From manpage of
The login program is used to establish a new session with the system. It is normally invoked automatically by responding to the login: prompt on the user's terminal. login may be special to the shell and may not be invoked as a sub-process. When called from a shell, login should be executed as exec login which will cause the user to exit from the current shell (and thus will prevent the new logged in user to return to the session of the caller). Attempting to execute login from any shell but the login shell will produce an error message.
In graphical console, I could run
exec sudo login t on an interactive nonlogin bash shell in a terminal emulator
lxterminal. So what do "login may be special to the shell and may not be invoked as a sub-process" and "Attempting to execute login
from any shell but the login shell will produce an error message" mean?
But I also notice that when I switch to a text console by Ctrl+Alt+F2, I got error messages, and are they related to the quotes? Thanks.