3.3. User and Group Management Tools

source

3.3. User and Group Management Tools

Managing users and groups can be tiresome; this is why Fedora provides tools and conventions to make this task easier to manage.

The easiest way to manage users and groups is through the graphical application, User Manager(system-config-users). For more information on User Manager, refer to Section 3.2, “User Manager Tool”.

The following command line tools can also be used to manage users and groups:

• useradd,usermod, anduserdel— Industry-standard methods of adding, deleting and modifying user accounts
• groupadd,groupmod, andgroupdel— Industry-standard methods of adding, deleting, and modifying user groups
• gpasswd— Industry-standard method of administering the/etc/groupfile
• pwck,grpck— Tools used for the verification of the password, group, and associated shadow files
• pwconv,pwunconv— Tools used for the conversion of passwords to shadow passwords and back to standard passwords

3.3.1. Command Line Configuration

If you prefer command line tools or do not have the X Window System installed, use following to configure users and groups.

Adding a User

To add a user to the system:

1. Issue theuseraddcommand to create a locked user account:

   useradd username

2.  Unlock the account by issuing thepasswdcommand to assign a password and set password aging guidelines:

   passwd username

Command line options foruseraddare detailed in Table 3.1, “useraddCommand Line Options”.

Table 3.1. useraddCommand Line Options

OPTION	DESCRIPTION
-c ‘comment‘	commentcan be replaced with any string. This option is generally used to specify the full name of a user.
-d home_directory	Home directory to be used instead of default/home/username/.
-e date	Date for the account to be disabled in the format YYYY-MM-DD.
-f days	Number of days after the password expires until the account is disabled. If0is specified, the account is disabled immediately after the password expires. If-1is specified, the account is not be disabled after the password expires.
-g group_name	Group name or group number for the user’s default group. The group must exist prior to being specified here.
-G group_list	List of additional (other than default) group names or group numbers, separated by commas, of which the user is a member. The groups must exist prior to being specified here.
-m	Create the home directory if it does not exist.
-M	Do not create the home directory.
-N	Do not create a user private group for the user.
-p password	The password encrypted withcrypt.
-r	Create a system account with a UID less than 500 and without a home directory.
-s	User’s login shell, which defaults to/bin/bash.
-u uid	User ID for the user, which must be unique and greater than 499.

Adding a Group

To add a group to the system, use the commandgroupadd:

groupadd group_name

Command line options forgroupaddare detailed in Table 3.2, “groupaddCommand Line Options”.

Table 3.2. groupaddCommand Line Options

OPTION	DESCRIPTION
-f,--force	When used with-g gidandgidalready exists,groupaddwill choose another uniquegidfor the group.
-g gid	Group ID for the group, which must be unique and greater than 499.
-K,--key key=value	Override/etc/login.defsdefaults.
-o,--non-unique	Allow to create groups with duplicate.
-p,--password password	Use this encrypted password for the new group.
-r	Create a system group with a GID less than 500.

Password Aging

For security reasons, it is advisable to require users to change their passwords periodically. This can be done when adding or editing a user on the Password Info tab of the User Manager.

To configure password expiration for a user from a shell prompt, use thechagecommand with an option fromTable 3.3, “chageCommand Line Options”, followed by the username.

Shadow passwords must be enabled to use chage

Shadow passwords must be enabled to use thechagecommand. For more information, see Section 3.7, “Shadow Passwords”.

Table 3.3. chageCommand Line Options

OPTION	DESCRIPTION
-d days	Specifies the number of days since January 1, 1970 the password was changed.
-E date	Specifies the date on which the account is locked, in the format YYYY-MM-DD. Instead of the date, the number of days since January 1, 1970 can also be used.
-I days	Specifies the number of inactive days after the password expiration before locking the account. If the value is0, the account is not locked after the password expires.
-l	Lists current account aging settings.
-m days	Specify the minimum number of days after which the user must change passwords. If the value is0, the password does not expire.
-M days	Specify the maximum number of days for which the password is valid. When the number of days specified by this option plus the number of days specified with the-doption is less than the current day, the user must change passwords before using the account.
-W days	Specifies the number of days before the password expiration date to warn the user.

chage interactivity

If thechagecommand is followed directly by a username (with no options), it displays the current password aging values and allows them to be changed interactively.

You can configure a password to expire the first time a user logs in. This forces users to change passwords immediately.

1. Set up an initial password — There are two common approaches to this step: the administrator can assign a default password, or he can use a null password.
   To assign a default password, type the following at a shell prompt:

   passwd username

   To assign a null password instead, use the following command:

   passwd -d username

   Avoid using null passwords whenever possible

   Using a null password, while convenient, is a highly insecure practice, as any third party can log in first and access the system using the insecure username. Always make sure that the user is ready to log in before unlocking an account with a null password.
2. Force immediate password expiration — Type the following command:

   chage -d 0 username

   This command sets the value for the date the password was last changed to the epoch (January 1, 1970). This value forces immediate password expiration no matter what password aging policy, if any, is in place.

Upon the initial log in, the user is now prompted for a new password.

3.3. User and Group Management Tools

3.3. User and Group Management Tools

تحرير

الوسومADMINISTRATION FEDORA FEDORA COMMAND HOWTO LINUX COMMAND SHELL