Symptom

david@netman1:~$ ssh -l admin msa01.storage
admin@msa01.storage's password:
shell request failed on channel 0

Here is a class that allows you to read the Windows Registry without having to install any JNI library. It is implemented purely using introspection and will therefore compile and run on any platform. It would be possible to extend this to also write to the registry, but I didn't need this functionality. I hesistate to call this "pure Java" as it does make native calls, but it does avoid the need for external dependencies to do so.

java.util.prefs is great. Since it arrived, I've not had to worry about storing configuration in property files, or where those files should go. It abstracts away any platform differences and stores the preferences in a suitable place for the platform, e.g. in the registry under Windows.

I recently received a request to allow an application to have its configuration stored in a file instead of the registry. The user wanted it to run on any computer from a flash drive, with the configuration moving too. You can easily change the Preferences implementation using the java.util.prefs.PreferencesFactory system property, but the Sun JVM only ships with the platform-specific Preferences implementation, i.e. WindowsPreferences under Windows. I therefore needed to create my own Preferences implementation, which is detailed in this article.

I've been investigating why qmail has been looping some messages through the same server. Even though MX records are configured correctly, the headers indicate that it is been sent back to the same server repeatedly until it reaches the hop limit.

Sometimes it is desirable to have the outgoing IPv6 address on an interface selected deterministically. All else being equal, Linux will default to using the latest address added to the interface as the source address. This is generally not what you would expect or want. This article describes how to influence the source address selection under Linux.

Sometimes it is necessary to have a Java application that can only have one open instance, but still is able to handle command-line arguments (for example, requests to open a file). For native applications, this is easy to accomplish using native methods, but with Java the facilities are limited. This article describes a method to accomplish the goal using pure Java, with java.nio locking and local TCP sockets. It also explains how and why this is unnecessary under Mac OS X.