Ubuntu18.04: Logging in loop after mounting sdb5 on /home

ubuntu18.04:

I found the space of / directory is not enough.So I tried mounting sdb(formatted through GParted) on /home.

Process:

1.After formatting a new part sdb4(10G) and sdb5(1.8T) on disk sdb using GParted, I found there was a "!" on /boot/efi part(mounted on sdb1)

2.mv -rf /home /backup

3.got uuid of /dev/sdb5 by blkid and edit /etc/fstab

4.sudo mount -a

5.I found the sdb5 really mounted on /home by df -h

6.mv -rf /backup/username /home

7. reboot(an error occurs on screen "failed deactivating swap /dev/disk/by-uuid/xxxx",but i have commented the swap in /etc/fstab)

8.come to the log-in interface:after entering password, it come back to the log-in....

So how could I solve this, plz?