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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 16. File, Directory, and Share Access Controls</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.0"><link rel="start" href="index.html" title="The Official Samba-3 HOWTO and Reference Guide"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="prev" href="rights.html" title="Chapter 15. User Rights and Privileges"><link rel="next" href="locking.html" title="Chapter 17. 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 16. File, Directory, and Share Access Controls</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="rights.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 16. 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><code class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></code></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><code class="email"><<a href="mailto:jra@samba.org">jra@samba.org</a>></code></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><code class="email"><<a href="mailto:jelmer@samba.org">jelmer@samba.org</a>></code></p></div></div></div></div><div><p class="pubdate">May 10, 2003</p></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="AccessControls.html#id373022">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="AccessControls.html#id373190">File System Access Controls</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id373202">MS Windows NTFS Comparison with UNIX File Systems</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id373499">Managing Directories</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id373620">File and Directory Access Control</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id374219">Share Definition Access Controls</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id374250">User- and Group-Based Controls</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id374546">File and Directory Permissions-Based Controls</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id374820">Miscellaneous Controls</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id375089">Access Controls on Shares</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id375225">Share Permissions Management</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id375547">MS Windows Access Control Lists and UNIX Interoperability</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id375553">Managing UNIX Permissions Using NT Security Dialogs</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375592">Viewing File Security on a Samba Share</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375657">Viewing File Ownership</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375783">Viewing File or Directory Permissions</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375970">Modifying File or Directory Permissions</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id376107">Interaction with the Standard Samba “<span class="quote">create mask</span>” Parameters</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id376409">Interaction with the Standard Samba File Attribute Mapping</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id376473">Windows NT/200X ACLs and POSIX ACLs Limitations</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id376834">Common Errors</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id376844">Users Cannot Write to a Public Share</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id377152">File Operations Done as <span class="emphasis"><em>root</em></span> with <span class="emphasis"><em>force user</em></span> Set</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id377189">MS Word with Samba Changes Owner of File</a></span></dt></dl></dd></dl></div><p>
<a class="indexterm" name="id372870"></a>
<a class="indexterm" name="id372877"></a>
<a class="indexterm" name="id372884"></a>
<a class="indexterm" name="id372891"></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>
<a class="indexterm" name="id372904"></a>
<a class="indexterm" name="id372911"></a>
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>
<a class="indexterm" name="id372923"></a>
<a class="indexterm" name="id372930"></a>
<a class="indexterm" name="id372937"></a>
<a class="indexterm" name="id372943"></a>
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="id372954"></a>
<a class="indexterm" name="id372961"></a>
<a class="indexterm" name="id372970"></a>
<a class="indexterm" name="id372977"></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>
<a class="indexterm" name="id372991"></a>
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>
<a class="indexterm" name="id373003"></a>
<a class="indexterm" name="id373010"></a>
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="id373022"></a>Features and Benefits</h2></div></div></div><p>
Samba offers much 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="id373041"></a>
<span class="emphasis"><em>UNIX File and Directory Permissions</em></span>
</p><p>
<a class="indexterm" name="id373057"></a>
<a class="indexterm" name="id373064"></a>
<a class="indexterm" name="id373070"></a>
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>
<a class="indexterm" name="id373094"></a>
In configuring share settings and controls in the <code class="filename">smb.conf</code> 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="id373122"></a>
</p><p>
<a class="indexterm" name="id373134"></a>
Just as it is possible in MS Windows NT to set ACLs on shares
themselves, so it is possible to do in Samba.
Few people make use of this facility, yet it remains one 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="id373149"></a>
<a class="indexterm" name="id373159"></a>
<span class="emphasis"><em>MS Windows ACLs through UNIX POSIX ACLs</em></span>
</p><p>
<a class="indexterm" name="id373175"></a>
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 support. 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="id373190"></a>File System Access Controls</h2></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="id373202"></a>MS Windows NTFS Comparison with UNIX File Systems</h3></div></div></div><p>
<a class="indexterm" name="id373210"></a>
<a class="indexterm" name="id373217"></a>
<a class="indexterm" name="id373223"></a>
<a class="indexterm" name="id373233"></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 overrides,
but for the greater part we stay within the bounds of default behavior. Those wishing to explore
the depths of control ability should review the <code class="filename">smb.conf</code> man page.
</p><p>The following compares file system features for UNIX with those of MS Windows NT/200x:
<a class="indexterm" name="id373261"></a>
</p><div class="variablelist"><dl><dt><span class="term">Name Space</span></dt><dd><p>
MS Windows NT4/200x/XP file 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 because 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="id373303"></a>
<a class="indexterm" name="id373310"></a>
MS Windows file names are generally uppercase 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 namespace 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. The Windows client will ask for a case-insensitive file
lookup, and that is the reason for which Samba must offer a consistent selection in the
event that the UNIX directory contains multiple files that would match a case insensitive
file listing.
</p></dd><dt><span class="term">Directory Separators</span></dt><dd><p>
<a class="indexterm" name="id373362"></a>
MS Windows and DOS use the backslash <code class="constant">\</code> as a directory delimiter, and UNIX uses
the forward-slash <code class="constant">/</code> 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="id373388"></a>
MS Windows products support a notion of drive letters, like <code class="literal">C:</code>, 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 <code class="constant">/</code> just as the root of a DOS drive is specified as
<code class="constant">C:\</code>.
</p></dd><dt><span class="term">File Naming Conventions</span></dt><dd><p>
<a class="indexterm" name="id373421"></a>
MS Windows generally never experiences file names that begin with a dot (<code class="constant">.</code>), while in UNIX these
are commonly found in a user's home directory. Files that begin with a dot (<code class="constant">.</code>) are typically
startup files for various UNIX applications, or they may be files that contain
startup configuration data.
</p></dd><dt><span class="term">Links and Short-Cuts</span></dt><dd><p>
<a class="indexterm" name="id373448"></a>
<a class="indexterm" name="id373457"></a>
<a class="indexterm" name="id373466"></a>
MS Windows make use of <span class="emphasis"><em>links and shortcuts</em></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="id373499"></a>Managing Directories</h3></div></div></div><p>
<a class="indexterm" name="id373507"></a>
<a class="indexterm" name="id373514"></a>
<a class="indexterm" name="id373520"></a>
There are three basic operations for managing directories: <code class="literal">create</code>, <code class="literal">delete</code>,
<code class="literal">rename</code>. <a href="AccessControls.html#TOSH-Accesstbl" title="Table 16.1. Managing Directories with UNIX and Windows">Managing Directories with UNIX and
Windows</a> compares the commands in Windows and UNIX that implement these operations.
</p><div class="table"><a name="TOSH-Accesstbl"></a><p class="title"><b>Table 16.1. Managing Directories with UNIX and Windows</b></p><div class="table-contents"><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></div><br class="table-break"></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id373620"></a>File and Directory Access Control</h3></div></div></div><p>
<a class="indexterm" name="id373628"></a>
<a class="indexterm" name="id373637"></a>
<a class="indexterm" name="id373644"></a>
The network administrator is strongly advised to read basic UNIX 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 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">
<code class="prompt">$ </code><strong class="userinput"><code>ls -la</code></strong>
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
<code class="prompt">$ </code>
</pre><p>
</p><p>
The columns represent (from left to right) permissions, number of hard links to file, owner, group, size
(bytes), access date, time of last modification, and file name.
</p><p>
An overview of the permissions field is shown in <a href="AccessControls.html#access1" title="Figure 16.1. Overview of UNIX permissions field.">Overview of UNIX permissions
field</a>.
</p><div class="figure"><a name="access1"></a><p class="title"><b>Figure 16.1. Overview of UNIX permissions field.</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/access1.png" width="216" alt="Overview of UNIX permissions field."></div></div></div><br class="figure-break"><p>
Any bit flag may be unset. An unset bit flag is the equivalent of "cannot" and is represented
as a “<span class="quote">-</span>” character (see <a href="AccessControls.html#access2" title="Example 16.1. Example File">???</a>)
<a class="indexterm" name="id373764"></a>
<a class="indexterm" name="id373770"></a>
<a class="indexterm" name="id373777"></a>
<a class="indexterm" name="id373784"></a>
<a class="indexterm" name="id373791"></a>
<a class="indexterm" name="id373798"></a>
</p><div class="example"><a name="access2"></a><p class="title"><b>Example 16.1. Example File</b></p><div class="example-contents"><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></div><br class="example-break"><p>
<a class="indexterm" name="id373825"></a>
<a class="indexterm" name="id373832"></a>
<a class="indexterm" name="id373839"></a>
<a class="indexterm" name="id373845"></a>
Additional possibilities in the [type] field are c = character device, b = block device, p = pipe device,
s = UNIX Domain Socket.
</p><p>
<a class="indexterm" name="id373857"></a>
<a class="indexterm" name="id373863"></a>
<a class="indexterm" name="id373870"></a>
<a class="indexterm" name="id373877"></a>
<a class="indexterm" name="id373884"></a>
The letters <code class="constant">rwxXst</code> 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 (SUID) or group ID (SGID) on execution (s), sticky (t).
</p><p>
<a class="indexterm" name="id373900"></a>
<a class="indexterm" name="id373907"></a>
<a class="indexterm" name="id373914"></a>
<a class="indexterm" name="id373920"></a>
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 <code class="filename">/tmp</code>, that are world-writable.
</p><p>
<a class="indexterm" name="id373939"></a>
<a class="indexterm" name="id373946"></a>
<a class="indexterm" name="id373953"></a>
<a class="indexterm" name="id373960"></a>
<a class="indexterm" name="id373969"></a>
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 <code class="constant">d-wx--x---</code>, the owner can read and create (write) files in it, but because
the (r) read 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 class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id373993"></a>Protecting Directories and Files from Deletion</h4></div></div></div><p>
<a class="indexterm" name="id374001"></a>
<a class="indexterm" name="id374008"></a>
<a class="indexterm" name="id374015"></a>
<a class="indexterm" name="id374022"></a>
People have asked on the Samba mailing list how is it possible to protect files or directories from deletion by users.
For example, Windows NT/2K/XP provides the capacity to set access controls on a directory into which people can
write files but not delete them. It is possible to set an ACL on a Windows file that permits the file to be written to
but not deleted. Such concepts are foreign to the UNIX operating system file space. Within the UNIX file system
anyone who has the ability to create a file can write to it. Anyone who has write permission on the
directory that contains a file and has write permission for it has the capability to delete it.
</p><p>
<a class="indexterm" name="id374038"></a>
<a class="indexterm" name="id374044"></a>
<a class="indexterm" name="id374051"></a>
For the record, in the UNIX environment the ability to delete a file is controlled by the permissions on
the directory that the file is in. In other words, a user can delete a file in a directory to which that
user has write access, even if that user does not own the file.
</p><p>
<a class="indexterm" name="id374064"></a>
<a class="indexterm" name="id374070"></a>
<a class="indexterm" name="id374077"></a>
<a class="indexterm" name="id374084"></a>
Of necessity, Samba is subject to the file system semantics of the host operating system. Samba is therefore
limited in the file system capabilities that can be made available through Windows ACLs, and therefore performs
a "best fit" translation to POSIX ACLs. Some UNIX file systems do, however support, a feature known
as extended attributes. Only the Windows concept of <span class="emphasis"><em>inheritance</em></span> is implemented by Samba through
the appropriate extended attribute.
</p><p>
<a class="indexterm" name="id374102"></a>
<a class="indexterm" name="id374108"></a>
<a class="indexterm" name="id374115"></a>
<a class="indexterm" name="id374122"></a>
The specific semantics of the extended attributes are not consistent across UNIX and UNIX-like systems such as Linux.
For example, it is possible on some implementations of the extended attributes to set a flag that prevents the directory
or file from being deleted. The extended attribute that may achieve this is called the <code class="constant">immutible</code> bit.
Unfortunately, the implementation of the immutible flag is NOT consistent with published documentation. For example, the
man page for the <code class="literal">chattr</code> on SUSE Linux 9.2 says:
</p><pre class="screen">
A file with the i attribute cannot be modified: it cannot be deleted
or renamed, no link can be created to this file and no data can be
written to the file. Only the superuser or a process possessing the
CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
</pre><p>
A simple test can be done to check if the immutible flag is supported on files in the file system of the Samba host
server.
</p><div class="procedure"><a name="id374153"></a><p class="title"><b>Procedure 16.1. Test for File Immutibility Support</b></p><ol type="1"><li><p>
Create a file called <code class="filename">filename</code>.
</p></li><li><p>
Login as the <code class="constant">root</code> user, then set the immutibile flag on a test file as follows:
</p><pre class="screen">
<code class="prompt">root# </code> chatter +i `filename'
</pre><p>
</p></li><li><p>
Login as the user who owns the file (not root) and attempt to remove the file as follows:
</p><pre class="screen">
mystic:/home/hannibal > rm filename
</pre><p>
It will not be possible to delete the file if the immutible flag is correctly honored.
</p></li></ol></div><p>
On operating systems and file system types that support the immutible bit, it is possible to create directories
that cannot be deleted. Check the man page on your particular host system to determine whether or not
immutable directories are writable. If they are not, then the entire directory and its contents will effectively
be protected from writing (file creation also) and deletion.
</p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id374219"></a>Share Definition Access Controls</h2></div></div></div><p>
<a class="indexterm" name="id374227"></a>
The following parameters in the <code class="filename">smb.conf</code> file sections define a share control or affect access controls.
Before using any of the following options, please refer to the man page for <code class="filename">smb.conf</code>.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id374250"></a>User- and Group-Based Controls</h3></div></div></div><p>
User- and group-based controls can prove quite useful. In some situations it is distinctly desirable to
force all file system operations as if a single user were doing so. The use of the
<a class="indexterm" name="id374260"></a>force user and <a class="indexterm" name="id374267"></a>force group behavior will achieve this.
In other situations it may be necessary to use 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="id374276"></a>valid users or the <a class="indexterm" name="id374283"></a>invalid users parameter may be useful.
</p><p>
As always, it is highly advisable to use the easiest 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 or she 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>
<a href="AccessControls.html#ugbc" title="Table 16.2. User- and Group-Based Controls">User and Group Based Controls</a> enumerates these controls.
</p><div class="table"><a name="ugbc"></a><p class="title"><b>Table 16.2. User- and Group-Based Controls</b></p><div class="table-contents"><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="id374360"></a>admin users</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 superuser (root).
Users 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="id374378"></a>force group</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="id374396"></a>force user</td><td align="justify"><p>
Specifies a UNIX username 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="id374415"></a>guest ok</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="id374433"></a>invalid users</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="id374450"></a>only user</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="id374468"></a>read list</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="id374486"></a>username</td><td align="justify"><p>
Refer to the <code class="filename">smb.conf</code> man page for more information; this is a complex and potentially misused parameter.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id374510"></a>valid users</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="id374527"></a>write list</td><td align="justify"><p>
List of users that are given read-write access to a service.
</p></td></tr></tbody></table></div></div><br class="table-break"></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id374546"></a>File and Directory Permissions-Based Controls</h3></div></div></div><p>
Directory permission-based controls, if misused, can result in considerable difficulty in diagnosing the causes of
misconfiguration. Use them sparingly and carefully. By gradually introducing each, one at a time, 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 <a href="AccessControls.html#fdpbc" title="Table 16.3. File and Directory Permission-Based Controls">File and Directory Permission Based Controls</a> for information
regarding the parameters that may be used to set file and directory permission-based access controls.
</p><div class="table"><a name="fdpbc"></a><p class="title"><b>Table 16.3. File and Directory Permission-Based Controls</b></p><div class="table-contents"><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="id374619"></a>create mask</td><td align="justify"><p>
Refer to the <code class="filename">smb.conf</code> man page.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id374642"></a>directory mask</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="id374659"></a>dos filemode</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="id374677"></a>force create mode</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="id374694"></a>force directory mode</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="id374712"></a>force directory security mode</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="id374730"></a>force security mode</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="id374748"></a>hide unreadable</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="id374765"></a>hide unwriteable files</td><td align="justify"><p>
Prevents clients from seeing the existence of files that cannot be written to. Unwritable directories are shown as usual.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id374783"></a>nt acl support</td><td align="justify"><p>
This parameter controls whether smbd will attempt to map UNIX permissions into Windows NT ACLs.
</p></td></tr><tr><td align="left"><a class="indexterm" name="id374801"></a>security mask</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><br class="table-break"></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id374820"></a>Miscellaneous Controls</h3></div></div></div><p>
The parameter documented in <a href="AccessControls.html#mcoc" title="Table 16.4. Other Controls">Other Controls</a> are often used by administrators
in ways that create inadvertent barriers to file access. Such are the consequences of not understanding the
full implications of <code class="filename">smb.conf</code> file settings.
</p><div class="table"><a name="mcoc"></a><p class="title"><b>Table 16.4. Other Controls</b></p><div class="table-contents"><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="id374896"></a>case sensitive,
<a class="indexterm" name="id374903"></a>default case,
<a class="indexterm" name="id374910"></a>short preserve case
</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="id374928"></a>csc policy</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="id374946"></a>dont descend</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="id374964"></a>dos filetime resolution</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="id374981"></a>dos filetimes</td><td align="justify"><p>
DOS and Windows allow users to change file timestamps 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="id375000"></a>fake oplocks</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="id375020"></a>hide dot files,
<a class="indexterm" name="id375027"></a>hide files,
<a class="indexterm" name="id375034"></a>veto files
</td><td align="justify"><p>
Note: MS Windows Explorer allows override of files marked as hidden so they will still be visible.
</p></td></tr><tr><td align="justify"><a class="indexterm" name="id375051"></a>read only</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="id375069"></a>veto files</td><td align="justify"><p>
List of files and directories that are neither visible nor accessible.
</p></td></tr></tbody></table></div></div><br class="table-break"></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id375089"></a>Access Controls on Shares</h2></div></div></div><p>
<a class="indexterm" name="id375097"></a>
<a class="indexterm" name="id375104"></a>
<a class="indexterm" name="id375110"></a>
<a class="indexterm" name="id375117"></a>
<a class="indexterm" name="id375124"></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 <code class="constant">Everyone - Full Control</code> (full control, change and read).
</p><p>
<a class="indexterm" name="id375144"></a>
<a class="indexterm" name="id375150"></a>
<a class="indexterm" name="id375157"></a>
At this time Samba does not provide a tool for configuring access control settings on the share
itself the only way to create those settings is to use either the NT4 Server Manager or the Windows 200x
Microsoft Management Console (MMC) for Computer Management. There are currently no plans to provide
this capability in the Samba command-line tool set.
</p><p>
<a class="indexterm" name="id375170"></a>
<a class="indexterm" name="id375177"></a>
<a class="indexterm" name="id375184"></a>
<a class="indexterm" name="id375190"></a>
Samba stores the per-share access control settings in a file called <code class="filename">share_info.tdb</code>.
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 <code class="filename">/usr/local/samba/var</code>. If the <code class="filename">tdbdump</code>
utility has been compiled and installed on your system, then you can examine the contents of this file
by executing <code class="literal">tdbdump share_info.tdb</code> in the directory containing the tdb files.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375225"></a>Share Permissions Management</h3></div></div></div><p>
The best tool for share permissions management is platform-dependent. Choose the best tool for your environment.
</p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375235"></a>Windows NT4 Workstation/Server</h4></div></div></div><p>
<a class="indexterm" name="id375243"></a>
<a class="indexterm" name="id375250"></a>
<a class="indexterm" name="id375257"></a>
<a class="indexterm" name="id375263"></a>
The tool you need to manage share permissions on a Samba server from a Windows NT4 Workstation or 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 the Microsoft
web site <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;173673" target="_top">support</a> section.
</p><div class="procedure"><a name="id375281"></a><p class="title"><b>Procedure 16.2. Instructions</b></p><ol type="1"><li><p>
Launch the <span class="application">NT4 Server Manager</span> and 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 and 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="id375334"></a>Windows 200x/XP</h4></div></div></div><p>
<a class="indexterm" name="id375341"></a>
<a class="indexterm" name="id375348"></a>
<a class="indexterm" name="id375355"></a>
<a class="indexterm" name="id375362"></a>
On <span class="application">MS Windows NT4/200x/XP</span> system, ACLs 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 "Everyone" full control on the share.
</p><p>
<a class="indexterm" name="id375392"></a>
<a class="indexterm" name="id375399"></a>
<a class="indexterm" name="id375405"></a>
MS Windows 200x and later versions come with a tool called the <span class="application">Computer Management</span>
snap-in for the MMC. This tool is located by clicking on <span class="guimenu">Control Panel ->
Administrative Tools -> Computer Management</span>.
</p><div class="procedure"><a name="id375427"></a><p class="title"><b>Procedure 16.3. 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>
<a class="indexterm" name="id375502"></a>
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 <code class="constant">Everyone</code> 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 <code class="constant">MaryK</code> who is
part of the group <code class="constant">Everyone</code> 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="id375547"></a>MS Windows Access Control Lists and UNIX Interoperability</h2></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375553"></a>Managing UNIX Permissions Using NT Security Dialogs</h3></div></div></div><p>
<a class="indexterm" name="id375561"></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="id375592"></a>Viewing File Security on a Samba Share</h3></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 <code class="constant">Properties</code> 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 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
nonfunctional with a Samba share at this time, because 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="id375657"></a>Viewing File Ownership</h3></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><pre class="screen">
<code class="constant">SERVER\user (Long name)</code>
</pre><p>
<em class="replaceable"><code>SERVER</code></em> is the NetBIOS name of the Samba server, <em class="replaceable"><code>user</code></em>
is the username of the UNIX user who owns the file, and <em class="replaceable"><code>(Long name)</code></em> 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="id375703"></a>nt acl support is set to <code class="constant">false</code>,
the file owner will be shown as the NT user <span class="emphasis"><em>Everyone</em></span>.
</p><p>
<a class="indexterm" name="id375721"></a>
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 as whom 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. Because clicking on this button causes
NT to attempt to change the ownership of a file to the current user logged into the NT client, this will
not work with Samba at this time.
</p><p>
<a class="indexterm" name="id375745"></a>
<a class="indexterm" name="id375752"></a>
<a class="indexterm" name="id375759"></a>
There is an NT <code class="literal">chown</code> 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 file system
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 downloadable from the main Samba FTP site.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375783"></a>Viewing File or Directory Permissions</h3></div></div></div><p>
The third button is the <span class="guibutton">Permissions</span> button. Clicking on it 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><code class="literal"><em class="replaceable"><code>SERVER</code></em>\
<em class="replaceable"><code>user</code></em>
<em class="replaceable"><code>(Long name)</code></em></code></p><p><em class="replaceable"><code>SERVER</code></em> is the NetBIOS name of the Samba server,
<em class="replaceable"><code>user</code></em> is the username of the UNIX user who owns the file, and
<em class="replaceable"><code>(Long name)</code></em> 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="id375832"></a>nt acl support is set to <code class="constant">false</code>,
the file owner will be shown as the NT user <code class="constant">Everyone</code>, and the permissions will be
shown as NT <span class="emphasis"><em>Full Control</em></span>.
</p><p>
The permissions field is displayed differently for files and directories. Both are discussed next.
</p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375856"></a>File Permissions</h4></div></div></div><p>
The standard UNIX user/group/world triplet and the corresponding <code class="constant">read, write,
execute</code> 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 <code class="constant">Everyone</code>, followed
by the list of permissions allowed for the 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 <code class="constant">read</code>,
<code class="constant">change</code>, or <code class="constant">full control</code>, usually the permissions will be prefixed
by the words <code class="constant">Special Access</code> 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="emphasis"><em>no permissions</em></span> to be seen and modified, Samba then overloads the NT
<code class="constant">Take Ownership</code> ACL attribute (which has no meaning in UNIX) and reports a component with
no permissions as having the NT <code class="literal">O</code> bit set. This was chosen, of course, to make it look
like a zero, meaning zero permissions. More details on the decision behind this action are given below.
</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375939"></a>Directory Permissions</h4></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 <code class="constant">RW</code>
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 <code class="constant">
inherited</code> permissions that any file created within this directory would inherit.
</p><p>
Samba synthesizes 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="id375970"></a>Modifying File or Directory Permissions</h3></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 also need to
be taken into account.
</p><p>
If the parameter <a class="indexterm" name="id375990"></a>nt acl support is set to <code class="constant">false</code>, 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 because 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="emphasis"><em>no
permissions</em></span> on the UNIX side. If you view the permissions again, the <span class="emphasis"><em>no
permissions</em></span> entry will appear as the NT <code class="literal">O</code> 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>
Because 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 <code class="constant">Delete Access</code> 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
<code class="constant">Take Ownership</code> permission (displayed as <code class="literal">O</code>) highlighted.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376107"></a>Interaction with the Standard Samba “<span class="quote">create mask</span>” Parameters</h3></div></div></div><p>There are four parameters that control interaction with the standard Samba <em class="parameter"><code>create mask</code></em> parameters:
</p><div class="itemizedlist"><ul type="disc"><li><p><a class="indexterm" name="id376129"></a>security mask</p></li><li><p><a class="indexterm" name="id376139"></a>force security mode</p></li><li><p><a class="indexterm" name="id376149"></a>directory security mask</p></li><li><p><a class="indexterm" name="id376160"></a>force directory security mode</p></li></ul></div><p>
</p><p>
When 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="id376180"></a>security mask parameter. Any bits that
were changed that are not set to <span class="emphasis"><em>1</em></span> in this parameter are left alone
in the file permissions.</p><p>
Essentially, zero bits in the <a class="indexterm" name="id376195"></a>security mask
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="id376210"></a>create mask 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="id376222"></a>force security mode parameter. Any bits
that were changed that correspond to bits set to <span class="emphasis"><em>1</em></span> in this parameter
are forced to be set.</p><p>
Essentially, bits set in the <em class="parameter"><code>force security mode</code></em> 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="emphasis"><em>on</em></span>.</p><p>
If not explicitly set, this parameter defaults to the same value
as the <a class="indexterm" name="id376251"></a>force create mode parameter.
To allow a user to modify all the user/group/world permissions on a file
with no restrictions, set this parameter to 000. The
<a class="indexterm" name="id376260"></a>security mask and <em class="parameter"><code>force
security mode</code></em> parameters are applied to the change
request in that order.</p><p>
For a directory, Samba performs the same operations as
described above for a file except it uses the parameter <em class="parameter"><code>
directory security mask</code></em> instead of <em class="parameter"><code>security
mask</code></em>, and <em class="parameter"><code>force directory security mode
</code></em> parameter instead of <em class="parameter"><code>force security mode
</code></em>.</p><p>
The <a class="indexterm" name="id376305"></a>directory security mask parameter
by default is set to the same value as the <em class="parameter"><code>directory mask
</code></em> parameter and the <em class="parameter"><code>force directory security
mode</code></em> parameter by default is set to the same value as
the <a class="indexterm" name="id376325"></a>force directory mode 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="emphasis"><em>on</em></span>,
then set the following parameters in the <code class="filename">smb.conf</code> file in that
share-specific section:
</p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id376358"></a><em class="parameter"><code>security mask = 0777</code></em></td></tr><tr><td><a class="indexterm" name="id376370"></a><em class="parameter"><code>force security mode = 0</code></em></td></tr><tr><td><a class="indexterm" name="id376383"></a><em class="parameter"><code>directory security mask = 0777</code></em></td></tr><tr><td><a class="indexterm" name="id376395"></a><em class="parameter"><code>force directory security mode = 0</code></em></td></tr></table></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376409"></a>Interaction with the Standard Samba File Attribute Mapping</h3></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 or herself 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 class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376473"></a>Windows NT/200X ACLs and POSIX ACLs Limitations</h3></div></div></div><p>
Windows administrators are familiar with simple ACL controls, and they typically
consider that UNIX user/group/other (ugo) permissions are inadequate and not
sufficiently fine-grained.
</p><p>
Competing SMB implementations differ in how they handle Windows ACLs. Samba handles
Windows ACLs from the perspective of UNIX file system administration and thus adopts
the limitations of POSIX ACLs. Therefore, where POSIX ACLs lack a capability of the
Windows NT/200X ACLs, the POSIX semantics and limitations are imposed on the Windows
administrator.
</p><p>
POSIX ACLs present an interesting challenge to the UNIX administrator and therefore
force a compromise to be applied to Windows ACLs administration. POSIX ACLs are not
covered by an official standard; rather, the latest standard is a draft standard
1003.1e revision 17. This is the POSIX document on which the Samba implementation has
been implemented.
</p><p>
UNIX vendors differ in the manner in which POSIX ACLs are implemented. There are a
number of Linux file systems that support ACLs. Samba has to provide a way to make
transparent all the differences between the various implementations of POSIX ACLs.
The pressure for ACLs support in Samba has noticeably increased the pressure to
standardize ACLs support in the UNIX world.
</p><p>
Samba has to deal with the complicated matter of handling the challenge of the Windows
ACL that implements <span class="emphasis"><em>inheritance</em></span>, a concept not anticipated by POSIX
ACLs as implemented in UNIX file systems. Samba provides support for <span class="emphasis"><em>masks</em></span>
that permit normal ugo and ACLs functionality to be overrided. This further complicates
the way in which Windows ACLs must be implemented.
</p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376517"></a>UNIX POSIX ACL Overview</h4></div></div></div><p>
In examining POSIX ACLs we must consider the manner in which they operate for
both files and directories. File ACLs have the following significance:
</p><pre class="screen">
# file: testfile <- the file name
# owner: jeremy <-- the file owner
# group: users <-- the POSIX group owner
user::rwx <-- perms for the file owner (user)
user:tpot:r-x <-- perms for the additional user `tpot'
group::r-- <-- perms for the file group owner (group)
group:engrs:r-- <-- perms for the additonal group `engineers'
mask:rwx <-- the mask that is `ANDed' with groups
other::--- <-- perms applied to everyone else (other)
</pre><p>
Directory ACLs have the following signficance:
</p><pre class="screen">
# file: testdir <-- the directory name
# owner: jeremy <-- the directory owner
# group: jeremy <-- the POSIX group owner
user::rwx <-- directory perms for owner (user)
group::rwx <-- directory perms for owning group (group)
mask::rwx <-- the mask that is `ANDed' with group perms
other:r-x <-- perms applied to everyone else (other)
default:user::rwx <-- inherited owner perms
default:user:tpot:rwx <-- inherited extra perms for user `tpot'
default:group::r-x <-- inherited group perms
default:mask:rwx <-- inherited default mask
default:other:--- <-- inherited permissions for everyone (other)
</pre><p>
</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376558"></a>Mapping of Windows File ACLs to UNIX POSIX ACLs</h4></div></div></div><p>
Microsoft Windows NT4/200X ACLs must of necessity be mapped to POSIX ACLs.
The mappings for file permissions are shown in <a href="AccessControls.html#fdsacls" title="Table 16.5. How Windows File ACLs Map to UNIX POSIX File ACLs">How
Windows File ACLs Map to UNIX POSIX File ACLs</a>.
The # character means this flag is set only when the Windows administrator
sets the <code class="constant">Full Control</code> flag on the file.
</p><div class="table"><a name="fdsacls"></a><p class="title"><b>Table 16.5. How Windows File ACLs Map to UNIX POSIX File ACLs</b></p><div class="table-contents"><table summary="How Windows File ACLs Map to UNIX POSIX File ACLs" border="1"><colgroup><col align="left"><col align="center"></colgroup><thead><tr><th align="left">Windows ACE</th><th align="center">File Attribute Flag</th></tr></thead><tbody><tr><td align="left"><p>Full Control</p></td><td align="center"><p>#</p></td></tr><tr><td align="left"><p>Traverse Folder/Execute File</p></td><td align="center"><p>x</p></td></tr><tr><td align="left"><p>List Folder/Read Data</p></td><td align="center"><p>r</p></td></tr><tr><td align="left"><p>Read Attributes</p></td><td align="center"><p>r</p></td></tr><tr><td align="left"><p>Read Extended Attribures</p></td><td align="center"><p>r</p></td></tr><tr><td align="left"><p>Create Files/Write Data</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Create Folders/Append Data</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Write Attributes</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Write Extended Attributes</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Delete Subfolders and Files</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Delete</p></td><td align="center"><p>#</p></td></tr><tr><td align="left"><p>Read Permissions</p></td><td align="center"><p>all</p></td></tr><tr><td align="left"><p>Change Permissions</p></td><td align="center"><p>#</p></td></tr><tr><td align="left"><p>Take Ownership</p></td><td align="center"><p>#</p></td></tr></tbody></table></div></div><br class="table-break"><p>
As can be seen from the mapping table, there is no one-to-one mapping capability, and therefore
Samba must make a logical mapping that will permit Windows to operate more-or-less the way
that is intended by the administrator.
</p><p>
In general the mapping of UNIX POSIX user/group/other permissions will be mapped to
Windows ACLs. This has precedence over the creation of POSIX ACLs. POSIX ACLs are necessary
to establish access controls for users and groups other than the user and group that
own the file or directory.
</p><p>
The UNIX administrator can set any directory permission from within the UNIX environment.
The Windows administrator is more restricted in that it is not possible from within
Windows Explorer to remove read permission for the file owner.
</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376814"></a>Mapping of Windows Directory ACLs to UNIX POSIX ACLs</h4></div></div></div><p>
Interesting things happen in the mapping of UNIX POSIX directory permissions and
UNIX POSIX ACLs to Windows ACEs (Access Control Entries, the discrete components of
an ACL) are mapped to Windows directory ACLs.
</p><p>
Directory permissions function in much the same way as shown for file permissions, but
there are some notable exceptions and a few peculiarities that the astute administrator
will want to take into account in the setting up of directory permissions.
</p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id376834"></a>Common Errors</h2></div></div></div><p>
File, directory, and share access problems are common topics on the mailing list. The following
are examples recently taken from the mailing list.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376844"></a>Users Cannot Write to a Public Share</h3></div></div></div><p>
The following complaint has frequently been voiced on the Samba mailing list:
“<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
<strong class="userinput"><code>chgrp -R users *</code></strong> and <strong class="userinput"><code>chown -R nobody *</code></strong> to allow
other users to change the file.
</span>”
</p><p>
Here is one way the problem can be solved:
</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 whatever public user and group you want
</p><pre class="screen">
<code class="prompt">$ </code>find `directory_name' -type d -exec chown user:group {}\;
<code class="prompt">$ </code>find `directory_name' -type d -exec chmod 2775 {}\;
<code class="prompt">$ </code>find `directory_name' -type f -exec chmod 0775 {}\;
<code class="prompt">$ </code>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 <code class="constant">SGID bit</code> on all directories. Read your
UNIX/Linux man page on what that does. This ensures that all files and directories
that are created in the directory tree will be owned by the current user and will
be owned by the group that owns the directory in which it is created.
</p></div></li><li><p>
Directory is <em class="replaceable"><code>/foodbar</code></em>:
</p><pre class="screen">
<code class="prompt">$ </code><strong class="userinput"><code>chown jack:engr /foodbar</code></strong>
</pre><p>
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This is the same as doing:</p><pre class="screen">
<code class="prompt">$ </code><strong class="userinput"><code>chown jack /foodbar</code></strong>
<code class="prompt">$ </code><strong class="userinput"><code>chgrp engr /foodbar</code></strong>
</pre></div></li><li><p>Now type:
</p><pre class="screen">
<code class="prompt">$ </code><strong class="userinput"><code>chmod 2775 /foodbar</code></strong>
<code class="prompt">$ </code><strong class="userinput"><code>ls -al /foodbar/..</code></strong>
</pre><p>
</p><p>You should see:
</p><pre class="screen">
drwxrwsr-x 2 jack engr 48 2003-02-04 09:55 foodbar
</pre><p>
</p></li><li><p>Now type:
</p><pre class="screen">
<code class="prompt">$ </code><strong class="userinput"><code>su - jill</code></strong>
<code class="prompt">$ </code><strong class="userinput"><code>cd /foodbar</code></strong>
<code class="prompt">$ </code><strong class="userinput"><code>touch Afile</code></strong>
<code class="prompt">$ </code><strong class="userinput"><code>ls -al</code></strong>
</pre><p>
</p><p>
You should see that the file <code class="filename">Afile</code> created by Jill will have ownership
and permissions of Jack, as follows:
</p><pre class="screen">
-rw-r--r-- 1 jill engr 0 2007-01-18 19:41 Afile
</pre><p>
</p></li><li><p>
If the user that must have write permission in the directory is not a member of the group
<span class="emphasis"><em>engr</em></span> set in the <code class="filename">smb.conf</code> entry for the share:
</p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id377136"></a><em class="parameter"><code>force group = engr</code></em></td></tr></table><p>
</p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id377152"></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><p>
When you have a user in <a class="indexterm" name="id377168"></a>admin users, Samba will always do file operations for
this user as <span class="emphasis"><em>root</em></span>, even if <a class="indexterm" name="id377179"></a>force user has been set.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id377189"></a>MS Word with Samba Changes Owner of File</h3></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, 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 workaround to solve the permissions problem. It involves understanding how you can manage file
system behavior from within the <code class="filename">smb.conf</code> file, as well as understanding how UNIX file systems work. Set on the directory
in which you are changing Word documents: <code class="literal">chmod g+s `directory_name'.</code> This ensures that all files will
be created with the group that owns the directory. In <code class="filename">smb.conf</code> share declaration section set:
</p><p>
</p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id377254"></a><em class="parameter"><code>force create mode = 0660</code></em></td></tr><tr><td><a class="indexterm" name="id377267"></a><em class="parameter"><code>force directory mode = 0770</code></em></td></tr></table><p>
</p><p>
These two settings will ensure that all directories and files that get created in the share will be readable/writable by the
owner and group set on the directory itself.
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