openssl TXT_DB error number 2 failed to update database

Reason:

This thing happens when certificates share common data. You cannot have two
certificates that look otherwise the same.

Method 1:

modifydemoCA下index.txt.attr

Change

unique_subject = yes

to

unique_subject = no

method 2:

Delete index.txt under democa, and then click touch

rm index.txt

touch index.txt

method 3:

Set common name to different