In computer programming, Fails To Build From Source (FTBFS) is the problem situation where source code cannot be compiled to machine code, which often happens during software development for many reasons. The term FTBFS tends to be used specifically with the Debian and Ubuntu Linux distributions.
Traditionally it has been used to call attention to a problem reported about a Debian package, early in its lifecycle. It has been used to alert users who may otherwise wish to install the package to which it refers. It has also been used in Debian bug reports, to alert a developer to the presence of a problem. However, since this is a generalized symptom of a problem and is not specific to Debian, it may be used elsewhere.