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Full Discussion: Check existence of a login
Top Forums UNIX for Advanced & Expert Users Check existence of a login Post 302172095 by xavier054 on Sunday 2nd of March 2008 03:09:02 PM
Old 03-02-2008
Quote:
Originally Posted by fpmurphy
When a user logs in using login(1) login sets the $HOME environmental variable. The shell uses that environmental variable to find a users home directory.

AFAIK, there is no single API which will check whether a login is known to all authentication methods (local, NIS, PAM, etc.) used on a particular system.
Thanks for your answer.
That is true for the current user, who is obviously logged in. However, if I have an existing user, say bob with HOME=/home/bob, on a system, then anyone will see ~bob expanded to /home/bob in their shell. Without that bob has ever logged in (and so called login(1)), and regardless of the authentication method as far as I could experiment...

On the other hand, if bob doesn't exist, then ~bob won't expand.
So the shell knows whether a user exists or not... the question is how? Smilie which I should find in the sources Smilie Smilie
 

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MESG(1)                                                            User Commands                                                           MESG(1)

NAME
mesg - display (or do not display) messages from other users SYNOPSIS
mesg [option] [n|y] DESCRIPTION
The mesg utility is invoked by a user to control write access others have to the terminal device associated with standard error output. If write access is allowed, then programs such as talk(1) and write(1) may display messages on the terminal. Traditionally, write access is allowed by default. However, as users become more conscious of various security risks, there is a trend to remove write access by default, at least for the primary login shell. To make sure your ttys are set the way you want them to be set, mesg should be executed in your login scripts. ARGUMENTS
n Disallow messages. y Allow messages to be displayed. If no arguments are given, mesg shows the current message status on standard error output. OPTIONS
-v, --verbose Explain what is being done. -V, --version Display version information and exit. -h, --help Display help text and exit. EXIT STATUS
The mesg utility exits with one of the following values: 0 Messages are allowed. 1 Messages are not allowed. >1 An error has occurred. FILES
/dev/[pt]ty[pq]? SEE ALSO
login(1), talk(1), write(1), wall(1), xterm(1) HISTORY
A mesg command appeared in Version 6 AT&T UNIX. AVAILABILITY
The mesg command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/. util-linux July 2014 MESG(1)
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