Transcript 9781111306366_PPT_Ch10

Guide to Operating Systems,
4th ed.
Chapter 10: Resource Sharing over a
Network
Objectives
• Explain the principles behind sharing disks, files,
and printers on a network
• Set up accounts, groups, security, and disk and file
sharing on network server operating systems
• Set up disk and file sharing on client (workstation)
operating systems
• Set up printer sharing on server and client
operating systems
• Discuss how network and Internet servers are used
for vast information-sharing networks
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Sharing Disks, Files, and Printers
• Sharing files was one of the first reasons to network
computers
• Network OSs were available at the start of the 1980’s
to share files through a server. There were two
methods:
– By downloading a file from a file server to a workstation
– Purchasing third-party software to create a special shared drive
for other workstations to access over a network
• Mapping – software process that enables a client
workstation to attach to a shared drive and assign it
a drive letter
– In UNIX/Linux and Mac OS X a mapped drive is called a
mounted volume
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Securing Shared Resources
• Sharing disks, files and printers is a potential
security risk (possible for non-authorized users to
access a file or use a printer)
• All OSs discussed in this book offer security
measures for protecting shared resources
– Access to a file can be denied to unauthorized users
– You may want a user to be able to read a file but not change it
• Security privileges can be used to limit users to only those
capabilities
– Access to a shared network printer can be given only to a
specific group of people
• Permission to manage print jobs can be assigned on a user by
user basis (only those who are qualified to do so)
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Sharing Disks and Files through
Server Network Operating Systems
• Windows Server 2003/R2 and Server 2008/R2,
UNIX/Linux, and Mac OS X are examples of server
network operating systems
– Enables the network administrator to establish security through
techniques such as:
•
•
•
•
Assigning accounts
Account passwords
Creating groups
Access privileges
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• The steps involved in sharing resources over a
network include setting up the following:
–
–
–
–
–
Groups
Account policies
User accounts
Permissions
Shared disks and folders
• Group – a collection of computers and users
– Reduce the amount of work of managing user accounts and
security
– Settings can be created for each group and applied to all
computers and users in that group instead of applying the settings
at one time
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• The following types of groups can be used in all
Windows Server 2003/Server 2008 OSs:
– Local – used on servers that are not part of a domain
– Domain local – used when there is a single domain or to
manage resources in a particular domain so that global and
universal groups can access those resources
– Global – used to group accounts from the same domain so that
those accounts can access resources in the same and other
domains
– Universal – used to provide access to resources in any domain
within a forest
• All of these groups are also defined as security or
distribution groups
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Security groups – used to enable access to
resources on a standalone server or in Active
Directory
– Active Directory is a database of computers, users, shared
printers, shared folders, and other network resources that are
used to manage a network
• Distribution groups – used for e-mail or telephone
lists, to provide quick, mass distribution of
information
• In a small office setting, Active Directory may not
be installed so only local groups can be created to
manage access
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Container object – an entity that is used to group
together resources in a directory service
• Directory service – provides 3 important functions:
– central listing of resources
– a way to quickly find resources
– the ability to access and manage resources
• Domain – fundamental component or container that
holds information about all network resources that
are grouped within it
• Tree – consists of one or more domains
• Forest – houses one or more trees
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
Sample Windows Server domain and tree models
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Example of working with groups:
– College – has a domain for:
• Students
• Faculty and staff
• Research organizations associated with the college
– College’s executive council – needs access to all 3 domains
• Create a domain local group called LocalExec in each domain
• Give that group access to files, folders and other resource
• Next, create a GlobalExec global group in the faculty and staff
domain that has the executive council as members
• Make that global group a member of all LocalExec groups
• See figure on next slide
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Windows Server 2003/Server 2003 R2 and
Server 2008/Server 2008 R2
Managing security through domain local and global
groups
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Guidelines to help simplify how to use groups:
– Use global groups to hold user accounts as members
• Give members access to resources by making the global group
members of domain local or universal groups (or both)
– Use domain local groups to provide access to resources in a
specific domain
• Avoid placing user accounts in domain local groups – give domain
local groups access to shared folders and printers
– Use universal groups to provide extensive access to resources
• To simplify access when there are multiple domains
• Give universal groups access to resources in any domain, tree or
forest
– Manage user account access by placing accounts in global groups
and join those groups to domain local or universal groups
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Trusted domain – is given access to resources in
another domain
• Trusting domain – allows the access to its
resources
– A mutual relationship of trust between domain, managed by an
Active Directory administrator or a security specialist
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Account Policies – used to set restrictions and
security to help ensure that only authorized users
are accessing the accounts
• Parameters you can configure through Account
Policies:
– Password Policy
– Account Lockout Policy
– Kerberos Policy
• Account policies should be configured before
setting up user accounts
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Password security enables you to set requirements
for how users set passwords
• Some password security options
– Enforce password history – users must choose new passwords
and cannot use previously used passwords
– Maximum password age – set a maximum time allowed until a
password expires
– Minimum password age – password must be used a minimum
amount of time before being changed
– Minimum password length
– Passwords must meet complexity requirements – create a filter of
customized password requirements
– Store password using reversible encryption
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Account lockout – ability to lock out an account
after a number of unsuccessful tries to login
• Some lockout parameters that can be configured:
– Account lockout duration – specify in minutes how long the
system will keep an account locked out after reaching the
specified number of unsuccessful logon attempts
– Account lockout threshold – set a limit to the number of
unsuccessful attempts to log onto an account
– Reset account lockout count after – specify the number of
minutes between two consecutive unsuccessful logon attempts
to make sure that the account will not be lockout out too soon
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Kerberos security – tickets are exchanged between
the client who requests logon and the server that
grants access
• Kerberos configuration options:
–
–
–
–
Enforce user logon restrictions – turns on Kerberos security
Maximum lifetime for a service ticket
Maximum lifetime for a user ticket
Maximum lifetime for user ticket renewal – maximum # of days
the same Kerberos ticket can be renewed each time a user
logs on
– Maximum tolerance for computer clock synchronization – how
long a client will wait until synchronizing its clock with that of a
server or Active Directory
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Configuring User Accounts – to be performed after
account policies have been configured
• When Active Directory is not installed:
– A user account is created by right-clicking My Computer,
Manage, and then click on Local Users and Groups
• When Active Directory is installed:
– Use the Active Directory Users and Computers tool to create a
new account
– Hands-on Project 10-4 enables you to create an account
• After creating users, they are typically added to
global groups
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Configuring Access Privileges (Permissions) –
enable you to protect the contents of files and
folders
• Permissions are set by clicking on Properties
(Security Tab) for the file or folder you wish to set
access to
– Permissions from a higher-level folder can be automatically
inherited. This is the default setting.
– See Table 10-1 on the next slide for some of the permissions
available for files and folders in Windows Server 2003/R2 and
Server 2008/R2
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• Configuring Shared Disks and Folders
– A drive or folder is shared through its properties
– When choosing to share a driver or folder you must provide a
name for the share and configure how many people can access
the share at the same time
– Available share permissions:
• Full Control – Provides full access to the folder including the ability
to take control or change share permissions
• Read – Permits groups or users to read and execute files
• Change – Enables users to read, add, modify, execute, and delete
files
– You can also setup Web sharing, which makes files available
on a Web server for HTML or FTP access
• Must have Internet Information Services (IIS) installed
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
Web sharing access permissions
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• NTFS permission conflicts
– If a user account has Read permission for a folder and belongs
to a group that has Write permission, that user has both Read
and Write permissions
• The exception is Deny – If a user who has Read permission of a
folder but belongs to a group for which all permissions are denied
to that folder, the user does not have access to the folder
– Summary of permission rules:
• NTFS permissions are cumulative with the exception that if an
account or group is denied access, this overrides other
permissions
• When a folder has both NTFS and share permissions, the most
restrictive permissions apply
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Windows Server 2003/Server 2003 R2
and Server 2008/Server 2008 R2
• When a file or folder is created, copied, or moved,
the permissions can be affected:
– A newly created file inherits the permissions already set up in a
folder
– A file that is copied from one folder to another on the same
volume inherits the permissions of the folder to which it is copied
– A file or folder moved from one folder to another on the same
volume takes its permissions with it
– A file or folder that is moved/copied to a different volume inherits
the permissions of the folder to which it is moved/copied
– A file or folder that is moved/copied from a FAT volume to a folder
in an NTFS volume inherits the permissions already assigned in
the NTFS folder
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UNIX and Linux
• Each user account is associated with a user
identification number (UID)
• Users who have common access needs can be
assigned to a group via a group identification
number (GID)
– Then permissions to access resources are assigned to the
group, instead of each user
• When a user logs on to access resources, the
password file is checked to permit logon
authorization
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UNIX and Linux
• The password file contains:
– The user name
– An encrypted password or a reference to a shadow file (file
associated with the password file that makes it difficult for
intruders to determine the passwords of others)
– The UID, can be a number as large as 60,000
– The GID, which is the primary group id
– Information about the user, such as a description of the user’s
job
– The location of the user’s home directory (a work area for the
user to store data on the server)
– A command that is executed as the user logs on, such as which
shell to use
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UNIX and Linux
• The shadow file (/etc/shadow) is normally only
available to the system administrator
• Contains password restriction information that
includes:
– The minimum and maximum number of days between
password changes
– Information on when the password was last changed
– Warning information about when a password will expire
– Amount of time that the account can be inactive before access
is prohibited
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UNIX and Linux
• Information about groups is stored in the etc/group
file
– Typically contains an entry for each group consisting of the
name, an encrypted group password, the GID, and a list of
group members
– In some versions of UNIX/Linux, every account is assigned to
at least one group
• User accounts and groups can be created by
editing the password, shadow, and group files
– Or by entering UNIX/Linux commands (recommended way)
– Important to make sure that each group has a unique GID
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UNIX and Linux
• The useradd command enables you to create a
new user
– See page 509 for a list of some of the parameters that can be
used with this command
• Example:
– useradd –c “Lisa Ramirez, Accounting Department, ext 221” –p
green$thumb –u 700 lramirez
– This command creates an account called lramirez with a
comment that includes personal information, a password set to
green$thumb, and a UID equal to 700
• Useradd, usermod, and userdel generally work in
all versions of UNIX/Linux
– Except IBM’s AIX which uses mkuser, chuser, and rmuser
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UNIX and Linux
• Groups are created using the groupadd command
– -g parameter is used to establish the GID and the group string
creates a group name
– Example – to create the auditors group:
• groupadd –g 2000 auditors
• Once a group is created, it is modified through the
groupmod command
• Groups are deleted using the groupdel command
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UNIX and Linux
• Files are assigned any combination of 3
permissions:
– Read – enables the user to display its contents (signified by the
letter r)
– Write – ability to modify, save, and delete a file (signified by the
letter w)
– Execute – enables a user or group of users to run a program
(signified by the letter x)
• Permissions are granted on the basis of 4 criteria:
–
–
–
–
Ownership
Group membership
Other (or World)
All (All is not used in every version of UNIX/Linux)
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UNIX and Linux
• The owner of a file or directory typically has:
– all permissions
– can assign permissions
– has the designation of u
• Group members (g) – users who may have a
complete set of permissions, one permission, or a
combination of two (such as read and execute)
• Other (o) – consists of non-owners who represent
generic users
• All (a) – represents the combination of u + g + o
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UNIX and Linux
• Permissions are set up by using the chmod
– In the command chmod go -r-w-x * (used on all files – signified
by the * )
• The g signifies groups and o signifies others
• The – means to remove a permission
• The -r-w-x signifies removing the read, write, and execute
permissions
– In this example, only the owner and members of the owner’s
group are left with read, write, and execute permissions on the
files in this directory
• Hands-On Project 10-10 offers practice configuring
permissions in UNIX/Linux
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Mac OS X Server
• Built on the foundation of Mac OS X but is
designed as a true server
• A computer running Mac OS X Server can support
up to several thousand users
• Might deploy this OS Server in a company that
creates publications or advertising materials or in a
school laboratory
• Mac OS X Server includes Apache Web server
software
• Permissions are similar to those for UNIX/Linux
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Mac OS X Server
• Mac OS X Server supports TCP/IP
– Opens door to communication with other computers that use
TCP/IP
– Compatible with the Internet e-mail protocol Simple Mail
Transfer Protocol (SMTP)
• Server Admin tool – used to:
–
–
–
–
Create and manage accounts and groups
Manage file and print sharing
Establishes share points (shared resources on the server)
Log events such as login and logout, opening, creating, and
deleting files and folders
– Monitor/create print queues
– Hold, release, and delete print jobs
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Accessing and Sharing Resources in
Windows XP/Server 2003/R2
• Click the Start menu, right click My Computer, and
click Map Network Drive
• Click the Browser button
• Find the workgroup, domain, or other entity in
which the computer sharing the drive resides, click
it
• Click the folder that you want to access, click OK
• Set the Drive letter to which you want to map the
network drive
• Click Finish
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Accessing and Sharing Resources in
Windows XP/Server 2003/R2
Configuring a shared folder in Windows XP
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Accessing and Sharing Resources in
Windows Vista/7/Server 2008/R2
• Click the Start menu, click Computer, and click Map
network drive
• Set the drive letter to which you want to map the
network drive
• Click the Browse button
• Find the workgroup, domain, or other entity in which the
computer sharing the drive resides, click it
• Click the folder you want to access, click OK
• Check the Reconnect at Login box if you want the
mapping to be there after a reboot
• Click Finished when done
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Accessing and Sharing Resources in
Windows Vista/7/Server 2008/R2
Mapping a drive in Windows 7
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Accessing Shared Resources via
UNIX/Linux and Specialized Utilities
• UNIX/Linux enable resource sharing by using
Network File System (NFS)
– NFS enables one computer to mount a partition on another
computer and then access file systems on the mounted
partition as if they were local
• To use NFS in Red Hat Enterprise Linux, the
following services must be enabled:
– portmap – establishes and manages the remote connections
through designated User Datagram Protocol (UDP) ports
– rpc.mounted – handles the RPC request to mount a partition
– rpc.nfsd – enables the Linux kernel to manage specific
requests from a client
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Accessing Shared Resources via
UNIX/Linux and Specialized Utilities
• Security that controls which clients can use NFS is
handled through entries in two files:
– /etc/hosts.allow – contains the clients that are allowed to use
NFS
– /etc/hosts.deny – contains computers that are not allowed to
use NFS
• Samba – utility that uses the Server Message
Block (SMB) protocol to allow access to shared
Windows drives
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Accessing and Sharing Resources via
Mac OS
• Uses Samba to connect to another computer that is
sharing a disk or folder
• To mount a shared drive:
– Open the Go menu, select Connect to Server, and enter the
address of the server or use the Browse button to find it
Connect to Server dialog box in Mac OS X
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Accessing and Sharing Resources via
Mac OS
• In Mac OS X – turn on file sharing through System
Preferences
• Some of the resources that you can configure for
sharing:
– File Sharing – To share folders with other Mac OS X computers
– Web Sharing – To share information on the Web
– Remote Login – To allow another computer to remotely log into
your computer
– Remote Apple Events – So that other Mac OS X computers can
send events to this computer
– Printer Sharing – To enable others to use your computer’s
printer
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Sharing Printing Devices
• Windows Systems – once a printer is setup, it can be
configured for printer sharing through Properties
– Different Windows versions have different steps in order to
share a printer
• When you configure sharing, make sure you
configure share permissions for the shared printer
– The following are share permissions you will see:
• Print – Can send print jobs and manage your own jobs
• Manage Documents – Can manage your print jobs or those sent
by any other user
• Manage Printers – Can access the share, change share
permissions, turn off sharing, configure printer properties
• Special Permissions – shows whether special permissions are
configured, and if they are allowed or denied
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Sharing Printing Devices
• UNIX/Linux printing is essentially the process of
logging onto the UNIX/Linux server and printing to
one of its printers
– Uses Berkeley Software Distribution (BSD) spooling system
– BSD uses 3 components for printing
• lpr print program
• lpd daemon
• The file /etc/printcap to specify printer properties (a text file that
can be modified via a text editor)
• In Red Hat Enterprise Linux or Fedora – use the
GNOME Print Manager tool
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Sharing Printing Devices
• In Mac OS X Systems there are 2 ways to set up
printer sharing
– First method:
• Open System Preferences from the Dock or by clicking Go,
clicking Applications, and double-clicking System Preferences
• Double-click Sharing
• Check the box for Printer Sharing
• Close the Sharing Window
– Second method:
• Open System Preferences from the Dock or by clicking Go,
clicking Applications, and double-click System Preferences
• Double-click Print & Fax
• Check the box for Share my printers with other computers and
close the window
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Sharing Printing Devices
Accessing a shared printer via Mac OS X
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Network and Internet Resource
Servers
• UNIX/Linux, Windows, and Mac OS X servers can
be set up as resource servers to provide network
and Internet resources
–
–
–
–
–
–
–
–
–
E-mail servers
E-commerce
Videoconferencing
Multimedia
Instant messaging
Alerts for weather and security-related activities
Web servers
Intranet and virtual private network (VPN) servers
FTP servers
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Chapter Summary
• Resource sharing is why networks exist starting with sharing
files, which led to sharing disks and folders, which led to
printing and program services
• Whenever network resources such as folder and printers are
shared, it is important to secure these resources to make
sure that only authorized users can access them
• When you configure Windows resources, the process
typically involves creating security groups for easier
management, establishing account policies and user
accounts, setting permissions on the resources, and
configuring sharing of the resources
• UNIX/Linux systems also use groups, user accounts, and
permissions to enable resource access and security
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Chapter Summary
• Mac OS X Server is a server version of Mac OS X for
providing more extensive access to resources through user
accounts and sharing services
• Client operating systems – such as Windows, UNIX/Linux,
and Mac OS X – come with utilities to enable them to access
shared resources over a network and to offer resources to
share
• All of the OSs discussed in this book offer the ability to share
printers and to access printers that are shared through a
network
• Network server OSs continue to offer more and more ways to
share resources such as e-mail, e-commerce,
videoconferencing, multimedia distribution, and database
access
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