1 <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 16. File and Record Locking</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.68.1"><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="AccessControls.html" title="Chapter 15. File, Directory, and Share Access Controls"><link rel="next" href="securing-samba.html" title="Chapter 17. Securing Samba"></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 and Record Locking</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="AccessControls.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="securing-samba.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="locking"></a>Chapter 16. File and Record Locking</h2></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><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><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">Eric</span> <span class="surname">Roseme</span></h3><div class="affiliation"><span class="orgname">HP Oplocks Usage Recommendations Whitepaper<br></span><div class="address"><p><code class="email"><<a href="mailto:eric.roseme@hp.com">eric.roseme@hp.com</a>></code></p></div></div></div></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="locking.html#id2583141">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="locking.html#id2583238">Discussion</a></span></dt><dd><dl><dt><span class="sect2"><a href="locking.html#id2583486">Opportunistic Locking Overview</a></span></dt></dl></dd><dt><span class="sect1"><a href="locking.html#id2584434">Samba Oplocks Control</a></span></dt><dd><dl><dt><span class="sect2"><a href="locking.html#id2584536">Example Configuration</a></span></dt></dl></dd><dt><span class="sect1"><a href="locking.html#id2584955">MS Windows Oplocks and Caching Controls</a></span></dt><dd><dl><dt><span class="sect2"><a href="locking.html#id2585142">Workstation Service Entries</a></span></dt><dt><span class="sect2"><a href="locking.html#id2585164">Server Service Entries</a></span></dt></dl></dd><dt><span class="sect1"><a href="locking.html#id2585230">Persistent Data Corruption</a></span></dt><dt><span class="sect1"><a href="locking.html#id2585255">Common Errors</a></span></dt><dd><dl><dt><span class="sect2"><a href="locking.html#id2585322">locking.tdb Error Messages</a></span></dt><dt><span class="sect2"><a href="locking.html#id2585353">Problems Saving Files in MS Office on Windows XP</a></span></dt><dt><span class="sect2"><a href="locking.html#id2585378">Long Delays Deleting Files over Network with XP SP1</a></span></dt></dl></dd><dt><span class="sect1"><a href="locking.html#id2585409">Additional Reading</a></span></dt></dl></div><p>
2 <a class="indexterm" name="id2583131"></a>
3 One area that causes trouble for many network administrators is locking.
4 The extent of the problem is readily evident from searches over the Internet.
5 </p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2583141"></a>Features and Benefits</h2></div></div></div><p>
6 <a class="indexterm" name="id2583149"></a>
7 Samba provides all the same locking semantics that MS Windows clients expect
8 and that MS Windows NT4/200x servers also provide.
10 <a class="indexterm" name="id2583162"></a>
11 The term <span class="emphasis"><em>locking</em></span> has exceptionally broad meaning and covers
12 a range of functions that are all categorized under this one term.
14 <a class="indexterm" name="id2583177"></a>
15 <a class="indexterm" name="id2583184"></a>
16 <a class="indexterm" name="id2583191"></a>
17 Opportunistic locking is a desirable feature when it can enhance the
18 perceived performance of applications on a networked client. However, the
19 opportunistic locking protocol is not robust and therefore can
20 encounter problems when invoked beyond a simplistic configuration or
21 on extended slow or faulty networks. In these cases, operating
22 system management of opportunistic locking and/or recovering from
23 repetitive errors can offset the perceived performance advantage that
24 it is intended to provide.
26 <a class="indexterm" name="id2583210"></a>
27 The MS Windows network administrator needs to be aware that file and record
28 locking semantics (behavior) can be controlled either in Samba or by way of registry
29 settings on the MS Windows client.
30 </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
31 <a class="indexterm" name="id2583226"></a>
32 Sometimes it is necessary to disable locking control settings on the Samba
33 server as well as on each MS Windows client!
34 </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2583238"></a>Discussion</h2></div></div></div><p>
35 <a class="indexterm" name="id2583246"></a>
36 <a class="indexterm" name="id2583253"></a>
37 There are two types of locking that need to be performed by an SMB server.
38 The first is <span class="emphasis"><em>record locking</em></span> that allows a client to lock
39 a range of bytes in an open file. The second is the <span class="emphasis"><em>deny modes</em></span>
40 that are specified when a file is open.
42 <a class="indexterm" name="id2583274"></a>
43 <a class="indexterm" name="id2583280"></a>
44 <a class="indexterm" name="id2583287"></a>
45 <a class="indexterm" name="id2583294"></a>
46 <a class="indexterm" name="id2583301"></a>
47 Record locking semantics under UNIX are very different from record locking under
48 Windows. Versions of Samba before 2.2 have tried to use the native fcntl() UNIX
49 system call to implement proper record locking between different Samba clients.
50 This cannot be fully correct for several reasons. The simplest is
51 that a Windows client is allowed to lock a byte range up to 2^32 or 2^64,
52 depending on the client OS. The UNIX locking only supports byte ranges up to 2^31.
53 So it is not possible to correctly satisfy a lock request above 2^31. There are
54 many more differences, too many to be listed here.
56 <a class="indexterm" name="id2583321"></a>
57 <a class="indexterm" name="id2583328"></a>
58 Samba 2.2 and above implement record locking completely independently of the
59 underlying UNIX system. If a byte-range lock that the client requests happens
60 to fall into the range of 0 to 2^31, Samba hands this request down to the UNIX system.
61 No other locks can be seen by UNIX, anyway.
63 <a class="indexterm" name="id2583343"></a>
64 <a class="indexterm" name="id2583350"></a>
65 Strictly speaking, an SMB server should check for locks before every read and write call on
66 a file. Unfortunately, with the way fcntl() works, this can be slow and may overstress
67 the <span><strong class="command">rpc.lockd</strong></span>. This is almost always unnecessary because clients are
68 independently supposed to make locking calls before reads and writes if locking is
69 important to them. By default, Samba only makes locking calls when explicitly asked
70 to by a client, but if you set <a class="indexterm" name="id2583370"></a>strict locking = yes, it
71 will make lock checking calls on <span class="emphasis"><em>every</em></span> read and write call.
73 <a class="indexterm" name="id2583386"></a>
74 You can also disable byte-range locking completely by using
75 <a class="indexterm" name="id2583394"></a>locking = no.
76 This is useful for those shares that do not support locking or do not need it
77 (such as CD-ROMs). In this case, Samba fakes the return codes of locking calls to
78 tell clients that everything is okay.
80 <a class="indexterm" name="id2583407"></a>
81 <a class="indexterm" name="id2583414"></a>
82 <a class="indexterm" name="id2583421"></a>
83 <a class="indexterm" name="id2583428"></a>
84 <a class="indexterm" name="id2583435"></a>
85 <a class="indexterm" name="id2583441"></a>
86 <a class="indexterm" name="id2583448"></a>
87 The second class of locking is the <span class="emphasis"><em>deny modes</em></span>. These
88 are set by an application when it opens a file to determine what types of
89 access should be allowed simultaneously with its open. A client may ask for
90 <code class="constant">DENY_NONE</code>, <code class="constant">DENY_READ</code>,
91 <code class="constant">DENY_WRITE</code>, or <code class="constant">DENY_ALL</code>. There are also special compatibility
92 modes called <code class="constant">DENY_FCB</code> and <code class="constant">DENY_DOS</code>.
93 </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2583486"></a>Opportunistic Locking Overview</h3></div></div></div><p>
94 <a class="indexterm" name="id2583494"></a>
95 <a class="indexterm" name="id2583501"></a>
96 <a class="indexterm" name="id2583508"></a>
97 Opportunistic locking (oplocks) is invoked by the Windows file system
98 (as opposed to an API) via registry entries (on the server and the client)
99 for the purpose of enhancing network performance when accessing a file
100 residing on a server. Performance is enhanced by caching the file
101 locally on the client that allows the following:
102 </p><div class="variablelist"><dl><dt><span class="term">Read-ahead:</span></dt><dd><p>
103 <a class="indexterm" name="id2583531"></a>
104 The client reads the local copy of the file, eliminating network latency.
105 </p></dd><dt><span class="term">Write caching:</span></dt><dd><p>
106 <a class="indexterm" name="id2583549"></a>
107 The client writes to the local copy of the file, eliminating network latency.
108 </p></dd><dt><span class="term">Lock caching:</span></dt><dd><p>
109 <a class="indexterm" name="id2583568"></a>
110 The client caches application locks locally, eliminating network latency.
111 </p></dd></dl></div><p>
112 <a class="indexterm" name="id2583581"></a>
113 <a class="indexterm" name="id2583588"></a>
114 <a class="indexterm" name="id2583595"></a>
115 The performance enhancement of oplocks is due to the opportunity of
116 exclusive access to the file even if it is opened with deny-none
117 because Windows monitors the file's status for concurrent access from
119 </p><div class="variablelist"><p class="title"><b>Windows Defines Four Kinds of Oplocks:</b></p><dl><dt><span class="term">Level1 Oplock</span></dt><dd><p>
120 <a class="indexterm" name="id2583627"></a>
121 <a class="indexterm" name="id2583633"></a>
122 <a class="indexterm" name="id2583640"></a>
123 <a class="indexterm" name="id2583647"></a>
124 The redirector sees that the file was opened with deny
125 none (allowing concurrent access), verifies that no
126 other process is accessing the file, checks that
127 oplocks are enabled, then grants deny-all/read-write/exclusive
128 access to the file. The client now performs
129 operations on the cached local file.
131 <a class="indexterm" name="id2583662"></a>
132 <a class="indexterm" name="id2583669"></a>
133 <a class="indexterm" name="id2583676"></a>
134 <a class="indexterm" name="id2583683"></a>
135 If a second process attempts to open the file, the open
136 is deferred while the redirector "breaks" the original
137 oplock. The oplock break signals the caching client to
138 write the local file back to the server, flush the
139 local locks, and discard read-ahead data. The break is
140 then complete, the deferred open is granted, and the
141 multiple processes can enjoy concurrent file access as
142 dictated by mandatory or byte-range locking options.
143 However, if the original opening process opened the
144 file with a share mode other than deny-none, then the
145 second process is granted limited or no access, despite
147 </p></dd><dt><span class="term">Level2 Oplock</span></dt><dd><p>
148 <a class="indexterm" name="id2583711"></a>
149 <a class="indexterm" name="id2583718"></a>
150 <a class="indexterm" name="id2583725"></a>
151 Performs like a Level1 oplock, except caching is only
152 operative for reads. All other operations are performed
153 on the server disk copy of the file.
154 </p></dd><dt><span class="term">Filter Oplock</span></dt><dd><p>
155 <a class="indexterm" name="id2583745"></a>
156 Does not allow write or delete file access.
157 </p></dd><dt><span class="term">Batch Oplock</span></dt><dd><p>
158 <a class="indexterm" name="id2583763"></a>
159 Manipulates file openings and closings and allows caching
161 </p></dd></dl></div><p>
162 <a class="indexterm" name="id2583778"></a>
163 An important detail is that oplocks are invoked by the file system, not
164 an application API. Therefore, an application can close an oplocked
165 file, but the file system does not relinquish the oplock. When the
166 oplock break is issued, the file system then simply closes the file in
167 preparation for the subsequent open by the second process.
169 <a class="indexterm" name="id2583793"></a>
170 <a class="indexterm" name="id2583800"></a>
171 <a class="indexterm" name="id2583808"></a>
172 <a class="indexterm" name="id2583814"></a>
173 <span class="emphasis"><em>Opportunistic locking</em></span> is actually an improper name for this feature.
174 The true benefit of this feature is client-side data caching, and
175 oplocks is merely a notification mechanism for writing data back to the
176 networked storage disk. The limitation of oplocks is the
177 reliability of the mechanism to process an oplock break (notification)
178 between the server and the caching client. If this exchange is faulty
179 (usually due to timing out for any number of reasons), then the
180 client-side caching benefit is negated.
182 <a class="indexterm" name="id2583837"></a>
183 The actual decision that a user or administrator should consider is
184 whether it is sensible to share among multiple users data that will
185 be cached locally on a client. In many cases the answer is no.
186 Deciding when to cache or not cache data is the real question, and thus
187 oplocks should be treated as a toggle for client-side
188 caching. Turn it “<span class="quote">on</span>” when client-side caching is desirable and
189 reliable. Turn it “<span class="quote">off</span>” when client-side caching is redundant,
190 unreliable, or counterproductive.
192 <a class="indexterm" name="id2583862"></a>
193 Oplocks is by default set to “<span class="quote">on</span>” by Samba on all
194 configured shares, so careful attention should be given to each case to
195 determine if the potential benefit is worth the potential for delays.
196 The following recommendations will help to characterize the environment
197 where oplocks may be effectively configured.
199 <a class="indexterm" name="id2583880"></a>
200 <a class="indexterm" name="id2583887"></a>
201 Windows oplocks is a lightweight performance-enhancing
202 feature. It is not a robust and reliable protocol. Every
203 implementation of oplocks should be evaluated as a
204 trade-off between perceived performance and reliability. Reliability
205 decreases as each successive rule above is not enforced. Consider a
206 share with oplocks enabled, over a wide-area network, to a client on a
207 South Pacific atoll, on a high-availability server, serving a
208 mission-critical multiuser corporate database during a tropical
209 storm. This configuration will likely encounter problems with oplocks.
211 <a class="indexterm" name="id2583907"></a>
212 Oplocks can be beneficial to perceived client performance when treated
213 as a configuration toggle for client-side data caching. If the data
214 caching is likely to be interrupted, then oplock usage should be
215 reviewed. Samba enables oplocks by default on all
216 shares. Careful attention should be given to the client usage of
217 shared data on the server, the server network reliability, and the
218 oplocks configuration of each share.
219 In mission-critical, high-availability environments, data integrity is
220 often a priority. Complex and expensive configurations are implemented
221 to ensure that if a client loses connectivity with a file server, a
222 failover replacement will be available immediately to provide
223 continuous data availability.
225 <a class="indexterm" name="id2583929"></a>
226 <a class="indexterm" name="id2583936"></a>
227 Windows client failover behavior is more at risk of application
228 interruption than other platforms because it is dependent upon an
229 established TCP transport connection. If the connection is interrupted
230 as in a file server failover a new session must be established.
231 It is rare for Windows client applications to be coded to recover
232 correctly from a transport connection loss; therefore, most applications
233 will experience some sort of interruption at worst, abort and
236 <a class="indexterm" name="id2583963"></a>
237 <a class="indexterm" name="id2583970"></a>
238 <a class="indexterm" name="id2583976"></a>
239 If a client session has been caching writes and reads locally due to
240 oplocks, it is likely that the data will be lost when the
241 application restarts or recovers from the TCP interrupt. When the TCP
242 connection drops, the client state is lost. When the file server
243 recovers, an oplock break is not sent to the client. In this case, the
244 work from the prior session is lost. Observing this scenario with
245 oplocks disabled and with the client writing data to the file server
246 real-time, the failover will provide the data on disk as it
247 existed at the time of the disconnect.
249 In mission-critical, high-availability environments, careful attention
250 should be given to oplocks. Ideally, comprehensive
251 testing should be done with all affected applications with oplocks
252 enabled and disabled.
253 </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584001"></a>Exclusively Accessed Shares</h4></div></div></div><p>
254 Oplocks is most effective when it is confined to shares
255 that are exclusively accessed by a single user, or by only one user at
256 a time. Because the true value of oplocks is the local
257 client caching of data, any operation that interrupts the caching
258 mechanism will cause a delay.
260 Home directories are the most obvious examples of where the performance
261 benefit of oplocks can be safely realized.
262 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584021"></a>Multiple-Accessed Shares or Files</h4></div></div></div><p>
263 As each additional user accesses a file in a share with oplocks
264 enabled, the potential for delays and resulting perceived poor
265 performance increases. When multiple users are accessing a file on a
266 share that has oplocks enabled, the management impact of sending and
267 receiving oplock breaks and the resulting latency while other clients
268 wait for the caching client to flush data offset the performance gains
271 As each additional client attempts to access a file with oplocks set,
272 the potential performance improvement is negated and eventually results
273 in a performance bottleneck.
274 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584045"></a>UNIX or NFS Client-Accessed Files</h4></div></div></div><p>
275 <a class="indexterm" name="id2584053"></a>
276 <a class="indexterm" name="id2584060"></a>
277 Local UNIX and NFS clients access files without a mandatory
278 file-locking mechanism. Thus, these client platforms are incapable of
279 initiating an oplock break request from the server to a Windows client
280 that has a file cached. Local UNIX or NFS file access can therefore
281 write to a file that has been cached by a Windows client, which
282 exposes the file to likely data corruption.
284 If files are shared between Windows clients and either local UNIX
285 or NFS users, turn oplocks off.
286 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584080"></a>Slow and/or Unreliable Networks</h4></div></div></div><p>
287 <a class="indexterm" name="id2584089"></a>
288 <a class="indexterm" name="id2584096"></a>
289 <a class="indexterm" name="id2584102"></a>
290 The biggest potential performance improvement for oplocks
291 occurs when the client-side caching of reads and writes delivers the
292 most differential over sending those reads and writes over the wire.
293 This is most likely to occur when the network is extremely slow,
294 congested, or distributed (as in a WAN). However, network latency also
295 has a high impact on the reliability of the oplock break
296 mechanism, and thus increases the likelihood of encountering oplock
297 problems that more than offset the potential perceived performance
298 gain. Of course, if an oplock break never has to be sent, then this is
299 the most advantageous scenario in which to utilize oplocks.
301 If the network is slow, unreliable, or a WAN, then do not configure
302 oplocks if there is any chance of multiple users
303 regularly opening the same file.
304 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584128"></a>Multiuser Databases</h4></div></div></div><p>
305 <a class="indexterm" name="id2584136"></a>
306 <a class="indexterm" name="id2584143"></a>
307 <a class="indexterm" name="id2584150"></a>
308 Multiuser databases clearly pose a risk due to their very nature they are typically heavily
309 accessed by numerous users at random intervals. Placing a multiuser database on a share with oplocks enabled
310 will likely result in a locking management bottleneck on the Samba server. Whether the database application is
311 developed in-house or a commercially available product, ensure that the share has oplocks disabled.
312 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584169"></a>PDM Data Shares</h4></div></div></div><p>
313 <a class="indexterm" name="id2584177"></a>
314 <a class="indexterm" name="id2584183"></a>
315 <a class="indexterm" name="id2584190"></a>
316 <a class="indexterm" name="id2584197"></a>
317 <a class="indexterm" name="id2584204"></a>
318 Process data management (PDM) applications such as IMAN, Enovia, and Clearcase are increasing in usage with
319 Windows client platforms and therefore with SMB datastores. PDM applications manage multiuser environments for
320 critical data security and access. The typical PDM environment is usually associated with sophisticated client
321 design applications that will load data locally as demanded. In addition, the PDM application will usually
322 monitor the data state of each client. In this case, client-side data caching is best left to the local
323 application and PDM server to negotiate and maintain. It is appropriate to eliminate the client OS from any
324 caching tasks, and the server from any oplocks management, by disabling oplocks on the share.
325 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584226"></a>Beware of Force User</h4></div></div></div><p>
326 <a class="indexterm" name="id2584234"></a>
327 Samba includes an <code class="filename">smb.conf</code> parameter called <a class="indexterm" name="id2584247"></a>force user that changes the user
328 accessing a share from the incoming user to whatever user is defined by the <code class="filename">smb.conf</code> variable. If oplocks is
329 enabled on a share, the change in user access causes an oplock break to be sent to the client, even if the
330 user has not explicitly loaded a file. In cases where the network is slow or unreliable, an oplock break can
331 become lost without the user even accessing a file. This can cause apparent performance degradation as the
332 client continually reconnects to overcome the lost oplock break.
334 Avoid the combination of the following:
335 </p><div class="itemizedlist"><ul type="disc"><li><p>
336 <a class="indexterm" name="id2584279"></a>force user in the <code class="filename">smb.conf</code> share configuration.
338 Slow or unreliable networks.
341 </p></li></ul></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584306"></a>Advanced Samba Oplocks Parameters</h4></div></div></div><p>
342 <a class="indexterm" name="id2584314"></a>
343 <a class="indexterm" name="id2584321"></a>
344 <a class="indexterm" name="id2584328"></a>
345 Samba provides oplock parameters that allow the
346 administrator to adjust various properties of the oplock mechanism to
347 account for timing and usage levels. These parameters provide good
348 versatility for implementing oplocks in environments where they would
349 likely cause problems. The parameters are
350 <a class="indexterm" name="id2584340"></a>oplock break wait time, and
351 <a class="indexterm" name="id2584347"></a>oplock contention limit.
353 <a class="indexterm" name="id2584358"></a>
354 For most users, administrators, and environments, if these parameters
355 are required, then the better option is simply to turn oplocks off.
356 The Samba SWAT help text for both parameters reads: “<span class="quote">Do not change
357 this parameter unless you have read and understood the Samba oplock code.</span>”
359 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584376"></a>Mission-Critical, High-Availability</h4></div></div></div><p>
360 In mission-critical, high-availability environments, data integrity is
361 often a priority. Complex and expensive configurations are implemented
362 to ensure that if a client loses connectivity with a file server, a
363 failover replacement will be available immediately to provide
364 continuous data availability.
366 Windows client failover behavior is more at risk of application
367 interruption than other platforms because it is dependent upon an
368 established TCP transport connection. If the connection is interrupted
369 as in a file server failover a new session must be established.
370 It is rare for Windows client applications to be coded to recover
371 correctly from a transport connection loss; therefore, most applications
372 will experience some sort of interruption at worst, abort and
375 If a client session has been caching writes and reads locally due to
376 oplocks, it is likely that the data will be lost when the
377 application restarts or recovers from the TCP interrupt. When the TCP
378 connection drops, the client state is lost. When the file server
379 recovers, an oplock break is not sent to the client. In this case, the
380 work from the prior session is lost. Observing this scenario with
381 oplocks disabled, if the client was writing data to the file server
382 real-time, then the failover will provide the data on disk as it
383 existed at the time of the disconnect.
385 In mission-critical, high-availability environments, careful attention
386 should be given to oplocks. Ideally, comprehensive
387 testing should be done with all affected applications with oplocks
388 enabled and disabled.
389 </p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2584434"></a>Samba Oplocks Control</h2></div></div></div><p>
390 Oplocks is a unique Windows file locking feature. It is
391 not really file locking, but is included in most discussions of Windows
392 file locking, so is considered a de facto locking feature.
393 Oplocks is actually part of the Windows client file
394 caching mechanism. It is not a particularly robust or reliable feature
395 when implemented on the variety of customized networks that exist in
396 enterprise computing.
398 Like Windows, Samba implements oplocks as a server-side
399 component of the client caching mechanism. Because of the lightweight
400 nature of the Windows feature design, effective configuration of
401 oplocks requires a good understanding of its limitations,
402 and then applying that understanding when configuring data access for
403 each particular customized network and client usage state.
405 Oplocks essentially means that the client is allowed to download and cache
406 a file on its hard drive while making changes; if a second client wants to access the
407 file, the first client receives a break and must synchronize the file back to the server.
408 This can give significant performance gains in some cases; some programs insist on
409 synchronizing the contents of the entire file back to the server for a single change.
411 Level1 Oplocks (also known as just plain “<span class="quote">oplocks</span>”) is another term for opportunistic locking.
413 Level2 Oplocks provides opportunistic locking for a file that will be treated as
414 <span class="emphasis"><em>read only</em></span>. Typically this is used on files that are read-only or
415 on files that the client has no initial intention to write to at time of opening the file.
417 Kernel Oplocks are essentially a method that allows the Linux kernel to co-exist with
418 Samba's oplocked files, although this has provided better integration of MS Windows network
419 file locking with the underlying OS. SGI IRIX and Linux are the only two OSs that are
420 oplock-aware at this time.
422 Unless your system supports kernel oplocks, you should disable oplocks if you are
423 accessing the same files from both UNIX/Linux and SMB clients. Regardless, oplocks should
424 always be disabled if you are sharing a database file (e.g., Microsoft Access) between
425 multiple clients, because any break the first client receives will affect synchronization of
426 the entire file (not just the single record), which will result in a noticeable performance
427 impairment and, more likely, problems accessing the database in the first place. Notably,
428 Microsoft Outlook's personal folders (*.pst) react quite badly to oplocks. If in doubt,
429 disable oplocks and tune your system from that point.
431 If client-side caching is desirable and reliable on your network, you will benefit from
432 turning on oplocks. If your network is slow and/or unreliable, or you are sharing your
433 files among other file sharing mechanisms (e.g., NFS) or across a WAN, or multiple people
434 will be accessing the same files frequently, you probably will not benefit from the overhead
435 of your client sending oplock breaks and will instead want to disable oplocks for the share.
437 Another factor to consider is the perceived performance of file access. If oplocks provide no
438 measurable speed benefit on your network, it might not be worth the hassle of dealing with them.
439 </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2584536"></a>Example Configuration</h3></div></div></div><p>
440 In the following section we examine two distinct aspects of Samba locking controls.
441 </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584546"></a>Disabling Oplocks</h4></div></div></div><p>
442 You can disable oplocks on a per-share basis with the following:
444 </p><table class="simplelist" border="0" summary="Simple list"><tr><td> </td></tr><tr><td><em class="parameter"><code>[acctdata]</code></em></td></tr><tr><td><a class="indexterm" name="id2584573"></a><em class="parameter"><code>oplocks = False</code></em></td></tr><tr><td><a class="indexterm" name="id2584586"></a><em class="parameter"><code>level2 oplocks = False</code></em></td></tr></table><p>
446 The default oplock type is Level1. Level2 oplocks are enabled on a per-share basis
447 in the <code class="filename">smb.conf</code> file.
449 Alternately, you could disable oplocks on a per-file basis within the share:
451 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2584623"></a><em class="parameter"><code>veto oplock files = /*.mdb/*.MDB/*.dbf/*.DBF/</code></em></td></tr></table><p>
453 If you are experiencing problems with oplocks, as apparent from Samba's log entries,
454 you may want to play it safe and disable oplocks and Level2 oplocks.
455 </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2584644"></a>Disabling Kernel Oplocks</h4></div></div></div><p>
456 Kernel oplocks is an <code class="filename">smb.conf</code> parameter that notifies Samba (if
457 the UNIX kernel has the capability to send a Windows client an oplock
458 break) when a UNIX process is attempting to open the file that is
459 cached. This parameter addresses sharing files between UNIX and
460 Windows with oplocks enabled on the Samba server: the UNIX process
461 can open the file that is Oplocked (cached) by the Windows client and
462 the smbd process will not send an oplock break, which exposes the file
463 to the risk of data corruption. If the UNIX kernel has the ability to
464 send an oplock break, then the kernel oplocks parameter enables Samba
465 to send the oplock break. Kernel oplocks are enabled on a per-server
466 basis in the <code class="filename">smb.conf</code> file.
468 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2584684"></a><em class="parameter"><code>kernel oplocks = yes</code></em></td></tr></table><p>
471 <span class="emphasis"><em>Veto oplocks</em></span> is an <code class="filename">smb.conf</code> parameter that identifies specific files for
472 which oplocks are disabled. When a Windows client opens a file that
473 has been configured for veto oplocks, the client will not be granted
474 the oplock, and all operations will be executed on the original file on
475 disk instead of a client-cached file copy. By explicitly identifying
476 files that are shared with UNIX processes and disabling oplocks for
477 those files, the server-wide oplock configuration can be enabled to
478 allow Windows clients to utilize the performance benefit of file
479 caching without the risk of data corruption. Veto oplocks can be
480 enabled on a per-share basis, or globally for the entire server, in the
481 <code class="filename">smb.conf</code> file as shown in <a href="locking.html#far1" title="Example 16.1. Share with Some Files Oplocked">???</a>.
483 </p><div class="example"><a name="far1"></a><p class="title"><b>Example 16.1. Share with Some Files Oplocked</b></p><table class="simplelist" border="0" summary="Simple list"><tr><td> </td></tr><tr><td><em class="parameter"><code>[global]</code></em></td></tr><tr><td><a class="indexterm" name="id2584762"></a><em class="parameter"><code>veto oplock files = /filename.htm/*.txt/</code></em></td></tr><tr><td> </td></tr><tr><td><em class="parameter"><code>[share_name]</code></em></td></tr><tr><td><a class="indexterm" name="id2584784"></a><em class="parameter"><code>veto oplock files = /*.exe/filename.ext/</code></em></td></tr></table></div><p>
485 <a class="indexterm" name="id2584801"></a>oplock break wait time is an <code class="filename">smb.conf</code> parameter
486 that adjusts the time interval for Samba to reply to an oplock break request. Samba recommends:
487 “<span class="quote">Do not change this parameter unless you have read and understood the Samba oplock code.</span>”
488 Oplock break wait time can only be configured globally in the <code class="filename">smb.conf</code> file as shown:
490 </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2584838"></a><em class="parameter"><code>oplock break wait time = 0 (default)</code></em></td></tr></table><p>
492 <span class="emphasis"><em>Oplock break contention limit</em></span> is an <code class="filename">smb.conf</code> parameter that limits the
493 response of the Samba server to grant an oplock if the configured
494 number of contending clients reaches the limit specified by the parameter. Samba recommends
495 “<span class="quote">Do not change this parameter unless you have read and understood the Samba oplock code.</span>”
496 Oplock break contention limit can be enabled on a per-share basis, or globally for
497 the entire server, in the <code class="filename">smb.conf</code> file as shown in <a href="locking.html#far3" title="Example 16.2. Configuration with Oplock Break Contention Limit">???</a>.
499 </p><div class="example"><a name="far3"></a><p class="title"><b>Example 16.2. Configuration with Oplock Break Contention Limit</b></p><table class="simplelist" border="0" summary="Simple list"><tr><td> </td></tr><tr><td><em class="parameter"><code>[global]</code></em></td></tr><tr><td><a class="indexterm" name="id2584913"></a><em class="parameter"><code>oplock break contention limit = 2 (default)</code></em></td></tr><tr><td> </td></tr><tr><td><em class="parameter"><code>[share_name]</code></em></td></tr><tr><td><a class="indexterm" name="id2584936"></a><em class="parameter"><code>oplock break contention limit = 2 (default)</code></em></td></tr></table></div><p>
500 </p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2584955"></a>MS Windows Oplocks and Caching Controls</h2></div></div></div><p>
501 There is a known issue when running applications (like Norton Antivirus) on a Windows 2000/ XP
502 workstation computer that can affect any application attempting to access shared database files
503 across a network. This is a result of a default setting configured in the Windows 2000/XP
504 operating system. When a workstation
505 attempts to access shared data files located on another Windows 2000/XP computer,
506 the Windows 2000/XP operating system will attempt to increase performance by locking the
507 files and caching information locally. When this occurs, the application is unable to
508 properly function, which results in an “<span class="quote">Access Denied</span>”
509 error message being displayed during network operations.
511 All Windows operating systems in the NT family that act as database servers for data files
512 (meaning that data files are stored there and accessed by other Windows PCs) may need to
513 have oplocks disabled in order to minimize the risk of data file corruption.
514 This includes Windows 9x/Me, Windows NT, Windows 200x, and Windows XP.
515 <sup>[<a name="id2584987" href="#ftn.id2584987">5</a>]</sup>
517 If you are using a Windows NT family workstation in place of a server, you must also
518 disable oplocks on that workstation. For example, if you use a
519 PC with the Windows NT Workstation operating system instead of Windows NT Server, and you
520 have data files located on it that are accessed from other Windows PCs, you may need to
521 disable oplocks on that system.
523 The major difference is the location in the Windows registry where the values for disabling
524 oplocks are entered. Instead of the LanManServer location, the LanManWorkstation location
527 You can verify (change or add, if necessary) this registry value using the Windows
528 Registry Editor. When you change this registry value, you will have to reboot the PC
529 to ensure that the new setting goes into effect.
531 The location of the client registry entry for oplocks has changed in
532 Windows 2000 from the earlier location in Microsoft Windows NT.
533 </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
534 Windows 2000 will still respect the EnableOplocks registry value used to disable oplocks
535 in earlier versions of Windows.
537 You can also deny the granting of oplocks by changing the following registry entries:
539 </p><pre class="programlisting">
540 HKEY_LOCAL_MACHINE\System\
541 CurrentControlSet\Services\MRXSmb\Parameters\
543 OplocksDisabled REG_DWORD 0 or 1
544 Default: 0 (not disabled)
546 </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
547 The OplocksDisabled registry value configures Windows clients to either request or not
548 request oplocks on a remote file. To disable oplocks, the value of
549 OplocksDisabled must be set to 1.
551 </p><pre class="programlisting">
552 HKEY_LOCAL_MACHINE\System\
553 CurrentControlSet\Services\LanmanServer\Parameters
555 EnableOplocks REG_DWORD 0 or 1
556 Default: 1 (Enabled by Default)
558 EnableOpLockForceClose REG_DWORD 0 or 1
559 Default: 0 (Disabled by Default)
561 </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
562 The EnableOplocks value configures Windows-based servers (including Workstations sharing
563 files) to allow or deny oplocks on local files.
565 To force closure of open oplocks on close or program exit, EnableOpLockForceClose must be set to 1.
567 An illustration of how Level2 oplocks work follows:
568 </p><div class="itemizedlist"><ul type="disc"><li><p>
569 Station 1 opens the file requesting oplock.
571 Since no other station has the file open, the server grants station 1 exclusive oplock.
573 Station 2 opens the file requesting oplock.
575 Since station 1 has not yet written to the file, the server asks station 1 to break
578 Station 1 complies by flushing locally buffered lock information to the server.
580 Station 1 informs the server that it has broken to level2 Oplock (alternately,
581 station 1 could have closed the file).
583 The server responds to station 2's open request, granting it Level2 oplock.
584 Other stations can likewise open the file and obtain Level2 oplock.
586 Station 2 (or any station that has the file open) sends a write request SMB.
587 The server returns the write response.
589 The server asks all stations that have the file open to break to none, meaning no
590 station holds any oplock on the file. Because the workstations can have no cached
591 writes or locks at this point, they need not respond to the break-to-none advisory;
592 all they need do is invalidate locally cashed read-ahead data.
593 </p></li></ul></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2585142"></a>Workstation Service Entries</h3></div></div></div><pre class="programlisting">
594 \HKEY_LOCAL_MACHINE\System\
595 CurrentControlSet\Services\LanmanWorkstation\Parameters
597 UseOpportunisticLocking REG_DWORD 0 or 1
600 This indicates whether the redirector should use oplocks performance
601 enhancement. This parameter should be disabled only to isolate problems.
602 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2585164"></a>Server Service Entries</h3></div></div></div><pre class="programlisting">
603 \HKEY_LOCAL_MACHINE\System\
604 CurrentControlSet\Services\LanmanServer\Parameters
606 EnableOplocks REG_DWORD 0 or 1
609 This specifies whether the server allows clients to use oplocks on files. Oplocks are a
610 significant performance enhancement, but have the potential to cause lost cached
611 data on some networks, particularly WANs.
612 </p><pre class="programlisting">
613 MinLinkThroughput REG_DWORD 0 to infinite bytes per second
616 This specifies the minimum link throughput allowed by the server before it disables
617 raw I/O and oplocks for this connection.
618 </p><pre class="programlisting">
619 MaxLinkDelay REG_DWORD 0 to 100,000 seconds
622 This specifies the maximum time allowed for a link delay. If delays exceed this number,
623 the server disables raw I/O and oplocks for this connection.
624 </p><pre class="programlisting">
625 OplockBreakWait REG_DWORD 10 to 180 seconds
628 This specifies the time that the server waits for a client to respond to an oplock break
629 request. Smaller values can allow detection of crashed clients more quickly but can
630 potentially cause loss of cached data.
631 </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2585230"></a>Persistent Data Corruption</h2></div></div></div><p>
632 If you have applied all of the settings discussed in this chapter but data corruption problems
633 and other symptoms persist, here are some additional things to check out.
635 We have credible reports from developers that faulty network hardware, such as a single
636 faulty network card, can cause symptoms similar to read caching and data corruption.
637 If you see persistent data corruption even after repeated re-indexing, you may have to
638 rebuild the data files in question. This involves creating a new data file with the
639 same definition as the file to be rebuilt and transferring the data from the old file
640 to the new one. There are several known methods for doing this that can be found in
642 </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2585255"></a>Common Errors</h2></div></div></div><p>
643 In some sites locking problems surface as soon as a server is installed; in other sites
644 locking problems may not surface for a long time. Almost without exception, when a locking
645 problem does surface, it will cause embarrassment and potential data corruption.
647 Over the past few years there have been a number of complaints on the Samba mailing lists
648 that have claimed that Samba caused data corruption. Three causes have been identified
650 </p><div class="itemizedlist"><ul type="disc"><li><p>
651 Incorrect configuration of oplocks (incompatible with the application
652 being used). This is a common problem even where MS Windows NT4 or MS Windows
653 200x-based servers were in use. It is imperative that the software application vendors'
654 instructions for configuration of file locking should be followed. If in doubt,
655 disable oplocks on both the server and the client. Disabling of all forms of file
656 caching on the MS Windows client may be necessary also.
658 Defective network cards, cables, or hubs/switches. This is generally a more
659 prevalent factor with low-cost networking hardware, although occasionally there
660 have also been problems with incompatibilities in more up-market hardware.
662 There have been some random reports of Samba log files being written over data
663 files. This has been reported by very few sites (about five in the past 3 years)
664 and all attempts to reproduce the problem have failed. The Samba Team has been
665 unable to catch this happening and thus unable to isolate any particular
666 cause. Considering the millions of systems that use Samba, for the sites that have
667 been affected by this as well as for the Samba Team, this is a frustrating and
668 vexing challenge. If you see this type of thing happening, please create a bug
669 report on Samba <a href="https://bugzilla.samba.org" target="_top">Bugzilla</a> without delay.
670 Make sure that you give as much information as you possibly can to help isolate the
671 cause and to allow replication of the problem (an essential step in problem isolation and correction).
672 </p></li></ul></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2585322"></a>locking.tdb Error Messages</h3></div></div></div><p>
673 “<span class="quote">
674 We are seeing lots of errors in the Samba logs, like:
676 </p><pre class="programlisting">
677 tdb(/usr/local/samba_2.2.7/var/locks/locking.tdb): rec_read bad magic
678 0x4d6f4b61 at offset=36116
681 “<span class="quote">
685 This error indicates a corrupted tdb. Stop all instances of smbd, delete locking.tdb, and restart smbd.
686 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2585353"></a>Problems Saving Files in MS Office on Windows XP</h3></div></div></div><a class="indexterm" name="id2585359"></a><p>This is a bug in Windows XP. More information can be
687 found in <a href="http://support.microsoft.com/?id=812937" target="_top">Microsoft Knowledge Base article 812937</a></p>.
689 </div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2585378"></a>Long Delays Deleting Files over Network with XP SP1</h3></div></div></div><p>“<span class="quote">It sometimes takes approximately 35 seconds to delete files over the network after XP SP1 has been applied.</span>”</p><a class="indexterm" name="id2585390"></a><p>This is a bug in Windows XP. More information can be found in <a href="http://support.microsoft.com/?id=811492" target="_top">
690 Microsoft Knowledge Base article 811492</a></p>.
691 </div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2585409"></a>Additional Reading</h2></div></div></div><p>
692 You may want to check for an updated documentation regarding file and record locking issues on the Microsoft
693 <a href="http://support.microsoft.com/" target="_top">Support</a> web site. Additionally, search for the word
694 <code class="literal">locking</code> on the Samba <a href="http://www.samba.org/" target="_top">web</a> site.
696 Section of the Microsoft MSDN Library on opportunistic locking:
698 <a class="indexterm" name="id2585446"></a>
699 Microsoft Knowledge Base, “<span class="quote">Maintaining Transactional Integrity with OPLOCKS</span>”,
700 Microsoft Corporation, April 1999, <a href="http://support.microsoft.com/?id=224992" target="_top">Microsoft
701 KB Article 224992</a>.
703 <a class="indexterm" name="id2585470"></a>
704 Microsoft Knowledge Base, “<span class="quote">Configuring Opportunistic Locking in Windows 2000</span>”,
705 Microsoft Corporation, April 2001 <a href="http://support.microsoft.com/?id=296264" target="_top">Microsoft KB Article 296264</a>.
707 <a class="indexterm" name="id2585494"></a>
708 Microsoft Knowledge Base, “<span class="quote">PC Ext: Explanation of Opportunistic Locking on Windows NT</span>”,
709 Microsoft Corporation, April 1995 <a href="http://support.microsoft.com/?id=129202" target="_top">Microsoft
710 KB Article 129202</a>.
711 </p></div><div class="footnotes"><br><hr width="100" align="left"><div class="footnote"><p><sup>[<a name="ftn.id2584987" href="#id2584987">5</a>] </sup>Microsoft has documented this in Knowledge Base article 300216.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="AccessControls.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="securing-samba.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 15. File, Directory, and Share Access Controls </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 17. Securing Samba</td></tr></table></div></body></html>
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