How to allocate unallocated space of hard disk in Ubuntu 12.04 after installation. My system is running fine with Windows and Linux. I am using Windows rarely and for my official purpose I am using Ubuntu 12.04. I forgot to allocate around 100 GB of space while installing. Now 100 GB is free in HDD and its not usable. How can I allocate that free space as another volume without formatting the current OS?