How to Build LSB Applications

The Linux Standard Base (LSB) specifies an interface between an application and a runtime environment. Many distributions have achieved certification for their runtime environments. This article outlines the steps needed to build applications that adhere to the LSB interface.

The LSB Project was founded in 1997 to address the application compatibility problem that was beginning to emerge. Different distributions were using different versions of upstream software and building them with different options enabled. The result was that an application built on one distribution might not run on another distribution. Worse yet, the application often would not work on a different version of the same distribution.

Originally, the LSB was intended to create a common reference implementation for the base of a GNU/Linux system. In addition to the reference implementation, a written specification was to be developed. This idea wasn't well received by many of the distributions that had considerable investments in their own base software, which they perceived as being a competitive advantage.

After further discussion among the interested parties, the LSB Project underwent a fundamental shift in focus in order to achieve consensus among the entire community. The shift gave priority to the written specification over the implementation, and it defined the LSB as a behavioral specification instead of a list of upstream feature/version pairs. This new focus was realized as a three-prong approach: a written specification, which defines the behavior of the system; a formal test suite, which measures an implementation against the specification; and a sample implementation, which provides an example of the specification.

The LSB Specification actually is made up of a generic portion, the gLSB, and an architecture-specific portion, archLSB. The gLSB contains everything that is common across all architectures; we try hard to define as much as possible in the gLSB. The archLSBs contain the things that are unique to each processor architecture, such as the machine instruction set and C library symbol versions.

As much as possible, the LSB builds on existing standards, including the Single UNIX Specification (SUS), which has evolved from POSIX, the System V Interface Definition (SVID) and the System V Application Binary Interface (ABI). The LSB uses the ELF definitions from the ABI and the interface behaviors from the SUS. It adds the formal listing of what interfaces are available in which library as well as the data structures and constants associated with them. See the “Linux Standard Base Libraries” sidebar for the list of libraries currently specified.

In addition to the ABI portion of the LSB, the specification also specifies a set of commands that may be used in scripts associated with the application. It also mandates that the application adhere to the filesystem hierarchy standard (FHS).

One additional component of the LSB is the packaging format. The LSB specifies the package file format to be a subset of the RPM file format. The LSB does not specify that the distribution has to be based on RPM, however, only that it has some way of correctly processing a file in the RPM format.

One final item to mention is the name of the program interpreter. The program interpreter is the first thing executed when an application is started, and it is responsible for loading the rest of the program and shared libraries into the process address space. Traditionally, /lib/ld-linux.so.2 has been used, but the LSB specifies /lib/ld-lsb.so.1 instead on IA32. Generally, /lib/ld-arch-lsb.so.1 is used for other architectures. This provides the operating system with a hook early in the process execution in case something special needs to be done to provide the correct runtime environment to the application. You can pass the following to GCC to change the program interpreter:

-Wl,--dynamic-linker=/lib/ld-lsb.so.1