Guide to Operating Systems, 4 th ed.

1. Guide to Operating Systems, 4th ed. Chapter 10: Resource Sharing over a Network

2. 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 Objectives Guide to Operating Systems, 4th ed. 2

3. Sharing Disks, Files, and Printers Sharing files was one of the first reasons for linking a workstation’s OS onto a network. It remains one of the most important reasons for networking. 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. Guide to Operating Systems, 4th ed.

4. Sharing Disks, Files, and Printers The concept of sharing resources quickly blossomed into other ways to access files, such as making shared drives available on a network, and making each shared drive look just like another local drive to the client. Mapping – A software process that enables a client workstation to attach to the shared drive a resource such as a folder or drive volume on another workstation or server, and assign it a drive letter. The network drive that is attached is called a mapped drive in Windows-based Oss. In UNIX/Linux and Mac OS X a mapped drive is called a mounted volume. Guide to Operating Systems, 4th ed.

5. Securing Shared Resources Sharing files also opened the way for printer sharing over a network. Where it is feasible, one printer connected to a network server OS or network client OS can be used by others in the same office area or location. Sharing disks, files and printers is a potential security risk because it is then possible for non-authorized users to access a file or use a printer. Guide to Operating Systems, 4th ed.

6. Securing Shared Resources All OSs discussed in this book offer security measures for protecting shared resources. Access to a file, directory, or disk can be denied to unauthorized users. You may want a user to be able to read a file but not change it. You want only specific users to be able to execute a file (program). For these situations, a file directory, or disk can be assigned security privileges that limit users to only these 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). Guide to Operating Systems, 4th ed.

7. 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 that can share disks and resources over a network. Each of these OSs: Offers a way for client workstations to access a combination of disk, file, and other shared resources. Enables the network administrator to establish security through techniques such as: Assigning accounts Account passwords Creating groups Access privileges Guide to Operating Systems, 4th ed.

8. 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. Reduces the amount of work for 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. Guide to Operating Systems, 4th ed.

9. 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. The reach (scope) of this group type does not go beyond the local server in which it is defined. 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. Guide to Operating Systems, 4th ed.

10. 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 to an individual server. Guide to Operating Systems, 4th ed.

11. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 When Active Directory is implemented, Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 add the ability to have container objects that include domains, trees, and forests. Container object – an entity that is used to group together resources in a directory service, such as Microsoft Active Directory. Directory service – provides 3 important functions on a network: A central listing of resources; a way to quickly find resources; the ability to access and manage resources. Guide to Operating Systems, 4th ed.

12. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Domain – a fundamental component or container that holds information about all network resources that are grouped within it. Servers, printers, and other physical resources, users, and user groups. Tree – consists of one or more domains. Forest – houses one or more trees Guide to Operating Systems, 4th ed.

13. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Sample Windows Server domain and tree models Guide to Operating Systems, 4th ed.

14. 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 that provides the appropriate access to folders, files, and other resources. 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 Guide to Operating Systems, 4th ed.

15. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Example of working with groups: These steps enable you to manage security for all of their accounts at one time from one global group. If a member of the executive council leaves to take another job, you simply delete (or disable) that person’s account from the global group and later add an account for the replacement. You also can manage access to resources in each domain one time through each domain local group, resulting in much less management work. If a new printer is added to a domain, you can give the domain local group full privileges to the printer. Guide to Operating Systems, 4th ed.

16. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Managing security through domain local and global groups Guide to Operating Systems, 4th ed.

17. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 • In an Active Directory context in which there are multiple hierarchies of domains, trees, and forests, universal security groups provide a means to span domains and trees. • Universal group membership can include user accounts from any domain, global groups from any domain, and other universal groups from any domain. • Universal groups are offered to provide an easy means to access any resource in a tree or among trees in a forest. Guide to Operating Systems, 4th ed.

18. 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 accounts access to resources by making the global groups to which they belong members of domain local groups 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 – but give domain local groups access to resources in the domain, such as 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 joining those groups to domain local or universal groups depending on which is most appropriate.

19. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 For group relationships to work between domains and trees, trust relationships are established when domains and trees are created. Thus, resources in one domain can be accessed by user accounts and groups in another domain. 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. Guide to Operating Systems, 4th ed.

20. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Before you set up user accounts and populate global groups with accounts, it is important to configure account policies. 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 Guide to Operating Systems, 4th ed.

21. 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 for 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 Guide to Operating Systems, 4th ed.

22. 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 locked out too soon. Guide to Operating Systems, 4th ed.

23. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 • Kerberos security – tickets are exchanged between the client who requests logon or network services access and the server or Active Directory that grants access. • When Active Directory is not used, each standalone server can be designated as a Kerberos key distribution center (The server stores user accounts and passwords). • When Active Directory is used, each domain controller is a key distribution center. • A domain controller is a server that authenticates logons and keeps track of all changes made to accounts in the domain. Guide to Operating Systems, 4th ed.

24. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 • Kerberos security – • When a user logs on: • The client computer sends an account name and pass word to the key distribution center. • The key distribution center issues a temporary ticket that grants the user access to the Kerberos ticket-granting service on a domain controller (or standalone server), which then grants a permanent ticket to that computer. • The permanent ticket (service ticket) is good for the duration of a logon session and enables the computer to access network services beginning with the Logon service. Guide to Operating Systems, 4th ed.

25. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 • Kerberos configuration options: • Enforce user logon restrictions –Turns on Kerberos security; • Maximum lifetime for a service ticket – The maximum amount of time in minutes that a service ticket can be used to continually access a particular service in one service session. • Maximum lifetime for a user ticket – The maximum amount of time in hours that a ticket can be used for one continuous session for access to a computer or domain; • Maximum lifetime for user ticket renewal – Maximum number of days that the same Kerberos ticket can be renewed each time a user logs on; • Maximum tolerance for computer clock synchronization – How long in minutes a client will wait until synchronizing its clock with that of the server or Active Directory it is accessing. Guide to Operating Systems, 4th ed.

26. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Configuring User Accounts – Performed after account policies have been configured. When Active Directory is not installed: A user account is created by right-clicking My Computer or Computer via the Start Menu, clicking 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 by clicking Start, pointing to All Programs, pointing Administrative Tools and click Active Directory Users and Computers. After creating users, they are typically added to the appropriate global groups. Guide to Operating Systems, 4th ed.

27. 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 so that only authorized people can access them. • Permissions on a file or folder are set by using My Computer or Windows Explorer. • After you locate the file or folder, right-click it; • Click Properties; • Click the Securities Tab. Guide to Operating Systems, 4th ed.

28. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 • In Windows servers, permissions from a higher-level folder can be automatically inherited through the Allow inheritable permissions from the parent to propagate to this object and all child objects. Include these with entries explicitly defined her option, which is the default setting. Guide to Operating Systems, 4th ed.

29. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Guide to Operating Systems, 4th ed.

30. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Configuring Shared Disks and Folders A share is an object – a disk or folder – that is given a name and made visible to network users. A drive or folder is shared through its properties. Access the drive or folder in My Computer or in Windows Explorer. Right-click the drive or folder. Click Sharing. 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. Click the Permissions button to set share permissions. Guide to Operating Systems, 4th ed.

31. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Configuring Shared Disks and Folders The available share permissions are: 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 set up Offline Settings. Enables you to set up as folder so that it can be accessed by a client, even when the client is not connected to the network. 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. Guide to Operating Systems, 4th ed.

32. Windows Server 2003/Server 2003 R2 and Server 2008/Server 2008 R2 Web sharing access permissions Guide to Operating Systems, 4th ed.

33. 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 Guide to Operating Systems, 4th ed.

34. 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 or 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 an NTFS volume to a FAT volume is not protected by NTFS permissions, but it does inherit share permissions if they are assigned to the FAT folder. A file or folder that is moved or copied from a FAT volume to a folder in an NTFS volume inherits the permissions already assigned in the NTFS folder.

35. UNIX and Linux Access to directories and files on a UNIX/Linux server is also governed through user accounts, groups, and access permissions. 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. Guide to Operating Systems, 4th ed.

36. UNIX and Linux • The password file (/etc/passwd) 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 Guide to Operating Systems, 4th ed.

37. 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 Guide to Operating Systems, 4th ed.

38. 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 Guide to Operating Systems, 4th ed.

39. 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 Guide to Operating Systems, 4th ed.

40. 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 Guide to Operating Systems, 4th ed.

41. 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) Guide to Operating Systems, 4th ed.

42. 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 Guide to Operating Systems, 4th ed.

43. UNIX and Linux • Permissions are set up by using chmod • Chmod has two different formats – symbolic and octal. • In the symbolic format, you specify three parameters; • (1) who has the permission; • (2) the actions to be taken on the permission; • (3) the permission. • In the command chmod go -r-w-x * that is used on all files (signified by the * ) in a directory. • 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 .

44. UNIX and Linux • Chmod has two different formats – symbolic and octal. • The octal format is more complex because it assigns a number on the basis of the type of permission and on the basis of owner, group, and other (World) – all is omitted from this scheme. • Execute permission is assigned a 1, write is 2, and read is 4. • These permission numbers are added together for a value between 0 and 7. • There are four numeric positions (xxxx) after the chmod command. • The first position gives the permission number of the SUID/SGID. • The second position gives the permission number of the owner. • The third gives group permissions. • The fourth position gives the permission number of other. • The command chmod 0755 * assigns no permissions to SUID/SGID (0); read, write, and execute permissions to owner (7); and read and execute permissions to both group and other (5 in both positions) for all files (*). .

45. Mac OS X Server • Built on the foundation of Mac OS X but is designed as a true server for file sharing, printer sharing, managing network users and groups, and providing Web services. • 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 the Apache Web server software. Guide to Operating Systems, 4th ed.

46. Mac OS X Server • File permissions on a Mac OS X Server are very similar to those for UNIX/Linux. • Mac OS X Server is based on the UNIX/Linux system. • There are basically three methods of setting permissions on a Mac OS X Server. • You can use the Info windows in the Mac OS X Finder; • A third-party tool; • UNIX/Linux commands. Guide to Operating Systems, 4th ed.

47. Mac OS X Server • Mac OS X Server supports TCP/IP. • Opens the door for communications with other computers that use TCP/IP. • Makes the Mac OS X Server compatible with the Internet e-mail protocol Simple Mail Transfer Protocol (SMTP). • Out of the box, Mac OS X Server includes: • A Mail Server for e-mail communications; • An FTP Service (File Transfer Protocol) that can be used to transfer documents to or from the server over the Internet. Guide to Operating Systems, 4th ed.

48. Mac OS X Server • Mac OS X includes ServerAdmin that enables server management: • Accounts and groups can be created and managed. • Users can set up: • A login shell. • Similar to a login script of actions that occur before the user logs on. • A home directory. • Manages 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. Guide to Operating Systems, 4th ed.

49. Accessing and Sharing Resources in Windows XP/Server 2003/R2 • You can find My Network Places using several techniques, such as through Control Panel, My Computer, or Windows Explorer. • The fastest is to use the following: • Click the Start menu, right click My Computer, and click Map Network Drive. • Click the Browse button. • Find the workgroup, domain, or other entity in which the computer sharing the drive resides, and 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. Guide to Operating Systems, 4th ed.

50. Accessing and Sharing Resources in Windows XP/Server 2003/R2 • Disconnecting from a shared drive involves the same steps as in earlier versions of Windows: • Find the drive in My Computer or Windows Explorer. • Right-click the drive. • Click Disconnect. Guide to Operating Systems, 4th ed.