I would have opened an "issue" on the boostorg/boostbook project, however, that is not enabled. (Perhaps someone should enable it?) I have duplicated the boostbook setup scripts into the docker setup environment for Ubuntu Bionic and I have found that all of the packages that boostbook depends on are ancient. PackageVersionLast ModifiedHost docbook-xsl 1.75.2 2009 SourceForge http://sourceforge.net/projects/docbook/files/docbook-xsl/1.75.2/docbook-xsl... docbook-xml 4.2 2002 oasis-open.org http://www.oasis-open.org/docbook/xml/4.2/docbook-xml-4.2.zip fop 0.94 2007 Apache http://archive.apache.org/dist/xmlgraphics/fop/binaries/fop-0.94-bin-jdk1.4.... These tools are quite old and it is only a matter of time before the older versions could be removed. These external sites are under no particular requirement to keep these older versions of software available. At some point some of these tools may no longer work with current operating system tools, for example "fop" says that it is for "JDK 1.4". Each of these tools has a newer version. A project should be initiated now to modernize the documentation build to use more recent versions of these tools before it becomes a critical release blocker at a bad time. - Jim