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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

1	This module supports the SMB3 family of advanced network protocols (as well
2	as older dialects, originally called "CIFS" or SMB1).
4	The CIFS VFS module for Linux supports many advanced network filesystem
5	features such as hierarchical DFS like namespace, hardlinks, locking and more.
6	It was designed to comply with the SNIA CIFS Technical Reference (which 
7	supersedes the 1992 X/Open SMB Standard) as well as to perform best practice 
8	practical interoperability with Windows 2000, Windows XP, Samba and equivalent 
9	servers.  This code was developed in participation with the Protocol Freedom
10	Information Foundation.  CIFS and now SMB3 has now become a defacto
11	standard for interoperating between Macs and Windows and major NAS appliances.
13	Please see
14	  http://protocolfreedom.org/ and
15	  http://samba.org/samba/PFIF/
16	for more details.
19	For questions or bug reports please contact:
20	    sfrench@samba.org (sfrench@us.ibm.com) 
22	See the project page at: https://wiki.samba.org/index.php/LinuxCIFS_utils
24	Build instructions:
25	==================
26	For Linux:
27	1) Download the kernel (e.g. from http://www.kernel.org)
28	and change directory into the top of the kernel directory tree
29	(e.g. /usr/src/linux-2.5.73)
30	2) make menuconfig (or make xconfig)
31	3) select cifs from within the network filesystem choices
32	4) save and exit
33	5) make
36	Installation instructions:
37	=========================
38	If you have built the CIFS vfs as module (successfully) simply
39	type "make modules_install" (or if you prefer, manually copy the file to
40	the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.o).
42	If you have built the CIFS vfs into the kernel itself, follow the instructions
43	for your distribution on how to install a new kernel (usually you
44	would simply type "make install").
46	If you do not have the utility mount.cifs (in the Samba 3.0 source tree and on 
47	the CIFS VFS web site) copy it to the same directory in which mount.smbfs and 
48	similar files reside (usually /sbin).  Although the helper software is not  
49	required, mount.cifs is recommended.  Most distros include a "cifs-utils"
50	package that includes this utility so it is recommended to install this.
52	Note that running the Winbind pam/nss module (logon service) on all of your
53	Linux clients is useful in mapping Uids and Gids consistently across the
54	domain to the proper network user.  The mount.cifs mount helper can be
55	found at cifs-utils.git on git.samba.org
57	If cifs is built as a module, then the size and number of network buffers
58	and maximum number of simultaneous requests to one server can be configured.
59	Changing these from their defaults is not recommended. By executing modinfo
60		modinfo kernel/fs/cifs/cifs.ko
61	on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
62	at module initialization time (by running insmod cifs.ko) can be seen.
64	Recommendations
65	===============
66	To improve security the SMB2.1 dialect or later (usually will get SMB3) is now
67	the new default. To use old dialects (e.g. to mount Windows XP) use "vers=1.0"
68	on mount (or vers=2.0 for Windows Vista).  Note that the CIFS (vers=1.0) is
69	much older and less secure than the default dialect SMB3 which includes
70	many advanced security features such as downgrade attack detection
71	and encrypted shares and stronger signing and authentication algorithms.
72	There are additional mount options that may be helpful for SMB3 to get
73	improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1):
74	     "mfsymlinks" and "cifsacl" and "idsfromsid"
76	Allowing User Mounts
77	====================
78	To permit users to mount and unmount over directories they own is possible
79	with the cifs vfs.  A way to enable such mounting is to mark the mount.cifs
80	utility as suid (e.g. "chmod +s /sbin/mount.cifs). To enable users to 
81	umount shares they mount requires
82	1) mount.cifs version 1.4 or later
83	2) an entry for the share in /etc/fstab indicating that a user may
84	unmount it e.g.
85	//server/usersharename  /mnt/username cifs user 0 0
87	Note that when the mount.cifs utility is run suid (allowing user mounts), 
88	in order to reduce risks, the "nosuid" mount flag is passed in on mount to
89	disallow execution of an suid program mounted on the remote target.
90	When mount is executed as root, nosuid is not passed in by default,
91	and execution of suid programs on the remote target would be enabled
92	by default. This can be changed, as with nfs and other filesystems, 
93	by simply specifying "nosuid" among the mount options. For user mounts 
94	though to be able to pass the suid flag to mount requires rebuilding 
95	mount.cifs with the following flag: CIFS_ALLOW_USR_SUID
97	There is a corresponding manual page for cifs mounting in the Samba 3.0 and
98	later source tree in docs/manpages/mount.cifs.8 
100	Allowing User Unmounts
101	======================
102	To permit users to ummount directories that they have user mounted (see above),
103	the utility umount.cifs may be used.  It may be invoked directly, or if 
104	umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
105	(at least for most versions of the umount utility) for umount of cifs
106	mounts, unless umount is invoked with -i (which will avoid invoking a umount
107	helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
108	as suid (e.g. "chmod +s /sbin/umount.cifs") or equivalent (some distributions
109	allow adding entries to a file to the /etc/permissions file to achieve the
110	equivalent suid effect).  For this utility to succeed the target path
111	must be a cifs mount, and the uid of the current user must match the uid
112	of the user who mounted the resource.
114	Also note that the customary way of allowing user mounts and unmounts is 
115	(instead of using mount.cifs and unmount.cifs as suid) to add a line
116	to the file /etc/fstab for each //server/share you wish to mount, but
117	this can become unwieldy when potential mount targets include many
118	or  unpredictable UNC names.
120	Samba Considerations 
121	==================== 
122	To get the maximum benefit from the CIFS VFS, we recommend using a server that 
123	supports the SNIA CIFS Unix Extensions standard (e.g.  Samba 2.2.5 or later or 
124	Samba 3.0) but the CIFS vfs works fine with a wide variety of CIFS servers.  
125	Note that uid, gid and file permissions will display default values if you do 
126	not have a server that supports the Unix extensions for CIFS (such as Samba 
127	2.2.5 or later).  To enable the Unix CIFS Extensions in the Samba server, add 
128	the line: 
130		unix extensions = yes
132	to your smb.conf file on the server.  Note that the following smb.conf settings 
133	are also useful (on the Samba server) when the majority of clients are Unix or 
134	Linux: 
136		case sensitive = yes
137		delete readonly = yes 
138		ea support = yes
140	Note that server ea support is required for supporting xattrs from the Linux
141	cifs client, and that EA support is present in later versions of Samba (e.g. 
142	3.0.6 and later (also EA support works in all versions of Windows, at least to
143	shares on NTFS filesystems).  Extended Attribute (xattr) support is an optional
144	feature of most Linux filesystems which may require enabling via
145	make menuconfig. Client support for extended attributes (user xattr) can be
146	disabled on a per-mount basis by specifying "nouser_xattr" on mount.
148	The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
149	version 3.10 and later.  Setting POSIX ACLs requires enabling both XATTR and 
150	then POSIX support in the CIFS configuration options when building the cifs
151	module.  POSIX ACL support can be disabled on a per mount basic by specifying
152	"noacl" on mount.
154	Some administrators may want to change Samba's smb.conf "map archive" and 
155	"create mask" parameters from the default.  Unless the create mask is changed
156	newly created files can end up with an unnecessarily restrictive default mode,
157	which may not be what you want, although if the CIFS Unix extensions are
158	enabled on the server and client, subsequent setattr calls (e.g. chmod) can
159	fix the mode.  Note that creating special devices (mknod) remotely 
160	may require specifying a mkdev function to Samba if you are not using 
161	Samba 3.0.6 or later.  For more information on these see the manual pages
162	("man smb.conf") on the Samba server system.  Note that the cifs vfs,
163	unlike the smbfs vfs, does not read the smb.conf on the client system 
164	(the few optional settings are passed in on mount via -o parameters instead).  
165	Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
166	open files (required for strict POSIX compliance).  Windows Servers already 
167	supported this feature. Samba server does not allow symlinks that refer to files
168	outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
169	files with absolute paths (ie beginning with slash) such as:
170		 ln -s /mnt/foo bar
171	would be forbidden. Samba 3.0.6 server or later includes the ability to create 
172	such symlinks safely by converting unsafe symlinks (ie symlinks to server 
173	files that are outside of the share) to a samba specific format on the server
174	that is ignored by local server applications and non-cifs clients and that will
175	not be traversed by the Samba server).  This is opaque to the Linux client
176	application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
177	later, but only for remote clients using the CIFS Unix extensions, and will
178	be invisbile to Windows clients and typically will not affect local
179	applications running on the same server as Samba.  
181	Use instructions:
182	================
183	Once the CIFS VFS support is built into the kernel or installed as a module 
184	(cifs.ko), you can use mount syntax like the following to access Samba or
185	Mac or Windows servers:
187	  mount -t cifs //$ /mnt -o username=myname,password=mypassword
189	Before -o the option -v may be specified to make the mount.cifs
190	mount helper display the mount steps more verbosely.  
191	After -o the following commonly used cifs vfs specific options
192	are supported:
194	  username=<username>
195	  password=<password>
196	  domain=<domain name>
198	Other cifs mount options are described below.  Use of TCP names (in addition to
199	ip addresses) is available if the mount helper (mount.cifs) is installed. If
200	you do not trust the server to which are mounted, or if you do not have
201	cifs signing enabled (and the physical network is insecure), consider use
202	of the standard mount options "noexec" and "nosuid" to reduce the risk of 
203	running an altered binary on your local system (downloaded from a hostile server
204	or altered by a hostile router).
206	Although mounting using format corresponding to the CIFS URL specification is
207	not possible in mount.cifs yet, it is possible to use an alternate format
208	for the server and sharename (which is somewhat similar to NFS style mount
209	syntax) instead of the more widely used UNC format (i.e. \\server\share):
210	  mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
212	When using the mount helper mount.cifs, passwords may be specified via alternate
213	mechanisms, instead of specifying it after -o using the normal "pass=" syntax
214	on the command line:
215	1) By including it in a credential file. Specify credentials=filename as one
216	of the mount options. Credential files contain two lines
217	        username=someuser
218	        password=your_password
219	2) By specifying the password in the PASSWD environment variable (similarly
220	the user name can be taken from the USER environment variable).
221	3) By specifying the password in a file by name via PASSWD_FILE
222	4) By specifying the password in a file by file descriptor via PASSWD_FD
224	If no password is provided, mount.cifs will prompt for password entry
226	Restrictions
227	============
228	Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC 
229	1001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a 
230	problem as most servers support this.
232	Valid filenames differ between Windows and Linux.  Windows typically restricts
233	filenames which contain certain reserved characters (e.g.the character : 
234	which is used to delimit the beginning of a stream name by Windows), while
235	Linux allows a slightly wider set of valid characters in filenames. Windows
236	servers can remap such characters when an explicit mapping is specified in
237	the Server's registry.  Samba starting with version 3.10 will allow such 
238	filenames (ie those which contain valid Linux characters, which normally
239	would be forbidden for Windows/CIFS semantics) as long as the server is
240	configured for Unix Extensions (and the client has not disabled
241	/proc/fs/cifs/LinuxExtensionsEnabled). In addition the mount option
242	"mapposix" can be used on CIFS (vers=1.0) to force the mapping of
243	illegal Windows/NTFS/SMB characters to a remap range (this mount parm
244	is the default for SMB3). This remap ("mapposix") range is also
245	compatible with Mac (and "Services for Mac" on some older Windows).
247	CIFS VFS Mount Options
248	======================
249	A partial list of the supported mount options follows:
250	  username	The user name to use when trying to establish
251			the CIFS session.
252	  password	The user password.  If the mount helper is
253			installed, the user will be prompted for password
254			if not supplied.
255	  ip		The ip address of the target server
256	  unc		The target server Universal Network Name (export) to 
257			mount.	
258	  domain	Set the SMB/CIFS workgroup name prepended to the
259			username during CIFS session establishment
260	  forceuid	Set the default uid for inodes to the uid
261			passed in on mount. For mounts to servers
262			which do support the CIFS Unix extensions, such as a
263			properly configured Samba server, the server provides
264			the uid, gid and mode so this parameter should not be
265			specified unless the server and clients uid and gid
266			numbering differ.  If the server and client are in the
267			same domain (e.g. running winbind or nss_ldap) and
268			the server supports the Unix Extensions then the uid
269			and gid can be retrieved from the server (and uid
270			and gid would not have to be specified on the mount.
271			For servers which do not support the CIFS Unix
272			extensions, the default uid (and gid) returned on lookup
273			of existing files will be the uid (gid) of the person
274			who executed the mount (root, except when mount.cifs
275			is configured setuid for user mounts) unless the "uid=" 
276			(gid) mount option is specified. Also note that permission
277			checks (authorization checks) on accesses to a file occur
278			at the server, but there are cases in which an administrator
279			may want to restrict at the client as well.  For those
280			servers which do not report a uid/gid owner
281			(such as Windows), permissions can also be checked at the
282			client, and a crude form of client side permission checking 
283			can be enabled by specifying file_mode and dir_mode on 
284			the client.  (default)
285	  forcegid	(similar to above but for the groupid instead of uid) (default)
286	  noforceuid	Fill in file owner information (uid) by requesting it from
287			the server if possible. With this option, the value given in
288			the uid= option (on mount) will only be used if the server
289			can not support returning uids on inodes.
290	  noforcegid	(similar to above but for the group owner, gid, instead of uid)
291	  uid		Set the default uid for inodes, and indicate to the
292			cifs kernel driver which local user mounted. If the server
293			supports the unix extensions the default uid is
294			not used to fill in the owner fields of inodes (files)
295			unless the "forceuid" parameter is specified.
296	  gid		Set the default gid for inodes (similar to above).
297	  file_mode     If CIFS Unix extensions are not supported by the server
298			this overrides the default mode for file inodes.
299	  fsc		Enable local disk caching using FS-Cache (off by default). This
300	  		option could be useful to improve performance on a slow link,
301			heavily loaded server and/or network where reading from the
302			disk is faster than reading from the server (over the network).
303			This could also impact scalability positively as the
304			number of calls to the server are reduced. However, local
305			caching is not suitable for all workloads for e.g. read-once
306			type workloads. So, you need to consider carefully your
307			workload/scenario before using this option. Currently, local
308			disk caching is functional for CIFS files opened as read-only.
309	  dir_mode      If CIFS Unix extensions are not supported by the server 
310			this overrides the default mode for directory inodes.
311	  port		attempt to contact the server on this tcp port, before
312			trying the usual ports (port 445, then 139).
313	  iocharset     Codepage used to convert local path names to and from
314			Unicode. Unicode is used by default for network path
315			names if the server supports it.  If iocharset is
316			not specified then the nls_default specified
317			during the local client kernel build will be used.
318			If server does not support Unicode, this parameter is
319			unused.
320	  rsize		default read size (usually 16K). The client currently
321			can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
322			defaults to 16K and may be changed (from 8K to the maximum
323			kmalloc size allowed by your kernel) at module install time
324			for cifs.ko. Setting CIFSMaxBufSize to a very large value
325			will cause cifs to use more memory and may reduce performance
326			in some cases.  To use rsize greater than 127K (the original
327			cifs protocol maximum) also requires that the server support
328			a new Unix Capability flag (for very large read) which some
329			newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
330			set from a minimum of 2048 to a maximum of 130048 (127K or
331			CIFSMaxBufSize, whichever is smaller)
332	  wsize		default write size (default 57344)
333			maximum wsize currently allowed by CIFS is 57344 (fourteen
334			4096 byte pages)
335	  actimeo=n	attribute cache timeout in seconds (default 1 second).
336			After this timeout, the cifs client requests fresh attribute
337			information from the server. This option allows to tune the
338			attribute cache timeout to suit the workload needs. Shorter
339			timeouts mean better the cache coherency, but increased number
340			of calls to the server. Longer timeouts mean reduced number
341			of calls to the server at the expense of less stricter cache
342			coherency checks (i.e. incorrect attribute cache for a short
343			period of time).
344	  rw		mount the network share read-write (note that the
345			server may still consider the share read-only)
346	  ro		mount network share read-only
347	  version	used to distinguish different versions of the
348			mount helper utility (not typically needed)
349	  sep		if first mount option (after the -o), overrides
350			the comma as the separator between the mount
351			parms. e.g.
352				-o user=myname,password=mypassword,domain=mydom
353			could be passed instead with period as the separator by
354				-o sep=.user=myname.password=mypassword.domain=mydom
355			this might be useful when comma is contained within username
356			or password or domain. This option is less important
357			when the cifs mount helper cifs.mount (version 1.1 or later)
358			is used.
359	  nosuid        Do not allow remote executables with the suid bit 
360			program to be executed.  This is only meaningful for mounts
361			to servers such as Samba which support the CIFS Unix Extensions.
362			If you do not trust the servers in your network (your mount
363			targets) it is recommended that you specify this option for
364			greater security.
365	  exec		Permit execution of binaries on the mount.
366	  noexec	Do not permit execution of binaries on the mount.
367	  dev		Recognize block devices on the remote mount.
368	  nodev		Do not recognize devices on the remote mount.
369	  suid          Allow remote files on this mountpoint with suid enabled to 
370			be executed (default for mounts when executed as root,
371			nosuid is default for user mounts).
372	  credentials   Although ignored by the cifs kernel component, it is used by 
373			the mount helper, mount.cifs. When mount.cifs is installed it
374			opens and reads the credential file specified in order  
375			to obtain the userid and password arguments which are passed to
376			the cifs vfs.
377	  guest         Although ignored by the kernel component, the mount.cifs
378			mount helper will not prompt the user for a password
379			if guest is specified on the mount options.  If no
380			password is specified a null password will be used.
381	  perm          Client does permission checks (vfs_permission check of uid
382			and gid of the file against the mode and desired operation),
383			Note that this is in addition to the normal ACL check on the
384			target machine done by the server software. 
385			Client permission checking is enabled by default.
386	  noperm        Client does not do permission checks.  This can expose
387			files on this mount to access by other users on the local
388			client system. It is typically only needed when the server
389			supports the CIFS Unix Extensions but the UIDs/GIDs on the
390			client and server system do not match closely enough to allow
391			access by the user doing the mount, but it may be useful with
392			non CIFS Unix Extension mounts for cases in which the default
393			mode is specified on the mount but is not to be enforced on the
394			client (e.g. perhaps when MultiUserMount is enabled)
395			Note that this does not affect the normal ACL check on the
396			target machine done by the server software (of the server
397			ACL against the user name provided at mount time).
398	  serverino	Use server's inode numbers instead of generating automatically
399			incrementing inode numbers on the client.  Although this will
400			make it easier to spot hardlinked files (as they will have
401			the same inode numbers) and inode numbers may be persistent,
402			note that the server does not guarantee that the inode numbers
403			are unique if multiple server side mounts are exported under a
404			single share (since inode numbers on the servers might not
405			be unique if multiple filesystems are mounted under the same
406			shared higher level directory).  Note that some older
407			(e.g. pre-Windows 2000) do not support returning UniqueIDs
408			or the CIFS Unix Extensions equivalent and for those
409			this mount option will have no effect.  Exporting cifs mounts
410			under nfsd requires this mount option on the cifs mount.
411			This is now the default if server supports the 
412			required network operation.
413	  noserverino   Client generates inode numbers (rather than using the actual one
414			from the server). These inode numbers will vary after
415			unmount or reboot which can confuse some applications,
416			but not all server filesystems support unique inode
417			numbers.
418	  setuids       If the CIFS Unix extensions are negotiated with the server
419			the client will attempt to set the effective uid and gid of
420			the local process on newly created files, directories, and
421			devices (create, mkdir, mknod).  If the CIFS Unix Extensions
422			are not negotiated, for newly created files and directories
423			instead of using the default uid and gid specified on
424			the mount, cache the new file's uid and gid locally which means
425			that the uid for the file can change when the inode is
426		        reloaded (or the user remounts the share).
427	  nosetuids     The client will not attempt to set the uid and gid on
428			on newly created files, directories, and devices (create, 
429			mkdir, mknod) which will result in the server setting the
430			uid and gid to the default (usually the server uid of the
431			user who mounted the share).  Letting the server (rather than
432			the client) set the uid and gid is the default. If the CIFS
433			Unix Extensions are not negotiated then the uid and gid for
434			new files will appear to be the uid (gid) of the mounter or the
435			uid (gid) parameter specified on the mount.
436	  netbiosname   When mounting to servers via port 139, specifies the RFC1001
437			source name to use to represent the client netbios machine 
438			name when doing the RFC1001 netbios session initialize.
439	  direct        Do not do inode data caching on files opened on this mount.
440			This precludes mmapping files on this mount. In some cases
441			with fast networks and little or no caching benefits on the
442			client (e.g. when the application is doing large sequential
443			reads bigger than page size without rereading the same data) 
444			this can provide better performance than the default
445			behavior which caches reads (readahead) and writes 
446			(writebehind) through the local Linux client pagecache 
447			if oplock (caching token) is granted and held. Note that
448			direct allows write operations larger than page size
449			to be sent to the server.
450	  strictcache   Use for switching on strict cache mode. In this mode the
451			client read from the cache all the time it has Oplock Level II,
452			otherwise - read from the server. All written data are stored
453			in the cache, but if the client doesn't have Exclusive Oplock,
454			it writes the data to the server.
455	  rwpidforward  Forward pid of a process who opened a file to any read or write
456			operation on that file. This prevent applications like WINE
457			from failing on read and write if we use mandatory brlock style.
458	  acl   	Allow setfacl and getfacl to manage posix ACLs if server
459			supports them.  (default)
460	  noacl 	Do not allow setfacl and getfacl calls on this mount
461	  user_xattr    Allow getting and setting user xattrs (those attributes whose
462			name begins with "user." or "os2.") as OS/2 EAs (extended
463			attributes) to the server.  This allows support of the
464			setfattr and getfattr utilities. (default)
465	  nouser_xattr  Do not allow getfattr/setfattr to get/set/list xattrs 
466	  mapchars      Translate six of the seven reserved characters (not backslash)
467				*?<>|:
468			to the remap range (above 0xF000), which also
469			allows the CIFS client to recognize files created with
470			such characters by Windows's POSIX emulation. This can
471			also be useful when mounting to most versions of Samba
472			(which also forbids creating and opening files
473			whose names contain any of these seven characters).
474			This has no effect if the server does not support
475			Unicode on the wire.
476	 nomapchars     Do not translate any of these seven characters (default).
477	 nocase         Request case insensitive path name matching (case
478			sensitive is the default if the server supports it).
479			(mount option "ignorecase" is identical to "nocase")
480	 posixpaths     If CIFS Unix extensions are supported, attempt to
481			negotiate posix path name support which allows certain
482			characters forbidden in typical CIFS filenames, without
483			requiring remapping. (default)
484	 noposixpaths   If CIFS Unix extensions are supported, do not request
485			posix path name support (this may cause servers to
486			reject creatingfile with certain reserved characters).
487	 nounix         Disable the CIFS Unix Extensions for this mount (tree
488			connection). This is rarely needed, but it may be useful
489			in order to turn off multiple settings all at once (ie
490			posix acls, posix locks, posix paths, symlink support
491			and retrieving uids/gids/mode from the server) or to
492			work around a bug in server which implement the Unix
493			Extensions.
494	 nobrl          Do not send byte range lock requests to the server.
495			This is necessary for certain applications that break
496			with cifs style mandatory byte range locks (and most
497			cifs servers do not yet support requesting advisory
498			byte range locks).
499	 forcemandatorylock Even if the server supports posix (advisory) byte range
500			locking, send only mandatory lock requests.  For some
501			(presumably rare) applications, originally coded for
502			DOS/Windows, which require Windows style mandatory byte range
503			locking, they may be able to take advantage of this option,
504			forcing the cifs client to only send mandatory locks
505			even if the cifs server would support posix advisory locks.
506			"forcemand" is accepted as a shorter form of this mount
507			option.
508	 nostrictsync   If this mount option is set, when an application does an
509			fsync call then the cifs client does not send an SMB Flush
510			to the server (to force the server to write all dirty data
511			for this file immediately to disk), although cifs still sends
512			all dirty (cached) file data to the server and waits for the
513			server to respond to the write.  Since SMB Flush can be
514			very slow, and some servers may be reliable enough (to risk
515			delaying slightly flushing the data to disk on the server),
516			turning on this option may be useful to improve performance for
517			applications that fsync too much, at a small risk of server
518			crash.  If this mount option is not set, by default cifs will
519			send an SMB flush request (and wait for a response) on every
520			fsync call.
521	 nodfs          Disable DFS (global name space support) even if the
522			server claims to support it.  This can help work around
523			a problem with parsing of DFS paths with Samba server
524			versions 3.0.24 and 3.0.25.
525	 remount        remount the share (often used to change from ro to rw mounts
526		        or vice versa)
527	 cifsacl        Report mode bits (e.g. on stat) based on the Windows ACL for
528		        the file. (EXPERIMENTAL)
529	 servern        Specify the server 's netbios name (RFC1001 name) to use
530			when attempting to setup a session to the server. 
531			This is needed for mounting to some older servers (such
532			as OS/2 or Windows 98 and Windows ME) since they do not
533			support a default server name.  A server name can be up
534			to 15 characters long and is usually uppercased.
535	 sfu            When the CIFS Unix Extensions are not negotiated, attempt to
536			create device files and fifos in a format compatible with
537			Services for Unix (SFU).  In addition retrieve bits 10-12
538			of the mode via the SETFILEBITS extended attribute (as
539			SFU does).  In the future the bottom 9 bits of the
540			mode also will be emulated using queries of the security
541			descriptor (ACL).
542	 mfsymlinks     Enable support for Minshall+French symlinks
543			(see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
544			This option is ignored when specified together with the
545			'sfu' option. Minshall+French symlinks are used even if
546			the server supports the CIFS Unix Extensions.
547	 sign           Must use packet signing (helps avoid unwanted data modification
548			by intermediate systems in the route).  Note that signing
549			does not work with lanman or plaintext authentication.
550	 seal           Must seal (encrypt) all data on this mounted share before
551			sending on the network.  Requires support for Unix Extensions.
552			Note that this differs from the sign mount option in that it
553			causes encryption of data sent over this mounted share but other
554			shares mounted to the same server are unaffected.
555	 locallease     This option is rarely needed. Fcntl F_SETLEASE is
556			used by some applications such as Samba and NFSv4 server to
557			check to see whether a file is cacheable.  CIFS has no way
558			to explicitly request a lease, but can check whether a file
559			is cacheable (oplocked).  Unfortunately, even if a file
560			is not oplocked, it could still be cacheable (ie cifs client
561			could grant fcntl leases if no other local processes are using
562			the file) for cases for example such as when the server does not
563			support oplocks and the user is sure that the only updates to
564			the file will be from this client. Specifying this mount option
565			will allow the cifs client to check for leases (only) locally
566			for files which are not oplocked instead of denying leases
567			in that case. (EXPERIMENTAL)
568	 sec            Security mode.  Allowed values are:
569				none	attempt to connection as a null user (no name)
570				krb5    Use Kerberos version 5 authentication
571				krb5i   Use Kerberos authentication and packet signing
572				ntlm    Use NTLM password hashing (default)
573				ntlmi   Use NTLM password hashing with signing (if
574					/proc/fs/cifs/PacketSigningEnabled on or if
575					server requires signing also can be the default) 
576				ntlmv2  Use NTLMv2 password hashing      
577				ntlmv2i Use NTLMv2 password hashing with packet signing
578				lanman  (if configured in kernel config) use older
579					lanman hash
580	hard		Retry file operations if server is not responding
581	soft		Limit retries to unresponsive servers (usually only
582			one retry) before returning an error.  (default)
584	The mount.cifs mount helper also accepts a few mount options before -o
585	including:
587		-S      take password from stdin (equivalent to setting the environment
588			variable "PASSWD_FD=0"
589		-V      print mount.cifs version
590		-?      display simple usage information
592	With most 2.6 kernel versions of modutils, the version of the cifs kernel
593	module can be displayed via modinfo.
595	Misc /proc/fs/cifs Flags and Debug Info
596	=======================================
597	Informational pseudo-files:
598	DebugData		Displays information about active CIFS sessions and
599				shares, features enabled as well as the cifs.ko
600				version.
601	Stats			Lists summary resource usage information as well as per
602				share statistics, if CONFIG_CIFS_STATS in enabled
603				in the kernel configuration.
605	Configuration pseudo-files:
606	PacketSigningEnabled	If set to one, cifs packet signing is enabled
607				and will be used if the server requires 
608				it.  If set to two, cifs packet signing is
609				required even if the server considers packet
610				signing optional. (default 1)
611	SecurityFlags		Flags which control security negotiation and
612				also packet signing. Authentication (may/must)
613				flags (e.g. for NTLM and/or NTLMv2) may be combined with
614				the signing flags.  Specifying two different password
615				hashing mechanisms (as "must use") on the other hand 
616				does not make much sense. Default flags are 
617					0x07007 
618				(NTLM, NTLMv2 and packet signing allowed).  The maximum 
619				allowable flags if you want to allow mounts to servers
620				using weaker password hashes is 0x37037 (lanman,
621				plaintext, ntlm, ntlmv2, signing allowed).  Some
622				SecurityFlags require the corresponding menuconfig
623				options to be enabled (lanman and plaintext require
624				CONFIG_CIFS_WEAK_PW_HASH for example).  Enabling
625				plaintext authentication currently requires also
626				enabling lanman authentication in the security flags
627				because the cifs module only supports sending
628				laintext passwords using the older lanman dialect
629				form of the session setup SMB.  (e.g. for authentication
630				using plain text passwords, set the SecurityFlags
631				to 0x30030):
633				may use packet signing 				0x00001
634				must use packet signing				0x01001
635				may use NTLM (most common password hash)	0x00002
636				must use NTLM					0x02002
637				may use NTLMv2					0x00004
638				must use NTLMv2					0x04004
639				may use Kerberos security			0x00008
640				must use Kerberos				0x08008
641				may use lanman (weak) password hash  		0x00010
642				must use lanman password hash			0x10010
643				may use plaintext passwords    			0x00020
644				must use plaintext passwords			0x20020
645				(reserved for future packet encryption)		0x00040
647	cifsFYI			If set to non-zero value, additional debug information
648				will be logged to the system error log.  This field
649				contains three flags controlling different classes of
650				debugging entries.  The maximum value it can be set
651				to is 7 which enables all debugging points (default 0).
652				Some debugging statements are not compiled into the
653				cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
654				kernel configuration. cifsFYI may be set to one or
655				nore of the following flags (7 sets them all):
657				log cifs informational messages			0x01
658				log return codes from cifs entry points		0x02
659				log slow responses (ie which take longer than 1 second)
660				  CONFIG_CIFS_STATS2 must be enabled in .config	0x04
663	traceSMB		If set to one, debug information is logged to the
664				system error log with the start of smb requests
665				and responses (default 0)
666	LookupCacheEnable	If set to one, inode information is kept cached
667				for one second improving performance of lookups
668				(default 1)
669	OplockEnabled		If set to one, safe distributed caching enabled.
670				(default 1)
671	LinuxExtensionsEnabled	If set to one then the client will attempt to
672				use the CIFS "UNIX" extensions which are optional
673				protocol enhancements that allow CIFS servers
674				to return accurate UID/GID information as well
675				as support symbolic links. If you use servers
676				such as Samba that support the CIFS Unix
677				extensions but do not want to use symbolic link
678				support and want to map the uid and gid fields 
679				to values supplied at mount (rather than the 
680				actual values, then set this to zero. (default 1)
682	These experimental features and tracing can be enabled by changing flags in 
683	/proc/fs/cifs (after the cifs module has been installed or built into the 
684	kernel, e.g.  insmod cifs).  To enable a feature set it to 1 e.g.  to enable 
685	tracing to the kernel message log type: 
687		echo 7 > /proc/fs/cifs/cifsFYI
689	cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
690	logging of various informational messages.  2 enables logging of non-zero
691	SMB return codes while 4 enables logging of requests that take longer
692	than one second to complete (except for byte range lock requests). 
693	Setting it to 4 requires defining CONFIG_CIFS_STATS2 manually in the
694	source code (typically by setting it in the beginning of cifsglob.h),
695	and setting it to seven enables all three.  Finally, tracing
696	the start of smb requests and responses can be enabled via:
698		echo 1 > /proc/fs/cifs/traceSMB
700	Per share (per client mount) statistics are available in /proc/fs/cifs/Stats
701	if the kernel was configured with cifs statistics enabled.  The statistics
702	represent the number of successful (ie non-zero return code from the server) 
703	SMB responses to some of the more common commands (open, delete, mkdir etc.).
704	Also recorded is the total bytes read and bytes written to the server for
705	that share.  Note that due to client caching effects this can be less than the
706	number of bytes read and written by the application running on the client.
707	The statistics for the number of total SMBs and oplock breaks are different in
708	that they represent all for that share, not just those for which the server
709	returned success.
711	Also note that "cat /proc/fs/cifs/DebugData" will display information about
712	the active sessions and the shares that are mounted.
714	Enabling Kerberos (extended security) works but requires version 1.2 or later
715	of the helper program cifs.upcall to be present and to be configured in the
716	/etc/request-key.conf file.  The cifs.upcall helper program is from the Samba
717	project(http://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
718	require this helper. Note that NTLMv2 security (which does not require the
719	cifs.upcall helper program), instead of using Kerberos, is sufficient for
720	some use cases.
722	DFS support allows transparent redirection to shares in an MS-DFS name space.
723	In addition, DFS support for target shares which are specified as UNC
724	names which begin with host names (rather than IP addresses) requires
725	a user space helper (such as cifs.upcall) to be present in order to
726	translate host names to ip address, and the user space helper must also
727	be configured in the file /etc/request-key.conf.  Samba, Windows servers and
728	many NAS appliances support DFS as a way of constructing a global name
729	space to ease network configuration and improve reliability.
731	To use cifs Kerberos and DFS support, the Linux keyutils package should be
732	installed and something like the following lines should be added to the
733	/etc/request-key.conf file:
735	create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
736	create dns_resolver * * /usr/local/sbin/cifs.upcall %k
738	CIFS kernel module parameters
739	=============================
740	These module parameters can be specified or modified either during the time of
741	module loading or during the runtime by using the interface
742		/proc/module/cifs/parameters/<param>
744	i.e. echo "value" > /sys/module/cifs/parameters/<param>
746	1. enable_oplocks - Enable or disable oplocks. Oplocks are enabled by default.
747			    [Y/y/1]. To disable use any of [N/n/0].
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