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From: Garrett Wollman <wollman@hergotha.csail.mit.edu>
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To: jilles@stack.nl
Subject: Re: login -f changing session getlogin(2)
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References: <20151001203436.GA22737@stack.nl> <560D826D.7000302@FreeBSD.org>
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In article <20151001203436.GA22737@stack.nl>, jilles@stack.nl writes:

>I think the supposed use case for login -f is a remote login daemon that
>handles authentication by itself but wants to delegate account and
>session functionality. Indeed, sshd has UseLogin, but it is rarely used
>and discouraged.

Historically, as I remember it, "login" was a shell built-in that was
effectively an alias for "exec login".  It may still be that way in
antique csh.  The assumption from time immemorial is that if login
exits, the parent process will not distinguish it from any other
logout, so login is permitted to overwrite persistent session state.

-GAWollman