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Resizing Partition on UBUNTU

SOURCE: 

https://askubuntu.com/questions/116351/increase-partition-size-on-which-ubuntu-is-installed/116367 

As a matter of fact, you CAN enlarge the root filesystem while Ubuntu is running (I learned this recently myself here) - this sounds incredible but it's true :)
Here's the list of steps for a simple scenario where you have two partitions, /dev/sda1 is an ext4 partition the OS is booted from and /dev/sdb2 is swap. For this exercise we want to remove the swap partition an extend /dev/sda1 to the whole disk.
As always, make sure you have a backup of your data - since we're going to modify the partition table there's a chance to lose all your data if you make a typo, for example.
Run sudo fdisk /dev/sda

• use p to list the partitions. Make note of the start cylinder of /dev/sda1

• use d to delete first the swap partition (2) and then the /dev/sda1 partition. This is very scary but is actually harmless as the data is not written to the disk until you write the changes to the disk.

• use n to create a new primary partition. Make sure its start cylinder is exactly the same as the old /dev/sda1 used to have. For the end cylinder agree with the default choice, which is to make the partition to span the whole disk.

• use a to toggle the bootable flag on the new /dev/sda1

• review your changes, make a deep breath and use w to write the new partition table to disk. You'll get a message telling that the kernel couldn't re-read the partition table because the device is busy, but that's ok.

Reboot with sudo reboot. When the system boots, you'll have a smaller filesystem living inside a larger partition.
The next magic command is resize2fs. Run sudo resize2fs /dev/sda1 - this form will default to making the filesystem to take all available space on the partition.
That's it, we've just resized a partition on which Ubuntu is installed, without booting from an external drive.