System Groups

System Groups

Post by Brian E. Seppane » Sat, 20 Jan 2001 05:57:59

Is there any difference between a system group and a regular group.  As
far as I can tell a system group is numbered below 500, but is this
numbering special or signify any additional level of priviledge?   from
the groupadd manpage the -r flag, -- which creates a system group
account, -- seems to be redhat specific.  Can anyone shed any lights on
this.  I noticed that there is also an /etc/gshadow that is a shadow of
/etc/groups, but I'm not sure what exactly what the difference is except
possibly permissions?

this is on  a redhat 6.2 server.
Brian Seppanen
Charter Communications
Regional Data Center                            906-228-4226 ext 23


1. Need information about system-users and system-groups

Is there any good place to find comprehensive information
about the different system-users (adm,lp,sync,halt)
and system-groups (bin,daemon,wheel,kmem)?

I'm looking for information about:

-what files/directories/devices should be owned by a
particular user and/or group.

-what programms should be SUID or SGID to a
particular user and/or group.

-what processess should be run on behalf of a
specific system-user.

-which system- and/or normal-users should belong
which groups (if any).

-when and *how* are some users (like sync and halt)
used (I actually get the "when", but how about
the *why*).

-the use of certain users and groups (like wheel --
I belive users allowed to su is supposed to be
meber of it, but how is it to be used correctly?).


I do see the purpose of the users and groups for
differenting the different types of files and for
running processes with as little privlige as possible.

That a program needing to *read* the passwords in
/etc/shadow could be made a member of the shadow-
group, and then run with SGID -- instead of running
it with full root-privlige *just* to *read*

Or making a user game whom all games are run as, and
then making game a member of the groups owning the
soundcard, console (i.e. screencard) and any other
resource it *really needs* to use -- rather than
letting it run with root-privliges.

But still there are some users and groups who's
purpose alludes me, and I'll also like to know
when and how to use them correctly (when to
make file SUID and/or GUID, when to run a process
as a system-user, when to create a new user and/or
group, and when and to which groups a new system-
user should be made member of).

If there isn't any documentation on the subject,
I'd like to know what experiences you've made, and
would appriciate a summed-up who's-who among Linux'
users and groups list.


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