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Chapter 5. Users and Groups

chown  R root.emacs

/usr/lib/emacs/site lisp

Now, it is possible to add the proper users to the group with

gpasswd

:

/usr/bin/gpasswd  a

username

emacs

:

;

Allow the users to actually create files in the directory with the following command:

chmod 775

/usr/lib/emacs/site lisp

When a user creates a new file, it is assigned the group of the user's default private group. To prevent

this, perform the following command, which causes everything in the directory to be created with the

emacs

group:

chmod 2775 /usr/lib/emacs/site lisp

If the new file needs to be mode 664 for another user in the emacs group to be able to edit it, make the

default umask 002.

At this point, by making the default umask 002, you can easily set up groups that users can take

advantage of without any extra work every time users write files to the group's common directory.

Just create the group, add the users, and do the above

chown

and

chmod

on the group's directories.

5.5. Shadow Utilities

If you are in a multiuser environment and not using a networked authentication scheme such as Ker 

beros, you should consider using Shadow Utilities (also known as shadow passwords) for the en 

hanced protection offered for your system's authentication files. During the installation of Red Hat

Linux, shadow password protection for your system is enabled by default, as are MD5 passwords (an

alternative and arguably more secure method of encrypting passwords for storage on your system).

Shadow passwords offer a few distinct advantages over the previous standard of storing passwords on

UNIX and Linux systems, including:

Improved system security by moving the encrypted passwords (normally found in

/etc/passwd

)

to

/etc/shadow

which is readable only by root

Information concerning password aging (how long it has been since a password was last changed)

Control over how long a password can remain unchanged before the user is required to change it

The ability to use the

/etc/login.defs

file to enforce a security policy, especially concerning

password aging

The

shadow utils

package contains a number of utilities that support:

Conversion from normal to shadow passwords and back (

pwconv

,

pwunconv

)

Verification of the password, group, and associated shadow files (

pwck

,

grpck

)

Industry standard methods of adding, deleting and modifying user accounts (

useradd

,

usermod

,

and

userdel

)

Industry standard methods of adding, deleting, and modifying user groups (

groupadd

,

groupmod

,

and

groupdel

)

Industry standard method of administering the

/etc/group

file using

gpasswd

There are some additional points of interest concerning these utilities: