Date: Tue, 9 Mar 2004 16:25:13 +0100 From: Ruben de Groot <mail25@bzerk.org> To: Matthew Seaman <m.seaman@infracaninophile.co.uk>, Ruben de Groot <mail25@bzerk.org>, Marty Landman <MLandman@face2interface.com>, Dan Nelson <dnelson@allantgroup.com>, Alex de Kruijff <freebsd@akruijff.dds.nl>, freebsd-questions@freebsd.org Subject: Re: Why can't I write this file? Message-ID: <20040309152513.GA38166@ei.bzerk.org> In-Reply-To: <20040309144405.GD16123@happy-idiot-talk.infracaninophile.co.uk> References: <20040308212749.GC894@alex.lan> <20040308214225.GA95503@dan.emsphone.com> <6.0.0.22.0.20040308165050.104aea98@pop.face2interface.com> <20040309141025.GB16123@happy-idiot-talk.infracaninophile.co.uk> <20040309142907.GA37091@ei.bzerk.org> <20040309144405.GD16123@happy-idiot-talk.infracaninophile.co.uk>
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On Tue, Mar 09, 2004 at 02:44:05PM +0000, Matthew Seaman typed: > On Tue, Mar 09, 2004 at 03:29:07PM +0100, Ruben de Groot wrote: > > On Tue, Mar 09, 2004 at 02:10:25PM +0000, Matthew Seaman typed: > > > > > > Yes, quite. Your login credentials are established when you login to > > > the system and only then -- that's when the limits of what you're > > > authorized to do are set, which includes amongst other things which > > > groups you're a member of. So you have to log out and back in again > > > to pick up any changes to /etc/master.passwd or /etc/group. > > > > Actually, when there's a change in /etc/group, you can use > > "newgrp <groupname>" to add the new group to your credentials without > > logging in again. It's not exactly the same, but it does the work. > > Not on BSD-ish Unices you can't: > > % which newgrp > newgrp: Command not found. > > That's a SysV-ism, and dates back to the days when SysV group handling > used very different semantics to the BSD style that almost every *nix > uses nowadays. On the early SysV systems your login session would > have one and only one group active at a time: any files you created > would have that group membership, irrespective of the group ownership > of the directory, and your access to files was tested by matching just > that group to the group ownership of the file, rather than comparing > to all groups you are a member of. If you wanted to change to a new > group, you had to use the newgrp command -- and in some cases, that > would require your giving the group password. If you ever wondered > why the /etc/group file has an encrypted password field that is almost > never used, this is where it comes from. Well, SysV-ism or not, it's back in FreeBSD 5.x, and it works as I described. I should have checked one of my older systems too though. ruben@ei:/home/ruben> uname -r 5.2.1-RELEASE-p1 ruben@ei:/home/ruben> which newgrp /usr/bin/newgrp (See also: http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/newgrp/newgrp.c) cheers, Ruben
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