[plug] Unix file permission problem (I think)

[Bernd Felsche]

Steve Boak <sboak at westnet.com.au> writes:
>On Fri, 8 Jul 2005 07:45 am, Bernd Felsche wrote:
>[...]
>> >As you suggest, I had created the 'share' group in this session.
>> >Can you explain why starting a new xterm does not pick up the
>> >new group settings?

>> Permissions are inherited from the parent process.

>> If you'd ssh'd into localhost, it would have worked for you.

>I think that's what I missed - I assumed xterm WAS a new session,
>but now thinking about it, of course I don't need to log in when
>creating a new xterm, it's just a new process under my X session.

>Where I slipped up was that I had two xterms open, one as 'steve'
>and the other as 'root'. I added myself to the 'share' group in the
>root xterm, and tried to create the new directory in the 'steve'
>xterm.

>Would changing the group membership using 'sudo chmod ...' in the
>'steve' xterm have worked as I expected? (I haven't set up sudo
>yet, as I am having 

A change to file permissions doesn't change your current process'
attributes.  If you weren't a member of the "share" group when you
started the process, then even a sub-shell's change of file
attributes won't change that process' attributes.

Every process is in its own virtual computer environment. That's
the basis (perhaps a prerequisite!) for a stable, multi-user,
multi-tasking system. There are avenues for several processes on the
same computer cooperating; which very early on in Unix history was
only possible by the filesystem (and process signals if the
processes were owned by the same user).

The only thing that can break through the boundaries (by design
anyway) of that virtual computer is a privileged task (root-owned).
Login processes of one type or another is what grants the process
privileges (once authenticated).
-- 
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