root@hebetude:~# df -h /
Filesystem          Size  Used Avail Use% Mounted on
/dev/mapper/h-root   19G  7.7G  9.9G  44% /
root@hebetude:~# lvextend -L +1G /dev/mapper/h-root
  Extending logical volume root to 19.62 GiB
  Logical volume root successfully resized
root@hebetude:~# resize2fs /
resize2fs 1.42.5 (29-Jul-2012)
open: Is a directory while opening /
root@hebetude:~# resize2fs /dev/mapper/h-root
resize2fs 1.42.5 (29-Jul-2012)
Filesystem at /dev/mapper/h-root is mounted on /; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 2
Performing an on-line resize of /dev/mapper/h-root to 5144576 (4k) blocks.
The filesystem on /dev/mapper/h-root is now 5144576 blocks long.

root@hebetude:~# df -h /
Filesystem          Size  Used Avail Use% Mounted on
/dev/mapper/h-root   20G  7.7G   11G  42% /
root@hebetude:~#