How can the root directory of Debian be expanded?

To expand the root directory of a Debian system, the following steps need to be taken:

1. Firstly, add extra disk space on a virtual machine or physical machine.
2. Partition the new hard drive using the fdisk command or other disk partitioning tools to create a new partition.
3. Format the new partition, for example, using the ext4 file system format.
4. Mount the new partition to a temporary directory, such as /mnt.
5. Backup the data from the existing root directory to a new partition.
6. Uninstall the current root directory.
7. Mount the new partition to the root directory.
8. Modify the /etc/fstab file so that the system can automatically mount the new partition as the root directory during startup.
9. Reboot the system to ensure that the new root directory is properly mounted.
10. Remove backup data from the temporary directory.

By following the aforementioned steps, you can successfully expand the root directory of the Debian system. However, before proceeding with these operations, be sure to backup important data to prevent any unexpected issues.