I’ve been frustrated with the number of instructions that involve deleting a partition and then creating a new partition with the same starting block. Totally unnecessary!
Life has gotten a lot easier thanks to the growpart command. The best part is that with the right filesystem you don’t even need to unmount. I suggest taking a backup or snapshot first in case something goes wrong.
growpart /dev/device_name partition_number
You can test it first with –dry-run:
growpart --dry-run /dev/sda 3
Once that is done, just run the command for your given filesystem to expand into the rest of the partition.
btrfs filesystem resize amount mount_point
The amount can be something like +50g or max. To resize the root partition to max simply type:
btrfs filesystem resize max /
For ext4 it is: