Re: Group for /dev/cdrom, Does not work for me :-(, addendum

[cjw44@cam.ac.uk (Colin Watson)]

rosef@eou.edu (esoR ocsirF) wrote:
>On Wed, Mar 22, 2000 at 01:27:56AM +0000, Colin Watson wrote:
>> If groups isn't displaying the right output after a useradd, then my
>> guess is that you haven't logged out and in again since the useradd ...?
>
>ACK! I have gotten so used to things working when I do them ( as opposed
>to Windoughs, where you have to reboot in order for anything to be
>current ). Is there a specific reason why this doesn't happen
>dynamically? Thanks for the help

You rarely have to reboot in Linux, but you often have to restart
processes. It's not really something that can be fixed; each process
(say, each shell) keeps its own list of the groups to which it belongs.
To change these dynamically, you'd have to have useradd invade every
other process and change its list of groups. When you consider that
processes owned by any given user can take on new supplementary groups
using things like newgrp, or even potentially have a completely
different set of groups if they're invoked by something setgid, this is
a very difficult problem, and violates expected inter-process protection
something horrific. (Although useradd has root privileges, admittedly.)

Basically, don't go there. :) I'd be amazed if it were possible to do
this cleanly. Don't start thinking you need to reboot, but do expect to
have to restart processes sometimes when something major affects them.
It's usually not too much of a problem.

-- 
Colin Watson                                           [cjw44@cam.ac.uk]