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From: Arthur Krewat <krewat@kilonet.net>
To: tuhs@minnie.tuhs.org
Subject: Re: [TUHS] Who's behind the UNIX filesystem permission
Date: Thu, 1 Aug 2019 12:35:29 -0400	[thread overview]
Message-ID: <6bdbf145-7bd3-971b-0ced-3ad1cae8b33d@kilonet.net> (raw)
In-Reply-To: <CAC0cEp8oZ6kYXZGrwSVKM64MdkKCEMnkwu_62k9z+bne9x-Gaw@mail.gmail.com>

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There's also the setgid bit on directories, that when files are created, 
they will be in the group that the parent directory has on it.

Also, I don't think it's been mentioned, but there's the setuid bit on 
directories - otherwise known as the sticky bit. When set, even if you 
have rights to "write" the directory (meaning, delete files), you can't 
delete those owned by other users. Useful for /tmp

I have no idea what the timeline is for either of these features :)


On 8/1/2019 12:22 PM, John P. Linderman wrote:
>
>     *Yet clean as the idea of groups was, it has been used only
>     sporadically (in my experience).*
>
>
> As I recall it, the original "basic groups" were essentially "us" and 
> "them". "Us" was everyone in the "in crowd", "them" was everyone else. 
> Since the basic groups were rather extensive, it was prudent to turn 
> group write permission off in your default umask. But that made groups 
> rather clunky. You were in only one group at a time, so you had to 
> "chgrp" to a select group, and then remember to set your umask to 
> allow group write permission so others in the group could modify 
> files. This changed when you could be in multiple groups at the same 
> time (a BSD invention?), and your primary group automatically changed 
> to the group owning your current working directory (iff you belonged 
> to that group). This made it unnecessary to do an explicit chgrp in 
> most cases. Having group write permission off in your default umask 
> was now a nuisance. We fixed that by giving everyone an unshared 
> primary group id, typically the same as the uid. It then became safe 
> to make group write permission on by default. This made groups much 
> more useful. Anyone in a group (but only those members) could create a 
> directory owned by that group, and group members working in that 
> directory defaulted to creating files (and subdirectories) group-owned 
> by and writable by all the members of the group. It just worked.
>


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  reply	other threads:[~2019-08-01 16:36 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-01 12:35 Doug McIlroy
2019-08-01 16:22 ` John P. Linderman
2019-08-01 16:35   ` Arthur Krewat [this message]
2019-08-02  8:35   ` [TUHS] Additional groups and additional directory permissions arnold
2019-08-02 11:18     ` Tony Finch
2019-08-04  6:40       ` arnold
2019-08-02 12:45     ` Arthur Krewat
2019-08-02 13:06     ` Clem Cole
2019-08-02 13:28     ` Clem Cole
2019-08-02 19:00       ` Thomas Paulsen
2019-08-01 17:01 ` [TUHS] Who's behind the UNIX filesystem permission Nemo Nusquam
2019-08-01 18:26   ` Arthur Krewat
2019-08-01 20:14     ` Lyndon Nerenberg
2019-08-01 21:23 ` Dave Horsfall
2019-08-01 23:43 Noel Chiappa
2019-08-02  1:03 ` David Arnold
2019-08-02  4:36   ` Rob Pike
2019-08-07  2:35 ` Dave Horsfall
2019-08-02 14:35 Noel Chiappa
2019-08-02 15:01 ` Clem Cole
2019-08-02 15:17 ` Arthur Krewat
2019-08-02 21:23   ` Dave Horsfall
2019-08-03 12:51     ` Nemo

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