Solutions to common problems will be posted here as we become aware of them. If you need help with something, please check our support group for a solution, or post a new question.
This occurs when KenLM failed to build. This can occur for a number of reasons:
Boost isn't installed. Boost is available through most package management tools, so try that first. You can also build it from source.
Boost is installed, but not in your path. The easiest solution is to add the boost library directory to your $LD_LIBRARY_PATH environment variable. You can also edit the file $JOSHUA/src/joshua/decoder/ff/lm/kenlm/Makefile and define BOOST_ROOT to point to your boost location. Then rebuild KenLM with the command
ant -f $JOSHUA/build.xml kenlm
You have run into boost's weird naming of multi-threaded libraries. For some reason, boost libraries sometimes have a -mt extension applied when they are built with multi-threaded support. This will cause the linker to fail, since it is looking for, e.g., -lboost_system instead of -lboost_system-mt. Edit the same Makefile as above and uncomment the BOOST_MT = -mt line, then try to compile again with
ant -f $JOSHUA.build.xml kenlm
You may find the following reference URLs to be useful.
https://groups.google.com/forum/#!topic/joshua_support/SiGO41tkpsw http://stackoverflow.com/questions/12583080/c-library-in-using-boost-library