1=====
2Usage
3=====
4
5This module supports the SMB3 family of advanced network protocols (as well
6as older dialects, originally called "CIFS" or SMB1).
7
8The CIFS VFS module for Linux supports many advanced network filesystem
9features such as hierarchical DFS like namespace, hardlinks, locking and more.
10It was designed to comply with the SNIA CIFS Technical Reference (which
11supersedes the 1992 X/Open SMB Standard) as well as to perform best practice
12practical interoperability with Windows 2000, Windows XP, Samba and equivalent
13servers.  This code was developed in participation with the Protocol Freedom
14Information Foundation.  CIFS and now SMB3 has now become a defacto
15standard for interoperating between Macs and Windows and major NAS appliances.
16
17Please see
18MS-SMB2 (for detailed SMB2/SMB3/SMB3.1.1 protocol specification)
19http://protocolfreedom.org/ and
20http://samba.org/samba/PFIF/
21for more details.
22
23
24For questions or bug reports please contact:
25
26    smfrench@gmail.com
27
28See the project page at: https://wiki.samba.org/index.php/LinuxCIFS_utils
29
30Build instructions
31==================
32
33For Linux:
34
351) Download the kernel (e.g. from http://www.kernel.org)
36   and change directory into the top of the kernel directory tree
37   (e.g. /usr/src/linux-2.5.73)
382) make menuconfig (or make xconfig)
393) select cifs from within the network filesystem choices
404) save and exit
415) make
42
43
44Installation instructions
45=========================
46
47If you have built the CIFS vfs as module (successfully) simply
48type ``make modules_install`` (or if you prefer, manually copy the file to
49the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.ko).
50
51If you have built the CIFS vfs into the kernel itself, follow the instructions
52for your distribution on how to install a new kernel (usually you
53would simply type ``make install``).
54
55If you do not have the utility mount.cifs (in the Samba 4.x source tree and on
56the CIFS VFS web site) copy it to the same directory in which mount helpers
57reside (usually /sbin).  Although the helper software is not
58required, mount.cifs is recommended.  Most distros include a ``cifs-utils``
59package that includes this utility so it is recommended to install this.
60
61Note that running the Winbind pam/nss module (logon service) on all of your
62Linux clients is useful in mapping Uids and Gids consistently across the
63domain to the proper network user.  The mount.cifs mount helper can be
64found at cifs-utils.git on git.samba.org
65
66If cifs is built as a module, then the size and number of network buffers
67and maximum number of simultaneous requests to one server can be configured.
68Changing these from their defaults is not recommended. By executing modinfo::
69
70	modinfo kernel/fs/cifs/cifs.ko
71
72on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
73at module initialization time (by running insmod cifs.ko) can be seen.
74
75Recommendations
76===============
77
78To improve security the SMB2.1 dialect or later (usually will get SMB3) is now
79the new default. To use old dialects (e.g. to mount Windows XP) use "vers=1.0"
80on mount (or vers=2.0 for Windows Vista).  Note that the CIFS (vers=1.0) is
81much older and less secure than the default dialect SMB3 which includes
82many advanced security features such as downgrade attack detection
83and encrypted shares and stronger signing and authentication algorithms.
84There are additional mount options that may be helpful for SMB3 to get
85improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1):
86
87     ``mfsymlinks`` and ``cifsacl`` and ``idsfromsid``
88
89Allowing User Mounts
90====================
91
92To permit users to mount and unmount over directories they own is possible
93with the cifs vfs.  A way to enable such mounting is to mark the mount.cifs
94utility as suid (e.g. ``chmod +s /sbin/mount.cifs``). To enable users to
95umount shares they mount requires
96
971) mount.cifs version 1.4 or later
982) an entry for the share in /etc/fstab indicating that a user may
99   unmount it e.g.::
100
101     //server/usersharename  /mnt/username cifs user 0 0
102
103Note that when the mount.cifs utility is run suid (allowing user mounts),
104in order to reduce risks, the ``nosuid`` mount flag is passed in on mount to
105disallow execution of an suid program mounted on the remote target.
106When mount is executed as root, nosuid is not passed in by default,
107and execution of suid programs on the remote target would be enabled
108by default. This can be changed, as with nfs and other filesystems,
109by simply specifying ``nosuid`` among the mount options. For user mounts
110though to be able to pass the suid flag to mount requires rebuilding
111mount.cifs with the following flag: CIFS_ALLOW_USR_SUID
112
113There is a corresponding manual page for cifs mounting in the Samba 3.0 and
114later source tree in docs/manpages/mount.cifs.8
115
116Allowing User Unmounts
117======================
118
119To permit users to ummount directories that they have user mounted (see above),
120the utility umount.cifs may be used.  It may be invoked directly, or if
121umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
122(at least for most versions of the umount utility) for umount of cifs
123mounts, unless umount is invoked with -i (which will avoid invoking a umount
124helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
125as suid (e.g. ``chmod +s /sbin/umount.cifs``) or equivalent (some distributions
126allow adding entries to a file to the /etc/permissions file to achieve the
127equivalent suid effect).  For this utility to succeed the target path
128must be a cifs mount, and the uid of the current user must match the uid
129of the user who mounted the resource.
130
131Also note that the customary way of allowing user mounts and unmounts is
132(instead of using mount.cifs and unmount.cifs as suid) to add a line
133to the file /etc/fstab for each //server/share you wish to mount, but
134this can become unwieldy when potential mount targets include many
135or  unpredictable UNC names.
136
137Samba Considerations
138====================
139
140Most current servers support SMB2.1 and SMB3 which are more secure,
141but there are useful protocol extensions for the older less secure CIFS
142dialect, so to get the maximum benefit if mounting using the older dialect
143(CIFS/SMB1), we recommend using a server that supports the SNIA CIFS
144Unix Extensions standard (e.g. almost any  version of Samba ie version
1452.2.5 or later) but the CIFS vfs works fine with a wide variety of CIFS servers.
146Note that uid, gid and file permissions will display default values if you do
147not have a server that supports the Unix extensions for CIFS (such as Samba
1482.2.5 or later).  To enable the Unix CIFS Extensions in the Samba server, add
149the line::
150
151	unix extensions = yes
152
153to your smb.conf file on the server.  Note that the following smb.conf settings
154are also useful (on the Samba server) when the majority of clients are Unix or
155Linux::
156
157	case sensitive = yes
158	delete readonly = yes
159	ea support = yes
160
161Note that server ea support is required for supporting xattrs from the Linux
162cifs client, and that EA support is present in later versions of Samba (e.g.
1633.0.6 and later (also EA support works in all versions of Windows, at least to
164shares on NTFS filesystems).  Extended Attribute (xattr) support is an optional
165feature of most Linux filesystems which may require enabling via
166make menuconfig. Client support for extended attributes (user xattr) can be
167disabled on a per-mount basis by specifying ``nouser_xattr`` on mount.
168
169The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
170version 3.10 and later.  Setting POSIX ACLs requires enabling both XATTR and
171then POSIX support in the CIFS configuration options when building the cifs
172module.  POSIX ACL support can be disabled on a per mount basic by specifying
173``noacl`` on mount.
174
175Some administrators may want to change Samba's smb.conf ``map archive`` and
176``create mask`` parameters from the default.  Unless the create mask is changed
177newly created files can end up with an unnecessarily restrictive default mode,
178which may not be what you want, although if the CIFS Unix extensions are
179enabled on the server and client, subsequent setattr calls (e.g. chmod) can
180fix the mode.  Note that creating special devices (mknod) remotely
181may require specifying a mkdev function to Samba if you are not using
182Samba 3.0.6 or later.  For more information on these see the manual pages
183(``man smb.conf``) on the Samba server system.  Note that the cifs vfs,
184unlike the smbfs vfs, does not read the smb.conf on the client system
185(the few optional settings are passed in on mount via -o parameters instead).
186Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
187open files (required for strict POSIX compliance).  Windows Servers already
188supported this feature. Samba server does not allow symlinks that refer to files
189outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
190files with absolute paths (ie beginning with slash) such as::
191
192	 ln -s /mnt/foo bar
193
194would be forbidden. Samba 3.0.6 server or later includes the ability to create
195such symlinks safely by converting unsafe symlinks (ie symlinks to server
196files that are outside of the share) to a samba specific format on the server
197that is ignored by local server applications and non-cifs clients and that will
198not be traversed by the Samba server).  This is opaque to the Linux client
199application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
200later, but only for remote clients using the CIFS Unix extensions, and will
201be invisbile to Windows clients and typically will not affect local
202applications running on the same server as Samba.
203
204Use instructions
205================
206
207Once the CIFS VFS support is built into the kernel or installed as a module
208(cifs.ko), you can use mount syntax like the following to access Samba or
209Mac or Windows servers::
210
211  mount -t cifs //9.53.216.11/e$ /mnt -o username=myname,password=mypassword
212
213Before -o the option -v may be specified to make the mount.cifs
214mount helper display the mount steps more verbosely.
215After -o the following commonly used cifs vfs specific options
216are supported::
217
218  username=<username>
219  password=<password>
220  domain=<domain name>
221
222Other cifs mount options are described below.  Use of TCP names (in addition to
223ip addresses) is available if the mount helper (mount.cifs) is installed. If
224you do not trust the server to which are mounted, or if you do not have
225cifs signing enabled (and the physical network is insecure), consider use
226of the standard mount options ``noexec`` and ``nosuid`` to reduce the risk of
227running an altered binary on your local system (downloaded from a hostile server
228or altered by a hostile router).
229
230Although mounting using format corresponding to the CIFS URL specification is
231not possible in mount.cifs yet, it is possible to use an alternate format
232for the server and sharename (which is somewhat similar to NFS style mount
233syntax) instead of the more widely used UNC format (i.e. \\server\share)::
234
235  mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
236
237When using the mount helper mount.cifs, passwords may be specified via alternate
238mechanisms, instead of specifying it after -o using the normal ``pass=`` syntax
239on the command line:
2401) By including it in a credential file. Specify credentials=filename as one
241of the mount options. Credential files contain two lines::
242
243	username=someuser
244	password=your_password
245
2462) By specifying the password in the PASSWD environment variable (similarly
247   the user name can be taken from the USER environment variable).
2483) By specifying the password in a file by name via PASSWD_FILE
2494) By specifying the password in a file by file descriptor via PASSWD_FD
250
251If no password is provided, mount.cifs will prompt for password entry
252
253Restrictions
254============
255
256Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
2571001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a
258problem as most servers support this.
259
260Valid filenames differ between Windows and Linux.  Windows typically restricts
261filenames which contain certain reserved characters (e.g.the character :
262which is used to delimit the beginning of a stream name by Windows), while
263Linux allows a slightly wider set of valid characters in filenames. Windows
264servers can remap such characters when an explicit mapping is specified in
265the Server's registry.  Samba starting with version 3.10 will allow such
266filenames (ie those which contain valid Linux characters, which normally
267would be forbidden for Windows/CIFS semantics) as long as the server is
268configured for Unix Extensions (and the client has not disabled
269/proc/fs/cifs/LinuxExtensionsEnabled). In addition the mount option
270``mapposix`` can be used on CIFS (vers=1.0) to force the mapping of
271illegal Windows/NTFS/SMB characters to a remap range (this mount parm
272is the default for SMB3). This remap (``mapposix``) range is also
273compatible with Mac (and "Services for Mac" on some older Windows).
274
275CIFS VFS Mount Options
276======================
277A partial list of the supported mount options follows:
278
279  username
280		The user name to use when trying to establish
281		the CIFS session.
282  password
283		The user password.  If the mount helper is
284		installed, the user will be prompted for password
285		if not supplied.
286  ip
287		The ip address of the target server
288  unc
289		The target server Universal Network Name (export) to
290		mount.
291  domain
292		Set the SMB/CIFS workgroup name prepended to the
293		username during CIFS session establishment
294  forceuid
295		Set the default uid for inodes to the uid
296		passed in on mount. For mounts to servers
297		which do support the CIFS Unix extensions, such as a
298		properly configured Samba server, the server provides
299		the uid, gid and mode so this parameter should not be
300		specified unless the server and clients uid and gid
301		numbering differ.  If the server and client are in the
302		same domain (e.g. running winbind or nss_ldap) and
303		the server supports the Unix Extensions then the uid
304		and gid can be retrieved from the server (and uid
305		and gid would not have to be specified on the mount.
306		For servers which do not support the CIFS Unix
307		extensions, the default uid (and gid) returned on lookup
308		of existing files will be the uid (gid) of the person
309		who executed the mount (root, except when mount.cifs
310		is configured setuid for user mounts) unless the ``uid=``
311		(gid) mount option is specified. Also note that permission
312		checks (authorization checks) on accesses to a file occur
313		at the server, but there are cases in which an administrator
314		may want to restrict at the client as well.  For those
315		servers which do not report a uid/gid owner
316		(such as Windows), permissions can also be checked at the
317		client, and a crude form of client side permission checking
318		can be enabled by specifying file_mode and dir_mode on
319		the client.  (default)
320  forcegid
321		(similar to above but for the groupid instead of uid) (default)
322  noforceuid
323		Fill in file owner information (uid) by requesting it from
324		the server if possible. With this option, the value given in
325		the uid= option (on mount) will only be used if the server
326		can not support returning uids on inodes.
327  noforcegid
328		(similar to above but for the group owner, gid, instead of uid)
329  uid
330		Set the default uid for inodes, and indicate to the
331		cifs kernel driver which local user mounted. If the server
332		supports the unix extensions the default uid is
333		not used to fill in the owner fields of inodes (files)
334		unless the ``forceuid`` parameter is specified.
335  gid
336		Set the default gid for inodes (similar to above).
337  file_mode
338		If CIFS Unix extensions are not supported by the server
339		this overrides the default mode for file inodes.
340  fsc
341		Enable local disk caching using FS-Cache (off by default). This
342		option could be useful to improve performance on a slow link,
343		heavily loaded server and/or network where reading from the
344		disk is faster than reading from the server (over the network).
345		This could also impact scalability positively as the
346		number of calls to the server are reduced. However, local
347		caching is not suitable for all workloads for e.g. read-once
348		type workloads. So, you need to consider carefully your
349		workload/scenario before using this option. Currently, local
350		disk caching is functional for CIFS files opened as read-only.
351  dir_mode
352		If CIFS Unix extensions are not supported by the server
353		this overrides the default mode for directory inodes.
354  port
355		attempt to contact the server on this tcp port, before
356		trying the usual ports (port 445, then 139).
357  iocharset
358		Codepage used to convert local path names to and from
359		Unicode. Unicode is used by default for network path
360		names if the server supports it.  If iocharset is
361		not specified then the nls_default specified
362		during the local client kernel build will be used.
363		If server does not support Unicode, this parameter is
364		unused.
365  rsize
366		default read size (usually 16K). The client currently
367		can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
368		defaults to 16K and may be changed (from 8K to the maximum
369		kmalloc size allowed by your kernel) at module install time
370		for cifs.ko. Setting CIFSMaxBufSize to a very large value
371		will cause cifs to use more memory and may reduce performance
372		in some cases.  To use rsize greater than 127K (the original
373		cifs protocol maximum) also requires that the server support
374		a new Unix Capability flag (for very large read) which some
375		newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
376		set from a minimum of 2048 to a maximum of 130048 (127K or
377		CIFSMaxBufSize, whichever is smaller)
378  wsize
379		default write size (default 57344)
380		maximum wsize currently allowed by CIFS is 57344 (fourteen
381		4096 byte pages)
382  actimeo=n
383		attribute cache timeout in seconds (default 1 second).
384		After this timeout, the cifs client requests fresh attribute
385		information from the server. This option allows to tune the
386		attribute cache timeout to suit the workload needs. Shorter
387		timeouts mean better the cache coherency, but increased number
388		of calls to the server. Longer timeouts mean reduced number
389		of calls to the server at the expense of less stricter cache
390		coherency checks (i.e. incorrect attribute cache for a short
391		period of time).
392  rw
393		mount the network share read-write (note that the
394		server may still consider the share read-only)
395  ro
396		mount network share read-only
397  version
398		used to distinguish different versions of the
399		mount helper utility (not typically needed)
400  sep
401		if first mount option (after the -o), overrides
402		the comma as the separator between the mount
403		parms. e.g.::
404
405			-o user=myname,password=mypassword,domain=mydom
406
407		could be passed instead with period as the separator by::
408
409			-o sep=.user=myname.password=mypassword.domain=mydom
410
411		this might be useful when comma is contained within username
412		or password or domain. This option is less important
413		when the cifs mount helper cifs.mount (version 1.1 or later)
414		is used.
415  nosuid
416		Do not allow remote executables with the suid bit
417		program to be executed.  This is only meaningful for mounts
418		to servers such as Samba which support the CIFS Unix Extensions.
419		If you do not trust the servers in your network (your mount
420		targets) it is recommended that you specify this option for
421		greater security.
422  exec
423		Permit execution of binaries on the mount.
424  noexec
425		Do not permit execution of binaries on the mount.
426  dev
427		Recognize block devices on the remote mount.
428  nodev
429		Do not recognize devices on the remote mount.
430  suid
431		Allow remote files on this mountpoint with suid enabled to
432		be executed (default for mounts when executed as root,
433		nosuid is default for user mounts).
434  credentials
435		Although ignored by the cifs kernel component, it is used by
436		the mount helper, mount.cifs. When mount.cifs is installed it
437		opens and reads the credential file specified in order
438		to obtain the userid and password arguments which are passed to
439		the cifs vfs.
440  guest
441		Although ignored by the kernel component, the mount.cifs
442		mount helper will not prompt the user for a password
443		if guest is specified on the mount options.  If no
444		password is specified a null password will be used.
445  perm
446		Client does permission checks (vfs_permission check of uid
447		and gid of the file against the mode and desired operation),
448		Note that this is in addition to the normal ACL check on the
449		target machine done by the server software.
450		Client permission checking is enabled by default.
451  noperm
452		Client does not do permission checks.  This can expose
453		files on this mount to access by other users on the local
454		client system. It is typically only needed when the server
455		supports the CIFS Unix Extensions but the UIDs/GIDs on the
456		client and server system do not match closely enough to allow
457		access by the user doing the mount, but it may be useful with
458		non CIFS Unix Extension mounts for cases in which the default
459		mode is specified on the mount but is not to be enforced on the
460		client (e.g. perhaps when MultiUserMount is enabled)
461		Note that this does not affect the normal ACL check on the
462		target machine done by the server software (of the server
463		ACL against the user name provided at mount time).
464  serverino
465		Use server's inode numbers instead of generating automatically
466		incrementing inode numbers on the client.  Although this will
467		make it easier to spot hardlinked files (as they will have
468		the same inode numbers) and inode numbers may be persistent,
469		note that the server does not guarantee that the inode numbers
470		are unique if multiple server side mounts are exported under a
471		single share (since inode numbers on the servers might not
472		be unique if multiple filesystems are mounted under the same
473		shared higher level directory).  Note that some older
474		(e.g. pre-Windows 2000) do not support returning UniqueIDs
475		or the CIFS Unix Extensions equivalent and for those
476		this mount option will have no effect.  Exporting cifs mounts
477		under nfsd requires this mount option on the cifs mount.
478		This is now the default if server supports the
479		required network operation.
480  noserverino
481		Client generates inode numbers (rather than using the actual one
482		from the server). These inode numbers will vary after
483		unmount or reboot which can confuse some applications,
484		but not all server filesystems support unique inode
485		numbers.
486  setuids
487		If the CIFS Unix extensions are negotiated with the server
488		the client will attempt to set the effective uid and gid of
489		the local process on newly created files, directories, and
490		devices (create, mkdir, mknod).  If the CIFS Unix Extensions
491		are not negotiated, for newly created files and directories
492		instead of using the default uid and gid specified on
493		the mount, cache the new file's uid and gid locally which means
494		that the uid for the file can change when the inode is
495		reloaded (or the user remounts the share).
496  nosetuids
497		The client will not attempt to set the uid and gid on
498		on newly created files, directories, and devices (create,
499		mkdir, mknod) which will result in the server setting the
500		uid and gid to the default (usually the server uid of the
501		user who mounted the share).  Letting the server (rather than
502		the client) set the uid and gid is the default. If the CIFS
503		Unix Extensions are not negotiated then the uid and gid for
504		new files will appear to be the uid (gid) of the mounter or the
505		uid (gid) parameter specified on the mount.
506  netbiosname
507		When mounting to servers via port 139, specifies the RFC1001
508		source name to use to represent the client netbios machine
509		name when doing the RFC1001 netbios session initialize.
510  direct
511		Do not do inode data caching on files opened on this mount.
512		This precludes mmapping files on this mount. In some cases
513		with fast networks and little or no caching benefits on the
514		client (e.g. when the application is doing large sequential
515		reads bigger than page size without rereading the same data)
516		this can provide better performance than the default
517		behavior which caches reads (readahead) and writes
518		(writebehind) through the local Linux client pagecache
519		if oplock (caching token) is granted and held. Note that
520		direct allows write operations larger than page size
521		to be sent to the server.
522  strictcache
523		Use for switching on strict cache mode. In this mode the
524		client read from the cache all the time it has Oplock Level II,
525		otherwise - read from the server. All written data are stored
526		in the cache, but if the client doesn't have Exclusive Oplock,
527		it writes the data to the server.
528  rwpidforward
529		Forward pid of a process who opened a file to any read or write
530		operation on that file. This prevent applications like WINE
531		from failing on read and write if we use mandatory brlock style.
532  acl
533		Allow setfacl and getfacl to manage posix ACLs if server
534		supports them.  (default)
535  noacl
536		Do not allow setfacl and getfacl calls on this mount
537  user_xattr
538		Allow getting and setting user xattrs (those attributes whose
539		name begins with ``user.`` or ``os2.``) as OS/2 EAs (extended
540		attributes) to the server.  This allows support of the
541		setfattr and getfattr utilities. (default)
542  nouser_xattr
543		Do not allow getfattr/setfattr to get/set/list xattrs
544  mapchars
545		Translate six of the seven reserved characters (not backslash)::
546
547			*?<>|:
548
549		to the remap range (above 0xF000), which also
550		allows the CIFS client to recognize files created with
551		such characters by Windows's POSIX emulation. This can
552		also be useful when mounting to most versions of Samba
553		(which also forbids creating and opening files
554		whose names contain any of these seven characters).
555		This has no effect if the server does not support
556		Unicode on the wire.
557  nomapchars
558		Do not translate any of these seven characters (default).
559  nocase
560		Request case insensitive path name matching (case
561		sensitive is the default if the server supports it).
562		(mount option ``ignorecase`` is identical to ``nocase``)
563  posixpaths
564		If CIFS Unix extensions are supported, attempt to
565		negotiate posix path name support which allows certain
566		characters forbidden in typical CIFS filenames, without
567		requiring remapping. (default)
568  noposixpaths
569		If CIFS Unix extensions are supported, do not request
570		posix path name support (this may cause servers to
571		reject creatingfile with certain reserved characters).
572  nounix
573		Disable the CIFS Unix Extensions for this mount (tree
574		connection). This is rarely needed, but it may be useful
575		in order to turn off multiple settings all at once (ie
576		posix acls, posix locks, posix paths, symlink support
577		and retrieving uids/gids/mode from the server) or to
578		work around a bug in server which implement the Unix
579		Extensions.
580  nobrl
581		Do not send byte range lock requests to the server.
582		This is necessary for certain applications that break
583		with cifs style mandatory byte range locks (and most
584		cifs servers do not yet support requesting advisory
585		byte range locks).
586  forcemandatorylock
587		Even if the server supports posix (advisory) byte range
588		locking, send only mandatory lock requests.  For some
589		(presumably rare) applications, originally coded for
590		DOS/Windows, which require Windows style mandatory byte range
591		locking, they may be able to take advantage of this option,
592		forcing the cifs client to only send mandatory locks
593		even if the cifs server would support posix advisory locks.
594		``forcemand`` is accepted as a shorter form of this mount
595		option.
596  nostrictsync
597		If this mount option is set, when an application does an
598		fsync call then the cifs client does not send an SMB Flush
599		to the server (to force the server to write all dirty data
600		for this file immediately to disk), although cifs still sends
601		all dirty (cached) file data to the server and waits for the
602		server to respond to the write.  Since SMB Flush can be
603		very slow, and some servers may be reliable enough (to risk
604		delaying slightly flushing the data to disk on the server),
605		turning on this option may be useful to improve performance for
606		applications that fsync too much, at a small risk of server
607		crash.  If this mount option is not set, by default cifs will
608		send an SMB flush request (and wait for a response) on every
609		fsync call.
610  nodfs
611		Disable DFS (global name space support) even if the
612		server claims to support it.  This can help work around
613		a problem with parsing of DFS paths with Samba server
614		versions 3.0.24 and 3.0.25.
615  remount
616		remount the share (often used to change from ro to rw mounts
617		or vice versa)
618  cifsacl
619		Report mode bits (e.g. on stat) based on the Windows ACL for
620		the file. (EXPERIMENTAL)
621  servern
622		Specify the server 's netbios name (RFC1001 name) to use
623		when attempting to setup a session to the server.
624		This is needed for mounting to some older servers (such
625		as OS/2 or Windows 98 and Windows ME) since they do not
626		support a default server name.  A server name can be up
627		to 15 characters long and is usually uppercased.
628  sfu
629		When the CIFS Unix Extensions are not negotiated, attempt to
630		create device files and fifos in a format compatible with
631		Services for Unix (SFU).  In addition retrieve bits 10-12
632		of the mode via the SETFILEBITS extended attribute (as
633		SFU does).  In the future the bottom 9 bits of the
634		mode also will be emulated using queries of the security
635		descriptor (ACL).
636  mfsymlinks
637		Enable support for Minshall+French symlinks
638		(see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
639		This option is ignored when specified together with the
640		'sfu' option. Minshall+French symlinks are used even if
641		the server supports the CIFS Unix Extensions.
642  sign
643		Must use packet signing (helps avoid unwanted data modification
644		by intermediate systems in the route).  Note that signing
645		does not work with lanman or plaintext authentication.
646  seal
647		Must seal (encrypt) all data on this mounted share before
648		sending on the network.  Requires support for Unix Extensions.
649		Note that this differs from the sign mount option in that it
650		causes encryption of data sent over this mounted share but other
651		shares mounted to the same server are unaffected.
652  locallease
653		This option is rarely needed. Fcntl F_SETLEASE is
654		used by some applications such as Samba and NFSv4 server to
655		check to see whether a file is cacheable.  CIFS has no way
656		to explicitly request a lease, but can check whether a file
657		is cacheable (oplocked).  Unfortunately, even if a file
658		is not oplocked, it could still be cacheable (ie cifs client
659		could grant fcntl leases if no other local processes are using
660		the file) for cases for example such as when the server does not
661		support oplocks and the user is sure that the only updates to
662		the file will be from this client. Specifying this mount option
663		will allow the cifs client to check for leases (only) locally
664		for files which are not oplocked instead of denying leases
665		in that case. (EXPERIMENTAL)
666  sec
667		Security mode.  Allowed values are:
668
669			none
670				attempt to connection as a null user (no name)
671			krb5
672				Use Kerberos version 5 authentication
673			krb5i
674				Use Kerberos authentication and packet signing
675			ntlm
676				Use NTLM password hashing (default)
677			ntlmi
678				Use NTLM password hashing with signing (if
679				/proc/fs/cifs/PacketSigningEnabled on or if
680				server requires signing also can be the default)
681			ntlmv2
682				Use NTLMv2 password hashing
683			ntlmv2i
684				Use NTLMv2 password hashing with packet signing
685			lanman
686				(if configured in kernel config) use older
687				lanman hash
688  hard
689		Retry file operations if server is not responding
690  soft
691		Limit retries to unresponsive servers (usually only
692		one retry) before returning an error.  (default)
693
694The mount.cifs mount helper also accepts a few mount options before -o
695including:
696
697=============== ===============================================================
698	-S      take password from stdin (equivalent to setting the environment
699		variable ``PASSWD_FD=0``
700	-V      print mount.cifs version
701	-?      display simple usage information
702=============== ===============================================================
703
704With most 2.6 kernel versions of modutils, the version of the cifs kernel
705module can be displayed via modinfo.
706
707Misc /proc/fs/cifs Flags and Debug Info
708=======================================
709
710Informational pseudo-files:
711
712======================= =======================================================
713DebugData		Displays information about active CIFS sessions and
714			shares, features enabled as well as the cifs.ko
715			version.
716Stats			Lists summary resource usage information as well as per
717			share statistics.
718======================= =======================================================
719
720Configuration pseudo-files:
721
722======================= =======================================================
723SecurityFlags		Flags which control security negotiation and
724			also packet signing. Authentication (may/must)
725			flags (e.g. for NTLM and/or NTLMv2) may be combined with
726			the signing flags.  Specifying two different password
727			hashing mechanisms (as "must use") on the other hand
728			does not make much sense. Default flags are::
729
730				0x07007
731
732			(NTLM, NTLMv2 and packet signing allowed).  The maximum
733			allowable flags if you want to allow mounts to servers
734			using weaker password hashes is 0x37037 (lanman,
735			plaintext, ntlm, ntlmv2, signing allowed).  Some
736			SecurityFlags require the corresponding menuconfig
737			options to be enabled (lanman and plaintext require
738			CONFIG_CIFS_WEAK_PW_HASH for example).  Enabling
739			plaintext authentication currently requires also
740			enabling lanman authentication in the security flags
741			because the cifs module only supports sending
742			laintext passwords using the older lanman dialect
743			form of the session setup SMB.  (e.g. for authentication
744			using plain text passwords, set the SecurityFlags
745			to 0x30030)::
746
747			  may use packet signing			0x00001
748			  must use packet signing			0x01001
749			  may use NTLM (most common password hash)	0x00002
750			  must use NTLM					0x02002
751			  may use NTLMv2				0x00004
752			  must use NTLMv2				0x04004
753			  may use Kerberos security			0x00008
754			  must use Kerberos				0x08008
755			  may use lanman (weak) password hash		0x00010
756			  must use lanman password hash			0x10010
757			  may use plaintext passwords			0x00020
758			  must use plaintext passwords			0x20020
759			  (reserved for future packet encryption)	0x00040
760
761cifsFYI			If set to non-zero value, additional debug information
762			will be logged to the system error log.  This field
763			contains three flags controlling different classes of
764			debugging entries.  The maximum value it can be set
765			to is 7 which enables all debugging points (default 0).
766			Some debugging statements are not compiled into the
767			cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
768			kernel configuration. cifsFYI may be set to one or
769			nore of the following flags (7 sets them all)::
770
771			  +-----------------------------------------------+------+
772			  | log cifs informational messages		  | 0x01 |
773			  +-----------------------------------------------+------+
774			  | log return codes from cifs entry points	  | 0x02 |
775			  +-----------------------------------------------+------+
776			  | log slow responses				  | 0x04 |
777			  | (ie which take longer than 1 second)	  |      |
778			  |                                               |      |
779			  | CONFIG_CIFS_STATS2 must be enabled in .config |      |
780			  +-----------------------------------------------+------+
781
782traceSMB		If set to one, debug information is logged to the
783			system error log with the start of smb requests
784			and responses (default 0)
785LookupCacheEnable	If set to one, inode information is kept cached
786			for one second improving performance of lookups
787			(default 1)
788LinuxExtensionsEnabled	If set to one then the client will attempt to
789			use the CIFS "UNIX" extensions which are optional
790			protocol enhancements that allow CIFS servers
791			to return accurate UID/GID information as well
792			as support symbolic links. If you use servers
793			such as Samba that support the CIFS Unix
794			extensions but do not want to use symbolic link
795			support and want to map the uid and gid fields
796			to values supplied at mount (rather than the
797			actual values, then set this to zero. (default 1)
798======================= =======================================================
799
800These experimental features and tracing can be enabled by changing flags in
801/proc/fs/cifs (after the cifs module has been installed or built into the
802kernel, e.g.  insmod cifs).  To enable a feature set it to 1 e.g.  to enable
803tracing to the kernel message log type::
804
805	echo 7 > /proc/fs/cifs/cifsFYI
806
807cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
808logging of various informational messages.  2 enables logging of non-zero
809SMB return codes while 4 enables logging of requests that take longer
810than one second to complete (except for byte range lock requests).
811Setting it to 4 requires CONFIG_CIFS_STATS2 to be set in kernel configuration
812(.config). Setting it to seven enables all three.  Finally, tracing
813the start of smb requests and responses can be enabled via::
814
815	echo 1 > /proc/fs/cifs/traceSMB
816
817Per share (per client mount) statistics are available in /proc/fs/cifs/Stats.
818Additional information is available if CONFIG_CIFS_STATS2 is enabled in the
819kernel configuration (.config).  The statistics returned include counters which
820represent the number of attempted and failed (ie non-zero return code from the
821server) SMB3 (or cifs) requests grouped by request type (read, write, close etc.).
822Also recorded is the total bytes read and bytes written to the server for
823that share.  Note that due to client caching effects this can be less than the
824number of bytes read and written by the application running on the client.
825Statistics can be reset to zero by ``echo 0 > /proc/fs/cifs/Stats`` which may be
826useful if comparing performance of two different scenarios.
827
828Also note that ``cat /proc/fs/cifs/DebugData`` will display information about
829the active sessions and the shares that are mounted.
830
831Enabling Kerberos (extended security) works but requires version 1.2 or later
832of the helper program cifs.upcall to be present and to be configured in the
833/etc/request-key.conf file.  The cifs.upcall helper program is from the Samba
834project(http://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
835require this helper. Note that NTLMv2 security (which does not require the
836cifs.upcall helper program), instead of using Kerberos, is sufficient for
837some use cases.
838
839DFS support allows transparent redirection to shares in an MS-DFS name space.
840In addition, DFS support for target shares which are specified as UNC
841names which begin with host names (rather than IP addresses) requires
842a user space helper (such as cifs.upcall) to be present in order to
843translate host names to ip address, and the user space helper must also
844be configured in the file /etc/request-key.conf.  Samba, Windows servers and
845many NAS appliances support DFS as a way of constructing a global name
846space to ease network configuration and improve reliability.
847
848To use cifs Kerberos and DFS support, the Linux keyutils package should be
849installed and something like the following lines should be added to the
850/etc/request-key.conf file::
851
852  create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
853  create dns_resolver * * /usr/local/sbin/cifs.upcall %k
854
855CIFS kernel module parameters
856=============================
857These module parameters can be specified or modified either during the time of
858module loading or during the runtime by using the interface::
859
860	/proc/module/cifs/parameters/<param>
861
862i.e.::
863
864    echo "value" > /sys/module/cifs/parameters/<param>
865
866================= ==========================================================
8671. enable_oplocks Enable or disable oplocks. Oplocks are enabled by default.
868		  [Y/y/1]. To disable use any of [N/n/0].
869================= ==========================================================
870