watch out when you modify /etc/ttys !!

[dbj.rice%rand-relay at sri-unix.UUCP]

From:  Dave Johnson <dbj.rice at rand-relay>

UCB Mail does a getlogin() to decide who to say the message is "From:", and
if this returns a NULL, it instead tries a getpwuid(getuid()).  Getlogin
uses ttyslot() to find the "slot" number of this tty in /etc/ttys, and then
uses this number also as the slot number in /etc/utmp (init maintains
/etc/utmp in order of tty "slot" number as returned by ttyslot()).  Thus, if
you change /etc/ttys, you change what value is returned by ttyslot(), and
thus, getlogin() starts looking at a different entry in /etc/utmp than was
used to record when this person logged on to this terminal.  Presumably,
Mail thought it was faster to read through /etc/ttys than to read all of
/etc/passwd to translate the uid...

It should be "safe" to add new entries to the bottom of /etc/ttys.  To
"delete" lines from /etc/ttys, you can just put a "0" as the first character
on the line and everybody will ignore that line.

                                        Dave Johnson
                                        Dept. of Math Science
                                        Rice University