The following commands are rquiered to expoand a partition and resize the file system of an EBS volume. Those steps work in EBS volumes including root volumes and can be done while they are attached to a running instance (zero downtime)
df -HlsblkSkip this step if the disk has no partitions (e.g. /dev/xvdf)
sudo growpart /dev/xvda 1lsblkUse xfs_growfs for XFS partitions (common in RHEL)
sudo resize2fs /dev/xvda1df -H
It works, may be in some ubuntu versions, you should skip to step on line 20, i.e
sudo resize2fs /dev/xvdf