root@localhost:~# df /
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/rootfs     14779408 5847484   8741216  41% /

root@localhost:~# resize2fs /dev/rootfs 
resize2fs 1.45.5 (07-Jan-2020)
Filesystem at /dev/rootfs is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
The filesystem on /dev/rootfs is now 7587840 (4k) blocks long.

root@localhost:~# df /
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/rootfs     29808700 5848092  23618452  20% /