Lecture #9 Administering User Accounts and Groups

Learner Outcomes

• Add, modify and delete user accounts on a system.
• Manage user passwords controlling expiration, aging, reseting, and disabling.
• Describe the processes that are created when a user logs in to a system.

Activities

• Convert a password file to use a shadow file.
• Demonstrate the encryption of a password
• Dangerous policies:
  1. Case sensitive usernames
  2. Changing the name of the root account
  3. Creating a back door user account
• Private groups and removing users
• Password management: the chage command
• Class Exercise:
  1. Change the gid of group cis191 to 191, and fix the gid of all files formerly belonging to the previous cis191 group.
  2. Create user accounts for yourself and the other members of your group using consistent uids and gids:
     1. Primary gid must be 191
     2. Set passwords to expire on 12/16/2009
     3. Initial password: Cabri11o
     4. Force the users to change their password at the first login.
  3. Come up with a name for your group and add it and its members to /etc/group.
  4. Change the root password to a unique password.
• Demonstrate each step of the login process: CCC Confer Video

Assignment

• Read Chapter 5 Sections 1-4 and Chapter 7 sections 3, 4 and 6 on File Systems and fsck.
• Prepare for quiz 3 by referring to the Review questions, which come predominantly from chapter 7.

Users and Groups

1. User and Group Management
   • The Importance of Multiple Users
     • Important to be able to add and remove accounts
     • There should be one account other than root
   • Where User and Group Information Resides
     • Stored in /etc/passwd file
     • Username, UID, GID, home directory, starting shell ...
     • /etc/group, /etc/shadow, and /etc/gshadow
2. Creating and Maintaining User Accounts
   • Password Files
   • Adding User Accounts
   • Deleting an Account
   • Modifying an Account
   • User Account Utilities
     • Changing login shell: chsh
     • Changing Passwords: passwd
     • Editing passwd files: vipw
   • Password Encryption
3. Creating and Maintaining Groups
   • Group files
   • Adding Groups
   • Creating Group Administrators and Users
   • Group Administration
   • Removing Groups
   • Modifying Existing Group Information
   • Group Switching
   • Password Encryption
4. Setting Account Defaults
   • User Profiles
     • System defaults
     • The role of /etc/profile versus /etc/bashrc
     • The order of precedence
   • Creating /etc/skel Account Templates
5. Password Rules and Aging
   • Changing Password Expiration

Relevant Commands and Files