Lately I’ve tried to bring my old Celeron 1,7GHz desktop back to life so I installed Ubuntu 12.04 LTS on it to check how it’s working with this configuration.
I was very supprised, because it’s incredibly fast even with Unity enabled despite fact there’s only 640MB RAM available in the system.
Anyway I was also very supprised, that there’s no GRUB boot menu at system startup which for e.g. would let me to run system in safe mode in case of some failure, so I started to look for some tips how to bring this menu back. As I soon found out the only thing users needs to do to bring this menu back is to edit file /etc/default/grub and comment following lines:

#GRUB_HIDDEN_TIMEOUT=0
#GRUB_HIDDEN_TIMEOUT_QUIET=TRUE

Save the file and execute update-grub command (remember to do it as root!). After next restart you’ll see Grub boot menu and will be able to choose between different startup options.
As I checked this config file on different computers it doesn’t matter what values are assigned to above settings – if they’re not commented out you won’t see the boot menu.