jmc@ptsfa.UUCP (Jerry Carlin) (01/14/86)
On the 3B2 (and maybe other computers), ttyname(3C) has a bug. When
you 'shutdown' the system from other than the console, /dev/syscon is
linked to the /dev/tty from which you are running shutdown.
ttyname() will return /dev/syscon after the system is rebooted if
'syscon' is before the tty in /dev. This is a problem since
ttyslot(3C) uses the name returned by ttyname() to find the utmp
entry. There will be no utmp entry for /dev/syscon and ttyslot() will
return -1 (not 0 as the manual incorrectly states).
Since getlogin(3C) uses ttyslot() (which uses ttyname()), it will
erroneously return NULL (process not attached to a terminal). This is
a classic "for want of a nail the shoe was lost; for want of a shoe
the horse was lost...".
If you are just looking for the login name, cuserid(3C) works fine as
it does not go thru this process. Alternatively, one could either
diddle /etc/rc to relink /dev/syscon or you could 'rm' and 'mknod' as
necessary to force syscon to come after all the regular tty's in /dev.
Or, for those with source, change ttyname.c to check for multiple
links and take some sane action (like checking if any of them are in
utmp) if such a condition is found.
--
voice= 415 823-2441
uucp={ihnp4,dual,qantel}!ptsfa!jmcjsdy@hadron.UUCP (01/28/86)
The problem, as stated, was that shutdown's
ln /dev/________ /dev/syscon
put syscon earlier in /dev than the tty that was being linked.
To fix this permanently, you must make sure that there are no
empty slots in /dev before all the tty names. Here are two ways
to do this.
To do either, you must first have an idea how many empty slots
there are and where they are. If you say 'od -c /dev', you will
get output that looks something like:
0000000 \9 \0 . \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
0000020 \2 \0 . . \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
0000040 \0 \0 r p 2 0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
0000060 d \2 c o n s o l e \0 \0 \0 \0 \0 \0 \0
0000100 c \2 t t y 0 0 \0 \0 \0 \0 \0 \0 \0 \0 \0
...
The slots that have "\0 \0" in the first two columns are your empty
slots. One example is "rp20" above. This gives you how many and
where.
One thing you could do is to create new device or regular files to
fill these empty slots. You could (if you trust yourself) remove
device files that are at the end of /dev and re-mknod them, so that
they will re-appear at the beginning. Or you could just 'tee x y z
<RET><CTL-D>'. This creates empty regular files.
Or, if you don't want to create useless files in /dev, but are not
sure you want to remove device files (after all, even _I_ make
mistakes! [;-)]), you can change the links. Since (presumably)
they already have the names you want them to have, you'll have to
make an extra link or two as intermediates:
ln ttyz8 x # right slot, wrong name
ln x y # wrong slot, wrong name
rm ttyz8 x
ln y ttyz8 # right slot, right name
rm y
Of course, you will want to do both of these techniques single-user
so that you can remove /dev/syscon b e f o r e you do any of this.
--
Joe Yao hadron!jsdy@seismo.{CSS.GOV,ARPA,UUCP}