“If your system accepts remote user logins via telnet or
serial ports, or console logins in text mode, you can present text
messages to your users simply by editing two files in the /etc
directory.”
“The /etc/issue file is displayed to connecting users before the
login prompt is displayed. This is an excellent place to display
warnings and login instructions… Because many distributions
automatically generate this file each time you boot, you may want
to mark it as read-only once you’ve edited it to your satisfaction
so that your changes won’t be overwritten…”
“The /etc/motd file is similar to the /etc/issue file in that it
is plain-text and is displayed to the user during login. However,
the /etc/motd file is displayed after successful password entry but
before the shell is started. This file is useful for displaying
information which should be seen only by valid users… Since this
file is displayed by login rather than by the shell, it is seen by
all users, even those not logging in to an interactive shell. Some
distributions may automatically generate this file each boot as
well; you can take the same steps to preserve the changes you make
to this file.”