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In the IT world there is often a saying that all problems are encountered because of poor planning. The corollary to this saying is that not all problems can be anticipated and planned for. Then again, good planning will anticipate most show-stopper-type situations.
Those wishing to migrate from MS Windows NT4 domain control to a Samba-3 domain control environment would do well to develop a detailed migration plan. So here are a few pointers to help migration get underway.
The key objective for most organizations is to make the migration from MS Windows NT4 to Samba-3 domain control as painless as possible. One of the challenges you may experience in your migration process may well be convincing management that the new environment should remain in place. Many who have introduced open source technologies have experienced pressure to return to a Microsoft-based platform solution at the first sign of trouble.
Before attempting a migration to a Samba-3-controlled network, make every possible effort to gain all-round commitment to the change. Know precisely why the change is important for the organization. Possible motivations to make a change include:
Improve network manageability.
Obtain better user-level functionality.
Reduce network operating costs.
Reduce exposure caused by Microsoft withdrawal of NT4 support.
Avoid MS License 6 implications.
Reduce organization's dependency on Microsoft.
Make sure everyone knows that Samba-3 is not MS Windows NT4. Samba-3 offers an alternative solution that is both different from MS Windows NT4 and offers advantages compared with it. Gain recognition that Samba-3 lacks many of the features that Microsoft has promoted as core values in migration from MS Windows NT4 to MS Windows 2000 and beyond (with or without Active Directory services).
What are the features that Samba-3 cannot provide?
Active Directory Server.
Group Policy Objects (in Active Directory).
Machine Policy Objects.
Logon Scripts in Active Directory.
Software Application and Access Controls in Active Directory.
The features that Samba-3 does provide and that may be of compelling interest to your site include:
Lower cost of ownership.
Global availability of support with no strings attached.
Dynamic SMB servers (can run more than one SMB/CIFS server per UNIX/Linux system).
Creation of on-the-fly logon scripts.
Creation of on-the-fly policy files.
Greater stability, reliability, performance, and availability.
Manageability via an SSH connection.
Flexible choices of backend authentication technologies (tdbsam, ldapsam).
Ability to implement a full single-sign-on architecture.
Ability to distribute authentication systems for absolute minimum wide-area network bandwidth demand.
Before migrating a network from MS Windows NT4 to Samba-3, consider all necessary factors. Users should be educated about changes they may experience so the change will be a welcome one and not become an obstacle to the work they need to do. The following sections explain factors that will help ensure a successful migration.
Samba-3 can be configured as a domain controller, a backup domain controller (probably best called a secondary controller), a domain member, or a standalone server. The Windows network security domain context should be sized and scoped before implementation. Particular attention needs to be paid to the location of the Primary Domain Controller (PDC) as well as backup controllers (BDCs). One way in which Samba-3 differs from Microsoft technology is that if one chooses to use an LDAP authentication backend, then the same database can be used by several different domains. In a complex organization, there can be a single LDAP database, which itself can be distributed (have a master server and multiple slave servers) that can simultaneously serve multiple domains.
A physical network segment may house several domains. Each may span multiple network segments. Where domains span routed network segments, consider and test the performance implications of the design and layout of a network. A centrally located domain controller that is designed to serve multiple routed network segments may result in severe performance problems. Check the response time (ping timing) between the remote segment and the PDC. If it's long (more than 100 ms), locate a BDC on the remote segment to serve as the local authentication and access control server.
There are cardinal rules to effective network design that cannot be broken with impunity. The most important rule: Simplicity is king in every well-controlled network. Every part of the infrastructure must be managed; the more complex it is, the greater will be the demand of keeping systems secure and functional.
Keep in mind the nature of how data must be shared. Physical disk space layout should be considered carefully. Some data must be backed up. The simpler the disk layout, the easier it will be to keep track of backup needs. Identify what backup media will meet your needs; consider backup to tape, CD-ROM or DVD-ROM, or other offline storage medium. Plan and implement for minimum maintenance. Leave nothing to chance in your design; above all, do not leave backups to chance: backup, test, and validate every backup; create a disaster recovery plan and prove that it works.
Users should be grouped according to data access control needs. File and directory access is best controlled via group permissions, and the use of the “sticky bit” on group-controlled directories may substantially avoid file access complaints from Samba share users.
Inexperienced network administrators often attempt elaborate techniques to set access controls on files, directories, shares, as well as in share definitions. Keep your design and implementation simple and document your design extensively. Have others audit your documentation. Do not create a complex mess that your successor will not understand. Remember, job security through complex design and implementation may cause loss of operations and downtime to users as the new administrator learns to untangle your knots. Keep access controls simple and effective, and make sure that users will never be interrupted by obtuse complexity.
Logon scripts can be created on the fly so all commands executed are specific to the
rights and privileges granted to the user. The preferred controls should be effected through
group membership so group information can be used to create a custom logon script using
the root preexec parameters to the
Some sites prefer to use a tool such as kixstart to establish a controlled user environment. In any case, you may wish to do a Google search for logon script process controls. In particular, you may wish to explore the use of the Microsoft Knowledge Base article KB189105 that deals with how to add printers without user intervention via the logon script process.
User and group profiles may be migrated using the tools described in the section titled Desktop Profile Management.
Profiles may also be managed using the Samba-3 tool profiles. This tool allows the MS
Windows NT-style security identifiers (SIDs) that are stored inside the profile
NTuser.DAT file to be changed to the SID of the Samba-3 domain.
It is possible to migrate all account settings from an MS Windows NT4 domain to Samba-3. Before attempting to migrate user and group accounts, you are STRONGLY advised to create in Samba-3 the groups that are present on the MS Windows NT4 domain AND to map them to suitable UNIX/Linux groups. By following this simple advice, all user and group attributes should migrate painlessly.
The approximate migration process is described below.
Procedure 36.1. The Account Migration Process
Note: Did the users migrate?
#!/bin/bash #### Keep this as a shell script for future re-use # First assign well known domain global groups net groupmap add ntgroup="Domain Admins" unixgroup=root rid=512 type=d net groupmap add ntgroup="Domain Users" unixgroup=users rid=513 type=d net groupmap add ntgroup="Domain Guests" unixgroup=nobody rid=514 type=d # Now for our added domain global groups net groupmap add ntgroup="Designers" unixgroup=designers type=d net groupmap add ntgroup="Engineers" unixgroup=engineers type=d net groupmap add ntgroup="QA Team" unixgroup=qateam type=d
net groupmap list
Check that all groups are recognized.
Migrate all the profiles, then migrate all policy files.
Sites that wish to migrate from MS Windows NT4 domain control to a Samba-based solution generally fit into three basic categories. Following table shows the possibilities.
Table 36.1. The Three Major Site Types
|Number of Users||Description|
Want simple conversion with no pain.
|50 - 250|
Want new features; can manage some inhouse complexity.
Solution/implementation must scale well; complex needs. Cross-departmental decision process. Local expertise in most areas.
There are three basic choices for sites that intend to migrate from MS Windows NT4 to Samba-3:
Simple conversion (total replacement).
Upgraded conversion (could be one of integration).
Complete redesign (completely new solution).
Minimize downstream problems by:
Taking sufficient time.
Testing all assumptions.
Testing the full roll-out program, including workstation deployment.
Following table lists the conversion choices given the type of migration being contemplated.
Table 36.2. Nature of the Conversion Choices
|Simple Install||Upgrade Decisions||Redesign Decisions|
Make use of minimal OS-specific features
Translate NT4 features to new host OS features
Improve on NT4 functionality, enhance management capabilities
Move all accounts from NT4 into Samba-3
Copy and improve
Authentication regime (database location and access)
Make least number of operational changes
Make progressive improvements
Desktop management methods
Take least amount of time to migrate
Minimize user impact
Better control of Desktops/Users
Live versus isolated conversion
Identify Needs for: Manageability, Scalability, Security, Availability
Integrate Samba-3, then migrate while users are active, then change of control (swap out)
Take advantage of lower maintenance opportunity
Samba-3 can use an external authentication backend:
Winbind (external Samba or NT4/200x server).
External server could use Active Directory or NT4 domain.
Can use pam_mkhomedir.so to autocreate home directories.
Samba-3 can use a local authentication backend:
Samba permits Access Control points to be set:
On the share itself using share ACLs.
On the file system using UNIX permissions on files and directories.
Note: Can enable Posix ACLs in file system also.
Through Samba share parameters not recommended except as last resort.
Using Group Policy Editor (NT4).
Watch out for tattoo effect.
Know how they work.
User and group mapping code is new. Many problems have been experienced as network administrators who are familiar with Samba-2.2.x migrate to Samba-3. Carefully study the chapters that document the new password backend behavior and the new group mapping functionality.
username map facility may be needed.
Use net groupmap to connect NT4 groups to UNIX groups.
Use pdbedit to set/change user configuration.
When migrating to LDAP backend, it may be easier to dump the initial LDAP database to LDIF, edit, then reload into LDAP.
Every operating system has its peculiarities. These are the result of engineering decisions that were based on the experience of the designer and may have side effects that were not anticipated. Limitations that may bite the Windows network administrator include:
Add/Delete Users: Note OS limits on size of name (Linux 8 chars, NT4 up to 254 chars).
Add/Delete Machines: Applied only to domain members (Note: machine names may be limited to 16 characters).
Use net groupmap to connect NT4 groups to UNIX groups.
Add/Delete Groups: Note OS limits on size and nature. Linux limit is 16 char, no spaces, and no uppercase chars (groupadd).
Samba: net, rpcclient, smbpasswd, pdbedit, profiles
Windows: NT4 Domain User Manager, Server Manager (NEXUS)