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)
19or https://samba.org/samba/PFIF/
20for more details.
21
22
23For questions or bug reports please contact:
24
25    smfrench@gmail.com
26
27See the project page at: https://wiki.samba.org/index.php/LinuxCIFS_utils
28
29Build instructions
30==================
31
32For Linux:
33
341) Download the kernel (e.g. from https://www.kernel.org)
35   and change directory into the top of the kernel directory tree
36   (e.g. /usr/src/linux-2.5.73)
372) make menuconfig (or make xconfig)
383) select cifs from within the network filesystem choices
394) save and exit
405) make
41
42
43Installation instructions
44=========================
45
46If you have built the CIFS vfs as module (successfully) simply
47type ``make modules_install`` (or if you prefer, manually copy the file to
48the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.ko).
49
50If you have built the CIFS vfs into the kernel itself, follow the instructions
51for your distribution on how to install a new kernel (usually you
52would simply type ``make install``).
53
54If you do not have the utility mount.cifs (in the Samba 4.x source tree and on
55the CIFS VFS web site) copy it to the same directory in which mount helpers
56reside (usually /sbin).  Although the helper software is not
57required, mount.cifs is recommended.  Most distros include a ``cifs-utils``
58package that includes this utility so it is recommended to install this.
59
60Note that running the Winbind pam/nss module (logon service) on all of your
61Linux clients is useful in mapping Uids and Gids consistently across the
62domain to the proper network user.  The mount.cifs mount helper can be
63found at cifs-utils.git on git.samba.org
64
65If cifs is built as a module, then the size and number of network buffers
66and maximum number of simultaneous requests to one server can be configured.
67Changing these from their defaults is not recommended. By executing modinfo::
68
69	modinfo kernel/fs/cifs/cifs.ko
70
71on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
72at module initialization time (by running insmod cifs.ko) can be seen.
73
74Recommendations
75===============
76
77To improve security the SMB2.1 dialect or later (usually will get SMB3) is now
78the new default. To use old dialects (e.g. to mount Windows XP) use "vers=1.0"
79on mount (or vers=2.0 for Windows Vista).  Note that the CIFS (vers=1.0) is
80much older and less secure than the default dialect SMB3 which includes
81many advanced security features such as downgrade attack detection
82and encrypted shares and stronger signing and authentication algorithms.
83There are additional mount options that may be helpful for SMB3 to get
84improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1):
85
86   ``mfsymlinks`` and either ``cifsacl`` or ``modefromsid`` (usually with ``idsfromsid``)
87
88Allowing User Mounts
89====================
90
91To permit users to mount and unmount over directories they own is possible
92with the cifs vfs.  A way to enable such mounting is to mark the mount.cifs
93utility as suid (e.g. ``chmod +s /sbin/mount.cifs``). To enable users to
94umount shares they mount requires
95
961) mount.cifs version 1.4 or later
972) an entry for the share in /etc/fstab indicating that a user may
98   unmount it e.g.::
99
100     //server/usersharename  /mnt/username cifs user 0 0
101
102Note that when the mount.cifs utility is run suid (allowing user mounts),
103in order to reduce risks, the ``nosuid`` mount flag is passed in on mount to
104disallow execution of an suid program mounted on the remote target.
105When mount is executed as root, nosuid is not passed in by default,
106and execution of suid programs on the remote target would be enabled
107by default. This can be changed, as with nfs and other filesystems,
108by simply specifying ``nosuid`` among the mount options. For user mounts
109though to be able to pass the suid flag to mount requires rebuilding
110mount.cifs with the following flag: CIFS_ALLOW_USR_SUID
111
112There is a corresponding manual page for cifs mounting in the Samba 3.0 and
113later source tree in docs/manpages/mount.cifs.8
114
115Allowing User Unmounts
116======================
117
118To permit users to unmount directories that they have user mounted (see above),
119the utility umount.cifs may be used.  It may be invoked directly, or if
120umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
121(at least for most versions of the umount utility) for umount of cifs
122mounts, unless umount is invoked with -i (which will avoid invoking a umount
123helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
124as suid (e.g. ``chmod +s /sbin/umount.cifs``) or equivalent (some distributions
125allow adding entries to a file to the /etc/permissions file to achieve the
126equivalent suid effect).  For this utility to succeed the target path
127must be a cifs mount, and the uid of the current user must match the uid
128of the user who mounted the resource.
129
130Also note that the customary way of allowing user mounts and unmounts is
131(instead of using mount.cifs and unmount.cifs as suid) to add a line
132to the file /etc/fstab for each //server/share you wish to mount, but
133this can become unwieldy when potential mount targets include many
134or  unpredictable UNC names.
135
136Samba Considerations
137====================
138
139Most current servers support SMB2.1 and SMB3 which are more secure,
140but there are useful protocol extensions for the older less secure CIFS
141dialect, so to get the maximum benefit if mounting using the older dialect
142(CIFS/SMB1), we recommend using a server that supports the SNIA CIFS
143Unix Extensions standard (e.g. almost any  version of Samba ie version
1442.2.5 or later) but the CIFS vfs works fine with a wide variety of CIFS servers.
145Note that uid, gid and file permissions will display default values if you do
146not have a server that supports the Unix extensions for CIFS (such as Samba
1472.2.5 or later).  To enable the Unix CIFS Extensions in the Samba server, add
148the line::
149
150	unix extensions = yes
151
152to your smb.conf file on the server.  Note that the following smb.conf settings
153are also useful (on the Samba server) when the majority of clients are Unix or
154Linux::
155
156	case sensitive = yes
157	delete readonly = yes
158	ea support = yes
159
160Note that server ea support is required for supporting xattrs from the Linux
161cifs client, and that EA support is present in later versions of Samba (e.g.
1623.0.6 and later (also EA support works in all versions of Windows, at least to
163shares on NTFS filesystems).  Extended Attribute (xattr) support is an optional
164feature of most Linux filesystems which may require enabling via
165make menuconfig. Client support for extended attributes (user xattr) can be
166disabled on a per-mount basis by specifying ``nouser_xattr`` on mount.
167
168The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
169version 3.10 and later.  Setting POSIX ACLs requires enabling both XATTR and
170then POSIX support in the CIFS configuration options when building the cifs
171module.  POSIX ACL support can be disabled on a per mount basic by specifying
172``noacl`` on mount.
173
174Some administrators may want to change Samba's smb.conf ``map archive`` and
175``create mask`` parameters from the default.  Unless the create mask is changed
176newly created files can end up with an unnecessarily restrictive default mode,
177which may not be what you want, although if the CIFS Unix extensions are
178enabled on the server and client, subsequent setattr calls (e.g. chmod) can
179fix the mode.  Note that creating special devices (mknod) remotely
180may require specifying a mkdev function to Samba if you are not using
181Samba 3.0.6 or later.  For more information on these see the manual pages
182(``man smb.conf``) on the Samba server system.  Note that the cifs vfs,
183unlike the smbfs vfs, does not read the smb.conf on the client system
184(the few optional settings are passed in on mount via -o parameters instead).
185Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
186open files (required for strict POSIX compliance).  Windows Servers already
187supported this feature. Samba server does not allow symlinks that refer to files
188outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
189files with absolute paths (ie beginning with slash) such as::
190
191	 ln -s /mnt/foo bar
192
193would be forbidden. Samba 3.0.6 server or later includes the ability to create
194such symlinks safely by converting unsafe symlinks (ie symlinks to server
195files that are outside of the share) to a samba specific format on the server
196that is ignored by local server applications and non-cifs clients and that will
197not be traversed by the Samba server).  This is opaque to the Linux client
198application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
199later, but only for remote clients using the CIFS Unix extensions, and will
200be invisible to Windows clients and typically will not affect local
201applications running on the same server as Samba.
202
203Use instructions
204================
205
206Once the CIFS VFS support is built into the kernel or installed as a module
207(cifs.ko), you can use mount syntax like the following to access Samba or
208Mac or Windows servers::
209
210  mount -t cifs //9.53.216.11/e$ /mnt -o username=myname,password=mypassword
211
212Before -o the option -v may be specified to make the mount.cifs
213mount helper display the mount steps more verbosely.
214After -o the following commonly used cifs vfs specific options
215are supported::
216
217  username=<username>
218  password=<password>
219  domain=<domain name>
220
221Other cifs mount options are described below.  Use of TCP names (in addition to
222ip addresses) is available if the mount helper (mount.cifs) is installed. If
223you do not trust the server to which are mounted, or if you do not have
224cifs signing enabled (and the physical network is insecure), consider use
225of the standard mount options ``noexec`` and ``nosuid`` to reduce the risk of
226running an altered binary on your local system (downloaded from a hostile server
227or altered by a hostile router).
228
229Although mounting using format corresponding to the CIFS URL specification is
230not possible in mount.cifs yet, it is possible to use an alternate format
231for the server and sharename (which is somewhat similar to NFS style mount
232syntax) instead of the more widely used UNC format (i.e. \\server\share)::
233
234  mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
235
236When using the mount helper mount.cifs, passwords may be specified via alternate
237mechanisms, instead of specifying it after -o using the normal ``pass=`` syntax
238on the command line:
2391) By including it in a credential file. Specify credentials=filename as one
240of the mount options. Credential files contain two lines::
241
242	username=someuser
243	password=your_password
244
2452) By specifying the password in the PASSWD environment variable (similarly
246   the user name can be taken from the USER environment variable).
2473) By specifying the password in a file by name via PASSWD_FILE
2484) By specifying the password in a file by file descriptor via PASSWD_FD
249
250If no password is provided, mount.cifs will prompt for password entry
251
252Restrictions
253============
254
255Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
2561001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a
257problem as most servers support this.
258
259Valid filenames differ between Windows and Linux.  Windows typically restricts
260filenames which contain certain reserved characters (e.g.the character :
261which is used to delimit the beginning of a stream name by Windows), while
262Linux allows a slightly wider set of valid characters in filenames. Windows
263servers can remap such characters when an explicit mapping is specified in
264the Server's registry.  Samba starting with version 3.10 will allow such
265filenames (ie those which contain valid Linux characters, which normally
266would be forbidden for Windows/CIFS semantics) as long as the server is
267configured for Unix Extensions (and the client has not disabled
268/proc/fs/cifs/LinuxExtensionsEnabled). In addition the mount option
269``mapposix`` can be used on CIFS (vers=1.0) to force the mapping of
270illegal Windows/NTFS/SMB characters to a remap range (this mount parameter
271is the default for SMB3). This remap (``mapposix``) range is also
272compatible with Mac (and "Services for Mac" on some older Windows).
273
274CIFS VFS Mount Options
275======================
276A partial list of the supported mount options follows:
277
278  username
279		The user name to use when trying to establish
280		the CIFS session.
281  password
282		The user password.  If the mount helper is
283		installed, the user will be prompted for password
284		if not supplied.
285  ip
286		The ip address of the target server
287  unc
288		The target server Universal Network Name (export) to
289		mount.
290  domain
291		Set the SMB/CIFS workgroup name prepended to the
292		username during CIFS session establishment
293  forceuid
294		Set the default uid for inodes to the uid
295		passed in on mount. For mounts to servers
296		which do support the CIFS Unix extensions, such as a
297		properly configured Samba server, the server provides
298		the uid, gid and mode so this parameter should not be
299		specified unless the server and clients uid and gid
300		numbering differ.  If the server and client are in the
301		same domain (e.g. running winbind or nss_ldap) and
302		the server supports the Unix Extensions then the uid
303		and gid can be retrieved from the server (and uid
304		and gid would not have to be specified on the mount.
305		For servers which do not support the CIFS Unix
306		extensions, the default uid (and gid) returned on lookup
307		of existing files will be the uid (gid) of the person
308		who executed the mount (root, except when mount.cifs
309		is configured setuid for user mounts) unless the ``uid=``
310		(gid) mount option is specified. Also note that permission
311		checks (authorization checks) on accesses to a file occur
312		at the server, but there are cases in which an administrator
313		may want to restrict at the client as well.  For those
314		servers which do not report a uid/gid owner
315		(such as Windows), permissions can also be checked at the
316		client, and a crude form of client side permission checking
317		can be enabled by specifying file_mode and dir_mode on
318		the client.  (default)
319  forcegid
320		(similar to above but for the groupid instead of uid) (default)
321  noforceuid
322		Fill in file owner information (uid) by requesting it from
323		the server if possible. With this option, the value given in
324		the uid= option (on mount) will only be used if the server
325		can not support returning uids on inodes.
326  noforcegid
327		(similar to above but for the group owner, gid, instead of uid)
328  uid
329		Set the default uid for inodes, and indicate to the
330		cifs kernel driver which local user mounted. If the server
331		supports the unix extensions the default uid is
332		not used to fill in the owner fields of inodes (files)
333		unless the ``forceuid`` parameter is specified.
334  gid
335		Set the default gid for inodes (similar to above).
336  file_mode
337		If CIFS Unix extensions are not supported by the server
338		this overrides the default mode for file inodes.
339  fsc
340		Enable local disk caching using FS-Cache (off by default). This
341		option could be useful to improve performance on a slow link,
342		heavily loaded server and/or network where reading from the
343		disk is faster than reading from the server (over the network).
344		This could also impact scalability positively as the
345		number of calls to the server are reduced. However, local
346		caching is not suitable for all workloads for e.g. read-once
347		type workloads. So, you need to consider carefully your
348		workload/scenario before using this option. Currently, local
349		disk caching is functional for CIFS files opened as read-only.
350  dir_mode
351		If CIFS Unix extensions are not supported by the server
352		this overrides the default mode for directory inodes.
353  port
354		attempt to contact the server on this tcp port, before
355		trying the usual ports (port 445, then 139).
356  iocharset
357		Codepage used to convert local path names to and from
358		Unicode. Unicode is used by default for network path
359		names if the server supports it.  If iocharset is
360		not specified then the nls_default specified
361		during the local client kernel build will be used.
362		If server does not support Unicode, this parameter is
363		unused.
364  rsize
365		default read size (usually 16K). The client currently
366		can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
367		defaults to 16K and may be changed (from 8K to the maximum
368		kmalloc size allowed by your kernel) at module install time
369		for cifs.ko. Setting CIFSMaxBufSize to a very large value
370		will cause cifs to use more memory and may reduce performance
371		in some cases.  To use rsize greater than 127K (the original
372		cifs protocol maximum) also requires that the server support
373		a new Unix Capability flag (for very large read) which some
374		newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
375		set from a minimum of 2048 to a maximum of 130048 (127K or
376		CIFSMaxBufSize, whichever is smaller)
377  wsize
378		default write size (default 57344)
379		maximum wsize currently allowed by CIFS is 57344 (fourteen
380		4096 byte pages)
381  actimeo=n
382		attribute cache timeout in seconds (default 1 second).
383		After this timeout, the cifs client requests fresh attribute
384		information from the server. This option allows to tune the
385		attribute cache timeout to suit the workload needs. Shorter
386		timeouts mean better the cache coherency, but increased number
387		of calls to the server. Longer timeouts mean reduced number
388		of calls to the server at the expense of less stricter cache
389		coherency checks (i.e. incorrect attribute cache for a short
390		period of time).
391  rw
392		mount the network share read-write (note that the
393		server may still consider the share read-only)
394  ro
395		mount network share read-only
396  version
397		used to distinguish different versions of the
398		mount helper utility (not typically needed)
399  sep
400		if first mount option (after the -o), overrides
401		the comma as the separator between the mount
402		parms. e.g.::
403
404			-o user=myname,password=mypassword,domain=mydom
405
406		could be passed instead with period as the separator by::
407
408			-o sep=.user=myname.password=mypassword.domain=mydom
409
410		this might be useful when comma is contained within username
411		or password or domain. This option is less important
412		when the cifs mount helper cifs.mount (version 1.1 or later)
413		is used.
414  nosuid
415		Do not allow remote executables with the suid bit
416		program to be executed.  This is only meaningful for mounts
417		to servers such as Samba which support the CIFS Unix Extensions.
418		If you do not trust the servers in your network (your mount
419		targets) it is recommended that you specify this option for
420		greater security.
421  exec
422		Permit execution of binaries on the mount.
423  noexec
424		Do not permit execution of binaries on the mount.
425  dev
426		Recognize block devices on the remote mount.
427  nodev
428		Do not recognize devices on the remote mount.
429  suid
430		Allow remote files on this mountpoint with suid enabled to
431		be executed (default for mounts when executed as root,
432		nosuid is default for user mounts).
433  credentials
434		Although ignored by the cifs kernel component, it is used by
435		the mount helper, mount.cifs. When mount.cifs is installed it
436		opens and reads the credential file specified in order
437		to obtain the userid and password arguments which are passed to
438		the cifs vfs.
439  guest
440		Although ignored by the kernel component, the mount.cifs
441		mount helper will not prompt the user for a password
442		if guest is specified on the mount options.  If no
443		password is specified a null password will be used.
444  perm
445		Client does permission checks (vfs_permission check of uid
446		and gid of the file against the mode and desired operation),
447		Note that this is in addition to the normal ACL check on the
448		target machine done by the server software.
449		Client permission checking is enabled by default.
450  noperm
451		Client does not do permission checks.  This can expose
452		files on this mount to access by other users on the local
453		client system. It is typically only needed when the server
454		supports the CIFS Unix Extensions but the UIDs/GIDs on the
455		client and server system do not match closely enough to allow
456		access by the user doing the mount, but it may be useful with
457		non CIFS Unix Extension mounts for cases in which the default
458		mode is specified on the mount but is not to be enforced on the
459		client (e.g. perhaps when MultiUserMount is enabled)
460		Note that this does not affect the normal ACL check on the
461		target machine done by the server software (of the server
462		ACL against the user name provided at mount time).
463  serverino
464		Use server's inode numbers instead of generating automatically
465		incrementing inode numbers on the client.  Although this will
466		make it easier to spot hardlinked files (as they will have
467		the same inode numbers) and inode numbers may be persistent,
468		note that the server does not guarantee that the inode numbers
469		are unique if multiple server side mounts are exported under a
470		single share (since inode numbers on the servers might not
471		be unique if multiple filesystems are mounted under the same
472		shared higher level directory).  Note that some older
473		(e.g. pre-Windows 2000) do not support returning UniqueIDs
474		or the CIFS Unix Extensions equivalent and for those
475		this mount option will have no effect.  Exporting cifs mounts
476		under nfsd requires this mount option on the cifs mount.
477		This is now the default if server supports the
478		required network operation.
479  noserverino
480		Client generates inode numbers (rather than using the actual one
481		from the server). These inode numbers will vary after
482		unmount or reboot which can confuse some applications,
483		but not all server filesystems support unique inode
484		numbers.
485  setuids
486		If the CIFS Unix extensions are negotiated with the server
487		the client will attempt to set the effective uid and gid of
488		the local process on newly created files, directories, and
489		devices (create, mkdir, mknod).  If the CIFS Unix Extensions
490		are not negotiated, for newly created files and directories
491		instead of using the default uid and gid specified on
492		the mount, cache the new file's uid and gid locally which means
493		that the uid for the file can change when the inode is
494		reloaded (or the user remounts the share).
495  nosetuids
496		The client will not attempt to set the uid and gid on
497		on newly created files, directories, and devices (create,
498		mkdir, mknod) which will result in the server setting the
499		uid and gid to the default (usually the server uid of the
500		user who mounted the share).  Letting the server (rather than
501		the client) set the uid and gid is the default. If the CIFS
502		Unix Extensions are not negotiated then the uid and gid for
503		new files will appear to be the uid (gid) of the mounter or the
504		uid (gid) parameter specified on the mount.
505  netbiosname
506		When mounting to servers via port 139, specifies the RFC1001
507		source name to use to represent the client netbios machine
508		name when doing the RFC1001 netbios session initialize.
509  direct
510		Do not do inode data caching on files opened on this mount.
511		This precludes mmapping files on this mount. In some cases
512		with fast networks and little or no caching benefits on the
513		client (e.g. when the application is doing large sequential
514		reads bigger than page size without rereading the same data)
515		this can provide better performance than the default
516		behavior which caches reads (readahead) and writes
517		(writebehind) through the local Linux client pagecache
518		if oplock (caching token) is granted and held. Note that
519		direct allows write operations larger than page size
520		to be sent to the server.
521  strictcache
522		Use for switching on strict cache mode. In this mode the
523		client read from the cache all the time it has Oplock Level II,
524		otherwise - read from the server. All written data are stored
525		in the cache, but if the client doesn't have Exclusive Oplock,
526		it writes the data to the server.
527  rwpidforward
528		Forward pid of a process who opened a file to any read or write
529		operation on that file. This prevent applications like WINE
530		from failing on read and write if we use mandatory brlock style.
531  acl
532		Allow setfacl and getfacl to manage posix ACLs if server
533		supports them.  (default)
534  noacl
535		Do not allow setfacl and getfacl calls on this mount
536  user_xattr
537		Allow getting and setting user xattrs (those attributes whose
538		name begins with ``user.`` or ``os2.``) as OS/2 EAs (extended
539		attributes) to the server.  This allows support of the
540		setfattr and getfattr utilities. (default)
541  nouser_xattr
542		Do not allow getfattr/setfattr to get/set/list xattrs
543  mapchars
544		Translate six of the seven reserved characters (not backslash)::
545
546			*?<>|:
547
548		to the remap range (above 0xF000), which also
549		allows the CIFS client to recognize files created with
550		such characters by Windows's POSIX emulation. This can
551		also be useful when mounting to most versions of Samba
552		(which also forbids creating and opening files
553		whose names contain any of these seven characters).
554		This has no effect if the server does not support
555		Unicode on the wire.
556  nomapchars
557		Do not translate any of these seven characters (default).
558  nocase
559		Request case insensitive path name matching (case
560		sensitive is the default if the server supports it).
561		(mount option ``ignorecase`` is identical to ``nocase``)
562  posixpaths
563		If CIFS Unix extensions are supported, attempt to
564		negotiate posix path name support which allows certain
565		characters forbidden in typical CIFS filenames, without
566		requiring remapping. (default)
567  noposixpaths
568		If CIFS Unix extensions are supported, do not request
569		posix path name support (this may cause servers to
570		reject creatingfile with certain reserved characters).
571  nounix
572		Disable the CIFS Unix Extensions for this mount (tree
573		connection). This is rarely needed, but it may be useful
574		in order to turn off multiple settings all at once (ie
575		posix acls, posix locks, posix paths, symlink support
576		and retrieving uids/gids/mode from the server) or to
577		work around a bug in server which implement the Unix
578		Extensions.
579  nobrl
580		Do not send byte range lock requests to the server.
581		This is necessary for certain applications that break
582		with cifs style mandatory byte range locks (and most
583		cifs servers do not yet support requesting advisory
584		byte range locks).
585  forcemandatorylock
586		Even if the server supports posix (advisory) byte range
587		locking, send only mandatory lock requests.  For some
588		(presumably rare) applications, originally coded for
589		DOS/Windows, which require Windows style mandatory byte range
590		locking, they may be able to take advantage of this option,
591		forcing the cifs client to only send mandatory locks
592		even if the cifs server would support posix advisory locks.
593		``forcemand`` is accepted as a shorter form of this mount
594		option.
595  nostrictsync
596		If this mount option is set, when an application does an
597		fsync call then the cifs client does not send an SMB Flush
598		to the server (to force the server to write all dirty data
599		for this file immediately to disk), although cifs still sends
600		all dirty (cached) file data to the server and waits for the
601		server to respond to the write.  Since SMB Flush can be
602		very slow, and some servers may be reliable enough (to risk
603		delaying slightly flushing the data to disk on the server),
604		turning on this option may be useful to improve performance for
605		applications that fsync too much, at a small risk of server
606		crash.  If this mount option is not set, by default cifs will
607		send an SMB flush request (and wait for a response) on every
608		fsync call.
609  nodfs
610		Disable DFS (global name space support) even if the
611		server claims to support it.  This can help work around
612		a problem with parsing of DFS paths with Samba server
613		versions 3.0.24 and 3.0.25.
614  remount
615		remount the share (often used to change from ro to rw mounts
616		or vice versa)
617  cifsacl
618		Report mode bits (e.g. on stat) based on the Windows ACL for
619		the file. (EXPERIMENTAL)
620  servern
621		Specify the server 's netbios name (RFC1001 name) to use
622		when attempting to setup a session to the server.
623		This is needed for mounting to some older servers (such
624		as OS/2 or Windows 98 and Windows ME) since they do not
625		support a default server name.  A server name can be up
626		to 15 characters long and is usually uppercased.
627  sfu
628		When the CIFS Unix Extensions are not negotiated, attempt to
629		create device files and fifos in a format compatible with
630		Services for Unix (SFU).  In addition retrieve bits 10-12
631		of the mode via the SETFILEBITS extended attribute (as
632		SFU does).  In the future the bottom 9 bits of the
633		mode also will be emulated using queries of the security
634		descriptor (ACL).
635  mfsymlinks
636		Enable support for Minshall+French symlinks
637		(see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
638		This option is ignored when specified together with the
639		'sfu' option. Minshall+French symlinks are used even if
640		the server supports the CIFS Unix Extensions.
641  sign
642		Must use packet signing (helps avoid unwanted data modification
643		by intermediate systems in the route).  Note that signing
644		does not work with lanman or plaintext authentication.
645  seal
646		Must seal (encrypt) all data on this mounted share before
647		sending on the network.  Requires support for Unix Extensions.
648		Note that this differs from the sign mount option in that it
649		causes encryption of data sent over this mounted share but other
650		shares mounted to the same server are unaffected.
651  locallease
652		This option is rarely needed. Fcntl F_SETLEASE is
653		used by some applications such as Samba and NFSv4 server to
654		check to see whether a file is cacheable.  CIFS has no way
655		to explicitly request a lease, but can check whether a file
656		is cacheable (oplocked).  Unfortunately, even if a file
657		is not oplocked, it could still be cacheable (ie cifs client
658		could grant fcntl leases if no other local processes are using
659		the file) for cases for example such as when the server does not
660		support oplocks and the user is sure that the only updates to
661		the file will be from this client. Specifying this mount option
662		will allow the cifs client to check for leases (only) locally
663		for files which are not oplocked instead of denying leases
664		in that case. (EXPERIMENTAL)
665  sec
666		Security mode.  Allowed values are:
667
668			none
669				attempt to connection as a null user (no name)
670			krb5
671				Use Kerberos version 5 authentication
672			krb5i
673				Use Kerberos authentication and packet signing
674			ntlm
675				Use NTLM password hashing (default)
676			ntlmi
677				Use NTLM password hashing with signing (if
678				/proc/fs/cifs/PacketSigningEnabled on or if
679				server requires signing also can be the default)
680			ntlmv2
681				Use NTLMv2 password hashing
682			ntlmv2i
683				Use NTLMv2 password hashing with packet signing
684			lanman
685				(if configured in kernel config) use older
686				lanman hash
687  hard
688		Retry file operations if server is not responding
689  soft
690		Limit retries to unresponsive servers (usually only
691		one retry) before returning an error.  (default)
692
693The mount.cifs mount helper also accepts a few mount options before -o
694including:
695
696=============== ===============================================================
697	-S      take password from stdin (equivalent to setting the environment
698		variable ``PASSWD_FD=0``
699	-V      print mount.cifs version
700	-?      display simple usage information
701=============== ===============================================================
702
703With most 2.6 kernel versions of modutils, the version of the cifs kernel
704module can be displayed via modinfo.
705
706Misc /proc/fs/cifs Flags and Debug Info
707=======================================
708
709Informational pseudo-files:
710
711======================= =======================================================
712DebugData		Displays information about active CIFS sessions and
713			shares, features enabled as well as the cifs.ko
714			version.
715Stats			Lists summary resource usage information as well as per
716			share statistics.
717open_files		List all the open file handles on all active SMB sessions.
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.  Enabling plaintext
738			authentication currently requires also enabling
739			lanman authentication in the security flags
740			because the cifs module only supports sending
741			laintext passwords using the older lanman dialect
742			form of the session setup SMB.  (e.g. for authentication
743			using plain text passwords, set the SecurityFlags
744			to 0x30030)::
745
746			  may use packet signing			0x00001
747			  must use packet signing			0x01001
748			  may use NTLM (most common password hash)	0x00002
749			  must use NTLM					0x02002
750			  may use NTLMv2				0x00004
751			  must use NTLMv2				0x04004
752			  may use Kerberos security			0x00008
753			  must use Kerberos				0x08008
754			  may use lanman (weak) password hash		0x00010
755			  must use lanman password hash			0x10010
756			  may use plaintext passwords			0x00020
757			  must use plaintext passwords			0x20020
758			  (reserved for future packet encryption)	0x00040
759
760cifsFYI			If set to non-zero value, additional debug information
761			will be logged to the system error log.  This field
762			contains three flags controlling different classes of
763			debugging entries.  The maximum value it can be set
764			to is 7 which enables all debugging points (default 0).
765			Some debugging statements are not compiled into the
766			cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
767			kernel configuration. cifsFYI may be set to one or
768			nore of the following flags (7 sets them all)::
769
770			  +-----------------------------------------------+------+
771			  | log cifs informational messages		  | 0x01 |
772			  +-----------------------------------------------+------+
773			  | log return codes from cifs entry points	  | 0x02 |
774			  +-----------------------------------------------+------+
775			  | log slow responses				  | 0x04 |
776			  | (ie which take longer than 1 second)	  |      |
777			  |                                               |      |
778			  | CONFIG_CIFS_STATS2 must be enabled in .config |      |
779			  +-----------------------------------------------+------+
780
781traceSMB		If set to one, debug information is logged to the
782			system error log with the start of smb requests
783			and responses (default 0)
784LookupCacheEnable	If set to one, inode information is kept cached
785			for one second improving performance of lookups
786			(default 1)
787LinuxExtensionsEnabled	If set to one then the client will attempt to
788			use the CIFS "UNIX" extensions which are optional
789			protocol enhancements that allow CIFS servers
790			to return accurate UID/GID information as well
791			as support symbolic links. If you use servers
792			such as Samba that support the CIFS Unix
793			extensions but do not want to use symbolic link
794			support and want to map the uid and gid fields
795			to values supplied at mount (rather than the
796			actual values, then set this to zero. (default 1)
797dfscache		List the content of the DFS cache.
798			If set to 0, the client will clear the cache.
799======================= =======================================================
800
801These experimental features and tracing can be enabled by changing flags in
802/proc/fs/cifs (after the cifs module has been installed or built into the
803kernel, e.g.  insmod cifs).  To enable a feature set it to 1 e.g.  to enable
804tracing to the kernel message log type::
805
806	echo 7 > /proc/fs/cifs/cifsFYI
807
808cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
809logging of various informational messages.  2 enables logging of non-zero
810SMB return codes while 4 enables logging of requests that take longer
811than one second to complete (except for byte range lock requests).
812Setting it to 4 requires CONFIG_CIFS_STATS2 to be set in kernel configuration
813(.config). Setting it to seven enables all three.  Finally, tracing
814the start of smb requests and responses can be enabled via::
815
816	echo 1 > /proc/fs/cifs/traceSMB
817
818Per share (per client mount) statistics are available in /proc/fs/cifs/Stats.
819Additional information is available if CONFIG_CIFS_STATS2 is enabled in the
820kernel configuration (.config).  The statistics returned include counters which
821represent the number of attempted and failed (ie non-zero return code from the
822server) SMB3 (or cifs) requests grouped by request type (read, write, close etc.).
823Also recorded is the total bytes read and bytes written to the server for
824that share.  Note that due to client caching effects this can be less than the
825number of bytes read and written by the application running on the client.
826Statistics can be reset to zero by ``echo 0 > /proc/fs/cifs/Stats`` which may be
827useful if comparing performance of two different scenarios.
828
829Also note that ``cat /proc/fs/cifs/DebugData`` will display information about
830the active sessions and the shares that are mounted.
831
832Enabling Kerberos (extended security) works but requires version 1.2 or later
833of the helper program cifs.upcall to be present and to be configured in the
834/etc/request-key.conf file.  The cifs.upcall helper program is from the Samba
835project(https://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
836require this helper. Note that NTLMv2 security (which does not require the
837cifs.upcall helper program), instead of using Kerberos, is sufficient for
838some use cases.
839
840DFS support allows transparent redirection to shares in an MS-DFS name space.
841In addition, DFS support for target shares which are specified as UNC
842names which begin with host names (rather than IP addresses) requires
843a user space helper (such as cifs.upcall) to be present in order to
844translate host names to ip address, and the user space helper must also
845be configured in the file /etc/request-key.conf.  Samba, Windows servers and
846many NAS appliances support DFS as a way of constructing a global name
847space to ease network configuration and improve reliability.
848
849To use cifs Kerberos and DFS support, the Linux keyutils package should be
850installed and something like the following lines should be added to the
851/etc/request-key.conf file::
852
853  create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
854  create dns_resolver * * /usr/local/sbin/cifs.upcall %k
855
856CIFS kernel module parameters
857=============================
858These module parameters can be specified or modified either during the time of
859module loading or during the runtime by using the interface::
860
861	/sys/module/cifs/parameters/<param>
862
863i.e.::
864
865    echo "value" > /sys/module/cifs/parameters/<param>
866
867================= ==========================================================
8681. enable_oplocks Enable or disable oplocks. Oplocks are enabled by default.
869		  [Y/y/1]. To disable use any of [N/n/0].
870================= ==========================================================
871