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The top ten open-source apps you've never heard of

Posted on 5 Sep 2008 at 15:18

Simon Brock runs through ten well-kept open-source secrets, and examines why some others didn't quite make the grade.

7. FUSE

When the laser was first invented, someone described it as a "solution looking for a problem", and at first glance FUSE is one of those projects that fits the same description. FUSE stands for Filesystem in User Space (http://fuse.sourceforge.net); in other words, it lets anyone who can write a program and run it on a Linux machine create a new filesystem. At first glance this may seem a pretty esoteric application but, like the laser, consider the various ways it could be used. For example, a really simple application is to enable an archive - such as a ZIP file - to be accessed as a collection of files. This way you can mount the ZIP file somewhere in your filesystem, change directory to it and use normal file-management commands to list its contents or delete files from that ZIP archive.

FUSE can also be used to change where and how files are stored. For example, there are a number of filesystems that work with FUSE to store the contents of files in relational databases. For certain operations this may be faster than a normal filesystem, but it has the extra advantage of enabling the user to apply database operations to search for files. For example, if you were to use MySQL as a back end, you could use full-text indexing to search for files.

Obviously if you can store your files in a database then you can also store them on different machines, and so there are a number of distributed replicating filesystems that mean whenever a file gets stored onto one machine it gets copied to other machines automatically. Other people have used FUSE to enable non-Linux filesystems such as Windows NTFS and Solaris ZFS to be mounted and accessed by Linux machines.

FUSE has also been used to build various more esoteric kinds of filesystem, one of the main variants being versioning filesystems. In such a system, each time you change a file, a copy of the old version is kept: in its simplest form this may be a full copy of the original but in some implementations only the differences are stored in some way. The power and applications of versioning filesystems, especially for developers and document archives, should be obvious to all. Other people have written modules for FUSE that allow multiple filesystems to be merged into one filesystem (a so-called union filesystem) and monitor for file changes in a filesystem. These systems work rather like triggers in a database, so that when a file in the filesystem gets changed an entry can be written to a log file or some other program automatically executed.

8. PowerDNS

A domain name server (DNS) is one of those applications that sits in your network and does the very boring job of mapping names such as www.pcpro.co.uk to numeric IP addresses like 194.70.234.209. Generally, no-one gives these programs a great deal of thought until something happens like the recent security flaw in DNS servers being exposed. As everyone now knows, the widely-used name servers for Unix and Windows were subject to this exploit, but there were other less well-known ones that were not. PowerDNS was one such name server that wasn't affected, but that's not our only reason for mentioning it here.

PowerDNS (www.powerdns.com) comes in two forms, in acknowledgement of the fact that there are two types of DNS server. Most DNS servers handle what are called recursive requests - that's when you query your local DNS server and it makes requests to other, authoritative servers that know about the requested domain. For example if your machine wants to know the IP address of www.pcpro.co.uk, it will make a request to the name servers mentioned in your machine's setup. To implement this type of name server you would use the PowerDNS recursor, an extremely efficient and fast-caching name server that was also immune to the flaw that affected other name servers.