After finishing up an installation of Gentoo, I reboot into the new system only to find that it needs maintenance. The probably usually is that the hard drive is assigned a different device file during the LiveCD than when the actual system is booting up.
After providing the root password I need to edit the /etc/fstab file. Problem is that the file system is mounted in read only. So we must remount the root partition in read write.
mount -no remount,rw /
Now we can make the changes we need and reboot the system.