I was trying to install manually gcc and forgot to specify --prefix=. So, after make install binaries were installed on standard paths (like /usr/bin/ or smth.) And now as I type gcc --version it responds gcc 6.0.0. How can I return my system gcc back which I had after installing my fedora 20?
Recover system gcc on linux
linux;gcc
If you compile a pristine GCC from source downloaded from its site, the default prefix is /usr/local/, not /usr/.Use which gcc to understand  what gcc is in your PATH then try gcc -v; then use echo $PATH to understand the current setting of your PATHSo your gcc is /usr/local/bin/gcc but the system gcc is still /usr/bin/gcc(In some Linux distributions, e.g. Debian, /usr/bin/gcc is an indirect symbolic link to e.g. /usr/bin/gcc-4.9 thru /etc/alternatives/gcc; I don't know what Fedora is doing)So just set up your PATH (probably in your ~/.bashrc) so that /usr/bin/ is before (or after, if you so wishes) /usr/local/bin/I even have two shell functions local_before_path and local_after_path which are switching between the two possibilities.You should probably be able to reinstall the system GCC, perhaps with yum reinstall gcc or some similar command. On some distributions (Debian notably) you can have several versions of system GCC (e.g. gcc-4.8 and gcc-4.9)Next time you compile GCC 5.2 (mid-july 2015) from its released source code pass both --prefix=/usr/local/ and --program-suffix=-mine to its ../gcc-5.2/configure script. You'll get gcc-mine in /usr/local/bin/ !