libtoolize redux ¶This error message results from Automake seeing Libtool being used in
Makefile.am, but the LIBTOOL variable is not defined.
There are two common reasons for this. First, LT_INIT is
missing from configure.ac; it can simply be added.
The second reason is more complicated: if you’ve installed Automake
under a separate prefix, Automake cannot know where to find the
LT_INIT macro. Automake looks in the aclocal.m4 file,
which is generated by the aclocal command (see Auto-generating aclocal.m4: Invoking aclocal). But since the default search paths for aclocal
are based on where it is installed (see Macro Search Path), if
Automake is installed in one place (e.g., because it’s for a test
release), and Libtool in another (e.g., for general system use),
libtool.m4 won’t be found by aclocal and thus
LT_INIT won’t be defined.
The best solution is to run libtoolize in the tree that is
using the separately-installed Automake. That will copy
libtool.m4 and the other Libtool M4 files and scripts into your
package, including ltmain.sh (see previous section). If you
have subpackages that use Libtool independently, you’ll need to run
libtoolize in each of them. See Invoking libtoolize in The Libtool Manual.
The libtoolize output suggests using an m4 subdirectory:
libtoolize: Consider adding 'AC_CONFIG_MACRO_DIRS([m4])' to configure.ac, libtoolize: and rerunning libtoolize and aclocal. libtoolize: Consider adding '-I m4' to ACLOCAL_AMFLAGS in Makefile.am.
For purposes of Libtool and Automake, however, an m4 subdirectory is
required, not just something to consider. Without having the Libtool
M4 files in the local package, aclocal will (frustratingly)
report the same ‘Libtool library used but ...’ error. (The name
of the subdirectory for the M4 files can be anything, but ‘m4’ is
by far the most common convention.)
Here is a concrete example. Suppose you’ve installed a test
release of Automake (thank you) with --prefix=/tmp/amtest, and
thus put /tmp/amtest/bin first in your PATH. You already
have Libtool installed under /usr/local/gnu. Then, your
Libtool-using package will fail to bootstrap, with the error:
Makefile.am:161: error: Libtool library used but 'LIBTOOL' is undefined ...
You can resolve this by ensuring your configure.ac includes
these lines (after the AM_INIT_AUTOMAKE):
AC_CONFIG_MACRO_DIRS([m4]) AM_PROG_AR LT_INIT
and then running:
libtoolize autoreconf
To summarize, the libtoolize (from the system directory)
copies libtool.m4 and the other Libtool support files into your
package. The subsequent autoreconf then runs
aclocal (under the test prefix) which can now find
LT_INIT.
(For more discussion of this, see https://bugs.gnu.org/71847.