Chapter 13. File, Directory and Share Access Controls

Advanced MS Windows users are frequently perplexed when file, directory and share manipulation of resources shared via Samba do not behave in the manner they might expect. MS Windows network -administrators are often confused regarding network access controls and what is the best way to -provide users with the type of access they need while protecting resources from the consequences -of untoward access capabilities. +administrators are often confused regarding network access controls and how to +provide users with the access they need while protecting resources from unauthorised access.

-Unix administrators frequently are not familiar with the MS Windows environment and in particular +Many UNIX administrators are unfamiliar with the MS Windows environment and in particular have difficulty in visualizing what the MS Windows user wishes to achieve in attempts to set file and directory access permissions.

The problem lies in the differences in how file and directory permissions and controls work between the two environments. This difference is one that Samba can not completely hide, even -though it does try to make the chasm transparent. -

+though it does try to bridge the chasm to a degree. +

POSIX Access Control List technology has been available (along with Extended Attributes) -for Unix for many years, yet there is little evidence today of any significant use. This +for UNIX for many years, yet there is little evidence today of any significant use. This explains to some extent the slow adoption of ACLs into commercial Linux products. MS Windows administrators are astounded at this given that ACLs were a foundational capability of the now decade old MS Windows NT operating system. @@ -26,25 +23,24 @@ The purpose of this chapter is to present each of the points of control that are Samba-3 in the hope that this will help the network administrator to find the optimum method for delivering the best environment for MS Windows desktop users.

-This is an opportune point to mention that it should be borne in mind that Samba was created to -provide a means of interoperability and interchange of data between two operating environments -that are quite different. It was never the intent to make Unix/Linux like MS Windows NT. Instead -the purpose was an is to provide a sufficient level of exchange of data between the two environments. -What is available today extends well beyond early plans and expectations, yet the gap continues to -shrink. -

Features and Benefits

+This is an opportune point to mention that Samba was created to provide a means of interoperability +and interchange of data between differing operating environments. Samba has no intent change +UNIX/Linux into a platform like MS Windows. Instead the purpose was and is to provide a sufficient +level of exchange of data between the two environments. What is available today extends well +beyond early plans and expectations, yet the gap continues to shrink. +

Features and Benefits

Samba offers a lot of flexibility in file system access management. These are the key access control facilities present in Samba today:

Samba Access Control Facilities

- Unix File and Directory Permissions + UNIX File and Directory Permissions
- Samba honours and implements Unix file system access controls. Users + Samba honours and implements UNIX file system access controls. Users who access a Samba server will do so as a particular MS Windows user. This information is passed to the Samba server as part of the logon or connection setup process. Samba uses this user identity to validate whether or not the user should be given access to file system resources (files and directories). This chapter provides an overview for those - to whom the Unix permissions and controls are a little strange or unknown. + to whom the UNIX permissions and controls are a little strange or unknown.
Samba Share Definitions
@@ -63,22 +59,22 @@ shrink. easiest ways to affect access controls (restrictions) and can often do so with minimum invasiveness compared with other methods.
- MS Windows ACLs through Unix POSIX ACLs + MS Windows ACLs through UNIX POSIX ACLs
- The use of POSIX ACLs on Unix/Linux is possible ONLY if the underlying + The use of POSIX ACLs on UNIX/Linux is possible ONLY if the underlying operating system supports them. If not, then this option will not be - available to you. Current Unix technology platforms have native support + available to you. Current UNIX technology platforms have native support for POSIX ACLs. There are patches for the Linux kernel that provide this also. Sadly, few Linux platforms ship today with native ACLs and Extended Attributes enabled. This chapter has pertinent information for users of platforms that support them. -

File System Access Controls

Perhaps the most important recognition to be made is the simple fact that MS Windows NT4 / 200x / XP -implement a totally divergent file system technology from what is provided in the Unix operating system +implement a totally divergent file system technology from what is provided in the UNIX operating system environment. Firstly we should consider what the most significant differences are, then we shall look at how Samba helps to bridge the differences. -

MS Windows NTFS Comparison with Unix File Systems

- Samba operates on top of the Unix file system. This means it is subject to Unix file system conventions +

MS Windows NTFS Comparison with UNIX File Systems

+ Samba operates on top of the UNIX file system. This means it is subject to UNIX file system conventions and permissions. It also means that if the MS Windows networking environment requires file system behaviour that differs from unix file system behaviour then somehow Samba is responsible for emulating that in a transparent and consistent manner. @@ -88,128 +84,108 @@ at how Samba helps to bridge the differences. but for the greater part we will stay within the bounds of default behaviour. Those wishing to explore to depths of control ability should review the smb.conf man page.

File System Feature Comparison

Name Space

- MS Windows NT4 / 200x/ XP files names may be up to 254 characters long, Unix file names + MS Windows NT4 / 200x/ XP files names may be up to 254 characters long, UNIX file names may be 1023 characters long. In MS Windows file extensions indicate particular file types, - in Unix this is not so rigorously observed as all names are considered arbitrary. + in UNIX this is not so rigorously observed as all names are considered arbitrary.

- What MS Windows calls a Folder, Unix calls a directory, + What MS Windows calls a Folder, UNIX calls a directory.

Case Sensitivity

- MS Windows file names are generally Upper Case if made up of 8.3 (ie: 8 character file name + + MS Windows file names are generally upper case if made up of 8.3 (ie: 8 character file name and 3 character extension. If longer than 8.3 file names are Case Preserving, and Case Insensitive.

- Unix file and directory names are Case Sensitive and Case Preserving. Samba implements the - MS Windows file name behaviour, but it does so as a user application. The Unix file system + UNIX file and directory names are case sensitive and case preserving. Samba implements the + MS Windows file name behaviour, but it does so as a user application. The UNIX file system provides no mechanism to perform case insensitive file name lookups. MS Windows does this by default. This means that Samba has to carry the processing overhead to provide features - that are NOT native to the Unix operating system environment. + that are NOT native to the UNIX operating system environment.

- Consider the following, all are unique Unix names but one single MS Windows file name: + Consider the following, all are unique UNIX names but one single MS Windows file name: MYFILE.TXT MyFile.txt myfile.txt - So clearly, In an MS Windows file name space these three files CAN NOT co-exist! But in Unix + So clearly, In an MS Windows file name space these three files CAN NOT co-exist! But in UNIX they can. So what should Samba do if all three are present? Answer, the one that is lexically first will be accessible to MS Windows users, the others are invisible and unaccessible - any other solution would be suicidal.

Directory Separators

- MS Windows and DOS uses the back-slash '\' as a directory delimiter, Unix uses the forward-slash '/' + MS Windows and DOS uses the back-slash '\' as a directory delimiter, UNIX uses the forward-slash '/' as it's directory delimiter. This is transparently handled by Samba.

Drive Identification

MS Windows products support a notion of drive letters, like C: to represent - disk partitions. Unix has NO concept if separate identifiers for file partitions since each + disk partitions. UNIX has NO concept if separate identifiers for file partitions since each such file system is mounted to become part of the over-all directory tree. - The Unix directory tree begins at '/', just like the root of a DOS drive is specified like + The UNIX directory tree begins at '/', just like the root of a DOS drive is specified like C:\.

File Naming Conventions

- MS Windows generally never experiences file names that begin with a '.', while in Unix these + MS Windows generally never experiences file names that begin with a '.', while in UNIX these are commonly found in a user's home directory. Files that begin with a '.' are typically - either start up files for various Unix applications, or they may be files that contain + either start up files for various UNIX applications, or they may be files that contain start-up configuration data.

Links and Short-Cuts

+ + + + MS Windows make use of "links and Short-Cuts" that are actually special types of files that will - redirect an attempt to execute the file to the real location of the file. Unix knows of file and directory + redirect an attempt to execute the file to the real location of the file. UNIX knows of file and directory links, but they are entirely different from what MS Windows users are used to.

- Symbolic links are files in Unix that contain the actual location of the data (file OR directory). An + Symbolic links are files in UNIX that contain the actual location of the data (file OR directory). An operation (like read or write) will operate directly on the file referenced. Symbolic links are also referred to as 'soft links'. A hard link is something that MS Windows is NOT familiar with. It allows one physical file to be known simultaneously by more than one file name.

There are many other subtle differences that may cause the MS Windows administrator some temporary discomfort - in the process of becoming familiar with Unix/Linux. These are best left for a text that is dedicated to the - purpose of Unix/Linux training/education. -

Managing Directories

+ in the process of becoming familiar with UNIX/Linux. These are best left for a text that is dedicated to the + purpose of UNIX/Linux training/education. +

Managing Directories

There are three basic operations for managing directories, create, delete, rename. -

Table 13.1. Managing directories with unix and windows

Action	MS Windows Command	Unix Command
create	md folder	mkdir folder
delete	rd folder	rmdir folder
rename	rename oldname newname	mv oldname newname

File and Directory Access Control

Table 13.1. Managing directories with unix and windows

Action	MS Windows Command	UNIX Command
create	md folder	mkdir folder
delete	rd folder	rmdir folder
rename	rename oldname newname	mv oldname newname

File and Directory Access Control

The network administrator is strongly advised to read foundational training manuals and reference materials - regarding file and directory permissions maintenance. Much can be achieved with the basic Unix permissions + regarding file and directory permissions maintenance. Much can be achieved with the basic UNIX permissions without having to resort to more complex facilities like POSIX Access Control Lists (ACLs) or Extended Attributes (EAs).

- Unix/Linux file and directory access permissions involves setting three (3) primary sets of data and one (1) control set. - A Unix file listing looks as follows:- + UNIX/Linux file and directory access permissions involves setting three (3) primary sets of data and one (1) control set. + A UNIX file listing looks as follows:- -

-	jht@frodo:~/stuff> ls -la
-	total 632
-	drwxr-xr-x   13 jht   users      816 2003-05-12 22:56 .
-	drwxr-xr-x   37 jht   users     3800 2003-05-12 22:29 ..
-	d---------    2 jht   users       48 2003-05-12 22:29 muchado00
-	d--x--x--x    2 jht   users       48 2003-05-12 22:29 muchado01
-	dr-xr-xr-x    2 jht   users       48 2003-05-12 22:29 muchado02
-	drwxrwxrwx    2 jht   users       48 2003-05-12 22:29 muchado03
-	drw-rw-rw-    2 jht   users       48 2003-05-12 22:29 muchado04
-	d-w--w--w-    2 jht   users       48 2003-05-12 22:29 muchado05
-	dr--r--r--    2 jht   users       48 2003-05-12 22:29 muchado06
-	drwxrwxrwt    2 jht   users       48 2003-05-12 22:29 muchado07
-	drwsrwsrwx    2 jht   users       48 2003-05-12 22:29 muchado08
-	----------    1 jht   users     1242 2003-05-12 22:31 mydata00.lst
-	---x--x--x    1 jht   users     1674 2003-05-12 22:33 mydata01.lst
-	--w--w--w-    1 jht   users     7754 2003-05-12 22:33 mydata02.lst
-	--wx-wx-wx    1 jht   users   260179 2003-05-12 22:33 mydata03.lst
-	-r--r--r--    1 jht   users    21017 2003-05-12 22:32 mydata04.lst
-	-r-xr-xr-x    1 jht   users   206339 2003-05-12 22:32 mydata05.lst
-	-rw-rw-rw-    1 jht   users    41105 2003-05-12 22:32 mydata06.lst
-	-rwxrwxrwx    1 jht   users    19312 2003-05-12 22:32 mydata07.lst
-	jht@frodo:~/stuff>
-

+$ ls -la
+total 632
+drwxr-xr-x   13 maryo   gnomes      816 2003-05-12 22:56 .
+drwxrwxr-x   37 maryo   gnomes     3800 2003-05-12 22:29 ..
+dr-xr-xr-x    2 maryo   gnomes       48 2003-05-12 22:29 muchado02
+drwxrwxrwx    2 maryo   gnomes       48 2003-05-12 22:29 muchado03
+drw-rw-rw-    2 maryo   gnomes       48 2003-05-12 22:29 muchado04
+d-w--w--w-    2 maryo   gnomes       48 2003-05-12 22:29 muchado05
+dr--r--r--    2 maryo   gnomes       48 2003-05-12 22:29 muchado06
+drwsrwsrwx    2 maryo   gnomes       48 2003-05-12 22:29 muchado08
+----------    1 maryo   gnomes     1242 2003-05-12 22:31 mydata00.lst
+--w--w--w-    1 maryo   gnomes     7754 2003-05-12 22:33 mydata02.lst
+-r--r--r--    1 maryo   gnomes    21017 2003-05-12 22:32 mydata04.lst
+-rw-rw-rw-    1 maryo   gnomes    41105 2003-05-12 22:32 mydata06.lst
+$ 
+

- The columns above represent (from left to right): permissions, no blocks used, owner, group, size (bytes), access date, access time, file name. -

- The permissions field is made up of: - -

-	 JRV: Put this into a diagram of some sort
-	[ type  ] [ users ] [ group ] [ others ]   [File, Directory Permissions]
-	[ d | l ] [ r w x ] [ r w x ] [ r w x  ]
-	  |   |     | | |     | | |     | | |
-	  |   |     | | |     | | |     | | |-----> Can Execute, List files
-	  |   |     | | |     | | |     | |-------> Can Write,   Create files
-	  |   |     | | |     | | |     |---------> Can Read,    Read files
-	  |   |     | | |     | | |---------------> Can Execute, List files
-	  |   |     | | |     | |-----------------> Can Write,   Create files
-	  |   |     | | |     |-------------------> Can Read,    Read files
-	  |   |     | | |-------------------------> Can Execute, List files
-	  |   |     | |---------------------------> Can Write,   Create files
-	  |   |     |-----------------------------> Can Read,    Read files
-	  |   |-----------------------------------> Is a symbolic Link
-	  |---------------------------------------> Is a directory
-

+ The columns above represent (from left to right): permissions, number of hard links to file, owner, group, size (bytes), access date, access time, file name.

+ An overview of the permissions field can be found in the image below. +

Figure 13.1. Overview of unix permissions field

Any bit flag may be unset. An unset bit flag is the equivalent of 'Can NOT' and is represented as a '-' character. -

Example 13.1. Example File

+	
Example 13.1. Example File
 		-rwxr-x---   Means: The owner (user) can read, write, execute
 		                    the group can read and execute
 		                    everyone else can NOT do anything with it
 		

 
 	

-	Additional possibilities in the [type] field are: c = character device, b = block device, p = pipe device, s = Unix Domain Socket.
+	Additional possibilities in the [type] field are: c = character device, b = block device, p = pipe device, s = UNIX Domain Socket.
 	

 	The letters `rwxXst' set permissions for the user, group and others as: read (r), write (w), execute (or access for directories) (x),
 	execute  only  if  the  file  is a directory or already has execute permission for some user (X), set user or group ID on execution (s),
@@ -228,101 +204,101 @@ at how Samba helps to bridge the differences.
 	the (x) execute flags are not set files can not be listed (seen) in the directory by anyone. The group can read files in the
 	directory but can NOT create new files. NOTE: If files in the directory are set to be readable and writable for the group, then
 	group members will be able to write to (or delete) them.
-

Share Definition Access Controls

The following parameters in the smb.conf file sections that define a share control or affect access controls. Before using any of the following options please refer to the man page for smb.conf. -

User and Group Based Controls

User and group based controls can prove very useful. In some situations it is distinctly desirable to affect all - file system operations as if a single user is doing this, the use of the force user and - force group behaviour will achieve this. In other situations it may be necessary to affect a + file system operations as if a single user is doing this, the use of the force user and + force group behaviour will achieve this. In other situations it may be necessary to affect a paranoia level of control to ensure that only particular authorised persons will be able to access a share or - it's contents, here the use of the valid users or the invalid users may + it's contents, here the use of the valid users or the invalid users may be most useful.

As always, it is highly advisable to use the least difficult to maintain and the least ambiguous method for controlling access. Remember, that when you leave the scene someone else will need to provide assistance and if that person finds too great a mess, or if they do not understand what you have done then there is risk of Samba being removed and an alternative solution being adopted. -

Table 13.2. User and Group Based Controls

Control Parameter Description - Action - Notes

admin users

Table 13.2. User and Group Based Controls

Control Parameter	Description - Action - Notes
`admin users`	List of users who will be granted administrative privileges on the share. They will do all file operations as the super-user (root). Any user in this list will be able to do anything they like on the share, irrespective of file permissions. -
force group	+
`force group`	Specifies a UNIX group name that will be assigned as the default primary group for all users connecting to this service. -
force user	+
`force user`	Specifies a UNIX user name that will be assigned as the default user for all users connecting to this service. This is useful for sharing files. Incorrect use can cause security problems. -
guest ok	+
`guest ok`	If this parameter is set for a service, then no password is required to connect to the service. Privileges will be those of the guest account. -
invalid users	+
`invalid users`	List of users that should not be allowed to login to this service. -
only user	+
`only user`	Controls whether connections with usernames not in the user list will be allowed. -
read list	+
`read list`	List of users that are given read-only access to a service. Users in this list will not be given write access, no matter what the read only option is set to. -
username	+
`username`	Refer to the `smb.conf` man page for more information - this is a complex and potentially misused parameter. -
valid users	+
`valid users`	List of users that should be allowed to login to this service. -
write list	+
`write list`	List of users that are given read-write access to a service. -

File and Directory Permissions Based Controls

The following file and directory permission based controls, if misused, can result in considerable difficulty to diagnose the cause of mis-configuration. Use them sparingly and carefully. By gradually introducing each one by one undesirable side-effects may be detected. In the event of a problem, always comment all of them out and then gradually re-introduce them in a controlled fashion. -

Table 13.3. File and Directory Permission Based Controls

Control Parameter Description - Action - Notes

create mask

Table 13.3. File and Directory Permission Based Controls

Control Parameter	Description - Action - Notes
`create mask`	Refer to the `smb.conf` man page. -
directory mask	+
`directory mask`	The octal modes used when converting DOS modes to UNIX modes when creating UNIX directories. See also: directory security mask. -
dos filemode	+
`dos filemode`	Enabling this parameter allows a user who has write access to the file to modify the permissions on it. -
force create mode	+
`force create mode`	This parameter specifies a set of UNIX mode bit permissions that will always be set on a file created by Samba. -
force directory mode	+
`force directory mode`	This parameter specifies a set of UNIX mode bit permissions that will always be set on a directory created by Samba. -
force directory security mode	+
`force directory security mode`	Controls UNIX permission bits modified when a Windows NT client is manipulating UNIX permissions on a directory -
force security mode	+
`force security mode`	Controls UNIX permission bits modified when a Windows NT client manipulates UNIX permissions. -
hide unreadable	+
`hide unreadable`	Prevents clients from seeing the existence of files that cannot be read. -
hide unwriteable files	+
`hide unwriteable files`	Prevents clients from seeing the existence of files that cannot be written to. Unwriteable directories are shown as usual. -
nt acl support	+
`nt acl support`	This parameter controls whether smbd will attempt to map UNIX permissions into Windows NT access control lists. -
security mask	+
`security mask`	Controls UNIX permission bits modified when a Windows NT client is manipulating the UNIX permissions on a file. -

Miscellaneous Controls

- The following are documented because of the prevalence of administrators creating inadvertant barriers to file +

Miscellaneous Controls

+ The following are documented because of the prevalence of administrators creating inadvertent barriers to file access by not understanding the full implications of smb.conf file settings. -

Table 13.4. Other Controls

Control Parameter Description - Action - Notes

case sensitive, default case, short preserve case

Table 13.4. Other Controls

Control Parameter	Description - Action - Notes
`case sensitive`, `default case`, `short preserve case`	This means that all file name lookup will be done in a case sensitive manner. Files will be created with the precise filename Samba received from the MS Windows client. -
csc policy	+
`csc policy`	Client Side Caching Policy - parallels MS Windows client side file caching capabilities. -
dont descend	+
`dont descend`	Allows to specify a comma-delimited list of directories that the server should always show as empty. -
dos filetime resolution	+
`dos filetime resolution`	This option is mainly used as a compatibility option for Visual C++ when used against Samba shares. -
dos filetimes	+
`dos filetimes`	DOS and Windows allows users to change file time stamps if they can write to the file. POSIX semantics prevent this. This options allows DOS and Windows behaviour. -
fake oplocks	+
`fake oplocks`	Oplocks are the way that SMB clients get permission from a server to locally cache file operations. If a server grants an oplock then the client is free to assume that it is the only one accessing the file and it will aggressively cache file data. -
hide dot files, hide files, veto files	+
`hide dot files`, `hide files`, `veto files`	Note: MS Windows Explorer allows over-ride of files marked as hidden so they will still be visible. -
read only	+
`read only`	If this parameter is yes, then users of a service may not create or modify files in the service's directory. -
veto files	+
`veto files`	List of files and directories that are neither visible nor accessible. -

Access Controls on Shares

This section deals with how to configure Samba per share access control restrictions. By default, Samba sets no restrictions on the share itself. Restrictions on the share itself can be set on MS Windows NT4/200x/XP shares. This can be a very effective way to limit who can @@ -339,9 +315,9 @@ Before using any of the following options please refer to the man page for /usr/local/samba/var. If the tdbdump utility has been compiled and installed on your system, then you can examine the contents of this file by: tdbdump share_info.tdb. -

Share Permissions Management

The best tool for the task is platform dependant. Choose the best tool for your environment. -

Windows NT4 Workstation/Server

The tool you need to use to manage share permissions on a Samba server is the NT Server Manager. Server Manager is shipped with Windows NT4 Server products but not with Windows NT4 Workstation. You can obtain the NT Server Manager for MS Windows NT4 Workstation from Microsoft - see details below. @@ -351,9 +327,9 @@ Before using any of the following options please refer to the man page for

Now click on the share that you wish to manage, then click on the Properties tab, next click on the Permissions tab. Now you can add or change access control settings as you wish. -

`Windows 200x/XP`

+

`Windows 200x/XP`

On MS Windows NT4/200x/XP system access control lists on the share itself are set using native - tools, usually from filemanager. For example, in Windows 200x: right click on the shared folder, + tools, usually from file manager. For example, in Windows 200x: right click on the shared folder, then select Sharing, then click on Permissions. The default Windows NT4/200x permission allows Everyone Full Control on the Share.

@@ -380,71 +356,70 @@ Before using any of the following options please refer to the man page for no access means that MaryK who is part of the group Everyone will have no access even if this user is given explicit full control access. -

`MS Windows Access Control Lists and Unix Interoperability`

`Managing UNIX permissions Using NT Security Dialogs`

Windows NT clients can use their native security settings - dialog box to view and modify the underlying UNIX permissions.

Note that this ability is careful not to compromise - the security of the UNIX host Samba is running on, and - still obeys all the file permission rules that a Samba - administrator can set.

`Note`

- All access to Unix/Linux system file via Samba is controlled at - the operating system file access control level. When trying to - figure out file access problems it is vitally important to identify - the identity of the Windows user as it is presented by Samba at - the point of file access. This can best be determined from the +

`MS Windows Access Control Lists and UNIX Interoperability`

`Managing UNIX permissions Using NT Security Dialogs`

+ Windows NT clients can use their native security settings dialog box to view and modify the + underlying UNIX permissions. +

+ Note that this ability is careful not to compromise the security of the UNIX host Samba is running on, and + still obeys all the file permission rules that a Samba administrator can set. +

+ Samba does not attempt to go beyond POSIX ACLs, so that the various finer-grained access control + options provided in Windows are actually ignore. +

`Note`

+ All access to UNIX/Linux system files via Samba is controlled by the operating system file access controls. + When trying to figure out file access problems it is vitally important to find the identity of the Windows + user as it is presented by Samba at the point of file access. This can best be determined from the Samba log files. -

`Viewing File Security on a Samba Share`

From an NT4/2000/XP client, single-click with the right - mouse button on any file or directory in a Samba mounted - drive letter or UNC path. When the menu pops-up, click - on the Properties entry at the bottom of - the menu. This brings up the file properties dialog - box. Click on the tab Security and you - will see three buttons, Permissions, - Auditing, and Ownership. - The Auditing button will cause either - an error message A requested privilege is not held - by the client to appear if the user is not the - NT Administrator, or a dialog which is intended to allow an - Administrator to add auditing requirements to a file if the - user is logged on as the NT Administrator. This dialog is - non-functional with a Samba share at this time, as the only - useful button, the Add button will not currently - allow a list of users to be seen.

`Viewing file ownership`

Clicking on the Ownership button - brings up a dialog box telling you who owns the given file. The - owner name will be of the form :

"SERVER\user (Long name)"

Where SERVER is the NetBIOS name of - the Samba server, user is the user name of - the UNIX user who owns the file, and (Long name) - is the descriptive string identifying the user (normally found in the - GECOS field of the UNIX password database). Click on the - Close button to remove this dialog.

If the parameter nt acl support - is set to false then the file owner will - be shown as the NT user "Everyone".

The Take Ownership button will not allow - you to change the ownership of this file to yourself (clicking on - it will display a dialog box complaining that the user you are - currently logged onto the NT client cannot be found). The reason - for this is that changing the ownership of a file is a privileged - operation in UNIX, available only to the root - user. As clicking on this button causes NT to attempt to change - the ownership of a file to the current user logged into the NT - client this will not work with Samba at this time.

There is an NT chown command that will work with Samba - and allow a user with Administrator privilege connected - to a Samba server as root to change the ownership of - files on both a local NTFS filesystem or remote mounted NTFS - or Samba drive. This is available as part of the Seclib - NT security library written by Jeremy Allison of - the Samba Team, available from the main Samba ftp site.

`Viewing File or Directory Permissions`

The third button is the Permissions - button. Clicking on this brings up a dialog box that shows both - the permissions and the UNIX owner of the file or directory. - The owner is displayed in the form :

"SERVER\ +

`Viewing File Security on a Samba Share`

+ From an NT4/2000/XP client, single-click with the right mouse button on any file or directory in a Samba + mounted drive letter or UNC path. When the menu pops-up, click on the Properties + entry at the bottom of the menu. This brings up the file properties dialog box. Click on the tab + Security and you will see three buttons, Permissions, + Auditing, and Ownership. The Auditing + button will cause either an error message A requested privilege is not held by the client + to appear if the user is not the NT Administrator, or a dialog which is intended to allow an Administrator + to add auditing requirements to a file if the user is logged on as the NT Administrator. This dialog is + non-functional with a Samba share at this time, as the only useful button, the Add + button will not currently allow a list of users to be seen. +

`Viewing file ownership`

+ Clicking on the Ownership button brings up a dialog box telling you who owns + the given file. The owner name will be of the form: +

+ "SERVER\user (Long name)" +

+ Where SERVER is the NetBIOS name of the Samba server, user + is the user name of the UNIX user who owns the file, and (Long name) is the + descriptive string identifying the user (normally found in the GECOS field of the UNIX password database). + Click on the Close button to remove this dialog. +

+ If the parameter nt acl support is set to false + then the file owner will be shown as the NT user "Everyone". +

+ The Take Ownership button will not allow you to change the ownership of this file to + yourself (clicking on it will display a dialog box complaining that the user you are currently logged onto + the NT client cannot be found). The reason for this is that changing the ownership of a file is a privileged + operation in UNIX, available only to the root user. As clicking on this button causes + NT to attempt to change the ownership of a file to the current user logged into the NT client this will + not work with Samba at this time.

+ There is an NT chown command that will work with Samba and allow a user with Administrator privilege connected + to a Samba server as root to change the ownership of files on both a local NTFS filesystem or remote mounted NTFS + or Samba drive. This is available as part of the Seclib NT security library written + by Jeremy Allison of the Samba-Team, available from the main Samba FTP site.

`Viewing File or Directory Permissions`

+ The third button is the Permissions button. Clicking on this brings up a dialog box + that shows both the permissions and the UNIX owner of the file or directory. The owner is displayed in the form: +

"SERVER\ user - (Long name)"

If the parameter nt acl support - is set to false then the file owner will - be shown as the NT user "Everyone" and the - permissions will be shown as NT "Full Control".

The permissions field is displayed differently for files - and directories, so I'll describe the way file permissions - are displayed first.

`File Permissions`

The standard UNIX user/group/world triplet and + (Long name)"

Where SERVER is the NetBIOS name of the Samba server, + user is the user name of the UNIX user who owns the file, and + (Long name) is the descriptive string identifying the user (normally found in the + GECOS field of the UNIX password database).

+ If the parameter nt acl support is set to false + then the file owner will be shown as the NT user "Everyone" and the permissions will be + shown as NT "Full Control". +

+ The permissions field is displayed differently for files and directories, so I'll describe the way file permissions + are displayed first. +

`File Permissions`

The standard UNIX user/group/world triplet and the corresponding "read", "write", "execute" permissions triplets are mapped by Samba into a three element NT ACL with the 'r', 'w', and 'x' bits mapped into the corresponding @@ -459,14 +434,14 @@ Before using any of the following options please refer to the man page for or full control then usually the permissions will be prefixed by the words "Special Access" in the NT display list.

But what happens if the file has no permissions allowed - for a particular UNIX user group or world component ? In order + for a particular UNIX user group or world component? In order to allow "no permissions" to be seen and modified then Samba overloads the NT "Take Ownership" ACL attribute (which has no meaning in UNIX) and reports a component with no permissions as having the NT "O" bit set. This was chosen of course to make it look like a zero, meaning zero permissions. More details on the decision behind this will - be given below.

`Directory Permissions`

Directories on an NT NTFS file system have two + be given below.

`Directory Permissions`

Directories on an NT NTFS file system have two different sets of permissions. The first set of permissions is the ACL set on the directory itself, this is usually displayed in the first set of parentheses in the normal "RW" @@ -477,12 +452,12 @@ Before using any of the following options please refer to the man page for permissions that any file created within this directory would inherit.

Samba synthesises these inherited permissions for NT by returning as an NT ACL the UNIX permission mode that a new file - created by Samba on this share would receive.

`Modifying file or directory permissions`

Modifying file and directory permissions is as simple + created by Samba on this share would receive.

`Modifying file or directory permissions`

Modifying file and directory permissions is as simple as changing the displayed permissions in the dialog box, and clicking the OK button. However, there are limitations that a user needs to be aware of, and also interactions with the standard Samba permission masks and mapping of DOS - attributes that need to also be taken into account.

If the parameter nt acl support + attributes that need to also be taken into account.

If the parameter nt acl support is set to false then any attempt to set security permissions will fail with an "Access Denied" message.

The first thing to note is that the "Add" @@ -511,59 +486,56 @@ Before using any of the following options please refer to the man page for Remove button, or set the component to only have the special Take Ownership permission (displayed as "O" - ) highlighted.

`Interaction with the standard Samba create mask + ) highlighted.`

`Interaction with the standard Samba create mask parameters`

There are four parameters to control interaction with the standard Samba create mask parameters. These are : -

security mask

force security mode

directory security mask

force directory security mode

+

security mask
force security mode
directory security mask
force directory security mode

Once a user clicks OK to apply the permissions Samba maps the given permissions into a user/group/world r/w/x triplet set, and then will check the changed permissions for a - file against the bits set in the - security mask parameter. Any bits that + file against the bits set in the + security mask parameter. Any bits that were changed that are not set to '1' in this parameter are left alone - in the file permissions.

Essentially, zero bits in the security mask + in the file permissions.

Essentially, zero bits in the security mask mask may be treated as a set of bits the user is not allowed to change, and one bits are those the user is allowed to change.

If not set explicitly this parameter is set to the same value as - the create mask - parameter. To allow a user to modify all the + the create mask parameter. To allow a user to modify all the user/group/world permissions on a file, set this parameter to 0777.

Next Samba checks the changed permissions for a file against - the bits set in the - force security mode parameter. Any bits + the bits set in the + force security mode parameter. Any bits that were changed that correspond to bits set to '1' in this parameter are forced to be set.

Essentially, bits set in the force security mode parameter may be treated as a set of bits that, when modifying security on a file, the user has always set to be 'on'.

If not set explicitly this parameter is set to the same value - as the force - create mode parameter. + as the force create mode parameter. To allow a user to modify all the user/group/world permissions on a file - with no restrictions set this parameter to 000.

The security mask and force + with no restrictions set this parameter to 000.

The security mask and force security mode parameters are applied to the change request in that order.

For a directory Samba will perform the same operations as described above for a file except using the parameter directory security mask instead of security mask, and force directory security mode parameter instead of force security mode - .

The directory security mask parameter + .

The directory security mask parameter by default is set to the same value as the directory mask parameter and the force directory security mode parameter by default is set to the same value as - the force directory mode parameter.

In this way Samba enforces the permission restrictions that + the force directory mode parameter.

In this way Samba enforces the permission restrictions that an administrator can set on a Samba share, whilst still allowing users to modify the permission bits within that restriction.

If you want to set up a share that allows users full control in modifying the permission bits on their files and directories and doesn't force any particular bits to be set 'on', then set the following parameters in the smb.conf file in that share specific section : -

security mask = 0777

force security mode = 0

directory security mask = 0777

force directory security mode = 0

`Interaction with the standard Samba file attribute - mapping`

Samba maps some of the DOS attribute bits (such as "read +

security mask = 0777

force security mode = 0

directory security mask = 0777

force directory security mode = 0

`Interaction with the standard Samba file attribute mapping`

`Note`

Samba maps some of the DOS attribute bits (such as "read only") into the UNIX permissions of a file. This means there can be a conflict between the permission bits set via the security dialog and the permission bits set by the file attribute mapping. -

One way this can show up is if a file has no UNIX read access +

One way this can show up is if a file has no UNIX read access for the owner it will show up as "read only" in the standard file attributes tabbed dialog. Unfortunately this dialog is the same one that contains the security info in another tab.

What this can mean is that if the owner changes the permissions @@ -575,10 +547,10 @@ Before using any of the following options please refer to the man page for OK to get back to the attributes dialog you should always hit Cancel rather than OK to ensure that your changes - are not overridden.

`Common Errors`

+ are not overridden.

`Common Errors`

File, Directory and Share access problems are very common on the mailing list. The following are examples taken from the mailing list in recent times. -

`Users can not write to a public share`

+

`Users can not write to a public share`

“ We are facing some troubles with file / directory permissions. I can log on the domain as admin user(root), and there's a public share, on which everyone needs to have permission to create / modify files, but only @@ -587,74 +559,83 @@ are examples taken from the mailing list in recent times. ”

There are many ways to solve this problem, here are a few hints: -

Procedure 13.3. Example Solution:

+

Go to the top of the directory that is shared

Set the ownership to what ever public owner and group you want -

-			find 'directory_name' -type d -exec chown user.group {}\;
-			find 'directory_name' -type d -exec chmod 6775 'directory_name'
-			find 'directory_name' -type f -exec chmod 0775 {} \;
-			find 'directory_name' -type f -exec chown user.group {}\;
-

+

+$ find 'directory_name' -type d -exec chown user.group {}\;
+$ find 'directory_name' -type d -exec chmod 6775 'directory_name'
+$ find 'directory_name' -type f -exec chmod 0775 {} \;
+$ find 'directory_name' -type f -exec chown user.group {}\;
+

`Note`

The above will set the 'sticky bit' on all directories. Read your - Unix/Linux man page on what that does. It causes the OS to assign + UNIX/Linux man page on what that does. It causes the OS to assign to all files created in the directories the ownership of the directory.

Directory is: /foodbar -

-				$ chown jack.engr /foodbar
-

-

`Note`

-

This is the same as doing:

-

-					$ chown jack /foodbar
-					$ chgrp engr /foodbar
-

-

Now do: +

+$ chown jack.engr /foodbar
+

+

`Note`

This is the same as doing:

+$ chown jack /foodbar
+$ chgrp engr /foodbar
+

Now do: -

-				$ chmod 6775 /foodbar
-				$ ls -al /foodbar/..
-

+

+$ chmod 6775 /foodbar
+$ ls -al /foodbar/..
+

You should see: -

-				drwsrwsr-x  2 jack  engr    48 2003-02-04 09:55 foodbar
-

+

+drwsrwsr-x  2 jack  engr    48 2003-02-04 09:55 foodbar
+

Now do: -

-				$ su - jill
-				$ cd /foodbar
-				$ touch Afile
-				$ ls -al
-

+

+$ su - jill
+$ cd /foodbar
+$ touch Afile
+$ ls -al
+

You should see that the file Afile created by Jill will have ownership and permissions of Jack, as follows: -

-		-rw-r--r--  1 jack  engr     0 2003-02-04 09:57 Afile
-

+

+-rw-r--r--  1 jack  engr     0 2003-02-04 09:57 Afile
+

Now in your smb.conf for the share add: -
```
-		force create mode = 0775
-		force directory mode = 6775
-		
```
+
force create mode = 0775
force direcrtory mode = 6775
Note
The above are only needed if your users are not members of the group you have used. ie: Within the OS do not have write permission on the directory.
An alternative is to set in the smb.conf entry for the share: -
```
-		force user = jack
-		force group = engr
-		
```
-

`I have set force user and Samba still makes root the owner of all the files - I touch!`

- When you have a user in 'admin users', Samba will always do file operations for - this user as root, even if force user has been set. -

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+ force user = jack force group = engr +

`I have set force user but Samba still makes root the owner of all the files I touch!`

+ When you have a user in admin users, samba will always do file operations for + this user as root, even if force user has been set. +

`MS Word with Samba changes owner of file`

+ Question: “When userB saves a word document that is owned by userA the updated file is now owned by userB. + Why is Samba doing this? How do I fix this?” +

+ Answer: Word does the following when you modify/change a Word document: Word Creates a NEW document with + a temporary name, Word then closes the old document and deletes it, Word then renames the new document to the original document name. + There is NO mechanism by which Samba CAN IN ANY WAY know that the new document really should be owned by the owners + of the original file. Samba has no way of knowing that the file will be renamed by MS Word. As far as Samba is able + to tell, the file that gets created is a NEW file, not one that the application (Word) is updating. +

+ There is a work-around to solve the permissions problem. That work-around involves understanding how you can manage file + system behaviour from within the smb.conf file, as well as understanding how Unix file systems work. Set on the directory + in which you are changing word documents: chmod g+s 'directory_name' This ensures that all files will + be created with the group that owns the directory. In smb.conf share declaration section set: +

+

force create mode = 0660

force directory mode = 0770

+

+ These two settings will ensure that all directories and files that get created in the share will be read/writable by the + owner and group set on the directory itself. +