Tag Archives: remote access

TT: Uni-directional file synchronization between different hosts with Unison

When you work with at least two computers on the same project on a daily basis you might have a problem. You need to get changed files from host A to host B and vice versa. The problem getting bigger when you work in addition on different operation systems or use more than two hosts. On UNIX/Linux the preferred tool for such a task is Rsync. Unfortunately Rsync synchronize only in one direction, it doesn’t work very well when more than two hosts are involved (and it isn’t really comfortable to set up on Windows) and can’t use a secure communication channel. Another approach is to check-in changed source files into a version control system, like CVS. On host A you check it in and on host B you check it out afterwards. But this means you always need a more or less stable variant of your code, so that other developer can, at least compile, or much better use it. That is not always the case (especially when you leave the office at 11:00 p.m.) and it also doesn’t cover files which aren’t handled by a version control system. Luckily there is a solution for all the problems mentioned which is called Unison. So here comes the second post in the ToolTips series, which covers an easy and portable way for file synchronization.

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Getting the backtrace from a kernel panic

You may know the following situation. You arrive in the morning in the office, do what you always do and check out the latest changes of the software you are working on. After a little bit of compile time and the first coffee you start the just build application. Bumm, kernel panic. After rebooting and locking through the changes you may have an idea what the reason for this could be. A colleague of you is working on a fancy new feature which needed changes to a kernel module. As you almost know nothing about this code you seek for help and, as it of course not happen on his computer, he is asking for a backtrace of this panic. You have two problems now. First you need to see the panic yourself and second it would be nice to get a copy of the backtrace for sharing this info within a bugtracker. In the following post I will show how both aims could be easily archived.

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FRITZ!Box tuning part 3: Using the VoIP phone line from everywhere

The contract with my Internet service provider includes a VoIP connection. Together with the FRITZ!Box 7270 all phone calls are done over the Internet, an additional conventional phone connection isn’t necessary anymore. One of the benefits of this is that you can connect to your registrar from everywhere in the world. But that’s theory, cause e.g. my provider doesn’t allow a connection if you are not in the network of the provider itself. Of course there are free services like sipgate or even Skype. There you could make free calls within the services itself, but as soon as you like to call a real phone number you have to pay. They are cheap, no question, but my contract includes a flat rate within Germany. That’s even cheaper. So what I like to do is to use my VoIP phone connection even when I’m not at home. In the following third part of the FRITZ!Box tuning series, I will explain how to achieve this. As already said in the first two post, where you at least should read the first one, I’m not responsible for anything happens to your FRITZ!Box after you have tried what is described here.

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FRITZ!Box tuning part 2: Access your home network with OpenVPN

AVM has built a VPN server into the FRITZ!Box, why should I use some other software for this job, you may ask. The reason is quite simple: the build in one is a piece of closed source software written by AVM and there is only one official client which could be used to connect to it, the FRITZ!VPN software. This client software is only available for the Windows operation system family and so by no means anything useful to me. I’m pretty sure they are using some official protocol like IPSec, so it might be possible to connect to the FRITZ!Box with other clients as well, but that’s something I didn’t want to try. OpenVPN on the other side is a rock solid open source software which could be used from many popular OS’s these days. Even graphical clients, like TunnelBlick for Mac OS X, are available. So here comes the second article of the FRITZ!Box tuning series, which will explain how to convert your FRITZ!Box into a OpenVPN server, where any number of clients can concurrently be connected. I highly recommend to read the first part of this series, because this post is build on top of the stuff done there. This count especially for the filesystem layout on the usbstick and the way additional software is started. Also in the following it will be helpful to have ssh access to the FRITZ!Box all the time. As already written in the first part, there is no guarantee that the information presented here will work on your side or that I’m responsible for anything happen to your FRITZ!Box. In preparation of the following you need access to a second OpenVPN installation which will be used to create all necessary certificates and keys and which could be used to test the installation afterward. I’m using a Gentoo Linux host where you could install OpenVPN simply by executing emerge openvpn. Make sure you have the examples USE flag set to get all the helper scripts which make the life much more easier.

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FRITZ!Box tuning part 1: Enable remote access over ssh

Recently I changed my Internet service provider to Kabel Deutschland which offers some really good bandwidth for a reasonable price. You get 32 MBit in the download direction and 2 Mbit in the upload direction. Additionally to this you can order a FRITZ!Box 7270 which allows you to use VoIP for the phone part. As I always try to maximize the usage of new hardware I started to explore what is possible with this combination. In this post I will explain how you get access to your FRITZ!Box using ssh. Following this post, some articles about how you can turn the FRITZ!Box into a OpenVPN server and how you can use the VoIP access point remotely from any computer having a VoIP software installed, will be done. As I said the hardware used is a FRITZ!Box Fon WLAN 7270 with the firmware 54/74.04.80 from 2009/12/15 which is an official one from AVM. Other firmware versions may work also, but I haven’t tested that. The following topics are all for advanced user. So if you aren’t in touch with Linux or start asking what the hell is vi and how get I out of it, stop reading now. All the information in this and the following posts are based on several websites I found in the Internet. Mainly this are some forum entries at http://www.ip-phone-forum.de, the series about the FRITZ!Box at http://www.tecchannel.de, the posts on http://www.teamarbyte.de, the blog at http://www.realriot.de and this article at http://www.cswpro.de. So thanks to all the people for sharing this kind of information. Before we start some words of caution: It’s easily possible to render the FRITZ!Box unusable. So there is no warranty of any kind if you do some of the things mentioned in this blog. Also I’m not responsible for anything happen to your FRITZ!Box or the Internet connection. After all making a backup of your current configuration might be a good idea.

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