Shutting down on low battery

[kmike]

What's the recommended way to force a laptop to shut down when the battery gets too low? I know the Gnome and KDE ports claim to have this functionality, but I'm not running a desktop manager.

I accidentally ran out of juice the other day and the laptop turned off without syncing. The filesystems were mostly ok, but I lost four of the nine cells in the battery.

Since then I've put a rule in sensorsd.conf to run shutdown when the battery gets too low, but it seems like this might something that is handled automatically by the ACPI or APM subsystem. But I can't find any setting that might control this. I am seeing a low capacity sensor (hw.sensors.acpibat0.watthour2) which is currently showing 0.02 Ah, but that is not settable and I don't think the OS uses it for anything.

The only thing google turned up was a blog post that described using a cron job to check the battery level, which sounds kludgier than just using sensord.

[pawaan]

I wish it were set as default like under NetBSD :
http://ftp.twaren.net/BSD/NetBSD/Net...sensor_battery

Many times I had to manually fsck after losing work and it took an eternity

[bceverly]

I made an entry in my sensorsd.conf but the problem is that within 60 seconds of boot, it fires the command so clearly I'm doing something wrong. Does anyone have a working /etc/sensorsd.conf that fires on low battery that I could please take a look at?

Thanks.

[kmike]

Edit: I have a new post below with updated rules and scripts that handle this more cleanly.

There really isn't much in the sensorsd file. Firing on boot is something you have to handle, because the rules are checked when the sensor changes, and at boot they change from uninitialized to their current value. You'll want to change the limits for your particular machine...

Anyway, here's my /etc/sensorsd.conf.:

# If the battery gets too low, shut down the machine in an orderly
# fashion.  When booted on mains the amphourX sensors are present,
# when booted on battery the watthourX sensors are present.

# low limit 9.2 Wh (20% of max)
hw.sensors.acpibat0.watthour3:low=9.2Wh:command=/usr/local/script/low_batt %x %t %n %l %2

# low limit 0.93 Ah (20% of max)
hw.sensors.acpibat0.amphour3:low=0.93Ah:command=/usr/local/script/low_batt %x %t %n %l %2

The important stuff is in my low_batt script. If I boot and the battery is too low, I schedule a shutdown in 5 minutes anyway. What I do handle is that if the battery is low but is charging, then I don't schedule the shut down. As it stands now, if the battery gets low enough to trigger the rule, and I plug it into the wall, I have to go and kill the shutdown task to prevent the shutdown. And if I then take it off the charger before it gets above the threshold, it won't re-fire the rule again. I really should configure this script to run on both the charging sensor and the low charge sensor, though this requires changes to the script. It could then kill a pending shutdown, or schedule a shutdown on a charging->not charging transition. But even in its current condition it should give you some ideas on how to handle your situation.

Here's my /usr/local/script/low_batt script:

#! /bin/sh
device=$1     # e.g. acpibat0
devtype=$2    # "watthour" or "amphour"
sensornum=$3  # e.g. "3"
exception=$4  # "below", "above", "within", "invalid", "uninitialized"
curval=$5

dbglog=/tmp/low_batt.log

date				>> $dbglog
echo device    = $device	>> $dbglog
echo devtype   = $devtype   >> $dbglog
echo sensornum = $sensornum >> $dbglog
echo exception = $exception >> $dbglog
echo curval    = $curval 	>> $dbglog

if [ "$device" = "acpibat0" -a "$sensornum" = "3" -a "$exception" = "below" ]; then
	sysctl hw.sensors.${device}.raw0 >> $dbglog
	charging_stat=`sysctl -n hw.sensors.${device}.raw0 | awk '{print $1}'`
	echo "Charging status code = $charging_stat" >> $dbglog
	if [ "$charging_stat" = "1" ]; then
		message="Low battery charge detected on $device $devtype $sensornum.  The battery is currently discharging.  Requesting shutdown since continued drainage risks damaging the battery."
		echo $message 	>> $dbglog
		logger "$message"
		/sbin/shutdown -ph +5 "$message"
	elif [ "$charging_stat" = "2" ]; then
		message="Low battery charge detected on $device $devtype $sensornum.  The battery is currently charging.  Will not shut down."
		echo "$message" >> $dbglog
		logger "$message"
	else
		message="Low battery charge detected on $device $devtype $sensornum.  Unknown charging status code $charging_stat.  Will not shut down."
		echo "$message" >> $dbglog
		logger "$message"
	fi

fi

echo . >> $dbglog

[kmike]

I've modified my sensorsd.conf and script files to handle the cases where the user fiddles with the power cable while the battery is low. This new version has rules on the two battery level sensors and the battery charging sensor (each with its own script).

/etc/sensorsd.conf

# If the battery gets too low, shut down the machine in an orderly
# fashion.  When booted on mains the amphourX sensors are present,
# when booted on battery the watthourX sensors are present.  When the
# battery charging status changes, make sure we are still doing the
# right thing.
#
# !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
# IF YOU CHANGE THE LIMITS ON THE AMP/WATT RULES, REMEMBER TO CHANGE
# THEM ON THE RAW0 ACTION AS WELL
# !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

# low limit 9.2 Wh (20% of max)
hw.sensors.acpibat0.watthour3:low=9.2Wh:command=/usr/local/script/bat0_low %x %t %n %2 %3

# low limit 0.93 Ah (20% of max)
hw.sensors.acpibat0.amphour3:low=0.93Ah:command=/usr/local/script/bat0_low %x %t %n %2 %3

# When wall power goes off, we need to doublecheck the battery level.
# When wall power goes on, we need to kill any pending shutdowns.
hw.sensors.acpibat0.raw0:command=/usr/local/script/bat0_charging %x %t %n %2 "9.2" "0.93"

Script to handle the low-battery exception /usr/local/script/bat0_low:

#! /bin/sh

#
# Configuration
#

dbglog=/tmp/low_batt.log

# production
logger=logger
shutdown=/sbin/shutdown

# debugging
#logger=false
#shutdown=false


#
# Parse command line
#
device=$1         # e.g. acpibat0
devtype=$2        # "watthour" or "amphour"
sensornum=$3      # e.g. "3"
curval=$4         # floating point number
curval_units=$5   #"Ah" or "Wh"
lowlim=$6         # floating point number
lowlim_units=$7   #"Ah" or "Wh"

# calculate exception
if (awk "BEGIN {exit(!($curval < $lowlim))}"); then
  exception='below'
else
  exception='within'
fi

date						           >> $dbglog
echo device    = $device	           >> $dbglog
echo devtype   = $devtype              >> $dbglog
echo sensornum = $sensornum            >> $dbglog
echo exception = $exception            >> $dbglog
echo curval    = $curval $curval_units >> $dbglog
echo lowlim    = $lowlim $lowlim_units >> $dbglog


#
# Handle the potential low-battery condition.
#
if [ "$device" = "acpibat0" -a "$sensornum" = "3" -a "$exception" = "below" ]; then
	sysctl hw.sensors.${device}.raw0 >> $dbglog
	charging_stat=`sysctl -n hw.sensors.${device}.raw0 | awk '{print $1}'`
	echo "Charging status code = $charging_stat" >> $dbglog
	if [ "$charging_stat" = "1" ]; then
		message="Low battery charge detected on $device $devtype $sensornum.  The battery is currently discharging.  Requesting shutdown since continued drainage risks damaging the battery."
		echo $message 	>> $dbglog
		$logger "$message"
		$shutdown -ph +5 "$message"
	elif [ "$charging_stat" = "2" ]; then
		message="Low battery charge detected on $device $devtype $sensornum.  The battery is currently charging.  Will not shut down."
		echo "$message" >> $dbglog
		$logger "$message"
	else
		message="Low battery charge detected on $device $devtype $sensornum.  Unknown charging status code $charging_stat.  Will not shut down."
		echo "$message" >> $dbglog
		$logger "$message"
	fi

fi

echo . >> $dbglog

And the script to handle the charging status change /usr/local/script/bat0_charging:

#! /bin/sh

#
# Configuration
#

dbglog=/tmp/batt_charging.log

# production
logger=logger

# debugging
#logger=false

#
# Parse command line
#
device=$1         # e.g. acpibat0
devtype=$2        # "watthour" or "amphour"
sensornum=$3      # e.g. "3"
curval=$4         # 1 = discharging, 2 = charging
lowlim_watthr=$5      
lowlim_amphr=$6

date						>> $dbglog
echo device    = $device	>> $dbglog
echo devtype   = $devtype   >> $dbglog
echo sensornum = $sensornum >> $dbglog
echo curval    = $curval	>> $dbglog
echo lowlim_watthr = $lowlim_watthr >> $dbglog
echo lowlim_amphr = $lowlim_amphr >> $dbglog

if [ "$curval" = "1" ]; then
	#
	# Discharging.
	# Run the low_batt script with the appropriate parameters.
	#
	watthours=`sysctl -n hw.sensors.acpibat0.watthour3 | awk '{print $1}'`
	amphours=`sysctl -n hw.sensors.acpibat0.amphour3 | awk '{print $1}'`
	if [ "$watthours" ]; then
		/usr/local/script/low_batt "acpibat0" "watthour" "3" "$watthours" "Wh" "$lowlim_watthr" "Wh"
	elif [ "$amphours" ]; then
		/usr/local/script/low_batt "acpibat0" "amphour" "3" "$amphours" "Ah" "$lowlim_amphr" "Ah"
	fi
elif [ "$curval" = "2" ]; then
	#
	# Charging.  We probably want to abort any shutdowns...
	#
	message="Stopping any shutdowns in progress that may have been issued by low_batt."
	echo $message >> $dbglog
	$logger "$message"

	kill -9 shutdown
fi

echo . >> $dbglog

[bceverly]

Appreciate the help.