[TUHS] Who's behind the UNIX filesystem permission
Arthur Krewat
krewat at kilonet.net
Fri Aug 2 02:35:29 AEST 2019
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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