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Sent: 15 March 2003 17:02
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Subject: Seawolf-list digest, Vol 1 #1670 - 1 msg
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Today's Topics:
1. Re:Groupd and User's Group Changing (Cameron Simpson)
--__--__--
Message: 1
Date: Sat, 15 Mar 2003 21:38:00 +1100
From: Cameron Simpson <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Re: Groupd and User's Group Changing
Reply-To: [EMAIL PROTECTED]
On 11:26 14 Mar 2003, Nestor Waldyd <[EMAIL PROTECTED]> wrote:
| I really don't have a good definition of what a group is in Linux... Would you please give me one? What i know
| is that a group is a set of users, but how can i change an user's group?
A group is a set of users, but the sets need not be disjoint. A user may
be a member of several groups for access to various things.
The mapping is mostly in the file /etc/group, whihc is a list of group
names, group ids (the internal numeric values used to represent each
group) and the users in each.
At any given time a process has
- a user id (uid)
- a primary group id
- a list of secondary groups ids
The uid and primary gid come from the /etc/passwd file.
The secondary gids come from the /etc/group file.
There's nothing special about the primary versus secondary gids; the
primary gid dates from an early revision of UNIX where there was only the
primary gid and no secondaries; the eatra groups were a BSD innovation,
now universal.
When accessing a file exactly _one_ of the three permission groups on the
file are considered:
- if the user id of the file matches the user id of file
then the first (user) set of permissions are used
- otherwise, if the gid of the file matches one of the gids of the
process, the second set is used
- otherwise, the third ("other") set is used
Cheers,
--
Cameron Simpson, DoD#743 [EMAIL PROTECTED] http://www.zip.com.au/~cs/
Success in software development depends on making a carefully planned
series of small mistakes in order to avoid making unplanned large
mistakes. - Steve McConnell, _Software Project Survival Guide_
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