the conversion utility gave message: can't open `/usr/lib/sgml-tools/dist/book/groff/mapping': No such file or directory. The command was: LINUXDOCLIB=/usr/lib/sgml-tools/dist/sgmltool sgml2txt /usr/doc/esound-0.2.17/esound.sgml. The same error was generated by the command without setting the LINUXDOCLIB environment variable.
esound.sgml is a docbook file, so the docbook tools are needed.