1 <chapter id="AccessControls">
5 <author>&person.jelmer;<contrib>drawing</contrib></author>
6 <pubdate>May 10, 2003</pubdate>
8 <title>File, Directory and Share Access Controls</title>
10 <indexterm><primary>ACLs</primary></indexterm>
12 Advanced MS Windows users are frequently perplexed when file, directory and share manipulation of
13 resources shared via Samba do not behave in the manner they might expect. MS Windows network
14 administrators are often confused regarding network access controls and how to
15 provide users with the access they need while protecting resources from unauthorised access.
19 Many UNIX administrators are unfamiliar with the MS Windows environment and in particular
20 have difficulty in visualizing what the MS Windows user wishes to achieve in attempts to set file
21 and directory access permissions.
25 The problem lies in the differences in how file and directory permissions and controls work
26 between the two environments. This difference is one that Samba can not completely hide, even
27 though it does try to bridge the chasm to a degree.
30 <indexterm><primary>Extended Attributes</primary></indexterm>
32 POSIX Access Control List technology has been available (along with Extended Attributes)
33 for UNIX for many years, yet there is little evidence today of any significant use. This
34 explains to some extent the slow adoption of ACLs into commercial Linux products. MS Windows
35 administrators are astounded at this given that ACLs were a foundational capability of the now
36 decade old MS Windows NT operating system.
40 The purpose of this chapter is to present each of the points of control that are possible with
41 Samba-3 in the hope that this will help the network administrator to find the optimum method
42 for delivering the best environment for MS Windows desktop users.
46 This is an opportune point to mention that Samba was created to provide a means of interoperability
47 and interchange of data between differing operating environments. Samba has no intent change
48 UNIX/Linux into a platform like MS Windows. Instead the purpose was and is to provide a sufficient
49 level of exchange of data between the two environments. What is available today extends well
50 beyond early plans and expectations, yet the gap continues to shrink.
54 <title>Features and Benefits</title>
57 Samba offers a lot of flexibility in file system access management. These are the key access control
58 facilities present in Samba today:
62 <title>Samba Access Control Facilities</title>
64 <emphasis>UNIX File and Directory Permissions</emphasis>
68 Samba honours and implements UNIX file system access controls. Users
69 who access a Samba server will do so as a particular MS Windows user.
70 This information is passed to the Samba server as part of the logon or
71 connection setup process. Samba uses this user identity to validate
72 whether or not the user should be given access to file system resources
73 (files and directories). This chapter provides an overview for those
74 to whom the UNIX permissions and controls are a little strange or unknown.
79 <emphasis>Samba Share Definitions</emphasis>
83 In configuring share settings and controls in the &smb.conf; file
84 the network administrator can exercise over-rides to native file
85 system permissions and behaviours. This can be handy and convenient
86 to affect behaviour that is more like what MS Windows NT users expect
87 but it is seldom the <emphasis>best</emphasis> way to achieve this.
88 The basic options and techniques are described herein.
93 <emphasis>Samba Share ACLs</emphasis>
97 Just like it is possible in MS Windows NT to set ACLs on shares
98 themselves, so it is possible to do this in Samba.
99 Very few people make use of this facility, yet it remains on of the
100 easiest ways to affect access controls (restrictions) and can often
101 do so with minimum invasiveness compared with other methods.
106 <emphasis>MS Windows ACLs through UNIX POSIX ACLs</emphasis>
110 The use of POSIX ACLs on UNIX/Linux is possible ONLY if the underlying
111 operating system supports them. If not, then this option will not be
112 available to you. Current UNIX technology platforms have native support
113 for POSIX ACLs. There are patches for the Linux kernel that provide
114 this also. Sadly, few Linux platforms ship today with native ACLs and
115 Extended Attributes enabled. This chapter has pertinent information
116 for users of platforms that support them.
124 <title>File System Access Controls</title>
127 Perhaps the most important recognition to be made is the simple fact that MS Windows NT4 / 200x / XP
128 implement a totally divergent file system technology from what is provided in the UNIX operating system
129 environment. Firstly we should consider what the most significant differences are, then we shall look
130 at how Samba helps to bridge the differences.
133 <indexterm><primary>NTFS</primary></indexterm>
134 <indexterm><primary>File System</primary></indexterm>
136 <title>MS Windows NTFS Comparison with UNIX File Systems</title>
139 Samba operates on top of the UNIX file system. This means it is subject to UNIX file system conventions
140 and permissions. It also means that if the MS Windows networking environment requires file system
141 behaviour that differs from unix file system behaviour then somehow Samba is responsible for emulating
142 that in a transparent and consistent manner.
146 It is good news that Samba does this to a very large extent and on top of that provides a high degree
147 of optional configuration to over-ride the default behaviour. We will look at some of these over-rides,
148 but for the greater part we will stay within the bounds of default behaviour. Those wishing to explore
149 to depths of control ability should review the &smb.conf; man page.
153 <title>File System Feature Comparison</title>
155 <term>Name Space</term>
158 MS Windows NT4 / 200x/ XP files names may be up to 254 characters long, UNIX file names
159 may be 1023 characters long. In MS Windows file extensions indicate particular file types,
160 in UNIX this is not so rigorously observed as all names are considered arbitrary.
163 What MS Windows calls a Folder, UNIX calls a directory.
168 <indexterm><primary>8.3</primary><secondary>file names</secondary></indexterm>
170 <term>Case Sensitivity</term>
173 MS Windows file names are generally upper case if made up of 8.3 (ie: 8 character file name
174 and 3 character extension. If longer than 8.3 file names are Case Preserving, and Case
178 UNIX file and directory names are case sensitive and case preserving. Samba implements the
179 MS Windows file name behaviour, but it does so as a user application. The UNIX file system
180 provides no mechanism to perform case insensitive file name lookups. MS Windows does this
181 by default. This means that Samba has to carry the processing overhead to provide features
182 that are NOT native to the UNIX operating system environment.
185 Consider the following, all are unique UNIX names but one single MS Windows file name:
191 So clearly, In an MS Windows file name space these three files CAN NOT co-exist! But in UNIX
192 they can. So what should Samba do if all three are present? Answer, the one that is lexically
193 first will be accessible to MS Windows users, the others are invisible and unaccessible - any
194 other solution would be suicidal.
200 <term>Directory Separators</term>
203 MS Windows and DOS uses the back-slash '\' as a directory delimiter, UNIX uses the forward-slash '/'
204 as it's directory delimiter. This is transparently handled by Samba.
210 <term>Drive Identification</term>
213 MS Windows products support a notion of drive letters, like <command>C:</command> to represent
214 disk partitions. UNIX has NO concept if separate identifiers for file partitions since each
215 such file system is <filename>mounted</filename> to become part of the over-all directory tree.
216 The UNIX directory tree begins at '/', just like the root of a DOS drive is specified like
217 <command>C:\</command>.
223 <term>File Naming Conventions</term>
226 MS Windows generally never experiences file names that begin with a '.', while in UNIX these
227 are commonly found in a user's home directory. Files that begin with a '.' are typically
228 either start up files for various UNIX applications, or they may be files that contain
229 start-up configuration data.
234 <indexterm><primary>Links</primary><secondary>hard</secondary></indexterm>
235 <indexterm><primary>Links</primary><secondary>soft</secondary></indexterm>
236 <indexterm><primary>Short-Cuts</primary></indexterm>
238 <term>Links and Short-Cuts</term>
241 MS Windows make use of "links and Short-Cuts" that are actually special types of files that will
242 redirect an attempt to execute the file to the real location of the file. UNIX knows of file and directory
243 links, but they are entirely different from what MS Windows users are used to.
246 Symbolic links are files in UNIX that contain the actual location of the data (file OR directory). An
247 operation (like read or write) will operate directly on the file referenced. Symbolic links are also
248 referred to as 'soft links'. A hard link is something that MS Windows is NOT familiar with. It allows
249 one physical file to be known simultaneously by more than one file name.
256 There are many other subtle differences that may cause the MS Windows administrator some temporary discomfort
257 in the process of becoming familiar with UNIX/Linux. These are best left for a text that is dedicated to the
258 purpose of UNIX/Linux training/education.
264 <title>Managing Directories</title>
267 There are three basic operations for managing directories, <command>create, delete, rename</command>.
269 <title>Managing directories with unix and windows</title>
270 <tgroup align="center" cols="3">
272 <row><entry>Action</entry><entry>MS Windows Command</entry><entry>UNIX Command</entry></row>
276 <row><entry>create</entry><entry>md folder</entry><entry>mkdir folder</entry></row>
277 <row><entry>delete</entry><entry>rd folder</entry><entry>rmdir folder</entry></row>
278 <row><entry>rename</entry><entry>rename oldname newname</entry><entry>mv oldname newname</entry></row>
287 <title>File and Directory Access Control</title>
290 The network administrator is strongly advised to read foundational training manuals and reference materials
291 regarding file and directory permissions maintenance. Much can be achieved with the basic UNIX permissions
292 without having to resort to more complex facilities like POSIX Access Control Lists (ACLs) or Extended
297 UNIX/Linux file and directory access permissions involves setting three (3) primary sets of data and one (1) control set.
298 A UNIX file listing looks as follows:-
301 &prompt;<userinput>ls -la</userinput>
303 drwxr-xr-x 13 maryo gnomes 816 2003-05-12 22:56 .
304 drwxrwxr-x 37 maryo gnomes 3800 2003-05-12 22:29 ..
305 dr-xr-xr-x 2 maryo gnomes 48 2003-05-12 22:29 muchado02
306 drwxrwxrwx 2 maryo gnomes 48 2003-05-12 22:29 muchado03
307 drw-rw-rw- 2 maryo gnomes 48 2003-05-12 22:29 muchado04
308 d-w--w--w- 2 maryo gnomes 48 2003-05-12 22:29 muchado05
309 dr--r--r-- 2 maryo gnomes 48 2003-05-12 22:29 muchado06
310 drwsrwsrwx 2 maryo gnomes 48 2003-05-12 22:29 muchado08
311 ---------- 1 maryo gnomes 1242 2003-05-12 22:31 mydata00.lst
312 --w--w--w- 1 maryo gnomes 7754 2003-05-12 22:33 mydata02.lst
313 -r--r--r-- 1 maryo gnomes 21017 2003-05-12 22:32 mydata04.lst
314 -rw-rw-rw- 1 maryo gnomes 41105 2003-05-12 22:32 mydata06.lst
320 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.
324 An overview of the permissions field can be found in <link linkend="access1"/>.
327 <image scale="40"><imagedescription>Overview of unix permissions field</imagedescription><imagefile>access1</imagefile></image>
330 Any bit flag may be unset. An unset bit flag is the equivalent of 'Can NOT' and is represented as a '-' character.
333 <title>Example File</title>
335 -rwxr-x--- Means: The owner (user) can read, write, execute
336 the group can read and execute
337 everyone else can NOT do anything with it
344 Additional possibilities in the [type] field are: c = character device, b = block device, p = pipe device, s = UNIX Domain Socket.
348 The letters `rwxXst' set permissions for the user, group and others as: read (r), write (w), execute (or access for directories) (x),
349 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),
354 When the sticky bit is set on a directory, files in that directory may be unlinked (deleted) or renamed only by root or their owner.
355 Without the sticky bit, anyone able to write to the directory can delete or rename files. The sticky bit is commonly found on
356 directories, such as /tmp, that are world-writable.
360 When the set user or group ID bit (s) is set on a directory, then all files created within it will be owned by the user and/or
361 group whose 'set user or group' bit is set. This can be very helpful in setting up directories that for which it is desired that
362 all users who are in a group should be able to write to and read from a file, particularly when it is undesirable for that file
363 to be exclusively owned by a user who's primary group is not the group that all such users belong to.
367 When a directory is set <constant>drw-r-----</constant> this means that the owner can read and create (write) files in it, but because
368 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
369 directory but can NOT create new files. NOTE: If files in the directory are set to be readable and writable for the group, then
370 group members will be able to write to (or delete) them.
378 <title>Share Definition Access Controls</title>
381 The following parameters in the &smb.conf; file sections that define a share control or affect access controls.
382 Before using any of the following options please refer to the man page for &smb.conf;.
386 <title>User and Group Based Controls</title>
389 User and group based controls can prove very useful. In some situations it is distinctly desirable to affect all
390 file system operations as if a single user is doing this, the use of the <smbconfoption><name>force user</name></smbconfoption> and
391 <smbconfoption><name>force group</name></smbconfoption> behaviour will achieve this. In other situations it may be necessary to affect a
392 paranoia level of control to ensure that only particular authorised persons will be able to access a share or
393 it's contents, here the use of the <smbconfoption><name>valid users</name></smbconfoption> or the <smbconfoption><name>invalid users</name></smbconfoption> may
398 As always, it is highly advisable to use the least difficult to maintain and the least ambiguous method for
399 controlling access. Remember, that when you leave the scene someone else will need to provide assistance and
400 if that person finds too great a mess, or if they do not understand what you have done then there is risk of
401 Samba being removed and an alternative solution being adopted.
404 <table frame='all' pgwide='0'><title>User and Group Based Controls</title>
406 <colspec align="left"/>
407 <colspec align="justify" width="1*"/>
410 <entry align="center">Control Parameter</entry>
411 <entry align="center">Description - Action - Notes</entry>
416 <entry><smbconfoption><name>admin users</name></smbconfoption></entry>
418 List of users who will be granted administrative privileges on the share.
419 They will do all file operations as the super-user (root).
420 Any user in this list will be able to do anything they like on the share,
421 irrespective of file permissions.
425 <entry><smbconfoption><name>force group</name></smbconfoption></entry>
427 Specifies a UNIX group name that will be assigned as the default primary group
428 for all users connecting to this service.
432 <entry><smbconfoption><name>force user</name></smbconfoption></entry>
434 Specifies a UNIX user name that will be assigned as the default user for all users connecting to this service.
435 This is useful for sharing files. Incorrect use can cause security problems.
439 <entry><smbconfoption><name>guest ok</name></smbconfoption></entry>
441 If this parameter is set for a service, then no password is required to connect to the service. Privileges will be
442 those of the guest account.
446 <entry><smbconfoption><name>invalid users</name></smbconfoption></entry>
448 List of users that should not be allowed to login to this service.
452 <entry><smbconfoption><name>only user</name></smbconfoption></entry>
454 Controls whether connections with usernames not in the user list will be allowed.
458 <entry><smbconfoption><name>read list</name></smbconfoption></entry>
460 List of users that are given read-only access to a service. Users in this list
461 will not be given write access, no matter what the read only option is set to.
465 <entry><smbconfoption><name>username</name></smbconfoption></entry>
467 Refer to the &smb.conf; man page for more information - this is a complex and potentially misused parameter.
471 <entry><smbconfoption><name>valid users</name></smbconfoption></entry>
473 List of users that should be allowed to login to this service.
477 <entry><smbconfoption><name>write list</name></smbconfoption></entry>
479 List of users that are given read-write access to a service.
489 <title>File and Directory Permissions Based Controls</title>
492 The following file and directory permission based controls, if misused, can result in considerable difficulty to
493 diagnose the cause of mis-configuration. Use them sparingly and carefully. By gradually introducing each one by one
494 undesirable side-effects may be detected. In the event of a problem, always comment all of them out and then gradually
495 re-introduce them in a controlled fashion.
498 <table frame='all'><title>File and Directory Permission Based Controls</title>
500 <colspec align="left"/>
501 <colspec align="justify" width="1*"/>
504 <entry align="center">Control Parameter</entry>
505 <entry align="center">Description - Action - Notes</entry>
510 <entry><smbconfoption><name>create mask</name></smbconfoption></entry>
512 Refer to the &smb.conf; man page.
516 <entry><smbconfoption><name>directory mask</name></smbconfoption></entry>
518 The octal modes used when converting DOS modes to UNIX modes when creating UNIX directories.
519 See also: directory security mask.
520 </para></entry></row>
522 <entry><smbconfoption><name>dos filemode</name></smbconfoption></entry>
524 Enabling this parameter allows a user who has write access to the file to modify the permissions on it.
528 <entry><smbconfoption><name>force create mode</name></smbconfoption></entry>
530 This parameter specifies a set of UNIX mode bit permissions that will always be set on a file created by Samba.
534 <entry><smbconfoption><name>force directory mode</name></smbconfoption></entry>
536 This parameter specifies a set of UNIX mode bit permissions that will always be set on a directory created by Samba.
540 <entry><smbconfoption><name>force directory security mode</name></smbconfoption></entry>
542 Controls UNIX permission bits modified when a Windows NT client is manipulating UNIX permissions on a directory
546 <entry><smbconfoption><name>force security mode</name></smbconfoption></entry>
548 Controls UNIX permission bits modified when a Windows NT client manipulates UNIX permissions.
552 <entry><smbconfoption><name>hide unreadable</name></smbconfoption></entry>
554 Prevents clients from seeing the existence of files that cannot be read.
558 <entry><smbconfoption><name>hide unwriteable files</name></smbconfoption></entry>
560 Prevents clients from seeing the existence of files that cannot be written to. Unwriteable directories are shown as usual.
564 <entry><smbconfoption><name>nt acl support</name></smbconfoption></entry>
566 This parameter controls whether smbd will attempt to map UNIX permissions into Windows NT access control lists.
570 <entry><smbconfoption><name>security mask</name></smbconfoption></entry>
572 Controls UNIX permission bits modified when a Windows NT client is manipulating the UNIX permissions on a file.
582 <title>Miscellaneous Controls</title>
585 The following are documented because of the prevalence of administrators creating inadvertent barriers to file
586 access by not understanding the full implications of &smb.conf; file settings.
589 <table frame='all'><title>Other Controls</title>
591 <colspec align="justify" width="1*"/>
592 <colspec align="justify" width="1*"/>
595 <entry align="center">Control Parameter</entry>
596 <entry align="center">Description - Action - Notes</entry>
601 <entry><smbconfoption><name>case sensitive</name></smbconfoption>, <smbconfoption><name>default case</name></smbconfoption>, <smbconfoption><name>short preserve case</name></smbconfoption></entry>
603 This means that all file name lookup will be done in a case sensitive manner.
604 Files will be created with the precise filename Samba received from the MS Windows client.
608 <entry><smbconfoption><name>csc policy</name></smbconfoption></entry>
610 Client Side Caching Policy - parallels MS Windows client side file caching capabilities.
614 <entry><smbconfoption><name>dont descend</name></smbconfoption></entry>
616 Allows to specify a comma-delimited list of directories that the server should always show as empty.
620 <entry><smbconfoption><name>dos filetime resolution</name></smbconfoption></entry>
622 This option is mainly used as a compatibility option for Visual C++ when used against Samba shares.
626 <entry><smbconfoption><name>dos filetimes</name></smbconfoption></entry>
628 DOS and Windows allows users to change file time stamps if they can write to the file. POSIX semantics prevent this.
629 This options allows DOS and Windows behaviour.
633 <entry><smbconfoption><name>fake oplocks</name></smbconfoption></entry>
635 Oplocks are the way that SMB clients get permission from a server to locally cache file operations. If a server grants an
636 oplock then the client is free to assume that it is the only one accessing the file and it will aggressively cache file data.
640 <entry><smbconfoption><name>hide dot files</name></smbconfoption>, <smbconfoption><name>hide files</name></smbconfoption>, <smbconfoption><name>veto files</name></smbconfoption></entry>
642 Note: MS Windows Explorer allows over-ride of files marked as hidden so they will still be visible.
646 <entry><smbconfoption><name>read only</name></smbconfoption></entry>
648 If this parameter is yes, then users of a service may not create or modify files in the service's directory.
652 <entry><smbconfoption><name>veto files</name></smbconfoption></entry>
654 List of files and directories that are neither visible nor accessible.
666 <title>Access Controls on Shares</title>
669 This section deals with how to configure Samba per share access control restrictions.
670 By default, Samba sets no restrictions on the share itself. Restrictions on the share itself
671 can be set on MS Windows NT4/200x/XP shares. This can be a very effective way to limit who can
672 connect to a share. In the absence of specific restrictions the default setting is to allow
673 the global user <constant>Everyone</constant> Full Control (ie: Full control, Change and Read).
677 At this time Samba does NOT provide a tool for configuring access control setting on the Share
678 itself. Samba does have the capacity to store and act on access control settings, but the only
679 way to create those settings is to use either the NT4 Server Manager or the Windows 200x MMC for
684 Samba stores the per share access control settings in a file called <filename>share_info.tdb</filename>.
685 The location of this file on your system will depend on how samba was compiled. The default location
686 for Samba's tdb files is under <filename>/usr/local/samba/var</filename>. If the <filename>tdbdump</filename>
687 utility has been compiled and installed on your system, then you can examine the contents of this file
688 by: <userinput>tdbdump share_info.tdb</userinput>.
692 <title>Share Permissions Management</title>
695 The best tool for the task is platform dependant. Choose the best tool for your environment.
699 <title>Windows NT4 Workstation/Server</title>
701 The tool you need to use to manage share permissions on a Samba server is the NT Server Manager.
702 Server Manager is shipped with Windows NT4 Server products but not with Windows NT4 Workstation.
703 You can obtain the NT Server Manager for MS Windows NT4 Workstation from Microsoft - see details below.
707 <title>Instructions</title>
709 Launch the <application>NT4 Server Manager</application>, click on the Samba server you want to administer, then from the menu
710 select <guimenu>Computer</guimenu>, then click on the <guimenuitem>Shared Directories</guimenuitem> entry.
714 Now click on the share that you wish to manage, then click on the <guilabel>Properties</guilabel> tab, next click on
715 the <guilabel>Permissions</guilabel> tab. Now you can add or change access control settings as you wish.
722 <title>Windows 200x/XP</title>
725 On <application>MS Windows NT4/200x/XP</application> system access control lists on the share itself are set using native
726 tools, usually from file manager. For example, in Windows 200x: right click on the shared folder,
727 then select <guimenuitem>Sharing</guimenuitem>, then click on <guilabel>Permissions</guilabel>. The default
728 Windows NT4/200x permission allows <emphasis>Everyone</emphasis> Full Control on the Share.
732 MS Windows 200x and later all comes with a tool called the <application>Computer Management</application> snap-in for the
733 Microsoft Management Console (MMC). This tool is located by clicking on <filename>Control Panel ->
734 Administrative Tools -> Computer Management</filename>.
738 <title>Instructions</title>
740 After launching the MMC with the Computer Management snap-in, click on the menu item <guimenuitem>Action</guimenuitem>,
741 select <guilabel>Connect to another computer</guilabel>. If you are not logged onto a domain you will be prompted
742 to enter a domain login user identifier and a password. This will authenticate you to the domain.
743 If you where already logged in with administrative privilege this step is not offered.
747 If the Samba server is not shown in the <guilabel>Select Computer</guilabel> box, then type in the name of the target
748 Samba server in the field <guilabel>Name:</guilabel>. Now click on the <guibutton>[+]</guibutton> next to
749 <guilabel>System Tools</guilabel>, then on the <guibutton>[+]</guibutton> next to <guilabel>Shared Folders</guilabel> in the
754 Now in the right panel, double-click on the share you wish to set access control permissions on.
755 Then click on the tab <guilabel>Share Permissions</guilabel>. It is now possible to add access control entities
756 to the shared folder. Do NOT forget to set what type of access (full control, change, read) you
757 wish to assign for each entry.
763 Be careful. If you take away all permissions from the <constant>Everyone</constant> user without removing this user
764 then effectively no user will be able to access the share. This is a result of what is known as
765 ACL precedence. ie: Everyone with <emphasis>no access</emphasis> means that MaryK who is part of the group
766 <constant>Everyone</constant> will have no access even if this user is given explicit full control access.
776 <title>MS Windows Access Control Lists and UNIX Interoperability</title>
779 <title>Managing UNIX permissions Using NT Security Dialogs</title>
782 Windows NT clients can use their native security settings dialog box to view and modify the
783 underlying UNIX permissions.
787 Note that this ability is careful not to compromise the security of the UNIX host Samba is running on, and
788 still obeys all the file permission rules that a Samba administrator can set.
792 Samba does not attempt to go beyond POSIX ACLs, so that the various finer-grained access control
793 options provided in Windows are actually ignore.
798 All access to UNIX/Linux system files via Samba is controlled by the operating system file access controls.
799 When trying to figure out file access problems it is vitally important to find the identity of the Windows
800 user as it is presented by Samba at the point of file access. This can best be determined from the
807 <title>Viewing File Security on a Samba Share</title>
810 From an NT4/2000/XP client, single-click with the right mouse button on any file or directory in a Samba
811 mounted drive letter or UNC path. When the menu pops-up, click on the <guilabel>Properties</guilabel>
812 entry at the bottom of the menu. This brings up the file properties dialog box. Click on the tab
813 <guilabel>Security</guilabel> and you will see three buttons, <guibutton>Permissions</guibutton>,
814 <guibutton>Auditing</guibutton>, and <guibutton>Ownership</guibutton>. The <guibutton>Auditing</guibutton>
815 button will cause either an error message <errorname>A requested privilege is not held by the client</errorname>
816 to appear if the user is not the NT Administrator, or a dialog which is intended to allow an Administrator
817 to add auditing requirements to a file if the user is logged on as the NT Administrator. This dialog is
818 non-functional with a Samba share at this time, as the only useful button, the <guibutton>Add</guibutton>
819 button will not currently allow a list of users to be seen.
825 <title>Viewing file ownership</title>
828 Clicking on the <guibutton>Ownership</guibutton> button brings up a dialog box telling you who owns
829 the given file. The owner name will be of the form:
833 <command>"SERVER\user (Long name)"</command>
837 Where <replaceable>SERVER</replaceable> is the NetBIOS name of the Samba server, <replaceable>user</replaceable>
838 is the user name of the UNIX user who owns the file, and <replaceable>(Long name)</replaceable> is the
839 descriptive string identifying the user (normally found in the GECOS field of the UNIX password database).
840 Click on the <guibutton>Close </guibutton> button to remove this dialog.
844 If the parameter <smbconfoption><name>nt acl support</name></smbconfoption> is set to <constant>false</constant>
845 then the file owner will be shown as the NT user <constant>"Everyone"</constant>.
849 The <guibutton>Take Ownership</guibutton> button will not allow you to change the ownership of this file to
850 yourself (clicking on it will display a dialog box complaining that the user you are currently logged onto
851 the NT client cannot be found). The reason for this is that changing the ownership of a file is a privileged
852 operation in UNIX, available only to the <emphasis>root</emphasis> user. As clicking on this button causes
853 NT to attempt to change the ownership of a file to the current user logged into the NT client this will
854 not work with Samba at this time.</para>
857 There is an NT chown command that will work with Samba and allow a user with Administrator privilege connected
858 to a Samba server as root to change the ownership of files on both a local NTFS filesystem or remote mounted NTFS
859 or Samba drive. This is available as part of the <application>Seclib</application> NT security library written
860 by Jeremy Allison of the Samba-Team, available from the main Samba FTP site.</para>
865 <title>Viewing File or Directory Permissions</title>
868 The third button is the <guibutton>Permissions</guibutton> button. Clicking on this brings up a dialog box
869 that shows both the permissions and the UNIX owner of the file or directory. The owner is displayed in the form:
872 <para><command>"<replaceable>SERVER</replaceable>\
873 <replaceable>user</replaceable>
874 <replaceable>(Long name)</replaceable>"</command></para>
876 <para>Where <replaceable>SERVER</replaceable> is the NetBIOS name of the Samba server,
877 <replaceable>user</replaceable> is the user name of the UNIX user who owns the file, and
878 <replaceable>(Long name)</replaceable> is the descriptive string identifying the user (normally found in the
879 GECOS field of the UNIX password database).</para>
882 If the parameter <smbconfoption><name>nt acl support</name></smbconfoption> is set to <constant>false</constant>
883 then the file owner will be shown as the NT user <constant>"Everyone"</constant> and the permissions will be
884 shown as NT "Full Control".
889 The permissions field is displayed differently for files and directories, so I'll describe the way file permissions
894 <title>File Permissions</title>
896 <para>The standard UNIX user/group/world triplet and
897 the corresponding "read", "write", "execute" permissions
898 triplets are mapped by Samba into a three element NT ACL
899 with the 'r', 'w', and 'x' bits mapped into the corresponding
900 NT permissions. The UNIX world permissions are mapped into
901 the global NT group <constant>Everyone</constant>, followed
902 by the list of permissions allowed for UNIX world. The UNIX
903 owner and group permissions are displayed as an NT
904 <guiicon>user</guiicon> icon and an NT <guiicon>local
905 group</guiicon> icon respectively followed by the list
906 of permissions allowed for the UNIX user and group.</para>
908 <para>As many UNIX permission sets don't map into common
909 NT names such as <constant>read</constant>, <constant>
910 "change"</constant> or <constant>full control</constant> then
911 usually the permissions will be prefixed by the words <constant>
912 "Special Access"</constant> in the NT display list.</para>
914 <para>But what happens if the file has no permissions allowed
915 for a particular UNIX user group or world component? In order
916 to allow "no permissions" to be seen and modified then Samba
917 overloads the NT <command>"Take Ownership"</command> ACL attribute
918 (which has no meaning in UNIX) and reports a component with
919 no permissions as having the NT <command>"O"</command> bit set.
920 This was chosen of course to make it look like a zero, meaning
921 zero permissions. More details on the decision behind this will
922 be given below.</para>
926 <title>Directory Permissions</title>
928 <para>Directories on an NT NTFS file system have two
929 different sets of permissions. The first set of permissions
930 is the ACL set on the directory itself, this is usually displayed
931 in the first set of parentheses in the normal <constant>"RW"</constant>
932 NT style. This first set of permissions is created by Samba in
933 exactly the same way as normal file permissions are, described
934 above, and is displayed in the same way.</para>
936 <para>The second set of directory permissions has no real meaning
937 in the UNIX permissions world and represents the <constant>
938 inherited</constant> permissions that any file created within
939 this directory would inherit.</para>
941 <para>Samba synthesises these inherited permissions for NT by
942 returning as an NT ACL the UNIX permission mode that a new file
943 created by Samba on this share would receive.</para>
948 <title>Modifying file or directory permissions</title>
950 <para>Modifying file and directory permissions is as simple
951 as changing the displayed permissions in the dialog box, and
952 clicking the <guibutton>OK</guibutton> button. However, there are
953 limitations that a user needs to be aware of, and also interactions
954 with the standard Samba permission masks and mapping of DOS
955 attributes that need to also be taken into account.</para>
957 <para>If the parameter <smbconfoption><name>nt acl support</name></smbconfoption>
958 is set to <constant>false</constant> then any attempt to set
959 security permissions will fail with an <errorname>"Access Denied"
960 </errorname> message.</para>
962 <para>The first thing to note is that the <guibutton>"Add"</guibutton>
963 button will not return a list of users in Samba (it will give
964 an error message of <errorname>The remote procedure call failed
965 and did not execute</errorname>). This means that you can only
966 manipulate the current user/group/world permissions listed in
967 the dialog box. This actually works quite well as these are the
968 only permissions that UNIX actually has.</para>
970 <para>If a permission triplet (either user, group, or world)
971 is removed from the list of permissions in the NT dialog box,
972 then when the <guibutton>OK</guibutton> button is pressed it will
973 be applied as "no permissions" on the UNIX side. If you then
974 view the permissions again the "no permissions" entry will appear
975 as the NT <command>"O"</command> flag, as described above. This
976 allows you to add permissions back to a file or directory once
977 you have removed them from a triplet component.</para>
979 <para>As UNIX supports only the "r", "w" and "x" bits of
980 an NT ACL then if other NT security attributes such as "Delete
981 access" are selected then they will be ignored when applied on
982 the Samba server.</para>
984 <para>When setting permissions on a directory the second
985 set of permissions (in the second set of parentheses) is
986 by default applied to all files within that directory. If this
987 is not what you want you must uncheck the <guilabel>Replace
988 permissions on existing files</guilabel> checkbox in the NT
989 dialog before clicking <guibutton>OK</guibutton>.</para>
991 <para>If you wish to remove all permissions from a
992 user/group/world component then you may either highlight the
993 component and click the <guibutton>Remove</guibutton> button,
994 or set the component to only have the special <constant>Take
995 Ownership</constant> permission (displayed as <command>"O"
996 </command>) highlighted.</para>
1000 <title>Interaction with the standard Samba create mask
1003 <para>There are four parameters
1004 to control interaction with the standard Samba create mask parameters.
1008 <listitem><para><smbconfoption><name>security mask</name></smbconfoption></para></listitem>
1009 <listitem><para><smbconfoption><name>force security mode</name></smbconfoption></para></listitem>
1010 <listitem><para><smbconfoption><name>directory security mask</name></smbconfoption></para></listitem>
1011 <listitem><para><smbconfoption><name>force directory security mode</name></smbconfoption></para></listitem>
1016 <para>Once a user clicks <guibutton>OK</guibutton> to apply the
1017 permissions Samba maps the given permissions into a user/group/world
1018 r/w/x triplet set, and then will check the changed permissions for a
1019 file against the bits set in the
1020 <smbconfoption><name>security mask</name></smbconfoption> parameter. Any bits that
1021 were changed that are not set to '1' in this parameter are left alone
1022 in the file permissions.</para>
1024 <para>Essentially, zero bits in the <smbconfoption><name>security mask</name></smbconfoption>
1025 mask may be treated as a set of bits the user is <emphasis>not</emphasis>
1026 allowed to change, and one bits are those the user is allowed to change.
1029 <para>If not set explicitly this parameter is set to the same value as
1030 the <smbconfoption><name>create mask</name></smbconfoption> parameter. To allow a user to modify all the
1031 user/group/world permissions on a file, set this parameter
1034 <para>Next Samba checks the changed permissions for a file against
1036 <smbconfoption><name>force security mode</name></smbconfoption> parameter. Any bits
1037 that were changed that correspond to bits set to '1' in this parameter
1038 are forced to be set.</para>
1040 <para>Essentially, bits set in the <parameter>force security mode
1041 </parameter> parameter may be treated as a set of bits that, when
1042 modifying security on a file, the user has always set to be 'on'.</para>
1044 <para>If not set explicitly this parameter is set to the same value
1045 as the <smbconfoption><name>force create mode</name></smbconfoption> parameter.
1046 To allow a user to modify all the user/group/world permissions on a file
1047 with no restrictions set this parameter to 000.</para>
1049 <para>The <smbconfoption><name>security mask</name></smbconfoption> and <parameter>force
1050 security mode</parameter> parameters are applied to the change
1051 request in that order.</para>
1053 <para>For a directory Samba will perform the same operations as
1054 described above for a file except using the parameter <parameter>
1055 directory security mask</parameter> instead of <parameter>security
1056 mask</parameter>, and <parameter>force directory security mode
1057 </parameter> parameter instead of <parameter>force security mode
1058 </parameter>.</para>
1060 <para>The <smbconfoption><name>directory security mask</name></smbconfoption> parameter
1061 by default is set to the same value as the <parameter>directory mask
1062 </parameter> parameter and the <parameter>force directory security
1063 mode</parameter> parameter by default is set to the same value as
1064 the <smbconfoption><name>force directory mode</name></smbconfoption> parameter. </para>
1066 <para>In this way Samba enforces the permission restrictions that
1067 an administrator can set on a Samba share, whilst still allowing users
1068 to modify the permission bits within that restriction.</para>
1070 <para>If you want to set up a share that allows users full control
1071 in modifying the permission bits on their files and directories and
1072 doesn't force any particular bits to be set 'on', then set the following
1073 parameters in the &smb.conf; file in that share specific section :
1077 <smbconfoption><name>security mask</name><value>0777</value></smbconfoption>
1078 <smbconfoption><name>force security mode</name><value>0</value></smbconfoption>
1079 <smbconfoption><name>directory security mask</name><value>0777</value></smbconfoption>
1080 <smbconfoption><name>force directory security mode</name><value>0</value></smbconfoption>
1085 <title>Interaction with the standard Samba file attribute mapping</title>
1088 <para>Samba maps some of the DOS attribute bits (such as "read
1089 only") into the UNIX permissions of a file. This means there can
1090 be a conflict between the permission bits set via the security
1091 dialog and the permission bits set by the file attribute mapping.
1095 <para>One way this can show up is if a file has no UNIX read access
1096 for the owner it will show up as "read only" in the standard
1097 file attributes tabbed dialog. Unfortunately this dialog is
1098 the same one that contains the security info in another tab.</para>
1100 <para>What this can mean is that if the owner changes the permissions
1101 to allow themselves read access using the security dialog, clicks
1102 <guibutton>OK</guibutton> to get back to the standard attributes tab
1103 dialog, and then clicks <guibutton>OK</guibutton> on that dialog, then
1104 NT will set the file permissions back to read-only (as that is what
1105 the attributes still say in the dialog). This means that after setting
1106 permissions and clicking <guibutton>OK</guibutton> to get back to the
1107 attributes dialog you should always hit <guibutton>Cancel</guibutton>
1108 rather than <guibutton>OK</guibutton> to ensure that your changes
1109 are not overridden.</para>
1114 <title>Common Errors</title>
1117 File, Directory and Share access problems are very common on the mailing list. The following
1118 are examples taken from the mailing list in recent times.
1123 <title>Users can not write to a public share</title>
1127 We are facing some troubles with file / directory permissions. I can log on the domain as admin user(root),
1128 and there's a public share, on which everyone needs to have permission to create / modify files, but only
1129 root can change the file, no one else can. We need to constantly go to server to
1130 <userinput>chgrp -R users *</userinput> and <userinput>chown -R nobody *</userinput> to allow others users to change the file.
1135 There are many ways to solve this problem, here are a few hints:
1141 Go to the top of the directory that is shared
1147 Set the ownership to what ever public owner and group you want
1149 &prompt;find 'directory_name' -type d -exec chown user.group {}\;
1150 &prompt;find 'directory_name' -type d -exec chmod 6775 'directory_name'
1151 &prompt;find 'directory_name' -type f -exec chmod 0775 {} \;
1152 &prompt;find 'directory_name' -type f -exec chown user.group {}\;
1157 The above will set the 'sticky bit' on all directories. Read your
1158 UNIX/Linux man page on what that does. It causes the OS to assign
1159 to all files created in the directories the ownership of the
1166 Directory is: <replaceable>/foodbar</replaceable>
1168 &prompt;<userinput>chown jack.engr /foodbar</userinput>
1173 <para>This is the same as doing:</para>
1175 &prompt;<userinput>chown jack /foodbar</userinput>
1176 &prompt;<userinput>chgrp engr /foodbar</userinput>
1184 &prompt;<userinput>chmod 6775 /foodbar</userinput>
1185 &prompt;<userinput>ls -al /foodbar/..</userinput>
1190 <para>You should see:
1192 drwsrwsr-x 2 jack engr 48 2003-02-04 09:55 foodbar
1200 &prompt;<userinput>su - jill</userinput>
1201 &prompt;<userinput>cd /foodbar</userinput>
1202 &prompt;<userinput>touch Afile</userinput>
1203 &prompt;<userinput>ls -al</userinput>
1208 You should see that the file <filename>Afile</filename> created by Jill will have ownership
1209 and permissions of Jack, as follows:
1211 -rw-r--r-- 1 jack engr 0 2003-02-04 09:57 Afile
1218 Now in your &smb.conf; for the share add:
1220 <smbconfoption><name>force create mode</name><value>0775</value></smbconfoption>
1221 <smbconfoption><name>force direcrtory mode</name><value>6775</value></smbconfoption>
1226 The above are only needed <emphasis>if</emphasis> your users are <emphasis>not</emphasis> members of the group
1227 you have used. ie: Within the OS do not have write permission on the directory.
1232 An alternative is to set in the &smb.conf; entry for the share:
1234 <smbconfoption><name>force user</name><value>jack</value></smbconfoption>
1235 <smbconfoption><name>force group</name><value>engr</value></smbconfoption>
1244 <title>I have set force user but Samba still makes <emphasis>root</emphasis> the owner of all the files I touch!</title>
1246 When you have a user in <smbconfoption><name>admin users</name></smbconfoption>, samba will always do file operations for
1247 this user as <emphasis>root</emphasis>, even if <smbconfoption><name>force user</name></smbconfoption> has been set.
1252 <title>MS Word with Samba changes owner of file</title>
1255 <emphasis>Question:</emphasis> <quote>When userB saves a word document that is owned by userA the updated file is now owned by userB.
1256 Why is Samba doing this? How do I fix this?</quote>
1260 <emphasis>Answer:</emphasis> Word does the following when you modify/change a Word document: Word Creates a NEW document with
1261 a temporary name, Word then closes the old document and deletes it, Word then renames the new document to the original document name.
1262 There is NO mechanism by which Samba CAN IN ANY WAY know that the new document really should be owned by the owners
1263 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
1264 to tell, the file that gets created is a NEW file, not one that the application (Word) is updating.
1268 There is a work-around to solve the permissions problem. That work-around involves understanding how you can manage file
1269 system behaviour from within the &smb.conf; file, as well as understanding how Unix file systems work. Set on the directory
1270 in which you are changing word documents: <command>chmod g+s 'directory_name'</command> This ensures that all files will
1271 be created with the group that owns the directory. In smb.conf share declaration section set:
1276 <smbconfoption><name>force create mode</name><value>0660</value></smbconfoption>
1277 <smbconfoption><name>force directory mode</name><value>0770</value></smbconfoption>
1282 These two settings will ensure that all directories and files that get created in the share will be read/writable by the
1283 owner and group set on the directory itself.