From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <12ee874bd1d1ca3246f99555054e2820@snellwilcox.com>
From: plan9fans@ntlworld.nospam.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Novice question - run as other
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Date: Wed, 17 Mar 2004 18:29:43 +0000
Topicbox-Message-UUID: 34770326-eacd-11e9-9e20-41e7f4b1d025

Hi,

My all-time favorite Unix story, lifted from
http://cm.bell-labs.com/cm/cs/who/dmr/hist.html

Although the multiple-process idea slipped in very easily indeed,
there were some aftereffects that weren't anticipated.  The most
memorable of these became evident soon after the new system came up
and apparently worked.  In the midst of our jubilation, it was
discovered that the chdir (change current directory) command had
stopped working.  There was much reading of code and anxious
introspection about how the addition of fork could have broken the
chdir call.  Finally the truth dawned: in the old system chdir was an
ordinary command; it adjusted the current directory of the (unique)
process attached to the terminal.  Under the new system, the chdir
command correctly changed the current directory of the process created
to execute it, but this process promptly terminated and had no effect
whatsoever on its parent shell!  It was necessary to make chdir a
special command, executed internally within the shell.  It turns out
that several command-like functions have the same property, for
example login.


-Steve