you'll need to know the path to at least one of your libraries, what are the contents of the /root/folleto-library/ directory? I have my libraries located like this:
/path/calibre-library/cookbooks
/path/calibre-library/fiction
/path/calibre-library/non-fiction
/path/calibre-library/technical
So, on my old 3.39.1 (hooray for out-of-date repos

) install, the bare-bones command (if I wanted to only serve up the Technical library) looks something like this:
Code:
calibre-server /path/calibre-library/technical --enable-local-write --enable-auth
If you have multiple libraries, it'll be something like:
Code:
calibre-server /path/to/library1 /path/to/library2 /path/to/library3 --enable-local-write --enable-auth
The "--enable-auth" is used if you have user accounts and passwords created in the calibre server that are used to authenticate before people can see the library and contents.
Good luck.