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From: jmc@ptsfa.UUCP (Jerry Carlin)
Newsgroups: net.bugs.usg,net.micro.att
Subject: ttyname(bug)
Message-ID: <1098@ptsfa.UUCP>
Date: Mon, 13-Jan-86 17:58:55 EST
Article-I.D.: ptsfa.1098
Posted: Mon Jan 13 17:58:55 1986
Date-Received: Wed, 15-Jan-86 08:08:12 EST
Organization: Pacific * Bell, San Francisco
Lines: 27
Keywords: ttyname, ttyslot, getlogin, syscon
Xref: watmath net.bugs.usg:413 net.micro.att:796


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. 

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