So you've got an ubuntu box you want on during business hours, but you don't need it on outside business hours. Maybe it's a build server or something similar. Obviously, you could manually start it every morning - but you might be ill or go on holiday. Let's automate it with wake-on-RTC! The instructions below are for Ubuntu 14.04.
First of all, create this file at /root/weekday-restart.sh (I use sudo pico /root/weekday-restart.sh but you can use any text editor you like!)
#!/bin/bash
set -e # Exit on failure
# For some reason, if wakealarm is already set it's an error to set it
# to a new value - unless we first clear it by writing 0 to it.
echo 0 > /sys/class/rtc/rtc0/wakealarm
# 1=Monday, 7=Sunday
current_day_of_week=$( date '+%u' )
if [ "$current_day_of_week" -lt "5" ]; then
sleep_for_days=1
else
sleep_for_days=$((8-current_day_of_week))
fi
# This bit determines the time of day for the next boot:
next_boot_text=$( date '+%Y-%m-%dT08:50:00' -d "+$sleep_for_days days" )
next_boot_unix=$( date '+%s' --date="$next_boot_text" )
echo "$next_boot_unix" > /sys/class/rtc/rtc0/wakealarm
cat /sys/class/rtc/rtc0/wakealarm
echo "Scheduled wake for $next_boot_text = $next_boot_unix"
# You can make a call to cronitor or healthchecks.io here if you like.
Then make it executable and edit root's crontab:
chmod u+x /root/weekday-restart.sh
sudo crontab -e
And add the following lines:
# m h dom mon dow command
0 10,17 * * * /root/weekday-restart.sh > /root/last-restart.log 2>&1
0 20 * * * pm-suspend
Scheduling the restart will log the results (and any errors) to /root/last-restart.log so if you have any trouble you can debug it easily.
The pm-suspend line suspends the box at 20:00 but the wake-on-rtc will work just as well if you power off the box entirely. This can also give you a convenient chance to apply any updates - but if you're going to run apt-get, make sure your script sets the path so it works right under cron.