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My ISP provides unlimited download from 2am to 8am. So i was not able to sleep after 2 from the time i switched to the new broadband plan. Keeping the system on and setting a cronjob to start downloading after 2 was an option. But i was more concerned about the increasing electricity charge, than my sleep. Besides it is my social responsibility to save energy as a gonna-be software engineer :p. After a bit of googling and hacking i was able to wake up my system at a particular time. Here i am going to explain how i made my arch linux system to boot automatically at 2 am.

The configuration is done in Arch Linux. For automatic wakeup it needs a BIOS which supports RTC alarm. Most of them manufactured after 2000 supports this feature.

1) Check if your BIOS supports automatic wakeup

Execute the command below as root.

# grep rtc /var/log/messages.log
rtc_cmos 00:03: RTC can wake from S4
rtc0: alarms up to one month

If you can find something like this in the output.It says that the system can wakeup and a wakeup time can be setup.

2) Enable automatic wakeup in BIOS

Go to your BIOS setup, Under Power Management search for something like “Wake by RTC Alarm” or “Resume by RTC alarm” or “RTC resume”.Then enable it.

3) Set the hardware clock time standard as UTC

Edit the /etc/rc.conf file as root and set the HARDWARECLOCK variable to UTC

[ragsagar@h4ckb0x ~]$ grep ^HARDWARECLOCK /etc/rc.conf
HARDWARECLOCK="UTC"

Make sure that your timezone is set correctly in /etc/rc.conf
More help : https://wiki.archlinux.org/index.php/Time

4) Set the alarm time

Execute the following commands as root

# echo 0 > /sys/class/rtc/rtc0/wakealarm
# echo `date '+%s' -d '+ 5 minutes'` > /sys/class/rtc/rtc0/wakealarm

This will set the the alarm time as 5 minutes into the future.

Now run

$ cat /sys/class/rtc/rtc0/wakealarm

If the output of above command is something like “1313383930”, the alarm is set. It is epoch time. If it doesn’t yield any result make sure that the HARDWARECLOCK variable is set to UTC and reboot and try again to set the alarm time.

Now run

$ cat /proc/driver/rtc

Go through rtc_time, alrm_time and alrm_date and check if they are correct(will be in UTC).Turn off the system and leave the power on. Check if the system is booting automatically after five mintues.

5) Setting the alarm to a particular time and date.

To set the alarm to woke up the system at 16th Aug 2:05am, Run the following as root

# echo 0 > /sys/class/rtc/rtc0/wakealarm
# date --date "Aug 16 , 2011 02:05:00" +%s > /sys/class/rtc/rtc0/wakealarm

You can convert the epoch time to readable format and check the alarm time is correct.

[root@h4ckb0x ragsagar]# cat /sys/class/rtc/rtc0/wakealarm
1313440500
[root@h4ckb0x ragsagar]# date -d @1313440500 +%F" "%T
2011-08-16 02:05:00

Note : The mythtv wiki about acpi wakeup says that setting the hardware clock after setting alarm will disable the alarm while most of the linux distribution sets hardware clock during shutdown. They suggest to disable hardware clock adjusting during shutdown. To do that in Archlinux set the HARDWARECLOCK=”” in /etc/rc.conf . But in my arch system the alarm was not working when i set HARDWARECLOCK=”” whereas it worked when i gave HARDWARECLOCK=”UTC”. So if the wake up alarm is not working do try after changing the value of this variable.

To start downloading when the system boots up, i added a cronjob to restart the router at 2:15 and 7:45 (to account the download in happy hours). Also added “transmission-gtk” to the gnome-session-properties. So that transmission will be launched on startup and downloading will be started.

Reference :
http://www.mythtv.org/wiki/ACPI_Wakeup
https://wiki.archlinux.org/index.php/Time

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