FVS318N netgear firewall config file checksum error

You will get Failed to update configuration (checksum error) if you manually edit the configuration file from a Netgear FVS318N firewall and try to upload it.  My colleague and I discovered that the checksum was generated from the config file, but with the checksum line removed.  To get around this problem you can do the following:

Checksum Error Workaround

  1. Load the configuration file in a text editor and make any necessary changes
  2. Search for the word “checksum” in the file, there should be only one which looks like this:
    • systemConfig[1][“checksum”] = “19cb09cf3123abc30b318a3b2a77c890”
    • The bit in quotes is a md5 checksum of the config file, but without this line in it.
  3. Copy this line to a new file, make a note of the line number and delete it from the existing config.  Then save your config.
  4. Now generate an md5 checksum of your configuration.  You can use a program such as md5 checker
  5. Now replace the old checksum in the line you copied (in step 3) with this new chesksum.
  6. Open up your config file and paste this new checksum line into the same place in the config file.
  7. Save the config and upload it.

I had to change 9 of these and although the above process works fine, scripting it was quicker.  So below is a python script that deletes the line, generates a hash and inserts the new checksum into the file.

Checksum Error Python Script

#!/usr/bin/env python
import hashlib
import fileinput
import shutil
def deletehash(fname):
infile = open(fname, "rb")
lines = infile.readlines()
outfile = open(fname, "wb")
for line in lines:
if not line.startswith('systemConfig[1]["checksum"]'):

def windowsfix(fname):
outfile = open(fname, "rb")
data = outfile.read()
newdata = data.replace(b"\r\n", b"\n")
outfile = open(fname, "wb")

def writehash(fname):
fobject = open(fname)
filehash = hashlib.md5(fobject.read()).hexdigest()
newline = 'systemConfig[1]["checksum"] = "' + filehash + '"'
for line in fileinput.input(fname, inplace=1):
print line,
if line.startswith("systemConfig[1] = {}"):
print newline

def main(cfgfile):
fsub = "path to config file"
fname = fsub + cfgfile
shutil.copy2(fname, fname + ".bak")

if __name__ == '__main__':

If you’re on unix, you will not need the windows fix function.  It compensates for windows putting a CR and LF at the end of each line where UNIX has just LF (in python 2.7 at least).  Undoubtedly there is a better way to do this.  When I get a moment I may investigate this.

Central heating controlled using wifi thermostat and phone app

I came across a micro-review of a phone app that could be used to control a wifi thermostat.  Intrigued I investigated further.  A company called Heatmiser sells a range of products for wireless and wifi thermostats and heating controls.  The prospect of controlling the control heating over the network/internet via a phone seemed like the sort of thing I could be interested in.

The existing system

The old central heating system is pretty standard.  One thermostat downstairs and a heating clock upstairs that allows for 24 hour/ once / twice /off operation.  The times are set using four sliders, which don’t exactly give you precise control.  The existing thermostat was an a 1970s plastic brown dial.

In time the boiler will need replacing and at that point the heating clock and wiring center will get replaced too.  However, replacing just the existing thermostat with a wifi thermostat will give the ability of finer heating control and remote control.

The new wifi thermostat

I went for a Heatmiser PRT-TS WiFi which is a touchscreen programmable thermostat.  It is a compatible replacement for standard three wire thermostats (before purchasing I took the cover off my existing thermostat and checked it would be compatible) and has a cool backlit touchscreen.

Heatmiser PRT-TS WiFi thermostat

The new wifi thermostat – Heatmiser PRT-TS WiFi

The unit comes with a mini-usb cable and some software so that you can configure the wireless and network settings before installation.  This allows you to test the wifi settings before installation on the wall.  It is designed to be flush fitted on the wall – which I will get around to – but temporarily I used a standard 25mm surface mount back box.

Fortunately, my existing thermostat had a wiring diagram inside the cover so I could identify what each wire was before removal and the instructions for wiring the new unit were clear and easy to follow.

On the old control unit upstairs I’ve set the central heating to be constantly on which gives total control over the system to the new wifi thermostat.


Through a web browser you can connect and set all aspects of the wifi thermostat.

screenshot of wifi thermostat web page

Webpage control of thermostat

Or you can control everything via the phone app:

Heatmiser wifi thermostat android app screenshot

Heatmiser wifi thermostat android app

I’m pretty happy with the functionality and look of the unit.  It is pretty cool to turn the heating up whilst sitting on the sofa, or lying in bed, or at my desk at work, or …