[ProblemSolving][Ubuntu][LyX] The selected document class ... requires external files that are not available...

　　I installed LyX in my Ubuntu(version LTS 18.04), but I just can't make it work.

　　Every time I open any file, I get a message similar to this one:

The selected document class
    Book (Standard Class)
requires external files that are not available.
The document class can still be used, but the
document cannot be compiled until the following
prerequisites are installed:
    book.cls
See section 3.1.2.2 (Class Availability) of the
User's Guide for more information.

　　And after a lot of googling, I find some solutions in the https://askubuntu.com/questions/256125/ which suggests that:

apt install texlive

 

And some additional document classes(Bold is compulsory):

• chktex: check for typographical errors
• dvipost: display tracked changes in DVI format output
• gnuhtml2latex:import HTML documents
• groff: improved table formatting in plain text exports
• librsvg2-bin, inkspace: use the SVG image format in LyX documents (if your using Inkscape as your graphics editor inr Lyx)
• linuxdoc-tools: export SGML LinuxDoc documents
• mythes-*: use the OpenOffice.org/LibreOffice Thesaurus
• noweb: import noweb files
• rcs: integrated version control
• sgmltools-lite: export SGML DocBook documents
• texlive-xetex, etoolbox: use the XeTex typesetting system
• wv: import MS Word documents

　　And then reconfigure, the problem is solved.