2.5 Libtool Development
Over time, Unix systems added support for shared libraries.
Conventional libraries, or static libraries, are linked into a program
image. This means that each program which uses a static library
includes some or all of the library in the program binary on disk.
Shared libraries, on the other hand, are a separate file. A program
which uses a shared library does not include a copy of the library; it
only includes the name of the library. Many programs can use a single
Using a shared library reduces disk space requirements. Since the
system can generally share a single executable instance of the shared
library among many programs, it also reduces swap space requirements at
run time. Another advantage is that it is possible to fix a bug by
updating the single shared library file on disk, without requiring all
the programs which use the library to be rebuilt.
The first Unix shared library implementation was in System V release 3
from AT&T. The idea was rapidly adopted by other Unix
vendors, appearing in SunOS, HP-UX, AIX, and Digital Unix
among others. Unfortunately, each implementation differed in the
creation and use of shared libraries and in the specific features which
Naturally, packages distributed as source code which included libraries
wanted to be able to build their own shared libraries. Several
different implementations were written in the Autoconf/Automake
In 1996, Gordon Matzigkeit began work on a package known as Libtool.
Libtool is a collection of shell scripts which handle the differences
between shared library generation and use on different systems. It is
closely tied to Automake, although it is possible to use it
Over time, Libtool has been enhanced to support more Unix variants and
to provide an interface for standardizing shared library features.