Tag Archives: Linux

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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FRITZ!Box tuning part 4: Cross-building and installing additional applications

The articles I wrote about the FRITZ!Box are pretty popular. They are creating the most traffic on my website. I understand this, cause the FRITZ!Box is a really great piece of hardware and AVM is also a company which knows how to make their users happy by serving regular updates to the firmware. Although I didn’t tuned my FRITZ!Box any further, I updated it with the latest Labor firmware version regularly. At some point the sshd setupĀ (with dropbear) doesn’t worked anymore and I decided it is the time to update my software as well. Beside that it didn’t work anymore it is always a good idea to update software which allow access to a host from everywhere very regularly. Anyway, it turned out this isn’t as simple as I initial thought. Therefore here is the next post in the FRITZ!Box tuning series, which shows how to cross-build software for the MIPS32 architecture used in the FRITZ!Box and in particular get the sshd software to life again. I use a FRITZ!Box Fon WLAN 7270 v2 and the firmware is 54.05.05. Please make sure you read the other FRITZ!Box articles as well, cause some of the information given there still applies.

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TT: Console navigation the easy way with Apparix

Today I will start a new series where I present small tools which I use on a daily basis and considered very useful. These tools haven’t to be killer applications, but doing the task they are written for, very well. Therefor also the name of this series: TT, which stands for ToolTips. Most of this applications are open source, so I will take the opportunity to say “Thank you” to all the people out there, which create such cool stuff in there free time.

We start with a tool called Apparix.

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Creating file shortcuts on three different operation systems

As you may know, developing for multiple platforms is one of my strengths. Strictly speaking, it’s a basic requirement if you are involved in such a product like VirtualBox, which runs on every major (and several minor) platform available today. Beside the GUI, which uses Qt and therewith is portable without any additional cost (which isn’t fully true if you want real native look and feel on every platform, especially on Mac OS X), all the rest of VirtualBox is written in a portable way. This is done by using only C/C++ and Assembler when necessary. Everything which needs a different approach, because of the design of the OS (and the API’s which are available there), is implemented in a platform dependent way. In the history of VirtualBox, several modules are created and grown by the time, which makes it really easy to deal with this differences. For stuff like file handling, paths, strings, semaphores or any other basic functionality, you can just use the modules which are available. On the other side it might be necessary, for a new feature we implement, to write it from the ground. In the following post I will show how to create a file shortcut for the three major operation systems available today.

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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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Using suppression files with Valgrind

Valgrind is one of the great tools in the long list of freely available applications for development. Beside several profiling tools it also contains a memory checker. Leaking memory is one of the more common errors a programmer could step into. Basically it means to forget freeing memory (or in a more general sense: any resource) a program has acquired. If you are a perfect developer, this will never happen to you. If you are a good developer it may happen and that’s where Valgrind will save you some trouble. As most of the developers out there are more or less good developers, their programs produce memory leaks, too ;). The right solution for this, is of course to write a bug report. But there are times where this isn’t possible or you are in hurry and don’t want to see all the errors of a third-party library you link against.

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Installing Linux on a USB hard disk for the MacBook Pro

One of the features of Mac OS X I love, is the possibility to install Mac OS X on any attached removable media, like a FireWire or USB hard disk. This makes it really easy for me to test VirtualBox on the several versions of Mac OS X we support (formerly Tiger, now Leopard and Snow Leopard). The advantage of this setup is that I don’t waste disk space for operation systems I usually don’t use very often. Currently I have a 150GB hard disk in my MacBook Pro which is really not that much if you deal in the virtualization business. There are several test VM’s of any kind of guest operation systems and of course the ISO’s to install them. The second main OS, I do much of my work, is Linux. For this I have a standard PC with Gentoo on it, which have all that I need. Unfortunately this doesn’t really help when I on travel. As I soon be away for some time, I decided I need, at least for testing, the same flexibility mentioned above for a Linux installation. And here the problems start to arise. Of course Apple didn’t really support installing other OS’s than Mac OS X on Apple hardware. Yes, there is Boot Camp, but this is mainly for Windows, is very inflexible and doesn’t really help if you try to install something on another place than the integrated hard disk. There are projects like rEFIt, which even makes Boot Camp superfluous, but this project has really bad USB boot support. In the following I will explain how it is even possible to install Ubuntu 9.10 on a USB hard disk.

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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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