Automatic shutdown after network inactivity

For my NAS, I tried a few options to go more green and save some energy. Besides the WOL which works well, I set up the NAS to shut down after some time of network inactivity (or at least few activity). To achieve that, I digged through the net and found a solution somewhere (probably here) which I adapted to my needs.

I named the script shutdown_if_inactive and put it to /usr/local/sbin/. The script is as follows:


#!/bin/bash
#
# This is scheduled in CRON. It will run every 20 minutes
# and check for inactivity. It compares the RX and TX packets
# from 20 minutes ago to detect if they significantly increased.
# If they haven't, it will force the system to sleep.
#

log=~/scripts/idle/log

# Extract the RX/TX
rx=`/sbin/ifconfig eth0 | grep -m 1 RX | cut -d: -f2 | sed 's/ //g' | sed 's/errors//g'`
tx=`/sbin/ifconfig eth0 | grep -m 1 TX | cut -d: -f2 | sed 's/ //g' | sed 's/errors//g'`

#Write Date to log
date >> $log
echo "Current Values" >> $log
echo "rx: "$rx >> $log
echo "tx: "$tx >> $log

# Check if RX/TX Files Exist
if [ -f ~/scripts/idle/rx ] || [ -f ~scripts/idle/tx ]; then
p_rx=`cat ~/scripts/idle/rx` ## store previous rx value in p_rx
p_tx=`cat ~/scripts/idle/tx` ## store previous tx value in p_tx

echo "Previous Values" >> $log
echo "p_rx: "$p_rx >> $log
echo "t_rx: "$p_tx >> $log

echo $rx > ~/scripts/idle/rx ## Write packets to RX file
echo $tx > ~/scripts/idle/tx ## Write packets to TX file

# Calculate threshold limit
t_rx=`expr $p_rx + 1000`
t_tx=`expr $p_tx + 1000`

echo "Threshold Values" >> $log
echo "t_rx: "$t_rx >> $log
echo "t_tx: "$t_tx >> $log
echo " " >> $log

if [ $rx -le $t_rx ] || [ $tx -le $t_tx ]; then ## If network packets have not changed that much
echo "Shutting down" >> $log
echo " " >> $log
rm ~/scripts/idle/rx
rm ~/scripts/idle/tx
sudo poweroff
fi
#Check if RX/TX Files Doesn't Exist
else
echo $rx > ~/scripts/idle/rx ## Write packets to file
echo $tx > ~/scripts/idle/tx
echo " " >> $log
fi

Finally I set up a cron job that calls the script regularly and then shuts down the device.


$ crontab -e


There I added the line:


*/20 * * * * sudo /usr/local/sbin/shutdown_if_inactive


which calls the script every 20 minutes.