~$  update-alternatives --config gcc
There are 2 choices for the alternative gcc (providing /usr/bin/gcc).

  Selection    Path              Priority   Status
------------------------------------------------------------
  0            /usr/bin/gcc-4.6   60        auto mode
  1            /usr/bin/gcc-4.6   60        manual mode
* 2            /usr/bin/gcc-4.7   40        manual mode

Press enter to keep the current choice[*], or type selection number:
update-alternatives: warning: forcing reinstallation of alternative /usr/bin/gcc-4.7 because link group gcc is broken.
update-alternatives: error: error creating symbolic link `/etc/alternatives/gcc.dpkg-tmp': Permission denied