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Options -d dir -D Description Sets the home directory of the new user. Displays defaults for all settings. Can also be used to reset default settings for the home directory (-b), group (-g), shell (-s), expiration date (-e), and password expirations (-f). Sets an expiration date for the account (none, by default). Specified as month/day/year. Sets the number of days an account remains active after its password expires. Sets a group. Creates user s home directory, if it does not exist. Sets the skeleton directory that holds skeleton files, such as .profile files, which are copied to the user s home directory automatically when it is created; the default is /etc/skel. Does not create user s home directory. Supplies an encrypted password (crypt or MD5). With no argument, the account is immediately disabled. A Red Hat-specific option that creates a system account (one whose user ID is lower than the minimum set in logon.defs). No home directory is created unless specified by -m. Sets the login shell of the new user. This is /bin/bash by default, the bash shell. Sets the user ID of the new user. The default is the increment of the highest number used so far. Options for useradd and usermod

Table 2-3.

you can use with the useradd command. You can use specific values in place of any of these defaults when

creating a particular account. The login is inaccessible until you do. In the next example, the group name for the chris account is set to intro1 and the user ID is set to 578: # useradd chris -g intro1 -u 578

Once you add a new user login, you need to give the new 2 login a password. Password entries are placed in the /etc/ passwd and /etc/shadow files. Use the passwd command 2 to create a new password for the user, as shown here. The password you enter will not appear on your screen. You will be prompted to repeat the password. A message 2 will then be issued indicating that the password was successfully changed.

# passwd chris Changing password for user chris New UNIX password: Retype new UNIX password: passwd: all authentication tokens updated successfully #

2 2 2 2 2 2 2 2 2 2 2 2

The usermod command enables you to change the values for any of these features. You can change the home directory or the user ID. You can even change the username for the account. The usermod command takes the same options as useradd, listed in Table 2-1.

When you want to remove a user from the system, you can use the userdel command to delete the user s login. With the -r option, the user s home directory will also be removed. In the next example, the user chris is removed from the system: # userdel -r chris

You can manage groups using either shell commands or window utilities like the Red Hat User Manager.

The system file that holds group entries is called /etc/group. The file consists of group records, with one record per line and its fields separated by colons. A group record has four fields: a group name, a password, its ID, and the users who are part of this group. The Password field can be left blank. The fields for a group record are as follows: Group name be unique The name of the group, which must

Password With shadow security implemented, this field is an x, with the password indicated in the /etc/gshadow file. Group ID The number assigned by the system to identify this group Users The list of users that belong to the group, separated by commas Here is an example of an entry in an /etc/group file. The group is called engines, the password is managed by shadow security, the group ID is 100, and the users who are part of this group are chris, robert, valerie, and aleina. engines:x:100:chris,robert,valerie,aleina As in the case of the /etc/passwd file, it is best to change group entries using a group management utility like groupmod, groupadd, or the Red Hat User Manager. All users have read access to the /etc/group file. With shadow security, secure group data like passwords are kept in the /etc/gshadow file, to which only the root user has access.