chapter11.. linux. Managing Users . ppt

its a presentation of linux management system

1. Chapter 11:
Managing Users
The Complete Guide to Linux System
Administration

2. The Complete Guide to Linux System Administration 2
Objectives
•Create and manage user accounts
•Manage complex file permissions
•Review advanced user security issues

3. The Complete Guide to Linux System Administration 3
Creating and Managing User
Accounts
•Process of creating new user accounts
–Add default files to be part of every user’s home
directory to /etc/skel directory
–Create home directory for all users
–Configure default settings for all users
–Create groups
–Create user account for each person
–Create valid password for each user

4. The Complete Guide to Linux System Administration 4
Managing User Accounts
Graphically
•/etc/passwd file defines user accounts, including:
–User name – Comment field
–Password – User’s home directory
–UID – User’s default shell
–GID
•vipw command edits /etc/passwd file
•passwd command defines password

5. The Complete Guide to Linux System Administration 5
Managing User Accounts
Graphically (continued)
•Utilities to create new user accounts
–Graphical tools
–Command-line utilities
•system-config-users utility
–Red Hat graphical user account creation tool
–Information from /etc/passwd file shown in window
–Can edit each fields
–Edit password information stored in /etc/shadow

6. The Complete Guide to Linux System Administration 6
Managing User Accounts
Graphically (continued)

7. The Complete Guide to Linux System Administration 7
Managing User Accounts
Graphically (continued)
•User Properties dialog, User Data tab
–User name
–Full name
–Password and confirm password
–Home directory
–Login shell
•User Properties dialog, Account Info tab
–Enable account expiration
–Lock local password

8. The Complete Guide to Linux System Administration 8
Managing User Accounts
Graphically (continued)
•User Properties dialog, Password Info tab
–View when user last changed password
–Enable password expiration
•Experts recommend changing password every
30 to 60 days
•User Properties dialog, Groups tab
–Lists groups from /etc/group file
–Each user assigned primary group

9. The Complete Guide to Linux System Administration 9
Managing User Accounts
Graphically (continued)
•User private group model
–Used by Red Hat Linux and Fedora
–User’s primary group has same name as user
–Contains only user as member
•Create new user
–system-config-users utility
–Add User button
–Enter information on dialog
–Utility creates home directory based on user name

10. The Complete Guide to Linux System Administration 10
Managing User Accounts
Graphically (continued)
•/etc/login.defs file
–Stores settings used to create new users
–Comments describe settings
•Create new group
–Click Add Group button
–Enter group name

11. The Complete Guide to Linux System Administration 11
Managing User Accounts
Graphically (continued)
•Delete user
–Select user name on Users tab
–Click delete button
–Some administrators prefer to permanently
disable, not delete

12. The Complete Guide to Linux System Administration 12
Creating New Users at the
Command Line
•useradd utility
–Create new users
–Must be logged in as root
–Example: useradd -g sales -c “Raley Solomon"
rsolomon
–-D option displays the default settings
–Edit /etc/default/useradd to change defaults

13. The Complete Guide to Linux System Administration 13
Creating New Users at the
Command Line (continued)
•passwd command
–Change user’s password
–Lock user account: passwd -l thomas
–Unlock account: passwd -u thomas

14. The Complete Guide to Linux System Administration 14
Creating New Groups
•groupadd command
–Preferred method for adding new group
–Example: groupadd managers

15. The Complete Guide to Linux System Administration 15
Modifying User and Group
Accounts at the Command Line
•usermod command
–Modify user account
–Uses same options as useradd command
•groupmod command
–Modify group
–-g option: change GID
–-n option: change name

16. The Complete Guide to Linux System Administration 16
Modifying User and Group
Accounts at the Command Line
(continued)
•grpck command
–Check integrity of /etc/group and /etc/gshadow
files
–Uses no parameters
•chage command
–Alter password aging information
–View password expiration
–Change aging for user
–Interactive mode

17. The Complete Guide to Linux System Administration 17
Modifying User and Group
Accounts at the Command Line
(continued)
•pwconv utility converts older /etc/passwd
password storage to /etc/shadow password
storage
•pwunconv utility converts existing /etc/shadow
passwords to older /etc/passwd system for
compatibility
•pwck command shows formatting errors that
make accounts unusable

18. The Complete Guide to Linux System Administration 18
Automating Home Directory
Creation
•Files in /etc/skel automatically copied into each
user’s home directory
–At time account created
–Includes hidden configuration files
–Files not added to existing user home directories

19. The Complete Guide to Linux System Administration 19
Disabling User Accounts
•Temporarily disable user’s account
–Change password
•passwd command
–passwd -l [username] to lock account
–Edit /etc/shadow file in text editor
•Place asterisk before encrypted password
–Place # at beginning of line for user account in
/etc/passwd
•Make line into comment

20. The Complete Guide to Linux System Administration 20
Disabling User Accounts
(continued)
•userdel command
–Delete user account permanently
–Does not remove user’s home directory or
contents
•groupdel command
–Remove group
–Be careful deleting groups

21. The Complete Guide to Linux System Administration 21
Complex File Permissions
•Sticky bit
–Directory can only be renamed or unlinked by
•User that owns it
•root
–Often used on directories all users should be able
to create files such as /tmp
–To set: chmod a+t /tmp

22. The Complete Guide to Linux System Administration 22
Complex File Permissions
(continued)
•Set user ID permission
–SUID
–Can be added to file that has execute permission
set
–Causes user who executes file to take on file
permissions of owner of file
–Very useful for few specialized programs
–To set: chmod u+s file

23. The Complete Guide to Linux System Administration 23
Complex File Permissions
(continued)
•Permissions not always what they seem at first
•Set group ID permission
–SGID
–Person who executes program has permissions of
file’s group while executing program
–To set: chmod g+s file
–Can also be set numerically

24. The Complete Guide to Linux System Administration 24
Complex File Permissions
(continued)
•SGID set on directory
–Any file created within directory assigned to group
of directory
•Permissions examined in order
–Owner first
–Group second
–Others third
–Can deny group permission without users having
other permission

25. The Complete Guide to Linux System Administration 25
User Security Issues
•Other ways of securing Linux
–Additional communications
–User security mechanisms

26. The Complete Guide to Linux System Administration 26
Communicating with Users
•/etc/motd file
–Contents displayed just before shell is started
each time user logs in
–“Message of the day”
–Does not appear unless:
•User opens command line
•Or logs in at text-mode console

27. The Complete Guide to Linux System Administration 27
Communicating with Users
(continued)
•wall command
–Write all
–Communicate immediate message to all users
who are logged in to system
–Displays broadcast message on command line for
all users
•Working in text mode
•Or with open terminal window

28. The Complete Guide to Linux System Administration 28
Communicating with Users
(continued)
•fuser command
–Learn about what users are doing
–View users accessing
•File system
•Serial port
•Network connection
–-k option kills processes

29. The Complete Guide to Linux System Administration 29
Granting Limited Root Access
•sudo command
–Assign root privileges to any user account
–User can execute just programs that sudo
configuration specifies
•/etc/sudoers configuration file
–Syntax can be very complex
–Basic format: user host = command_list

30. The Complete Guide to Linux System Administration 30
Granting Limited Root Access
(continued)
•/etc/sudoers configuration file
–Can define aliases for:
•Collection of users
•Collection of hosts
•Collection of programs
•Set of sudo options
•visudo program edits /etc/sudoers file
•System administrator must hand out sudo power
carefully

31. The Complete Guide to Linux System Administration 31
Using Pluggable Authentication
Modules
•Pluggable authentication module (PAM)
–Architecture and set of libraries
–Programmer can create module to perform
specific security-related function
–System administrators can select, configure, and
use one or more modules
•Control operation of program that is aware of PAM
capabilities
–Configured by default for Red Hat Linux

32. The Complete Guide to Linux System Administration 32
Using Pluggable Authentication
Modules (continued)
•To use PAM, select PAM modules for program
•Configured using:
–Single configuration file /etc/pam.conf
–Series of configuration files in directory /etc/pam.d
–Person compiling software selects which
configuration style is used

33. The Complete Guide to Linux System Administration 33
Using Pluggable Authentication
Modules (continued)
•Red Hat Linux and Fedora use directory
configuration method
•/etc/pam.d directory contains file with name
matching program being configured
•When PAM-compatible program executed,
checks to see which applicable modules are
configured for given task
•Stacked modules
–Multiple modules are listed for module type

34. The Complete Guide to Linux System Administration 34
Using Pluggable Authentication
Modules (continued)
•control_flag element
–Determines how PAM processes stacked modules
–Has two forms

35. The Complete Guide to Linux System Administration 35
Using Network Information
Service
•Network Information Service (NIS)
–Lets system administrator manage single set of
configuration files for multiple Linux servers
–Sometimes called yellow pages service or yp
•When user logs in, server contacts NIS server to
see if user has valid user account

36. The Complete Guide to Linux System Administration 36
Using Network Information
Service (continued)
•NIS+ or NISplus
–More recent version of NIS
•authconfig program
–Set up system to use NIS server
•/etc/nsswitch.conf file
–Instructs various system programs in Linux on
where to look for configuration information
–Often includes multiple options

37. The Complete Guide to Linux System Administration 37
Summary
•User accounts can be managed graphically
•useradd command creates user accounts on the
command line
•usermod command modifies existing user
accounts
•User accounts can be disabled using various
methods

38. The Complete Guide to Linux System Administration 38
Summary (continued)
•SUID and SGID permissions cause user to
assume permissions of owner of executable file
when program is executed
•Sticky bit and other special file permissions allow
administrators to control shared files
•Administrators can broadcast messages to users
•sudo program lets regular users perform tasks
that require root privileges

39. The Complete Guide to Linux System Administration 39
Summary (continued)
•PAMs provide flexible and powerful way for
system administrators to configure exactly how
user security is handled
•NIS or NIS+ server
–Multiple systems can share user files