In computer programming, FTBFS is an acronym that stands for "Fails To Build From Source". It describes the situation where source code cannot be compiled to machine code. This is often-seen during software development. There are several reasons that code may not compile so its use is non-specific but it always refers to the presence of a problem. Because it is non-specific, it is considered slang. It may also be considered vernacular language because its use tends to be specific to the Debian and Ubuntu Linux distributions.
The following example shows one way it is used. It is preceded by information that makes the example useful.
The Unstable Debian branch is so-called because changes to it are occurring frequently. With time, changes within the Unstable branch occur less frequently. Eventually the Unstable build is moved to the Testing branch, and the Testing branch is moved to the Stable branch (although other process-specific detail may be involved).
FTBFS is used in output from apt-get (a front-end to "dpkg", which is the Debian package manager). In the example below, it is used to make the user aware that a problem was reported earlier about the package considered for installation. Note that the user has the option of continuing to install the package or not continuing with installation. This is the reason for using "FTBFS". Note too, that it is considered a bug. This is important because a failure to compile the package is not an error (itself), but errors are usually the reason a package will not compile.
-- preceding output omitted—serious bugs of libsql-statement-perl (-> 1.15-3) <forwarded> #531238 - libsql-statement-perl: FTBFS Summary: libsql-statement-perl(1 bug) Are you sure you want to install/upgrade the above packages? [Y/n/?/...]
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 generalized symptom of a problem and is not specific to Debian, it may be used elsewhere.
See also 
- Package management system
- Advanced Packaging Tool