environment variables required for notify-send to work.
env_vars_path="$HOME/.env_vars"
source "${env_vars_path}"

low_notif_percentage=20
critical_notif_percentage=15
critical_action_percentage=10

if [ "${level}" -le ${critical_action_percentage} ]; then
  # sudo is required when running from cron
  sudo systemctl hibernate
  exit 0
fi

if [ "${level}" -le ${critical_notif_percentage} ]; then
  notify-send -i '/usr/share/icons/gnome/256x256/status/battery-caution.png' "Battery critical: ${level}%"
  exit 0
fi

if [ "${level}" -le ${low_notif_percentage} ]; then
  notify-send -i '/usr/share/icons/gnome/256x256/status/battery-low.png' "Battery low: $level%"
  exit 0
fi

The environment variables required for notify-send to work are created using this script:

#!/usr/bin/env bash

# Create a new file containing the values of the environment variables
# required for cron scripts to work.
# This script is supposed to be scheduled to run at startup.

env_vars_path="$HOME/.env_vars"

rm -f "${env_vars_path}"
touch "${env_vars_path}"
chmod 600 "${env_vars_path}"

# Array of the environment variables.
env_vars=("DBUS_SESSION_BUS_ADDRESS" "XAUTHORITY" "DISPLAY")

for env_var in "${env_vars[@]}"
do
  echo "$env_var"
  env | grep "${env_var}" >> "${env_vars_path}";
  echo "export ${env_var}" >> "${env_vars_path}";
done

This file needs to run at startup (can be done using any method of your choice; I use Ubuntu's builtin Startup Applications).

Note: sudo systemctl hibernate might not work from cron. Follow this to solve it.

View more solutions

Comments

[o_o_o--]

Hm, I tried running sleepd -b 40 and nothing happened after the 40% mark. I also tried sudo sleepd -b 40 -s pm-suspend and nothing happens...

[o_o_o--]

(TIL "cut".) The script works! I have acpi | cut -f2 -d, | cut -f1 d% -- I'll read about cron to get it to run on its own. Thanks!

[Tam Borine]

I don't have /sys/devices/platform/smapi/ directory. Where can I find the remaining percentage of battery power? I am using custom kernel 3.10

[Marco]

@MartinVegter It depends on your hardware, you can try /sys/class/power_supply/BAT0/capacity. Otherwise use the acpi command.

[Admin]

Note: I think HybridSleep requires to have a swap space.

[Admin]

that seems very nice! but could that be used with systemd timer instead of cron? (example here) I'm on Solus OS where cron is absent.

[josch]

@cipricus that is correct but upower will gracefully choose to shut the machine down instead if it cannot hibernate.

[Matija Nalis]

@cipricus I guess so, but I avoid systemd so can't give example. I do seem to recall systemd has its own ACPI power handlers, so if you're stuck with systemd you would probably want to avoid clashing with that

[Admin]

thanks, I have found an alternative involving uname: github.com/jerrinfrncs/batterynotif/blob/master/…

[lucidbrot]

Is the upower answer obsolete?

[Eoin]

I don't know if the upower answer is obsolete or not. It just didn't work for me, and I didn't find enough time to investigate and to debug that stuff. And to put it bluntly: Why should I? This simple one-liner is doing its job well. It is reliable since the day I created it, with a minimum of dependencies and system requirements. The only thing I changed since then is increasing the threshold from 10% to 30%.

[mathur]

What do the stars mean? Why did you write them?

[Eoin]

Every file in /etc/cron.d/ is a crontab. The 5 stars mean that the following command is to be executed every minute, and "root" is the user under whose permissions the command is to be executed. See man 5 crontab for more details.

[ipcjs]

note: .../BAT0/status maybe return Unknown，so it is better to use [ "$(cat /sys/class/power_supply/BAT0/status)" = Discharging -a "$(cat /sys/class/power_supply/BAT0/capacity)" -lt 10 ] && systemctl suspend instead.

[Eoin]

@ipcjs Thanks for the hint. I improved my answer accordingly. Note that I'm preferring "!= Discharging" over inverting the whole logic, as the latter would make the command return with a non-zero exit code when everything is fine, which would be quite confusing.

[Martin Massera]

is resume automatic when the battery gets charged or does one have to manually press the power button?

[josch]

@MartinMassera one has to manually press the power button

[Alexei Martianov]

@lucidbrot, Just now to Linux Mint 20.2 at least on the fly (w/out reboot) editing UPower.conf has not resulted in action(s) when thresholds were achieved and % decreased even further. Maybe it needs daemon restart, but help (as man page itself notices "not fully documented").

[Alexei Martianov]

Should it (editing UPower.conf) work w/out reboot? I've tried on Linux Mint and it does not. Maybe daemon restart is needed?