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From: bzs@bu-cs.bu.EDU (Barry Shein)
Newsgroups: comp.unix.wizards
Subject: umask under 4.3
Message-ID: <7582@brl-adm.ARPA>
Date: Fri, 29-May-87 12:31:05 EDT
Article-I.D.: brl-adm.7582
Posted: Fri May 29 12:31:05 1987
Date-Received: Sun, 31-May-87 15:53:54 EDT
Sender: news@brl-adm.ARPA
Lines: 33


I always figured a good way to do these kinds of things (set the umask
etc) would be to use a program other than the shell in a user's login
entry and then use that to exec or fork (if there's post-processing
desired, I used that once to produce summary session accounting
records so I could shut off per-process accounting but still produce
short summaries with minimal disk space, just write out the user's
getrusage() structure when the shell fork returns) the user's shell.
It's probably a tiny process that gets swapped right out if need be as
it just sits in a wait() (if forked, if the shell is exec'd it's gone.)

This doesn't require sources and seems much more flexible, just change
a user's passwd entry to something like:

johndoe::uid:gid:gecos:homedir:/bin/shell

It could be setuid if need be and it would be easy to check argv[0] as
a hook for which shell to start, /bin/cshell etc. You could re-work
environment variables before starting the user's shell, limits,
whatever, even install things like permissible login time windows or
other security hooks (secondary password, secure ttys etc.) Might have
to play with chsh but other than that I don't think there would be
much problem.

There are a number of details, some poorly documented (eg. args that
need to be passed) but fairly easily determined heuristically (the
first cut could dump argv and envp.)

I dunno, seems like a nice and general hook. Could be a good
net.sources contribution by someone all full of hooks for typical
needs.

	-Barry Shein, Boston University