Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Scaricare il pdf (Pagina 96)

96 Chapter 6. Users and Groups

Group GID Members

mailnull 47 mailnull

rpcusers 29

nfsnobody 65534

xfs 43 xfs

gdm 42 gdm

apache 48 apache

squid 23 squid

named 25 named

junkbust 73 junkbust

mysql 27 mysql

mailman 41 mailman

ldap 55 ldap

Table 6-2. Standard Groups

6.4. User Private Groups

Red Hat Linux uses a user private group (UPG) scheme, which makes UNIX groups easier to use.

The UPG scheme does not add or change anything in the standard UNIX way of handling groups;

it simply offers a new convention. Whenever you create a new user, by default, they have a unique

group. The scheme works as follows:

User Private Group

Every user has a primary group; the user is the only member of that group.

umask = 002

Traditionally, on UNIX systems the umask is 022, which prevents other users and other members

of a user’s primary group from modifying a user’s ﬁles. Since every user has their own private

group in the UPG scheme, this "group protection" is not needed. A umask of 002 will prevent

users from modifying other users’ private ﬁles. The umask is set in /etc/profile.

setgid bit on Directories

If you set the setgid bit on a directory (with chmod g+s directory ), ﬁles created in that direc-

tory will have their group set to the directory’s group.

Many IT organizations like to create a group for each major project and then assign people to the

group if they need to access that group’s ﬁles. Using this traditional scheme, managing ﬁles has been

difﬁcult because when someone creates a ﬁle, it is associated with the primary group to which they

belong. When a single person works on multiple projects, it is difﬁcult to associate the right ﬁles with

the right group. Using the UPG scheme, however, groups are automatically assigned to ﬁles created

within a directory with the setgid bit set, which makes managing group projects that share a common

directory very simple.

For example, say you have a big project called devel, with many people editing the devel ﬁles in a

devel directory. Make a group called devel, chgrp the devel directory to devel, and add all of

the devel users to the devel group.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 96