User Private Groups; Group Directories - Red Hat ENTERPRISE LINUX 4 System Administration Manual

Chapter 32. Users and Groups
Group
gdm
htt
mysql
webalizer
mailnull
smmsp
squid
ldap
netdump
pcap
quaggavt
quagga
radvd
slocate
wnn
dovecot
radiusd
Table 32.5. Standard Groups

32.5. User Private Groups

Red Hat Enterprise Linux uses a user private group (UPG) scheme, which makes UNIX groups easier
to manage.
A UPG is created whenever a new user is added to the system. A UPG has the same name as the
user for which it was created and that user is the only member of the UPG.
UPGs make it safe to set default permissions for a newly created file or directory, allowing both the
user and the group of that user to make modifications to the file or directory.
The setting which determines what permissions are applied to a newly created file or directory is called
a umask and is configured in the /etc/bashrc file. Traditionally on UNIX systems, the umask is
set to 022, which allows only the user who created the file or directory to make modifications. Under
this scheme, all other users, including members of the creator's group, are not allowed to make any
modifications. However, under the UPG scheme, this "group protection" is not necessary since every
user has their own private group.

32.5.1. Group Directories

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 project's files. Using this traditional scheme, managing files has been
difficult; 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. The setgid bit makes managing group projects that share a common
304
GID
42
101
27
67
47
51
23
55
34
77
102
92
75
21
49
97
95
Members