Convert bib file to bbl file

I have a bibliography database file which was created by kbib. I want to use it on latex. In the tex file, I add

"
\bibliographystyle{plain}
\bibliography{bibfile}
"
just begin the end of documentation.

When I first compile the file, it told me it can not find reference .bbl file. So I use bibtex to build a .bbl file which can be used in latex.

$ bibtex filename.aux


here .aux was created by first run of latex. It automatically transfer data from bibfile.bib to filename.bbl by filename.aux.

It's great. Because you just need one database, then you can use it forever.

Thanks latex.