Red Hat Linux 9 Professional Secrets [Electronic resources] نسخه متنی

Managing User Accounts

Adding user accounts to the system is a key system-administration function. You get the chance to add user accounts when you boot Red Hat Linux for the first time. If you didn't add other user accounts at that time, you can do so now. You can use the Red Hat User Manager or the

useradd command to add a new user account to your system.

Using Red Hat User Manager to Add User Accounts

You can use the Red Hat User Manager to add user accounts. To start the Red Hat User Manager, log in as root at the graphical login screen and then select Main Menu>System Settings>Users and Groups from the GNOME or KDE Panel. If you're not logged in as

root , the Red Hat User Manager prompts you for the root password. You can enter the password and click OK, then the Red Hat User Manager window appears.

The window shows two tabs: Users and Groups (see Figure 12-2). The Users tab displays the current list of users from the

/etc/passwd file. The Groups tab lists the name of groups from the

/etc/group file. Initially, the Red Hat User Manager filters out any system users and groups. However, you can turn off the filer by selecting Preferences>Filter system users and groups. Figure 12-2 shows the Red Hat User Manager window with a listing of all user accounts, including the system ones.

Figure 12-2: Red Hat User Manager Window.

You can add new users and groups or edit existing users and groups from the Red Hat User Manager. To edit the information for an existing user, click the user name in the list in the Users tab, and then click the Properties button on the toolbar. That user's information appears in a User Properties dialog box. You can then edit the information and click OK to make the changes.

To add a new user, click the New User button on the toolbar. This action opens the Create New User dialog box, as shown in Figure 12-3.

Figure 12-3: Entering Information for a New User.

Fill in the requested information. In particular, you must enter the user name and the password. After filling in all the fields, click the OK button. The new user should now appear in the list on the Users tab in the Red Hat User Manager window.

Notice the checkbox labeled

Create a private group for the user in Figure 12-3. It's checked by default, and that means each new user is in a separate private user group. However, sometimes you want a user to be in a specific group so that the user can access the files owned by that group. It's easy to add a user to another group. For example, suppose that I want to add the user name

naba to the group called

wheel . I can do this simply by typing the following command in a terminal window:

usermod -G wheel naba

If you simply uncheck that check box labeled

Create a private group for the user (see Figure 12-3), the new user is assigned the group named

users . Type more /etc/group to see the group names and group ID.

Using Commands to Manage User Accounts

If you're working from a text console, you can create a new user account by using the

useradd command. Follow these steps to add an account for a new user:

1. 
   

   Log in as

   root . (If you're not already logged in as root, type su - to become root.)



2. 
   

   Type the following

   useradd command with the

   -c option to create the account:

   
   /usr/sbin/useradd -c "Ashley Barkakati" ashley
   

   
   


3. 
   

   Set Ashley's password by using the

   passwd command, as follows:

   
   passwd ashley
   Changing password for user ashley
   New password: (Type the password and then press Enter.)
   Retype new password: (Type the password again and press Enter.)
   passwd: all authentication tokens updated successfully

   
   

   Notice that, if you type a password that someone can easily guess, the passwd program rejects it.

The

useradd command consults the files

/etc/default/useradd and

/etc/ login.defs to obtain default information on various parameters for the new user account. The

/etc/default/useradd file, for example, specifies the default shell (

/bin/bash ) and default home directory location (

/home ). The

/etc/login.defs file provides systemwide defaults for automatic group and user IDs, as well as password expiration parameters.

You can delete a user account by using the

userdel command. Simply type userdel username at the command prompt to delete a user's account. To wipe out that user's home directory as well, type userdel -r username.

To modify any information in a user account, use the

usermod command. For example, if I want my user name,

naba , to have

root as the primary group, I would type:

usermod -g root naba

To learn more about the

useradd and

userdel commands, type man useradd or man userdel in a terminal window.

Understanding the /etc/passwd File

The

/etc/passwd file is a list of all user accounts. It's a text file, and any user can read it; no special privileges are needed. Each line in /etc/passwd has seven fields, separated by colons (

: ).

Here is a typical entry from the

/etc/passwd file:

naba:x:500:10:Naba Barkakati:/home/naba:/bin/bash

Figure 12-4 uses this typical entry to explain the meaning of the seven fields.

Figure 12-4: Meaning of Fields in a Typical /etc/passwd Entry.

As the example shows, the format of each line in

/etc/passwd looks like this:

username:password:UID:GID:GECOS:homedir:shell

Table 12-1 explains the meaning of the seven fields in each /etc/passwd entry.

Managing Groups

A group is an something to which users belong. A group has a name and an identification number (GID). After a group is defined, users can belong to one or more of these groups.

You'll find all the existing groups listed in

/etc/group . For example, here is the line that defines the group named

wheel :

wheel:x:10:root,naba

As this example shows, each line in

/etc/group has the following format with four fields separated by colons:

groupname:password:GID:membership

Table 12-2 explains the meaning of the four fields in a group definition.

If you want to create a new group, you can simply click the Add Group button in the Red Hat User Manager (Figure 12-2). An even quicker way is to use the

groupadd command. For example, to add a new group called

class with an automatically-selected group ID, just type the following command in a terminal window (you have to be logged in as

root ):

groupadd class

Then, you can add users to this group with the

usermod command. For example, to add the users

naba and

ashley to the group named

class , I type the following commands:

usermod -G class naba
usermod -G class ashley

That's it. Now I check

/etc/group to find that it contains the following definition of class:

class:x:502:naba,ashley

If you want to remove a group, use the

groupdel command. For example, to remove the group named

class , type

groupdel class