About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / filesystems / cifs

Custom Search

Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	The CIFS VFS support for Linux supports many advanced network filesystem 
2	features such as hierarchical dfs like namespace, hardlinks, locking and more.  
3	It was designed to comply with the SNIA CIFS Technical Reference (which 
4	supersedes the 1992 X/Open SMB Standard) as well as to perform best practice 
5	practical interoperability with Windows 2000, Windows XP, Samba and equivalent 
6	servers.  This code was developed in participation with the Protocol Freedom
7	Information Foundation.
9	Please see
10	  http://protocolfreedom.org/ and
11	  http://samba.org/samba/PFIF/
12	for more details.
15	For questions or bug reports please contact:
16	    sfrench@samba.org (sfrench@us.ibm.com) 
18	Build instructions:
19	==================
20	For Linux 2.4:
21	1) Get the kernel source (e.g.from http://www.kernel.org)
22	and download the cifs vfs source (see the project page
23	at http://us1.samba.org/samba/Linux_CIFS_client.html)
24	and change directory into the top of the kernel directory
25	then patch the kernel (e.g. "patch -p1 < cifs_24.patch") 
26	to add the cifs vfs to your kernel configure options if
27	it has not already been added (e.g. current SuSE and UL
28	users do not need to apply the cifs_24.patch since the cifs vfs is
29	already in the kernel configure menu) and then
30	mkdir linux/fs/cifs and then copy the current cifs vfs files from
31	the cifs download to your kernel build directory e.g.
33		cp <cifs_download_dir>/fs/cifs/* to <kernel_download_dir>/fs/cifs
35	2) make menuconfig (or make xconfig)
36	3) select cifs from within the network filesystem choices
37	4) save and exit
38	5) make dep
39	6) make modules (or "make" if CIFS VFS not to be built as a module)
41	For Linux 2.6:
42	1) Download the kernel (e.g. from http://www.kernel.org)
43	and change directory into the top of the kernel directory tree
44	(e.g. /usr/src/linux-2.5.73)
45	2) make menuconfig (or make xconfig)
46	3) select cifs from within the network filesystem choices
47	4) save and exit
48	5) make
51	Installation instructions:
52	=========================
53	If you have built the CIFS vfs as module (successfully) simply
54	type "make modules_install" (or if you prefer, manually copy the file to
55	the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.o).
57	If you have built the CIFS vfs into the kernel itself, follow the instructions
58	for your distribution on how to install a new kernel (usually you
59	would simply type "make install").
61	If you do not have the utility mount.cifs (in the Samba 3.0 source tree and on 
62	the CIFS VFS web site) copy it to the same directory in which mount.smbfs and 
63	similar files reside (usually /sbin).  Although the helper software is not  
64	required, mount.cifs is recommended.  Eventually the Samba 3.0 utility program 
65	"net" may also be helpful since it may someday provide easier mount syntax for
66	users who are used to Windows e.g.
67		net use <mount point> <UNC name or cifs URL>
68	Note that running the Winbind pam/nss module (logon service) on all of your
69	Linux clients is useful in mapping Uids and Gids consistently across the
70	domain to the proper network user.  The mount.cifs mount helper can be
71	trivially built from Samba 3.0 or later source e.g. by executing:
73		gcc samba/source/client/mount.cifs.c -o mount.cifs
75	If cifs is built as a module, then the size and number of network buffers
76	and maximum number of simultaneous requests to one server can be configured.
77	Changing these from their defaults is not recommended. By executing modinfo
78		modinfo kernel/fs/cifs/cifs.ko
79	on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
80	at module initialization time (by running insmod cifs.ko) can be seen.
82	Allowing User Mounts
83	====================
84	To permit users to mount and unmount over directories they own is possible
85	with the cifs vfs.  A way to enable such mounting is to mark the mount.cifs
86	utility as suid (e.g. "chmod +s /sbin/mount.cifs). To enable users to 
87	umount shares they mount requires
88	1) mount.cifs version 1.4 or later
89	2) an entry for the share in /etc/fstab indicating that a user may
90	unmount it e.g.
91	//server/usersharename  /mnt/username cifs user 0 0
93	Note that when the mount.cifs utility is run suid (allowing user mounts), 
94	in order to reduce risks, the "nosuid" mount flag is passed in on mount to
95	disallow execution of an suid program mounted on the remote target.
96	When mount is executed as root, nosuid is not passed in by default,
97	and execution of suid programs on the remote target would be enabled
98	by default. This can be changed, as with nfs and other filesystems, 
99	by simply specifying "nosuid" among the mount options. For user mounts 
100	though to be able to pass the suid flag to mount requires rebuilding 
101	mount.cifs with the following flag: 
103	        gcc samba/source/client/mount.cifs.c -DCIFS_ALLOW_USR_SUID -o mount.cifs
105	There is a corresponding manual page for cifs mounting in the Samba 3.0 and
106	later source tree in docs/manpages/mount.cifs.8 
108	Allowing User Unmounts
109	======================
110	To permit users to ummount directories that they have user mounted (see above),
111	the utility umount.cifs may be used.  It may be invoked directly, or if 
112	umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
113	(at least for most versions of the umount utility) for umount of cifs
114	mounts, unless umount is invoked with -i (which will avoid invoking a umount
115	helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
116	as suid (e.g. "chmod +s /sbin/umount.cifs") or equivalent (some distributions
117	allow adding entries to a file to the /etc/permissions file to achieve the
118	equivalent suid effect).  For this utility to succeed the target path
119	must be a cifs mount, and the uid of the current user must match the uid
120	of the user who mounted the resource.
122	Also note that the customary way of allowing user mounts and unmounts is 
123	(instead of using mount.cifs and unmount.cifs as suid) to add a line
124	to the file /etc/fstab for each //server/share you wish to mount, but
125	this can become unwieldy when potential mount targets include many
126	or  unpredictable UNC names.
128	Samba Considerations 
129	==================== 
130	To get the maximum benefit from the CIFS VFS, we recommend using a server that 
131	supports the SNIA CIFS Unix Extensions standard (e.g.  Samba 2.2.5 or later or 
132	Samba 3.0) but the CIFS vfs works fine with a wide variety of CIFS servers.  
133	Note that uid, gid and file permissions will display default values if you do 
134	not have a server that supports the Unix extensions for CIFS (such as Samba 
135	2.2.5 or later).  To enable the Unix CIFS Extensions in the Samba server, add 
136	the line: 
138		unix extensions = yes
140	to your smb.conf file on the server.  Note that the following smb.conf settings 
141	are also useful (on the Samba server) when the majority of clients are Unix or 
142	Linux: 
144		case sensitive = yes
145		delete readonly = yes 
146		ea support = yes
148	Note that server ea support is required for supporting xattrs from the Linux
149	cifs client, and that EA support is present in later versions of Samba (e.g. 
150	3.0.6 and later (also EA support works in all versions of Windows, at least to
151	shares on NTFS filesystems).  Extended Attribute (xattr) support is an optional
152	feature of most Linux filesystems which may require enabling via
153	make menuconfig. Client support for extended attributes (user xattr) can be
154	disabled on a per-mount basis by specifying "nouser_xattr" on mount.
156	The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
157	version 3.10 and later.  Setting POSIX ACLs requires enabling both XATTR and 
158	then POSIX support in the CIFS configuration options when building the cifs
159	module.  POSIX ACL support can be disabled on a per mount basic by specifying
160	"noacl" on mount.
162	Some administrators may want to change Samba's smb.conf "map archive" and 
163	"create mask" parameters from the default.  Unless the create mask is changed
164	newly created files can end up with an unnecessarily restrictive default mode,
165	which may not be what you want, although if the CIFS Unix extensions are
166	enabled on the server and client, subsequent setattr calls (e.g. chmod) can
167	fix the mode.  Note that creating special devices (mknod) remotely 
168	may require specifying a mkdev function to Samba if you are not using 
169	Samba 3.0.6 or later.  For more information on these see the manual pages
170	("man smb.conf") on the Samba server system.  Note that the cifs vfs,
171	unlike the smbfs vfs, does not read the smb.conf on the client system 
172	(the few optional settings are passed in on mount via -o parameters instead).  
173	Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
174	open files (required for strict POSIX compliance).  Windows Servers already 
175	supported this feature. Samba server does not allow symlinks that refer to files
176	outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
177	files with absolute paths (ie beginning with slash) such as:
178		 ln -s /mnt/foo bar
179	would be forbidden. Samba 3.0.6 server or later includes the ability to create 
180	such symlinks safely by converting unsafe symlinks (ie symlinks to server 
181	files that are outside of the share) to a samba specific format on the server
182	that is ignored by local server applications and non-cifs clients and that will
183	not be traversed by the Samba server).  This is opaque to the Linux client
184	application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
185	later, but only for remote clients using the CIFS Unix extensions, and will
186	be invisbile to Windows clients and typically will not affect local
187	applications running on the same server as Samba.  
189	Use instructions:
190	================
191	Once the CIFS VFS support is built into the kernel or installed as a module 
192	(cifs.o), you can use mount syntax like the following to access Samba or Windows 
193	servers: 
195	  mount -t cifs //$ /mnt -o user=myname,pass=mypassword
197	Before -o the option -v may be specified to make the mount.cifs
198	mount helper display the mount steps more verbosely.  
199	After -o the following commonly used cifs vfs specific options
200	are supported:
202	  user=<username>
203	  pass=<password>
204	  domain=<domain name>
206	Other cifs mount options are described below.  Use of TCP names (in addition to
207	ip addresses) is available if the mount helper (mount.cifs) is installed. If
208	you do not trust the server to which are mounted, or if you do not have
209	cifs signing enabled (and the physical network is insecure), consider use
210	of the standard mount options "noexec" and "nosuid" to reduce the risk of 
211	running an altered binary on your local system (downloaded from a hostile server
212	or altered by a hostile router).
214	Although mounting using format corresponding to the CIFS URL specification is
215	not possible in mount.cifs yet, it is possible to use an alternate format
216	for the server and sharename (which is somewhat similar to NFS style mount
217	syntax) instead of the more widely used UNC format (i.e. \\server\share):
218	  mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
220	When using the mount helper mount.cifs, passwords may be specified via alternate
221	mechanisms, instead of specifying it after -o using the normal "pass=" syntax
222	on the command line:
223	1) By including it in a credential file. Specify credentials=filename as one
224	of the mount options. Credential files contain two lines
225	        username=someuser
226	        password=your_password
227	2) By specifying the password in the PASSWD environment variable (similarly
228	the user name can be taken from the USER environment variable).
229	3) By specifying the password in a file by name via PASSWD_FILE
230	4) By specifying the password in a file by file descriptor via PASSWD_FD
232	If no password is provided, mount.cifs will prompt for password entry
234	Restrictions
235	============
236	Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC 
237	1001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a 
238	problem as most servers support this.
240	Valid filenames differ between Windows and Linux.  Windows typically restricts
241	filenames which contain certain reserved characters (e.g.the character : 
242	which is used to delimit the beginning of a stream name by Windows), while
243	Linux allows a slightly wider set of valid characters in filenames. Windows
244	servers can remap such characters when an explicit mapping is specified in
245	the Server's registry.  Samba starting with version 3.10 will allow such 
246	filenames (ie those which contain valid Linux characters, which normally
247	would be forbidden for Windows/CIFS semantics) as long as the server is
248	configured for Unix Extensions (and the client has not disabled
249	/proc/fs/cifs/LinuxExtensionsEnabled).
252	CIFS VFS Mount Options
253	======================
254	A partial list of the supported mount options follows:
255	  user		The user name to use when trying to establish
256			the CIFS session.
257	  password	The user password.  If the mount helper is
258			installed, the user will be prompted for password
259			if not supplied.
260	  ip		The ip address of the target server
261	  unc		The target server Universal Network Name (export) to 
262			mount.	
263	  domain	Set the SMB/CIFS workgroup name prepended to the
264			username during CIFS session establishment
265	  forceuid	Set the default uid for inodes to the uid
266			passed in on mount. For mounts to servers
267			which do support the CIFS Unix extensions, such as a
268			properly configured Samba server, the server provides
269			the uid, gid and mode so this parameter should not be
270			specified unless the server and clients uid and gid
271			numbering differ.  If the server and client are in the
272			same domain (e.g. running winbind or nss_ldap) and
273			the server supports the Unix Extensions then the uid
274			and gid can be retrieved from the server (and uid
275			and gid would not have to be specified on the mount.
276			For servers which do not support the CIFS Unix
277			extensions, the default uid (and gid) returned on lookup
278			of existing files will be the uid (gid) of the person
279			who executed the mount (root, except when mount.cifs
280			is configured setuid for user mounts) unless the "uid=" 
281			(gid) mount option is specified. Also note that permission
282			checks (authorization checks) on accesses to a file occur
283			at the server, but there are cases in which an administrator
284			may want to restrict at the client as well.  For those
285			servers which do not report a uid/gid owner
286			(such as Windows), permissions can also be checked at the
287			client, and a crude form of client side permission checking 
288			can be enabled by specifying file_mode and dir_mode on 
289			the client.  (default)
290	  forcegid	(similar to above but for the groupid instead of uid) (default)
291	  noforceuid	Fill in file owner information (uid) by requesting it from
292			the server if possible. With this option, the value given in
293			the uid= option (on mount) will only be used if the server
294			can not support returning uids on inodes.
295	  noforcegid	(similar to above but for the group owner, gid, instead of uid)
296	  uid		Set the default uid for inodes, and indicate to the
297			cifs kernel driver which local user mounted. If the server
298			supports the unix extensions the default uid is
299			not used to fill in the owner fields of inodes (files)
300			unless the "forceuid" parameter is specified.
301	  gid		Set the default gid for inodes (similar to above).
302	  file_mode     If CIFS Unix extensions are not supported by the server
303			this overrides the default mode for file inodes.
304	  fsc		Enable local disk caching using FS-Cache (off by default). This
305	  		option could be useful to improve performance on a slow link,
306			heavily loaded server and/or network where reading from the
307			disk is faster than reading from the server (over the network).
308			This could also impact scalability positively as the
309			number of calls to the server are reduced. However, local
310			caching is not suitable for all workloads for e.g. read-once
311			type workloads. So, you need to consider carefully your
312			workload/scenario before using this option. Currently, local
313			disk caching is functional for CIFS files opened as read-only.
314	  dir_mode      If CIFS Unix extensions are not supported by the server 
315			this overrides the default mode for directory inodes.
316	  port		attempt to contact the server on this tcp port, before
317			trying the usual ports (port 445, then 139).
318	  iocharset     Codepage used to convert local path names to and from
319			Unicode. Unicode is used by default for network path
320			names if the server supports it.  If iocharset is
321			not specified then the nls_default specified
322			during the local client kernel build will be used.
323			If server does not support Unicode, this parameter is
324			unused.
325	  rsize		default read size (usually 16K). The client currently
326			can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
327			defaults to 16K and may be changed (from 8K to the maximum
328			kmalloc size allowed by your kernel) at module install time
329			for cifs.ko. Setting CIFSMaxBufSize to a very large value
330			will cause cifs to use more memory and may reduce performance
331			in some cases.  To use rsize greater than 127K (the original
332			cifs protocol maximum) also requires that the server support
333			a new Unix Capability flag (for very large read) which some
334			newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
335			set from a minimum of 2048 to a maximum of 130048 (127K or
336			CIFSMaxBufSize, whichever is smaller)
337	  wsize		default write size (default 57344)
338			maximum wsize currently allowed by CIFS is 57344 (fourteen
339			4096 byte pages)
340	  actimeo=n	attribute cache timeout in seconds (default 1 second).
341			After this timeout, the cifs client requests fresh attribute
342			information from the server. This option allows to tune the
343			attribute cache timeout to suit the workload needs. Shorter
344			timeouts mean better the cache coherency, but increased number
345			of calls to the server. Longer timeouts mean reduced number
346			of calls to the server at the expense of less stricter cache
347			coherency checks (i.e. incorrect attribute cache for a short
348			period of time).
349	  rw		mount the network share read-write (note that the
350			server may still consider the share read-only)
351	  ro		mount network share read-only
352	  version	used to distinguish different versions of the
353			mount helper utility (not typically needed)
354	  sep		if first mount option (after the -o), overrides
355			the comma as the separator between the mount
356			parms. e.g.
357				-o user=myname,password=mypassword,domain=mydom
358			could be passed instead with period as the separator by
359				-o sep=.user=myname.password=mypassword.domain=mydom
360			this might be useful when comma is contained within username
361			or password or domain. This option is less important
362			when the cifs mount helper cifs.mount (version 1.1 or later)
363			is used.
364	  nosuid        Do not allow remote executables with the suid bit 
365			program to be executed.  This is only meaningful for mounts
366			to servers such as Samba which support the CIFS Unix Extensions.
367			If you do not trust the servers in your network (your mount
368			targets) it is recommended that you specify this option for
369			greater security.
370	  exec		Permit execution of binaries on the mount.
371	  noexec	Do not permit execution of binaries on the mount.
372	  dev		Recognize block devices on the remote mount.
373	  nodev		Do not recognize devices on the remote mount.
374	  suid          Allow remote files on this mountpoint with suid enabled to 
375			be executed (default for mounts when executed as root,
376			nosuid is default for user mounts).
377	  credentials   Although ignored by the cifs kernel component, it is used by 
378			the mount helper, mount.cifs. When mount.cifs is installed it
379			opens and reads the credential file specified in order  
380			to obtain the userid and password arguments which are passed to
381			the cifs vfs.
382	  guest         Although ignored by the kernel component, the mount.cifs
383			mount helper will not prompt the user for a password
384			if guest is specified on the mount options.  If no
385			password is specified a null password will be used.
386	  perm          Client does permission checks (vfs_permission check of uid
387			and gid of the file against the mode and desired operation),
388			Note that this is in addition to the normal ACL check on the
389			target machine done by the server software. 
390			Client permission checking is enabled by default.
391	  noperm        Client does not do permission checks.  This can expose
392			files on this mount to access by other users on the local
393			client system. It is typically only needed when the server
394			supports the CIFS Unix Extensions but the UIDs/GIDs on the
395			client and server system do not match closely enough to allow
396			access by the user doing the mount, but it may be useful with
397			non CIFS Unix Extension mounts for cases in which the default
398			mode is specified on the mount but is not to be enforced on the
399			client (e.g. perhaps when MultiUserMount is enabled)
400			Note that this does not affect the normal ACL check on the
401			target machine done by the server software (of the server
402			ACL against the user name provided at mount time).
403	  serverino	Use server's inode numbers instead of generating automatically
404			incrementing inode numbers on the client.  Although this will
405			make it easier to spot hardlinked files (as they will have
406			the same inode numbers) and inode numbers may be persistent,
407			note that the server does not guarantee that the inode numbers
408			are unique if multiple server side mounts are exported under a
409			single share (since inode numbers on the servers might not
410			be unique if multiple filesystems are mounted under the same
411			shared higher level directory).  Note that some older
412			(e.g. pre-Windows 2000) do not support returning UniqueIDs
413			or the CIFS Unix Extensions equivalent and for those
414			this mount option will have no effect.  Exporting cifs mounts
415			under nfsd requires this mount option on the cifs mount.
416			This is now the default if server supports the 
417			required network operation.
418	  noserverino   Client generates inode numbers (rather than using the actual one
419			from the server). These inode numbers will vary after
420			unmount or reboot which can confuse some applications,
421			but not all server filesystems support unique inode
422			numbers.
423	  setuids       If the CIFS Unix extensions are negotiated with the server
424			the client will attempt to set the effective uid and gid of
425			the local process on newly created files, directories, and
426			devices (create, mkdir, mknod).  If the CIFS Unix Extensions
427			are not negotiated, for newly created files and directories
428			instead of using the default uid and gid specified on
429			the mount, cache the new file's uid and gid locally which means
430			that the uid for the file can change when the inode is
431		        reloaded (or the user remounts the share).
432	  nosetuids     The client will not attempt to set the uid and gid on
433			on newly created files, directories, and devices (create, 
434			mkdir, mknod) which will result in the server setting the
435			uid and gid to the default (usually the server uid of the
436			user who mounted the share).  Letting the server (rather than
437			the client) set the uid and gid is the default. If the CIFS
438			Unix Extensions are not negotiated then the uid and gid for
439			new files will appear to be the uid (gid) of the mounter or the
440			uid (gid) parameter specified on the mount.
441	  netbiosname   When mounting to servers via port 139, specifies the RFC1001
442			source name to use to represent the client netbios machine 
443			name when doing the RFC1001 netbios session initialize.
444	  direct        Do not do inode data caching on files opened on this mount.
445			This precludes mmapping files on this mount. In some cases
446			with fast networks and little or no caching benefits on the
447			client (e.g. when the application is doing large sequential
448			reads bigger than page size without rereading the same data) 
449			this can provide better performance than the default
450			behavior which caches reads (readahead) and writes 
451			(writebehind) through the local Linux client pagecache 
452			if oplock (caching token) is granted and held. Note that
453			direct allows write operations larger than page size
454			to be sent to the server.
455	  strictcache   Use for switching on strict cache mode. In this mode the
456			client read from the cache all the time it has Oplock Level II,
457			otherwise - read from the server. All written data are stored
458			in the cache, but if the client doesn't have Exclusive Oplock,
459			it writes the data to the server.
460	  rwpidforward  Forward pid of a process who opened a file to any read or write
461			operation on that file. This prevent applications like WINE
462			from failing on read and write if we use mandatory brlock style.
463	  acl   	Allow setfacl and getfacl to manage posix ACLs if server
464			supports them.  (default)
465	  noacl 	Do not allow setfacl and getfacl calls on this mount
466	  user_xattr    Allow getting and setting user xattrs (those attributes whose
467			name begins with "user." or "os2.") as OS/2 EAs (extended
468			attributes) to the server.  This allows support of the
469			setfattr and getfattr utilities. (default)
470	  nouser_xattr  Do not allow getfattr/setfattr to get/set/list xattrs 
471	  mapchars      Translate six of the seven reserved characters (not backslash)
472				*?<>|:
473			to the remap range (above 0xF000), which also
474			allows the CIFS client to recognize files created with
475			such characters by Windows's POSIX emulation. This can
476			also be useful when mounting to most versions of Samba
477			(which also forbids creating and opening files
478			whose names contain any of these seven characters).
479			This has no effect if the server does not support
480			Unicode on the wire.
481	 nomapchars     Do not translate any of these seven characters (default).
482	 nocase         Request case insensitive path name matching (case
483			sensitive is the default if the server supports it).
484			(mount option "ignorecase" is identical to "nocase")
485	 posixpaths     If CIFS Unix extensions are supported, attempt to
486			negotiate posix path name support which allows certain
487			characters forbidden in typical CIFS filenames, without
488			requiring remapping. (default)
489	 noposixpaths   If CIFS Unix extensions are supported, do not request
490			posix path name support (this may cause servers to
491			reject creatingfile with certain reserved characters).
492	 nounix         Disable the CIFS Unix Extensions for this mount (tree
493			connection). This is rarely needed, but it may be useful
494			in order to turn off multiple settings all at once (ie
495			posix acls, posix locks, posix paths, symlink support
496			and retrieving uids/gids/mode from the server) or to
497			work around a bug in server which implement the Unix
498			Extensions.
499	 nobrl          Do not send byte range lock requests to the server.
500			This is necessary for certain applications that break
501			with cifs style mandatory byte range locks (and most
502			cifs servers do not yet support requesting advisory
503			byte range locks).
504	 forcemandatorylock Even if the server supports posix (advisory) byte range
505			locking, send only mandatory lock requests.  For some
506			(presumably rare) applications, originally coded for
507			DOS/Windows, which require Windows style mandatory byte range
508			locking, they may be able to take advantage of this option,
509			forcing the cifs client to only send mandatory locks
510			even if the cifs server would support posix advisory locks.
511			"forcemand" is accepted as a shorter form of this mount
512			option.
513	 nostrictsync   If this mount option is set, when an application does an
514			fsync call then the cifs client does not send an SMB Flush
515			to the server (to force the server to write all dirty data
516			for this file immediately to disk), although cifs still sends
517			all dirty (cached) file data to the server and waits for the
518			server to respond to the write.  Since SMB Flush can be
519			very slow, and some servers may be reliable enough (to risk
520			delaying slightly flushing the data to disk on the server),
521			turning on this option may be useful to improve performance for
522			applications that fsync too much, at a small risk of server
523			crash.  If this mount option is not set, by default cifs will
524			send an SMB flush request (and wait for a response) on every
525			fsync call.
526	 nodfs          Disable DFS (global name space support) even if the
527			server claims to support it.  This can help work around
528			a problem with parsing of DFS paths with Samba server
529			versions 3.0.24 and 3.0.25.
530	 remount        remount the share (often used to change from ro to rw mounts
531		        or vice versa)
532	 cifsacl        Report mode bits (e.g. on stat) based on the Windows ACL for
533		        the file. (EXPERIMENTAL)
534	 servern        Specify the server 's netbios name (RFC1001 name) to use
535			when attempting to setup a session to the server. 
536			This is needed for mounting to some older servers (such
537			as OS/2 or Windows 98 and Windows ME) since they do not
538			support a default server name.  A server name can be up
539			to 15 characters long and is usually uppercased.
540	 sfu            When the CIFS Unix Extensions are not negotiated, attempt to
541			create device files and fifos in a format compatible with
542			Services for Unix (SFU).  In addition retrieve bits 10-12
543			of the mode via the SETFILEBITS extended attribute (as
544			SFU does).  In the future the bottom 9 bits of the
545			mode also will be emulated using queries of the security
546			descriptor (ACL).
547	 mfsymlinks     Enable support for Minshall+French symlinks
548			(see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
549			This option is ignored when specified together with the
550			'sfu' option. Minshall+French symlinks are used even if
551			the server supports the CIFS Unix Extensions.
552	 sign           Must use packet signing (helps avoid unwanted data modification
553			by intermediate systems in the route).  Note that signing
554			does not work with lanman or plaintext authentication.
555	 seal           Must seal (encrypt) all data on this mounted share before
556			sending on the network.  Requires support for Unix Extensions.
557			Note that this differs from the sign mount option in that it
558			causes encryption of data sent over this mounted share but other
559			shares mounted to the same server are unaffected.
560	 locallease     This option is rarely needed. Fcntl F_SETLEASE is
561			used by some applications such as Samba and NFSv4 server to
562			check to see whether a file is cacheable.  CIFS has no way
563			to explicitly request a lease, but can check whether a file
564			is cacheable (oplocked).  Unfortunately, even if a file
565			is not oplocked, it could still be cacheable (ie cifs client
566			could grant fcntl leases if no other local processes are using
567			the file) for cases for example such as when the server does not
568			support oplocks and the user is sure that the only updates to
569			the file will be from this client. Specifying this mount option
570			will allow the cifs client to check for leases (only) locally
571			for files which are not oplocked instead of denying leases
572			in that case. (EXPERIMENTAL)
573	 sec            Security mode.  Allowed values are:
574				none	attempt to connection as a null user (no name)
575				krb5    Use Kerberos version 5 authentication
576				krb5i   Use Kerberos authentication and packet signing
577				ntlm    Use NTLM password hashing (default)
578				ntlmi   Use NTLM password hashing with signing (if
579					/proc/fs/cifs/PacketSigningEnabled on or if
580					server requires signing also can be the default) 
581				ntlmv2  Use NTLMv2 password hashing      
582				ntlmv2i Use NTLMv2 password hashing with packet signing
583				lanman  (if configured in kernel config) use older
584					lanman hash
585	hard		Retry file operations if server is not responding
586	soft		Limit retries to unresponsive servers (usually only
587			one retry) before returning an error.  (default)
589	The mount.cifs mount helper also accepts a few mount options before -o
590	including:
592		-S      take password from stdin (equivalent to setting the environment
593			variable "PASSWD_FD=0"
594		-V      print mount.cifs version
595		-?      display simple usage information
597	With most 2.6 kernel versions of modutils, the version of the cifs kernel
598	module can be displayed via modinfo.
600	Misc /proc/fs/cifs Flags and Debug Info
601	=======================================
602	Informational pseudo-files:
603	DebugData		Displays information about active CIFS sessions and
604				shares, features enabled as well as the cifs.ko
605				version.
606	Stats			Lists summary resource usage information as well as per
607				share statistics, if CONFIG_CIFS_STATS in enabled
608				in the kernel configuration.
610	Configuration pseudo-files:
611	PacketSigningEnabled	If set to one, cifs packet signing is enabled
612				and will be used if the server requires 
613				it.  If set to two, cifs packet signing is
614				required even if the server considers packet
615				signing optional. (default 1)
616	SecurityFlags		Flags which control security negotiation and
617				also packet signing. Authentication (may/must)
618				flags (e.g. for NTLM and/or NTLMv2) may be combined with
619				the signing flags.  Specifying two different password
620				hashing mechanisms (as "must use") on the other hand 
621				does not make much sense. Default flags are 
622					0x07007 
623				(NTLM, NTLMv2 and packet signing allowed).  The maximum 
624				allowable flags if you want to allow mounts to servers
625				using weaker password hashes is 0x37037 (lanman,
626				plaintext, ntlm, ntlmv2, signing allowed).  Some
627				SecurityFlags require the corresponding menuconfig
628				options to be enabled (lanman and plaintext require
629				CONFIG_CIFS_WEAK_PW_HASH for example).  Enabling
630				plaintext authentication currently requires also
631				enabling lanman authentication in the security flags
632				because the cifs module only supports sending
633				laintext passwords using the older lanman dialect
634				form of the session setup SMB.  (e.g. for authentication
635				using plain text passwords, set the SecurityFlags
636				to 0x30030):
638				may use packet signing 				0x00001
639				must use packet signing				0x01001
640				may use NTLM (most common password hash)	0x00002
641				must use NTLM					0x02002
642				may use NTLMv2					0x00004
643				must use NTLMv2					0x04004
644				may use Kerberos security			0x00008
645				must use Kerberos				0x08008
646				may use lanman (weak) password hash  		0x00010
647				must use lanman password hash			0x10010
648				may use plaintext passwords    			0x00020
649				must use plaintext passwords			0x20020
650				(reserved for future packet encryption)		0x00040
652	cifsFYI			If set to non-zero value, additional debug information
653				will be logged to the system error log.  This field
654				contains three flags controlling different classes of
655				debugging entries.  The maximum value it can be set
656				to is 7 which enables all debugging points (default 0).
657				Some debugging statements are not compiled into the
658				cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
659				kernel configuration. cifsFYI may be set to one or
660				nore of the following flags (7 sets them all):
662				log cifs informational messages			0x01
663				log return codes from cifs entry points		0x02
664				log slow responses (ie which take longer than 1 second)
665				  CONFIG_CIFS_STATS2 must be enabled in .config	0x04
668	traceSMB		If set to one, debug information is logged to the
669				system error log with the start of smb requests
670				and responses (default 0)
671	LookupCacheEnable	If set to one, inode information is kept cached
672				for one second improving performance of lookups
673				(default 1)
674	OplockEnabled		If set to one, safe distributed caching enabled.
675				(default 1)
676	LinuxExtensionsEnabled	If set to one then the client will attempt to
677				use the CIFS "UNIX" extensions which are optional
678				protocol enhancements that allow CIFS servers
679				to return accurate UID/GID information as well
680				as support symbolic links. If you use servers
681				such as Samba that support the CIFS Unix
682				extensions but do not want to use symbolic link
683				support and want to map the uid and gid fields 
684				to values supplied at mount (rather than the 
685				actual values, then set this to zero. (default 1)
687	These experimental features and tracing can be enabled by changing flags in 
688	/proc/fs/cifs (after the cifs module has been installed or built into the 
689	kernel, e.g.  insmod cifs).  To enable a feature set it to 1 e.g.  to enable 
690	tracing to the kernel message log type: 
692		echo 7 > /proc/fs/cifs/cifsFYI
694	cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
695	logging of various informational messages.  2 enables logging of non-zero
696	SMB return codes while 4 enables logging of requests that take longer
697	than one second to complete (except for byte range lock requests). 
698	Setting it to 4 requires defining CONFIG_CIFS_STATS2 manually in the
699	source code (typically by setting it in the beginning of cifsglob.h),
700	and setting it to seven enables all three.  Finally, tracing
701	the start of smb requests and responses can be enabled via:
703		echo 1 > /proc/fs/cifs/traceSMB
705	Per share (per client mount) statistics are available in /proc/fs/cifs/Stats
706	if the kernel was configured with cifs statistics enabled.  The statistics
707	represent the number of successful (ie non-zero return code from the server) 
708	SMB responses to some of the more common commands (open, delete, mkdir etc.).
709	Also recorded is the total bytes read and bytes written to the server for
710	that share.  Note that due to client caching effects this can be less than the
711	number of bytes read and written by the application running on the client.
712	The statistics for the number of total SMBs and oplock breaks are different in
713	that they represent all for that share, not just those for which the server
714	returned success.
716	Also note that "cat /proc/fs/cifs/DebugData" will display information about
717	the active sessions and the shares that are mounted.
719	Enabling Kerberos (extended security) works but requires version 1.2 or later
720	of the helper program cifs.upcall to be present and to be configured in the
721	/etc/request-key.conf file.  The cifs.upcall helper program is from the Samba
722	project(http://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
723	require this helper. Note that NTLMv2 security (which does not require the
724	cifs.upcall helper program), instead of using Kerberos, is sufficient for
725	some use cases.
727	DFS support allows transparent redirection to shares in an MS-DFS name space.
728	In addition, DFS support for target shares which are specified as UNC
729	names which begin with host names (rather than IP addresses) requires
730	a user space helper (such as cifs.upcall) to be present in order to
731	translate host names to ip address, and the user space helper must also
732	be configured in the file /etc/request-key.conf.  Samba, Windows servers and
733	many NAS appliances support DFS as a way of constructing a global name
734	space to ease network configuration and improve reliability.
736	To use cifs Kerberos and DFS support, the Linux keyutils package should be
737	installed and something like the following lines should be added to the
738	/etc/request-key.conf file:
740	create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
741	create dns_resolver * * /usr/local/sbin/cifs.upcall %k
743	CIFS kernel module parameters
744	=============================
745	These module parameters can be specified or modified either during the time of
746	module loading or during the runtime by using the interface
747		/proc/module/cifs/parameters/<param>
749	i.e. echo "value" > /sys/module/cifs/parameters/<param>
751	1. enable_oplocks - Enable or disable oplocks. Oplocks are enabled by default.
752			    [Y/y/1]. To disable use any of [N/n/0].
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.