1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
|
<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 13. File, Directory and Share Access Controls</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.60.1"><link rel="home" href="index.html" title="SAMBA Project Documentation"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="previous" href="groupmapping.html" title="Chapter 12. Group Mapping MS Windows and UNIX"><link rel="next" href="locking.html" title="Chapter 14. File and Record Locking"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 13. File, Directory and Share Access Controls</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="groupmapping.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="locking.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="AccessControls"></a>Chapter 13. File, Directory and Share Access Controls</h2></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jeremy</span> <span class="surname">Allison</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jra@samba.org">jra@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jelmer</span> <span class="othername">R.</span> <span class="surname">Vernooij</span></h3><span class="contrib">drawing</span><div class="affiliation"><span class="orgname">The Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jelmer@samba.org">jelmer@samba.org</a>></tt></p></div></div></div></div><div><p class="pubdate">May 10, 2003</p></div></div><div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><a href="AccessControls.html#id2911341">Features and Benefits</a></dt><dt><a href="AccessControls.html#id2911525">File System Access Controls</a></dt><dd><dl><dt><a href="AccessControls.html#id2911543">MS Windows NTFS Comparison with UNIX File Systems</a></dt><dt><a href="AccessControls.html#id2911956">Managing Directories</a></dt><dt><a href="AccessControls.html#id2912050">File and Directory Access Control</a></dt></dl></dd><dt><a href="AccessControls.html#id2912290">Share Definition Access Controls</a></dt><dd><dl><dt><a href="AccessControls.html#id2912329">User and Group-Based Controls</a></dt><dt><a href="AccessControls.html#id2912779">File and Directory Permissions-Based Controls</a></dt><dt><a href="AccessControls.html#id2913187">Miscellaneous Controls</a></dt></dl></dd><dt><a href="AccessControls.html#id2913585">Access Controls on Shares</a></dt><dd><dl><dt><a href="AccessControls.html#id2913670">Share Permissions Management</a></dt></dl></dd><dt><a href="AccessControls.html#id2913978">MS Windows Access Control Lists and UNIX Interoperability</a></dt><dd><dl><dt><a href="AccessControls.html#id2913986">Managing UNIX Permissions Using NT Security Dialogs</a></dt><dt><a href="AccessControls.html#id2914042">Viewing File Security on a Samba Share</a></dt><dt><a href="AccessControls.html#id2914124">Viewing File Ownership</a></dt><dt><a href="AccessControls.html#id2914264">Viewing File or Directory Permissions</a></dt><dt><a href="AccessControls.html#id2914515">Modifying File or Directory Permissions</a></dt><dt><a href="AccessControls.html#id2914698">Interaction with the Standard Samba create mask Parameters</a></dt><dt><a href="AccessControls.html#id2915106">Interaction with the Standard Samba File Attribute Mapping</a></dt></dl></dd><dt><a href="AccessControls.html#id2915195">Common Errors</a></dt><dd><dl><dt><a href="AccessControls.html#id2915209">Users Cannot Write to a Public Share</a></dt><dt><a href="AccessControls.html#id2915635">File Operations Done as root with force user Set</a></dt><dt><a href="AccessControls.html#id2915690">MS Word with Samba Changes Owner of File</a></dt></dl></dd></dl></div><p>
<a class="indexterm" name="id2911255"></a>
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 how to
provide users with the access they need while protecting resources from unauthorized access.
</p><p>
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.
</p><p>
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 cannot completely hide, even
though it does try to bridge the chasm to a degree.
</p><p>
<a class="indexterm" name="id2911291"></a>
<a class="indexterm" name="id2911300"></a>
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
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.
</p><p>
The purpose of this chapter is to present each of the points of control that are possible with
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.
</p><p>
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 to 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.
</p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2911341"></a>Features and Benefits</h2></div></div><div></div></div><p>
Samba offers a lot of flexibility in file system access management. These are the key access control
facilities present in Samba today:
</p><div class="itemizedlist"><p class="title"><b>Samba Access Control Facilities</b></p><ul type="disc"><li><p>
<a class="indexterm" name="id2911368"></a>
<span class="emphasis"><em>UNIX File and Directory Permissions</em></span>
</p><p>
Samba honors 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.
</p></li><li><p>
<span class="emphasis"><em>Samba Share Definitions</em></span>
</p><p>
In configuring share settings and controls in the <tt class="filename">smb.conf</tt> file,
the network administrator can exercise overrides to native file
system permissions and behaviors. This can be handy and convenient
to effect behavior that is more like what MS Windows NT users expect
but it is seldom the <span class="emphasis"><em>best</em></span> way to achieve this.
The basic options and techniques are described herein.
</p></li><li><p>
<span class="emphasis"><em>Samba Share ACLs</em></span>
<a class="indexterm" name="id2911453"></a>
</p><p>
Just like it is possible in MS Windows NT to set ACLs on shares
themselves, so it is possible to do this in Samba.
Few people make use of this facility, yet it remains on of the
easiest ways to affect access controls (restrictions) and can often
do so with minimum invasiveness compared with other methods.
</p></li><li><p>
<a class="indexterm" name="id2911481"></a>
<a class="indexterm" name="id2911492"></a>
<span class="emphasis"><em>MS Windows ACLs through UNIX POSIX ACLs</em></span>
</p><p>
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
for POSIX ACLs. There are patches for the Linux kernel that also provide
this. 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.
</p></li></ul></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2911525"></a>File System Access Controls</h2></div></div><div></div></div><p>
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
environment. First we consider what the most significant differences are, then we look
at how Samba helps to bridge the differences.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2911543"></a>MS Windows NTFS Comparison with UNIX File Systems</h3></div></div><div></div></div><p>
<a class="indexterm" name="id2911555"></a>
<a class="indexterm" name="id2911563"></a>
<a class="indexterm" name="id2911571"></a>
<a class="indexterm" name="id2911582"></a>
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
behavior that differs from UNIX file system behavior then somehow Samba is responsible for emulating
that in a transparent and consistent manner.
</p><p>
It is good news that Samba does this to a large extent and on top of that provides a high degree
of optional configuration to override the default behavior. We look at some of these over-rides,
but for the greater part we will stay within the bounds of default behavior. Those wishing to explore
the depths of control ability should review the <tt class="filename">smb.conf</tt> man page.
</p><p>The following compares file system features for UNIX with those of Microsoft Windows NT/200x:
<a class="indexterm" name="id2911624"></a>
</p><div class="variablelist"><dl><dt><span class="term">Name Space</span></dt><dd><p>
MS Windows NT4/200x/XP files names may be up to 254 characters long, and 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.
</p><p>
What MS Windows calls a folder, UNIX calls a directory.
</p></dd><dt><span class="term">Case Sensitivity</span></dt><dd><p>
<a class="indexterm" name="id2911680"></a>
<a class="indexterm" name="id2911689"></a>
MS Windows file names are generally upper case if made up of 8.3 (8 character file name
and 3 character extension. File names that are longer than 8.3 are case preserving and case
insensitive.
</p><p>
UNIX file and directory names are case sensitive and case preserving. Samba implements the
MS Windows file name behavior, 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.
</p><p>
Consider the following. All are unique UNIX names but one single MS Windows file name:
</p><pre class="screen">
MYFILE.TXT
MyFile.txt
myfile.txt
</pre><p>
So clearly, in an MS Windows file name space these three files cannot co-exist, but in UNIX
they can.
</p><p>
So what should Samba do if all three are present? That which is lexically first will be
accessible to MS Windows users, the others are invisible and unaccessible any
other solution would be suicidal.
</p></dd><dt><span class="term">Directory Separators</span></dt><dd><p>
<a class="indexterm" name="id2911762"></a>
MS Windows and DOS uses the backslash <tt class="constant">\</tt> as a directory delimiter, and UNIX uses
the forward-slash <tt class="constant">/</tt> as its directory delimiter. This is handled transparently by Samba.
</p></dd><dt><span class="term">Drive Identification</span></dt><dd><p>
<a class="indexterm" name="id2911799"></a>
MS Windows products support a notion of drive letters, like <b class="command">C:</b> to represent
disk partitions. UNIX has no concept of separate identifiers for file partitions, each
such file system is mounted to become part of the overall directory tree.
The UNIX directory tree begins at <tt class="constant">/</tt> just like the root of a DOS drive is specified as
<tt class="constant">C:\</tt>.
</p></dd><dt><span class="term">File Naming Conventions</span></dt><dd><p>
<a class="indexterm" name="id2911846"></a>
MS Windows generally never experiences file names that begin with a dot (<tt class="constant">.</tt>) while in UNIX these
are commonly found in a user's home directory. Files that begin with a dot (<tt class="constant">.</tt>) are typically
either start-up files for various UNIX applications, or they may be files that contain
start-up configuration data.
</p></dd><dt><span class="term">Links and Short-Cuts</span></dt><dd><p>
<a class="indexterm" name="id2911886"></a>
<a class="indexterm" name="id2911897"></a>
<a class="indexterm" name="id2911908"></a>
MS Windows make use of “<span class="quote">links and short-cuts</span>” 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
links, but they are entirely different from what MS Windows users are used to.
</p><p>
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 “<span class="quote">soft links.</span>” 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.
</p></dd></dl></div><p>
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 and education.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2911956"></a>Managing Directories</h3></div></div><div></div></div><p>
There are three basic operations for managing directories: <b class="command">create, delete, rename</b>.
</p><div class="table"><a name="id2911975"></a><p class="title"><b>Table 13.1. Managing Directories with UNIX and Windows</b></p><table summary="Managing Directories with UNIX and Windows" border="1"><colgroup><col><col><col></colgroup><thead><tr><th align="center">Action</th><th align="center">MS Windows Command</th><th align="center">UNIX Command</th></tr></thead><tbody><tr><td align="center">create</td><td align="center">md folder</td><td align="center">mkdir folder</td></tr><tr><td align="center">delete</td><td align="center">rd folder</td><td align="center">rmdir folder</td></tr><tr><td align="center">rename</td><td align="center">rename oldname newname</td><td align="center">mv oldname newname</td></tr></tbody></table></div><p>
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2912050"></a>File and Directory Access Control</h3></div></div><div></div></div><p>
<a class="indexterm" name="id2912062"></a>
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
without having to resort to more complex facilities like POSIX Access Control Lists (ACLs) or Extended
Attributes (EAs).
</p><p>
UNIX/Linux file and directory access permissions involves setting three primary sets of data and one control set.
A UNIX file listing looks as follows:
</p><pre class="screen">
<tt class="prompt">$ </tt><b class="userinput"><tt>ls -la</tt></b>
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
<tt class="prompt">$ </tt>
</pre><p>
</p><p>
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.
</p><p>
An overview of the permissions field can be found in <link linkend="access1">.
</p><div class="figure"><a name="access1"></a><p class="title"><b>Figure 13.1. Overview of UNIX permissions field.</b></p><div class="mediaobject"><img src="projdoc/imagefiles/access1.png" width="270" alt="Overview of UNIX permissions field."></div></div><p>
Any bit flag may be unset. An unset bit flag is the equivalent of “<span class="quote">cannot</span>” and is represented as a “<span class="quote">-</span>” character.
</p><div class="example"><a name="id2912202"></a><p class="title"><b>Example 13.1. Example File</b></p><pre class="programlisting">
-rwxr-x--- Means: The owner (user) can read, write, execute
the group can read and execute
everyone else cannot do anything with it.
</pre></div><p>
</p><p>
Additional possibilities in the [type] field are: c = character device, b = block device, p = pipe device, s = UNIX Domain Socket.
</p><p>
The letters <tt class="constant">rwxXst</tt> 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),
sticky (t).
</p><p>
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.
Without the sticky bit, anyone able to write to the directory can delete or rename files. The sticky bit is commonly found on
directories, such as <tt class="filename">/tmp</tt>, that are world-writable.
</p><p>
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
group whose `set user or group' bit is set. This can be helpful in setting up directories for which it is desired that
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
to be exclusively owned by a user whose primary group is not the group that all such users belong to.
</p><p>
When a directory is set <tt class="constant">drw-r-----</tt> this means that the owner can read and create (write) files in it, but because
the (x) execute flags are not set, files cannot be listed (seen) in the directory by anyone. The group can read files in the
directory but cannot create new files. 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.
</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2912290"></a>Share Definition Access Controls</h2></div></div><div></div></div><p>
<a class="indexterm" name="id2912301"></a>
The following parameters in the <tt class="filename">smb.conf</tt> file sections define a share control or effect access controls.
Before using any of the following options, please refer to the man page for <tt class="filename">smb.conf</tt>.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2912329"></a>User and Group-Based Controls</h3></div></div><div></div></div><p>
User and group-based controls can prove quite useful. In some situations it is distinctly desirable to affect all
file system operations as if a single user were doing so. The use of the <a class="indexterm" name="id2912343"></a><i class="parameter"><tt>force user</tt></i> and
<a class="indexterm" name="id2912356"></a><i class="parameter"><tt>force group</tt></i> behavior will achieve this. In other situations it may be necessary to effect a
paranoia level of control to ensure that only particular authorized persons will be able to access a share or
its contents. Here the use of the <a class="indexterm" name="id2912374"></a><i class="parameter"><tt>valid users</tt></i> or the
<a class="indexterm" name="id2912388"></a><i class="parameter"><tt>invalid users</tt></i> may be most useful.
</p><p>
As always, it is highly advisable to use the least difficult to maintain and the least ambiguous method for
controlling access. Remember, when you leave the scene someone else will need to provide assistance and
if he finds too great a mess or does not understand what you have done, there is risk of
Samba being removed and an alternative solution being adopted.
</p><p>
<link linkend="ugbc"> enumerates these controls.
</p><div class="table"><a name="ugbc"></a><p class="title"><b>Table 13.2. User and Group Based Controls</b></p><table summary="User and Group Based Controls" border="1"><colgroup><col align="left"><col align="justify"></colgroup><thead><tr><th align="center">Control Parameter</th><th align="center">Description - Action - Notes</th></tr></thead><tbody><tr><td align="left"><a class="indexterm" name="id2912501"></a><i class="parameter"><tt>admin users</tt></i></td><td align="justify"><p>
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.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912530"></a><i class="parameter"><tt>force group</tt></i></td><td align="justify"><p>
Specifies a UNIX group name that will be assigned as the default primary group
for all users connecting to this service.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912558"></a><i class="parameter"><tt>force user</tt></i></td><td align="justify"><p>
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.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912586"></a><i class="parameter"><tt>guest ok</tt></i></td><td align="justify"><p>
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.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912614"></a><i class="parameter"><tt>invalid users</tt></i></td><td align="justify"><p>
List of users that should not be allowed to login to this service.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912640"></a><i class="parameter"><tt>only user</tt></i></td><td align="justify"><p>
Controls whether connections with usernames not in the user list will be allowed.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912666"></a><i class="parameter"><tt>read list</tt></i></td><td align="justify"><p>
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.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912694"></a><i class="parameter"><tt>username</tt></i></td><td align="justify"><p>
Refer to the <tt class="filename">smb.conf</tt> man page for more information -- this is a complex and potentially misused parameter.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912727"></a><i class="parameter"><tt>valid users</tt></i></td><td align="justify"><p>
List of users that should be allowed to login to this service.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912754"></a><i class="parameter"><tt>write list</tt></i></td><td align="justify"><p>
List of users that are given read-write access to a service.
</p></td></tr></tbody></table></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2912779"></a>File and Directory Permissions-Based Controls</h3></div></div><div></div></div><p>
The following file and directory permission-based controls, if misused, can result in considerable difficulty to
diagnose causes of misconfiguration. 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
reintroduce them in a controlled way.
</p><p>
Refer to <link linkend="fdpbc"> for information regarding the parameters that may be used to affect file and
directory permission-based access controls.
</p><div class="table"><a name="fdpbc"></a><p class="title"><b>Table 13.3. File and Directory Permission Based Controls</b></p><table summary="File and Directory Permission Based Controls" border="1"><colgroup><col align="left"><col align="justify"></colgroup><thead><tr><th align="center">Control Parameter</th><th align="center">Description - Action - Notes</th></tr></thead><tbody><tr><td align="left"><a class="indexterm" name="id2912884"></a><i class="parameter"><tt>create mask</tt></i></td><td align="justify"><p>
Refer to the <tt class="filename">smb.conf</tt> man page.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912916"></a><i class="parameter"><tt>directory mask</tt></i></td><td align="justify"><p>
The octal modes used when converting DOS modes to UNIX modes when creating UNIX directories.
See also: directory security mask.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912942"></a><i class="parameter"><tt>dos filemode</tt></i></td><td align="justify"><p>
Enabling this parameter allows a user who has write access to the file to modify the permissions on it.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912969"></a><i class="parameter"><tt>force create mode</tt></i></td><td align="justify"><p>
This parameter specifies a set of UNIX mode bit permissions that will always be set on a file created by Samba.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2912996"></a><i class="parameter"><tt>force directory mode</tt></i></td><td align="justify"><p>
This parameter specifies a set of UNIX mode bit permissions that will always be set on a directory created by Samba.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2913024"></a><i class="parameter"><tt>force directory security mode</tt></i></td><td align="justify"><p>
Controls UNIX permission bits modified when a Windows NT client is manipulating UNIX permissions on a directory.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2913052"></a><i class="parameter"><tt>force security mode</tt></i></td><td align="justify"><p>
Controls UNIX permission bits modified when a Windows NT client manipulates UNIX permissions.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2913079"></a><i class="parameter"><tt>hide unreadable</tt></i></td><td align="justify"><p>
Prevents clients from seeing the existence of files that cannot be read.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2913105"></a><i class="parameter"><tt>hide unwriteable files</tt></i></td><td align="justify"><p>
Prevents clients from seeing the existence of files that cannot be written to. Unwriteable directories are shown as usual.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2913133"></a><i class="parameter"><tt>nt acl support</tt></i></td><td align="justify"><p>
This parameter controls whether smbd will attempt to map UNIX permissions into Windows NT access control lists.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id2913160"></a><i class="parameter"><tt>security mask</tt></i></td><td align="justify"><p>
Controls UNIX permission bits modified when a Windows NT client is manipulating the UNIX permissions on a file.
</p></td></tr></tbody></table></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2913187"></a>Miscellaneous Controls</h3></div></div><div></div></div><p>
The following are documented because of the prevalence of administrators creating inadvertent barriers to file
access by not understanding the full implications of <tt class="filename">smb.conf</tt> file settings. See <link linkend="mcoc">.
</p><div class="table"><a name="mcoc"></a><p class="title"><b>Table 13.4. Other Controls</b></p><table summary="Other Controls" border="1"><colgroup><col align="justify"><col align="justify"></colgroup><thead><tr><th align="center">Control Parameter</th><th align="center">Description - Action - Notes</th></tr></thead><tbody><tr><td align="justify"><a class="indexterm" name="id2913282"></a><i class="parameter"><tt>case sensitive</tt></i>, <a class="indexterm" name="id2913296"></a><i class="parameter"><tt>default case</tt></i>, <a class="indexterm" name="id2913310"></a><i class="parameter"><tt>short preserve case</tt></i></td><td align="justify"><p>
This means that all file name lookup will be done in a case sensitive manner.
Files will be created with the precise file name Samba received from the MS Windows client.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913339"></a><i class="parameter"><tt>csc policy</tt></i></td><td align="justify"><p>
Client Side Caching Policy - parallels MS Windows client side file caching capabilities.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913365"></a><i class="parameter"><tt>dont descend</tt></i></td><td align="justify"><p>
Allows specifying a comma-delimited list of directories that the server should always show as empty.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913392"></a><i class="parameter"><tt>dos filetime resolution</tt></i></td><td align="justify"><p>
This option is mainly used as a compatibility option for Visual C++ when used against Samba shares.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913419"></a><i class="parameter"><tt>dos filetimes</tt></i></td><td align="justify"><p>
DOS and Windows allow users to change file time stamps if they can write to the file. POSIX semantics prevent this.
This option allows DOS and Windows behavior.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913448"></a><i class="parameter"><tt>fake oplocks</tt></i></td><td align="justify"><p>
Oplocks are the way that SMB clients get permission from a server to locally cache file operations. If a server grants an
oplock, the client is free to assume that it is the only one accessing the file and it will aggressively cache file data.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913477"></a><i class="parameter"><tt>hide dot files</tt></i>, <a class="indexterm" name="id2913492"></a><i class="parameter"><tt>hide files</tt></i>, <a class="indexterm" name="id2913505"></a><i class="parameter"><tt>veto files</tt></i></td><td align="justify"><p>
Note: MS Windows Explorer allows over-ride of files marked as hidden so they will still be visible.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913532"></a><i class="parameter"><tt>read only</tt></i></td><td align="justify"><p>
If this parameter is yes, then users of a service may not create or modify files in the service's directory.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id2913559"></a><i class="parameter"><tt>veto files</tt></i></td><td align="justify"><p>
List of files and directories that are neither visible nor accessible.
</p></td></tr></tbody></table></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2913585"></a>Access Controls on Shares</h2></div></div><div></div></div><p>
<a class="indexterm" name="id2913597"></a>
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 an effective way to limit who can
connect to a share. In the absence of specific restrictions the default setting is to allow
the global user <tt class="constant">Everyone - Full Control</tt> (full control, change and read).
</p><p>
At this time Samba does not provide a tool for configuring access control setting on the share
itself. Samba does have the capacity to store and act on access control settings, but the only
way to create those settings is to use either the NT4 Server Manager or the Windows 200x MMC for
Computer Management.
</p><p>
Samba stores the per share access control settings in a file called <tt class="filename">share_info.tdb</tt>.
The location of this file on your system will depend on how Samba was compiled. The default location
for Samba's tdb files is under <tt class="filename">/usr/local/samba/var</tt>. If the <tt class="filename">tdbdump</tt>
utility has been compiled and installed on your system, then you can examine the contents of this file
by executing: <b class="command">tdbdump share_info.tdb</b> in the directory containing the tdb files.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2913670"></a>Share Permissions Management</h3></div></div><div></div></div><p>
The best tool for the task is platform dependant. Choose the best tool for your environment.
</p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2913682"></a>Windows NT4 Workstation/Server</h4></div></div><div></div></div><p>
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.
</p><div class="procedure"><p class="title"><b>Procedure 13.1. Instructions</b></p><ol type="1"><li><p>
Launch the <span class="application">NT4 Server Manager</span>, click on the Samba server you want to administer. From the menu
select <span class="guimenu">Computer</span>, then click on <span class="guimenuitem">Shared Directories</span>.
</p></li><li><p>
Click on the share that you wish to manage, then click the <span class="guilabel">Properties</span> tab. then click
the <span class="guilabel">Permissions</span> tab. Now you can add or change access control settings as you wish.
</p></li></ol></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2913771"></a>Windows 200x/XP</h4></div></div><div></div></div><p>
On <span class="application">MS Windows NT4/200x/XP</span> system access control lists on the share itself are set using native
tools, usually from File Manager. For example, in Windows 200x, right click on the shared folder,
then select <span class="guimenuitem">Sharing</span>, then click on <span class="guilabel">Permissions</span>. The default
Windows NT4/200x permission allows “<span class="quote">Everyone</span>” full control on the share.
</p><p>
MS Windows 200x and later versions come with a tool called the <span class="application">Computer Management</span> snap-in for the
Microsoft Management Console (MMC). This tool is located by clicking on <span class="guimenu">Control Panel ->
Administrative Tools -> Computer Management</span>.
</p><div class="procedure"><p class="title"><b>Procedure 13.2. Instructions</b></p><ol type="1"><li><p>
After launching the MMC with the Computer Management snap-in, click the menu item <span class="guimenuitem">Action</span>,
and select <span class="guilabel">Connect to another computer</span>. If you are not logged onto a domain you will be prompted
to enter a domain login user identifier and a password. This will authenticate you to the domain.
If you are already logged in with administrative privilege, this step is not offered.
</p></li><li><p>
If the Samba server is not shown in the <span class="guilabel">Select Computer</span> box, type in the name of the target
Samba server in the field <span class="guilabel">Name:</span>. Now click the on <span class="guibutton">[+]</span> next to
<span class="guilabel">System Tools</span>, then on the <span class="guibutton">[+]</span> next to <span class="guilabel">Shared Folders</span> in the
left panel.
</p></li><li><p>
In the right panel, double-click on the share on which you wish to set access control permissions.
Then click the tab <span class="guilabel">Share Permissions</span>. It is now possible to add access control entities
to the shared folder. Remember to set what type of access (full control, change, read) you
wish to assign for each entry.
</p></li></ol></div><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>
Be careful. If you take away all permissions from the <tt class="constant">Everyone</tt> user without removing this user,
effectively no user will be able to access the share. This is a result of what is known as
ACL precedence. Everyone with <span class="emphasis"><em>no access</em></span> means that <tt class="constant">MaryK</tt> who is part of the group
<tt class="constant">Everyone</tt> will have no access even if she is given explicit full control access.
</p></div></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2913978"></a>MS Windows Access Control Lists and UNIX Interoperability</h2></div></div><div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2913986"></a>Managing UNIX Permissions Using NT Security Dialogs</h3></div></div><div></div></div><p>
<a class="indexterm" name="id2913998"></a>
Windows NT clients can use their native security settings dialog box to view and modify the
underlying UNIX permissions.
</p><p>
This ability is careful not to compromise the security of the UNIX host on which Samba is running, and
still obeys all the file permission rules that a Samba administrator can set.
</p><p>
Samba does not attempt to go beyond POSIX ACLs, so the various finer-grained access control
options provided in Windows are actually ignored.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
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.
</p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2914042"></a>Viewing File Security on a Samba Share</h3></div></div><div></div></div><p>
From an NT4/2000/XP client, right click on any file or directory in a Samba-mounted drive letter
or UNC path. When the menu pops up, click on the <span class="guilabel">Properties</span> entry at the bottom
of the menu. This brings up the file <tt class="constant">Properties</tt> dialog box. Click on the
<span class="guilabel">Security</span> tab and you will see three buttons: <span class="guibutton">Permissions</span>,
<span class="guibutton">Auditing</span>, and <span class="guibutton">Ownership</span>. The <span class="guibutton">Auditing</span>
button will cause either an error message <span class="errorname">`A requested privilege is not held by the client'</span>
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 <span class="guibutton">Add</span>
button, will not currently allow a list of users to be seen.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2914124"></a>Viewing File Ownership</h3></div></div><div></div></div><p>
Clicking on the <span class="guibutton">Ownership</span> button brings up a dialog box telling you who owns
the given file. The owner name will be displayed like this:
</p><p>
<b class="command">“<span class="quote">SERVER\user (Long name)</span>”</b>
</p><p>
<i class="replaceable"><tt>SERVER</tt></i> is the NetBIOS name of the Samba server, <i class="replaceable"><tt>user</tt></i>
is the user name of the UNIX user who owns the file, and <i class="replaceable"><tt>(Long name)</tt></i> is the
descriptive string identifying the user (normally found in the GECOS field of the UNIX password database).
Click on the <span class="guibutton">Close </span> button to remove this dialog.
</p><p>
If the parameter <a class="indexterm" name="id2914189"></a><i class="parameter"><tt>nt acl support</tt></i> is set to <tt class="constant">false</tt>,
the file owner will be shown as the NT user <span class="emphasis"><em>Everyone</em></span>.
</p><p>
The <span class="guibutton">Take Ownership</span> button will not allow you to change the ownership of this file to
yourself (clicking 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 <span class="emphasis"><em>root</em></span> 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 clienti, this will
not work with Samba at this time.</p><p>
There is an NT <b class="command">chown</b> 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 <span class="application">Seclib</span> NT security library written
by Jeremy Allison of the Samba Team, and is available from the main Samba FTP site.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2914264"></a>Viewing File or Directory Permissions</h3></div></div><div></div></div><p>
The third button is the <span class="guibutton">Permissions</span> 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 like this:
</p><p><b class="command"><i class="replaceable"><tt>SERVER</tt></i>\
<i class="replaceable"><tt>user</tt></i>
<i class="replaceable"><tt>(Long name)</tt></i></b></p><p>Where <i class="replaceable"><tt>SERVER</tt></i> is the NetBIOS name of the Samba server,
<i class="replaceable"><tt>user</tt></i> is the user name of the UNIX user who owns the file, and
<i class="replaceable"><tt>(Long name)</tt></i> is the descriptive string identifying the user (normally found in the
GECOS field of the UNIX password database).</p><p>
If the parameter <a class="indexterm" name="id2914328"></a><i class="parameter"><tt>nt acl support</tt></i> is set to <tt class="constant">false</tt>,
the file owner will be shown as the NT user <tt class="constant">Everyone</tt> and the permissions will be
shown as NT “<span class="quote">Full Control</span>”.
</p><p>
The permissions field is displayed differently for files and directories, so I'll describe the way file permissions
are displayed first.
</p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2914362"></a>File Permissions</h4></div></div><div></div></div><p>The standard UNIX user/group/world triplet and the corresponding <tt class="constant">read, write, execute</tt> permissions
triplets are mapped by Samba into a three element NT ACL with the “<span class="quote">r</span>”, “<span class="quote">w</span>” and “<span class="quote">x</span>” bits mapped into the corresponding
NT permissions. The UNIX world permissions are mapped into the global NT group <tt class="constant">Everyone</tt>, followed
by the list of permissions allowed for UNIX world. The UNIX owner and group permissions are displayed as an NT
<span class="guiicon">user</span> icon and an NT <span class="guiicon">local group</span> icon, respectively, followed by the list
of permissions allowed for the UNIX user and group.</p><p>Because many UNIX permission sets do not map into common NT names such as <tt class="constant">read</tt>,
<tt class="constant">change</tt> or <tt class="constant">full control</tt>, usually the permissions will be prefixed
by the words <tt class="constant">Special Access</tt> in the NT display list.</p><p>But what happens if the file has no permissions allowed for a particular UNIX user group or world component? In order
to allow “<span class="quote">no permissions</span>” to be seen and modified Samba then overloads the NT <tt class="constant">Take Ownership</tt> ACL attribute
(which has no meaning in UNIX) and reports a component with no permissions as having the NT <b class="command">O</b> bit set.
This was chosen, of course, to make it look like a zero, meaning zero permissions. More details on the decision behind this is
given below.</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2914471"></a>Directory Permissions</h4></div></div><div></div></div><p>Directories on an NT NTFS file system have two different sets of permissions. The first set is the ACL set on the
directory itself, which is usually displayed in the first set of parentheses in the normal <tt class="constant">RW</tt>
NT style. This first set of permissions is created by Samba in exactly the same way as normal file permissions are, described
above, and is displayed in the same way.</p><p>The second set of directory permissions has no real meaning in the UNIX permissions world and represents the <tt class="constant">
inherited</tt> permissions that any file created within this directory would inherit.</p><p>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.</p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2914515"></a>Modifying File or Directory Permissions</h3></div></div><div></div></div><p>Modifying file and directory permissions is as simple
as changing the displayed permissions in the dialog box, and
clicking on <span class="guibutton">OK</span>. 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.</p><p>If the parameter <a class="indexterm" name="id2914543"></a><i class="parameter"><tt>nt acl support</tt></i>
is set to <tt class="constant">false</tt>, any attempt to set
security permissions will fail with an <span class="errorname">`Access Denied'
</span> message.</p><p>The first thing to note is that the <span class="guibutton">Add</span>
button will not return a list of users in Samba (it will give
an error message saying <span class="errorname">`The remote procedure call failed
and did not execute'</span>). This means that you can only
manipulate the current user/group/world permissions listed in
the dialog box. This actually works quite well as these are the
only permissions that UNIX actually has.</p><p>If a permission triplet (either user, group, or world)
is removed from the list of permissions in the NT dialog box,
then when the <span class="guibutton">OK</span> button is pressed it will
be applied as “<span class="quote">no permissions</span>” on the UNIX side. If you then
view the permissions again, the “<span class="quote">no permissions</span>” entry will appear
as the NT <b class="command">O</b> flag, as described above. This
allows you to add permissions back to a file or directory once
you have removed them from a triplet component.</p><p>As UNIX supports only the “<span class="quote">r</span>”, “<span class="quote">w</span>” and “<span class="quote">x</span>” bits of
an NT ACL, if other NT security attributes such as <tt class="constant">Delete Access</tt> are
selected they will be ignored when applied on the Samba server.</p><p>When setting permissions on a directory, the second
set of permissions (in the second set of parentheses) is
by default applied to all files within that directory. If this
is not what you want, you must uncheck the <span class="guilabel">Replace
permissions on existing files</span> checkbox in the NT
dialog before clicking on <span class="guibutton">OK</span>.</p><p>If you wish to remove all permissions from a
user/group/world component, you may either highlight the
component and click on the <span class="guibutton">Remove</span> button,
or set the component to only have the special <tt class="constant">Take
Ownership</tt> permission (displayed as <b class="command">O
</b>) highlighted.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2914698"></a>Interaction with the Standard Samba “<span class="quote">create mask</span>” Parameters</h3></div></div><div></div></div><p>There are four parameters that control interaction with the standard Samba <i class="parameter"><tt>create mask</tt></i> parameters.
These are:
</p><div class="itemizedlist"><ul type="disc"><li><a class="indexterm" name="id2914726"></a><i class="parameter"><tt>security mask</tt></i></li><li><a class="indexterm" name="id2914742"></a><i class="parameter"><tt>force security mode</tt></i></li><li><a class="indexterm" name="id2914757"></a><i class="parameter"><tt>directory security mask</tt></i></li><li><a class="indexterm" name="id2914773"></a><i class="parameter"><tt>force directory security mode</tt></i></li></ul></div><p>
</p><p>Once a user clicks on <span class="guibutton">OK</span> to apply the
permissions, Samba maps the given permissions into a user/group/world
r/w/x triplet set, and then checks the changed permissions for a
file against the bits set in the
<a class="indexterm" name="id2914803"></a><i class="parameter"><tt>security mask</tt></i> parameter. Any bits that
were changed that are not set to “<span class="quote">1</span>” in this parameter are left alone
in the file permissions.</p><p>Essentially, zero bits in the <a class="indexterm" name="id2914828"></a><i class="parameter"><tt>security mask</tt></i>
may be treated as a set of bits the user is <span class="emphasis"><em>not</em></span>
allowed to change, and one bits are those the user is allowed to change.
</p><p>If not explicitly set, this parameter defaults to the same value as
the <a class="indexterm" name="id2914853"></a><i class="parameter"><tt>create mask</tt></i> parameter. To allow a user to modify all the
user/group/world permissions on a file, set this parameter to 0777.
</p><p>Next Samba checks the changed permissions for a file against the bits set in the
<a class="indexterm" name="id2914875"></a><i class="parameter"><tt>force security mode</tt></i> parameter. Any bits
that were changed that correspond to bits set to “<span class="quote">1</span>” in this parameter
are forced to be set.</p><p>Essentially, bits set in the <i class="parameter"><tt>force security mode</tt></i> parameter
may be treated as a set of bits that, when modifying security on a file, the user has always set to be “<span class="quote">on</span>”.</p><p>If not explicitly set, this parameter defaults to the same value
as the <a class="indexterm" name="id2914918"></a><i class="parameter"><tt>force create mode</tt></i> 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
<a class="indexterm" name="id2914935"></a><i class="parameter"><tt>security mask</tt></i> and <i class="parameter"><tt>force
security mode</tt></i> parameters are applied to the change
request in that order.</p><p>For a directory, Samba will perform the same operations as
described above for a file except it uses the parameter <i class="parameter"><tt>
directory security mask</tt></i> instead of <i class="parameter"><tt>security
mask</tt></i>, and <i class="parameter"><tt>force directory security mode
</tt></i> parameter instead of <i class="parameter"><tt>force security mode
</tt></i>.</p><p>The <a class="indexterm" name="id2914996"></a><i class="parameter"><tt>directory security mask</tt></i> parameter
by default is set to the same value as the <i class="parameter"><tt>directory mask
</tt></i> parameter and the <i class="parameter"><tt>force directory security
mode</tt></i> parameter by default is set to the same value as
the <a class="indexterm" name="id2915027"></a><i class="parameter"><tt>force directory mode</tt></i> parameter.
In this way Samba enforces the permission restrictions that
an administrator can set on a Samba share, while still allowing users
to modify the permission bits within that restriction.</p><p>If you want to set up a share that allows users full control
in modifying the permission bits on their files and directories and
does not force any particular bits to be set “<span class="quote">on</span>”, then set the following
parameters in the <tt class="filename">smb.conf</tt> file in that share-specific section:
</p><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>security mask = 0777</tt></i></td></tr><tr><td><i class="parameter"><tt>force security mode = 0</tt></i></td></tr><tr><td><i class="parameter"><tt>directory security mask = 0777</tt></i></td></tr><tr><td><i class="parameter"><tt>force directory security mode = 0</tt></i></td></tr></table></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2915106"></a>Interaction with the Standard Samba File Attribute Mapping</h3></div></div><div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Samba maps some of the DOS attribute bits (such as “<span class="quote">read
only</span>”) 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.
</p></div><p>If a file has no UNIX read access for the owner, it will show up
as “<span class="quote">read only</span>” in the standard file attributes tabbed dialog.
Unfortunately, this dialog is the same one that contains the security information
in another tab.</p><p>What this can mean is that if the owner changes the permissions
to allow himself read access using the security dialog, clicks on
<span class="guibutton">OK</span> to get back to the standard attributes tab
dialog, and clicks on <span class="guibutton">OK</span> on that dialog, then
NT will set the file permissions back to read-only (as that is what
the attributes still say in the dialog). This means that after setting
permissions and clicking on <span class="guibutton">OK</span> to get back to the
attributes dialog, you should always press <span class="guibutton">Cancel</span>
rather than <span class="guibutton">OK</span> to ensure that your changes
are not overridden.</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2915195"></a>Common Errors</h2></div></div><div></div></div><p>
File, directory and share access problems are common on the mailing list. The following
are examples taken from the mailing list in recent times.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2915209"></a>Users Cannot Write to a Public Share</h3></div></div><div></div></div><p>
“<span class="quote">
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
root can change the file, no one else can. We need to constantly go to the server to
<b class="userinput"><tt>chgrp -R users *</tt></b> and <b class="userinput"><tt>chown -R nobody *</tt></b> to allow others users to change the file.
</span>”
</p><p>
There are many ways to solve this problem and here are a few hints:
</p><div class="procedure"><ol type="1"><li><p>
Go to the top of the directory that is shared.
</p></li><li><p>
Set the ownership to what ever public owner and group you want
</p><pre class="screen">
<tt class="prompt">$ </tt>find 'directory_name' -type d -exec chown user.group {}\;
<tt class="prompt">$ </tt>find 'directory_name' -type d -exec chmod 6775 'directory_name'
<tt class="prompt">$ </tt>find 'directory_name' -type f -exec chmod 0775 {} \;
<tt class="prompt">$ </tt>find 'directory_name' -type f -exec chown user.group {}\;
</pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
The above will set the <tt class="constant">sticky bit</tt> on all directories. Read your
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.
</p></div></li><li><p>
Directory is: <i class="replaceable"><tt>/foodbar</tt></i>
</p><pre class="screen">
<tt class="prompt">$ </tt><b class="userinput"><tt>chown jack.engr /foodbar</tt></b>
</pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
</p><p>This is the same as doing:</p><p>
</p><pre class="screen">
<tt class="prompt">$ </tt><b class="userinput"><tt>chown jack /foodbar</tt></b>
<tt class="prompt">$ </tt><b class="userinput"><tt>chgrp engr /foodbar</tt></b>
</pre><p>
</p></div></li><li><p>Now type:
</p><pre class="screen">
<tt class="prompt">$ </tt><b class="userinput"><tt>chmod 6775 /foodbar</tt></b>
<tt class="prompt">$ </tt><b class="userinput"><tt>ls -al /foodbar/..</tt></b>
</pre><p>
</p><p>You should see:
</p><pre class="screen">
drwsrwsr-x 2 jack engr 48 2003-02-04 09:55 foodbar
</pre><p>
</p></li><li><p>Now type:
</p><pre class="screen">
<tt class="prompt">$ </tt><b class="userinput"><tt>su - jill</tt></b>
<tt class="prompt">$ </tt><b class="userinput"><tt>cd /foodbar</tt></b>
<tt class="prompt">$ </tt><b class="userinput"><tt>touch Afile</tt></b>
<tt class="prompt">$ </tt><b class="userinput"><tt>ls -al</tt></b>
</pre><p>
</p><p>
You should see that the file <tt class="filename">Afile</tt> created by Jill will have ownership
and permissions of Jack, as follows:
</p><pre class="screen">
-rw-r--r-- 1 jack engr 0 2003-02-04 09:57 Afile
</pre><p>
</p></li><li><p>
Now in your <tt class="filename">smb.conf</tt> for the share add:
</p><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>force create mode = 0775</tt></i></td></tr><tr><td><i class="parameter"><tt>force direcrtory mode = 6775</tt></i></td></tr></table><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
These procedures are needed only if your users are not members of the group
you have used. That is if within the OS do not have write permission on the directory.
</p></div><p>
An alternative is to set in the <tt class="filename">smb.conf</tt> entry for the share:
</p><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>force user = jack</tt></i></td></tr><tr><td><i class="parameter"><tt>force group = engr</tt></i></td></tr></table><p>
</p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2915635"></a>File Operations Done as <span class="emphasis"><em>root</em></span> with <span class="emphasis"><em>force user</em></span> Set</h3></div></div><div></div></div><p>
When you have a user in <a class="indexterm" name="id2915654"></a><i class="parameter"><tt>admin users</tt></i>, Samba will always do file operations for
this user as <span class="emphasis"><em>root</em></span>, even if <a class="indexterm" name="id2915674"></a><i class="parameter"><tt>force user</tt></i> has been set.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2915690"></a>MS Word with Samba Changes Owner of File</h3></div></div><div></div></div><p>
<span class="emphasis"><em>Question:</em></span> “<span class="quote">When user B saves a word document that is owned by user A the updated file is now owned by user B.
Why is Samba doing this? How do I fix this?</span>”
</p><p>
<span class="emphasis"><em>Answer:</em></span> Word does the following when you modify/change a Word document: MS 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.
</p><p>
There is a work-around to solve the permissions problem. That work-around involves understanding how you can manage file
system behavior from within the <tt class="filename">smb.conf</tt> file, as well as understanding how UNIX file systems work. Set on the directory
in which you are changing Word documents: <b class="command">chmod g+s `directory_name'</b> This ensures that all files will
be created with the group that owns the directory. In <tt class="filename">smb.conf</tt> share declaration section set:
</p><p>
</p><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>force create mode = 0660</tt></i></td></tr><tr><td><i class="parameter"><tt>force directory mode = 0770</tt></i></td></tr></table><p>
</p><p>
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.
</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="groupmapping.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="locking.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 12. Group Mapping MS Windows and UNIX </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 14. File and Record Locking</td></tr></table></div></body></html>
|
