Answer by RenRen for Tab Autocomplete for New User

When you add a user with useradd there is no special shell added.
You can see this with the command:cat /etc/passwd

test1:x:1004:1005:,,,:/home/test1:/bin/bash
test3:x:1007:1008::/home/test3:

You can see that the user test1 has a shell of /bin/bash but the user test3 has no shell added.

To fix this you can change the shell of user test3 with this command:

chsh -s /bin/bash test3

Or when you create a new user you can use the s option:

useradd -s /bin/bash test4