Table of Contents
The administration of Windows user, group, and machine accounts in the Samba domain-controlled network necessitates interfacing between the MS Windows networking environment and the UNIX operating system environment. The right (permission) to add machines to the Windows security domain can be assigned (set) to non-administrative users both in Windows NT4 domains and Active Directory domains.
The addition of Windows NT4/2kX/XPPro machines to the domain necessitates the creation of a machine account for each machine added. The machine account is a necessity that is used to validate that the machine can be trusted to permit user logons.
Machine accounts are analogous to user accounts, and thus in implementing them on a UNIX machine that is
hosting Samba (i.e., on which Samba is running), it is necessary to create a special type of user account.
Machine accounts differ from normal user accounts in that the account name (login ID) is terminated with a
$ sign. An additional difference is that this type of account should not ever be able to
log into the UNIX environment as a system user and therefore is set to have a shell of
/bin/false and a home directory of
/dev/null. The machine
account is used only to authenticate domain member machines during start-up. This security measure
is designed to block man-in-the-middle attempts to violate network integrity.
Machine (computer) accounts are used in the Windows NT OS family to store security credentials for domain member servers and workstations. When the domain member starts up, it goes through a validation process that includes an exchange of credentials with a domain controller. If the domain member fails to authenticate using the credentials known for it by domain controllers, the machine will be refused all access by domain users. The computer account is essential to the way that MS Windows secures authentication.
The creation of UNIX system accounts has traditionally been the sole right of
the system administrator, better known as the
It is possible in the UNIX environment to create multiple users who have the
same UID. Any UNIX user who has a UID=0 is inherently the same as the
root account user.
All versions of Samba call system interface scripts that permit CIFS function
calls that are used to manage users, groups, and machine accounts
in the UNIX environment. All versions of Samba up to and including version 3.0.10
required the use of a Windows administrator account that unambiguously maps to
root account to permit the execution of these
interface scripts. The requirement to do this has understandably met with some
disdain and consternation among Samba administrators, particularly where it became
necessary to permit people who should not possess
access to the UNIX host system.
Samba 3.0.11 introduced support for the Windows privilege model. This model
allows certain rights to be assigned to a user or group SID. In order to enable
this feature, enable privileges = yes
must be defined in the
global section of the
Currently, the rights supported in Samba-3 are listed in “Current Privilege Capabilities”. The remainder of this chapter explains how to manage and use these privileges on Samba servers.
Table 15.1. Current Privilege Capabilities
Add machines to domain
Add users and groups to the domain
Force shutdown from a remote system
Manage disk share
Take ownership of files or other objects
There are two primary means of managing the rights assigned to users and groups
on a Samba server. The
NT4 User Manager for Domains may be
used from any Windows NT4, 2000, or XP Professional domain member client to
connect to a Samba domain controller and view/modify the rights assignments.
This application, however, appears to have bugs when run on a client running
Windows 2000 or later; therefore, Samba provides a command-line utility for
performing the necessary administrative actions.
net rpc rights utility in Samba 3.0.11 has three new subcommands:
When called with no arguments,
net rpc list
simply lists the available rights on the server. When passed
a specific user or group name, the tool lists the privileges
currently assigned to the specified account. When invoked using
the special string
net rpc rights list returns a list of all
privileged accounts on the server and the assigned rights.
When called with no arguments, this function is used to assign a list of rights to a specified user or group. For example, to grant the members of the Domain Admins group on a Samba domain controller, the capability to add client machines to the domain, one would run:
root#net -S server -U domadmin rpc rights grant \ 'DOMAIN\Domain Admins' SeMachineAccountPrivilege
root#net rpc rights grant 'DOMAIN\Domain Admins' \ SeMachineAccountPrivilege -S server -U domadmin
More than one privilege can be assigned by specifying a list of rights separated by spaces. The parameter 'Domain\Domain Admins' must be quoted with single ticks or using double-quotes to prevent the backslash and the space from being interpreted by the system shell.
This command is similar in format to
net rpc rights grant. Its
effect is to remove an assigned right (or list of rights) from a user or group.
You must be connected as a member of the Domain Admins group to be able to grant or revoke privileges assigned to an account. This capability is inherent to the Domain Admins group and is not configurable. There are no default rights and privileges, except the ability for a member of the Domain Admins group to assign them. This means that all administrative rights and privileges (other than the ability to assign them) must be explicitly assigned, even for the Domain Admins group.
By default, no privileges are initially assigned to any account because certain actions will be performed as
root once smbd determines that a user has the necessary rights. For example, when joining a client to a
add machine script must be executed with superuser rights in most
cases. For this reason, you should be very careful about handing out privileges to accounts.
The privileges that have been implemented in Samba-3.0.11 are shown below. It is possible, and likely, that additional privileges may be implemented in later releases of Samba. It is also likely that any privileges currently implemented but not used may be removed from future releases as a housekeeping matter, so it is important that the successful as well as unsuccessful use of these facilities should be reported on the Samba mailing lists.
Accounts that possess this right will be able to execute
scripts defined by the
share command in
smb.conf file as root. Such users will
also be able to modify the ACL associated with file shares
on the Samba server.
This privilege operates identically to the printer admin
option in the
smb.conf file (see section 5 man page for
except that it is a global right (not on a per-printer basis).
Eventually the smb.conf option will be deprecated and administrative
rights to printers will be controlled exclusively by this right and
the security descriptor associated with the printer object in the
Samba provides two hooks for shutting down or rebooting the server and for aborting a previously issued shutdown command. Since this is an operation normally limited by the operating system to the root user, an account must possess this right to be able to execute either of these hooks.
SeCreateTokenPrivilege Create a token object SeAssignPrimaryTokenPrivilege Replace a process level token SeLockMemoryPrivilege Lock pages in memory SeIncreaseQuotaPrivilege Increase quotas SeMachineAccountPrivilege Add workstations to domain SeTcbPrivilege Act as part of the operating system SeSecurityPrivilege Manage auditing and security log SeTakeOwnershipPrivilege Take ownership of files or other objects SeLoadDriverPrivilege Load and unload device drivers SeSystemProfilePrivilege Profile system performance SeSystemtimePrivilege Change the system time SeProfileSingleProcessPrivilege Profile single process SeIncreaseBasePriorityPrivilege Increase scheduling priority SeCreatePagefilePrivilege Create a pagefile SeCreatePermanentPrivilege Create permanent shared objects SeBackupPrivilege Back up files and directories SeRestorePrivilege Restore files and directories SeShutdownPrivilege Shut down the system SeDebugPrivilege Debug programs SeAuditPrivilege Generate security audits SeSystemEnvironmentPrivilege Modify firmware environment values SeChangeNotifyPrivilege Bypass traverse checking SeRemoteShutdownPrivilege Force shutdown from a remote system
SeCreateTokenPrivilege Create a token object SeAssignPrimaryTokenPrivilege Replace a process level token SeLockMemoryPrivilege Lock pages in memory SeIncreaseQuotaPrivilege Increase quotas SeMachineAccountPrivilege Add workstations to domain SeTcbPrivilege Act as part of the operating system SeSecurityPrivilege Manage auditing and security log SeTakeOwnershipPrivilege Take ownership of files or other objects SeLoadDriverPrivilege Load and unload device drivers SeSystemProfilePrivilege Profile system performance SeSystemtimePrivilege Change the system time SeProfileSingleProcessPrivilege Profile single process SeIncreaseBasePriorityPrivilege Increase scheduling priority SeCreatePagefilePrivilege Create a pagefile SeCreatePermanentPrivilege Create permanent shared objects SeBackupPrivilege Back up files and directories SeRestorePrivilege Restore files and directories SeShutdownPrivilege Shut down the system SeDebugPrivilege Debug programs SeAuditPrivilege Generate security audits SeSystemEnvironmentPrivilege Modify firmware environment values SeChangeNotifyPrivilege Bypass traverse checking SeRemoteShutdownPrivilege Force shutdown from a remote system SeUndockPrivilege Remove computer from docking station SeSyncAgentPrivilege Synchronize directory service data SeEnableDelegationPrivilege Enable computer and user accounts to be trusted for delegation SeManageVolumePrivilege Perform volume maintenance tasks SeImpersonatePrivilege Impersonate a client after authentication SeCreateGlobalPrivilege Create global objects
Please note that every Windows NT4 and later server requires a domain Administrator account. Samba versions commencing with 3.0.11 permit Administrative duties to be performed via assigned rights and privileges (see User Rights and Privileges). An account in the server's passdb backend can be set to the well-known RID of the default administrator account. To obtain the domain SID on a Samba domain controller, run the following command:
root#net getlocalsid SID for domain FOO is: S-1-5-21-4294955119-3368514841-2087710299
root#pdbedit -U S-1-5-21-4294955119-3368514841-2087710299-500 -u root -r
The RID 500 is the well known standard value of the default Administrator account. It is the RID that confers the rights and privileges that the Administrator account has on a Windows machine or domain. Under UNIX/Linux the equivalent is UID=0 (the root account).
Releases of Samba version 3.0.11 and later make it possible to operate without an Administrator account provided equivalent rights and privileges have been established for a Windows user or a Windows group account.
When a Windows NT4 (or later) client joins a domain, the domain global
Domain Admins group
is added to the membership of the local
Administrators group on the client. Any user who is
a member of the domain global
Domain Admins group will have administrative rights on the
This is often not the most desirable solution because it means that the user will have administrative
rights and privileges on domain servers also. The
Power Users group on Windows client
workstations permits local administration of the workstation alone. Any domain global user or domain global
group can be added to the membership of the local workstation group
See Nested Group Support for an example of how to add domain users
and groups to a local group that is on a Windows workstation. The use of the
command permits this to be done from the Samba server.
C:\>net localgroup administrators /add
entity is either a domain user or a domain group account name.