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Just to be sure, if I compile with source, does the installation will update my emacs currently installed?
No, it will not touch the original emacs files. "make install" just copies all relevant files into directories which can be specified as arguments of the "configure" command. The default "prefix" directory is /usr/local and the emacs executable is placed in /usr/local/bin. If you are not sure about destination directories then "make -n install" shows actions that will be performed by make when "make install" is invoked (without performing them). Since PATH=/usr/local/bin:/usr/bin:/usr/X11R6/bin:/bin in /etc/profile the old emacs will be started only if you type the full path /usr/bin/emacs, otherwise the new one will be launched.
Does I need to uninstall or it will update?
You don't need to uninstall and it will not update. Actually, I prefer to keep both versions since I haven't installed in 21.1 all lisp packages I use (e.g. AucTeX) yet. Your own RPM package has some advantages but I haven't made it. -- Alexandr.Malusek@imv.liu.se