 | | | Seawolf-list digest, Vol 1 #1670 - 1 msg | Seawolf-list digest, Vol 1 #1670 - 1 msg 2003-03-17 - By Dhadda, Baldev
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-- --Original Message-- --
From: seawolf-list-request@(protected)
[mailto:seawolf-list-request@(protected)]
Sent: 15 March 2003 17:02
To: seawolf-list@(protected)
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 <cs@(protected)>
To: seawolf-list@(protected)
Subject: Re: Groupd and User's Group Changing
Reply-To: seawolf-list@(protected)
On 11:26 14 Mar 2003, Nestor Waldyd <nwaldyd@(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 cs@(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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<P><FONT SIZE=2>-- --Original Message-- --</FONT>
<BR><FONT SIZE=2>From: seawolf-list-request@(protected)</FONT>
<BR><FONT SIZE=2>[<A HREF="mailto:seawolf-list-request@(protected)">mailto
:seawolf-list-request@(protected)</A>]</FONT>
<BR><FONT SIZE=2>Sent: 15 March 2003 17:02</FONT>
<BR><FONT SIZE=2>To: seawolf-list@(protected)</FONT>
<BR><FONT SIZE=2>Subject: Seawolf-list digest, Vol 1 #1670 - 1 msg</FONT>
</P>
<BR>
<P><FONT SIZE=2>Send Seawolf-list mailing list submissions to</FONT>
<BR> <FONT SIZE=2>seawolf-list@(protected)
.com</FONT>
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<BR> <FONT SIZE=2><A HREF="https:/
/listman.redhat.com/mailman/listinfo/seawolf-list" TARGET="_blank">https:/
/listman.redhat.com/mailman/listinfo/seawolf-list</A></FONT>
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<P><FONT SIZE=2>When replying, please edit your Subject line so it is more
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</P>
<BR>
<P><FONT SIZE=2>Today's Topics:</FONT>
</P>
<P><FONT SIZE=2> 1. Re:Groupd and User's Group Changing (Cameron
Simpson)</FONT>
</P>
<P><FONT SIZE=2>--__--__--</FONT>
</P>
<P><FONT SIZE=2>Message: 1</FONT>
<BR><FONT SIZE=2>Date: Sat, 15 Mar 2003 21:38:00 +1100</FONT>
<BR><FONT SIZE=2>From: Cameron Simpson <cs@(protected)></FONT>
<BR><FONT SIZE=2>To: seawolf-list@(protected)</FONT>
<BR><FONT SIZE=2>Subject: Re: Groupd and User's Group Changing</FONT>
<BR><FONT SIZE=2>Reply-To: seawolf-list@(protected)</FONT>
</P>
<P><FONT SIZE=2>On 11:26 14 Mar 2003, Nestor Waldyd <nwaldyd@(protected)
.co> wrote:</FONT>
<BR><FONT SIZE=2>| I really don't have a good definition of what a group is in
Linux... Would you please give me one? What i know </FONT>
<BR><FONT SIZE=2>| is that a group is a set of users, but how can i change an
user's group?</FONT>
</P>
<P><FONT SIZE=2>A group is a set of users, but the sets need not be disjoint.
A user may</FONT>
<BR><FONT SIZE=2>be a member of several groups for access to various things.<
/FONT>
</P>
<P><FONT SIZE=2>The mapping is mostly in the file /etc/group, whihc is a list
of group</FONT>
<BR><FONT SIZE=2>names, group ids (the internal numeric values used to
represent each</FONT>
<BR><FONT SIZE=2>group) and the users in each.</FONT>
</P>
<P><FONT SIZE=2>At any given time a process has</FONT>
<BR> <FONT SIZE=2>- a user id (uid)<
/FONT>
<BR> <FONT SIZE=2>- a primary group
id</FONT>
<BR> <FONT SIZE=2>- a list of
secondary groups ids</FONT>
</P>
<P><FONT SIZE=2>The uid and primary gid come from the /etc/passwd file.</FONT>
<BR><FONT SIZE=2>The secondary gids come from the /etc/group file.</FONT>
</P>
<P><FONT SIZE=2>There's nothing special about the primary versus secondary gids
; the</FONT>
<BR><FONT SIZE=2>primary gid dates from an early revision of UNIX where there
was only the</FONT>
<BR><FONT SIZE=2>primary gid and no secondaries; the eatra groups were a BSD
innovation,</FONT>
<BR><FONT SIZE=2>now universal.</FONT>
</P>
<P><FONT SIZE=2>When accessing a file exactly _one_ of the three permission
groups on the</FONT>
<BR><FONT SIZE=2>file are considered:</FONT>
</P>
<P> <FONT SIZE=2>- if the user id of
the file matches the user id of file</FONT>
<BR> <FONT SIZE=2> then the
first (user) set of permissions are used</FONT>
</P>
<P> <FONT SIZE=2>- otherwise, if the
gid of the file matches one of the gids of the</FONT>
<BR> <FONT SIZE=2> process, the
second set is used</FONT>
</P>
<P> <FONT SIZE=2>- otherwise, the
third ("other") set is used</FONT>
</P>
<P><FONT SIZE=2>Cheers,</FONT>
<BR><FONT SIZE=2>-- </FONT>
<BR><FONT SIZE=2>Cameron Simpson, DoD#743
cs@(protected) <A HREF="http://www.zip.com.au/~cs/"
TARGET="_blank">http://www.zip.com.au/~cs/</A></FONT>
</P>
<P><FONT SIZE=2>Success in software development depends on making a carefully
planned</FONT>
<BR><FONT SIZE=2>series of small mistakes in order to avoid making unplanned
large</FONT>
<BR><FONT SIZE=2>mistakes. - Steve
McConnell, _Software Project Survival Guide_</FONT>
</P>
<BR>
<BR>
<BR>
<BR>
<P><FONT SIZE=2>--__--__--</FONT>
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