1. Overview
   Linux partition background
   In Linux, each disk is used in the form of mounting to a directory.
   Example:
   When disk 1 is mounted to / directory and disk 2 is mounted to /home directory.
   When a folder or file is created under the / directory, it is stored in Disk 1, and when a folder or file is created under the /home directory, it is stored in Disk 2.

Specific steps
Check the current disk partition

[root@localhost ~]# df -lh
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 925G 47G 879G 6% /
devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs 1.9G 116K 1.9G 1% /dev/shm
tmpfs 1.9G 191M 1.7G 11% /run
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/sda1 494M 97M 398M 20% /boot
tmpfs 376M 0 376M 0% /run/user/0
/dev/mapper/centos-home 2.0G 33M 2.0G 2% /home

Note: Just pay attention to the /dev/ directory, and the rest should be handled by the system.
You can see that there are only three here, namely /dev/mapper/centos-root, /dev/sda1, /dev/mapper/centos-home

Unmount /home partition
Back up the content of /home, then delete the logical volume where the /home file system is located, and expand the / file system.

tar cvf /tmp/home.tar /home #Backup/home, there is nothing to back up

• Record how much free space is available under home, such as 2G, and you will need to expand the root directory later
• Uninstall /home

umount /home
# "Logical volume contains a filesystem in use" appears when deleting lvm

• If it cannot be uninstalled, first terminate the process using the /home file system
  Delete the lv where /home is located, if it prompts that the file system is in use, terminate the process first, use the command in the first paragraph below to find the process and kill.

fuser -m /dev/mapper/centos-home
kill -9 

• Uninstall again

3. Delete /home partition

• View lv partition information

lvdisplay

• Delete the lv partition
  If the deletion fails, you can delete it again after reboot

lvremove /dev/centos/home

4. extensions/directory

• Extend the lv where /root is located to increase the size of /home

lvextend -L +2G /dev/centos/root
# must appear success, failure may be insufficient space

• extension/filesystem

xfs_growfs /dev/centos/root

5. Restore files under /home

# cd /
# tar -xvf /tmp/home.ar

Edit /etc/fstab file to delete /home partition

The /home partition must be deleted, otherwise it cannot be started normally.

[root@master etc]# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Sat Apr 4 15:25:10 2020
#
# Accessible filesystems, by reference, are maintained under '/dev/disk/'.
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info.
#
# After editing this file, run 'systemctl daemon-reload' to update systemd
# units generated from this file.
#
/dev/mapper/centos-root/xfs defaults 0 0
UUID=9cf092ac-81b6-483e-bb48-fd1e5224340b /boot ext4 defaults 1 2
#/dev/mapper/centos-home /home xfs defaults 0 0
/dev/mapper/centos-swap swap swap defaults 0 0
[root@master etc]#

Confirm result

[root@localhost ~]# df -lh