Run command when temperature exceeds threshold, without daemon

If you're running the daemon from your own account, start it at boot time with Cron. Run crontab -e to edit your crontab file and add the line

@reboot ~/.dropbox-dist/dropboxd

It depends on what is the output of sensors. If yours is something like mine:

% sensors
k10temp-pci-00c3
Adapter: PCI adapter
temp1:        +44.0°C  (high = +70.0°C)

then you can use the following script, adapting it accordingly. Besides TEMP_STOP and TEMP_START, you should change the regular expression that filters the line from sensors you want to use. It's the parameter to grep, in the temp function.

#!/bin/bash

TEMP_STOP=98
TEMP_START=90

temp() {
    sensors | grep '^temp1:' | sed -e 's/.*: \+\([+-][0-9.]\+\)°C.*$/0\1/'
}

while true; do
    TEMP=$(temp)
    # keep waiting until temp is too hot
    while [ $(echo "$TEMP < $TEMP_STOP" | bc) = 1 ]; do
        sleep 10
        TEMP=$(temp)
    done

    echo temp $TEMP too hot, stopping.

    # now wait for it to cool down...
    while [ $(echo "$TEMP > $TEMP_START" | bc) = 1 ]; do
        sleep 10
        TEMP=$(temp)
    done

    echo ok now, restarting...
done