Loading...
Note: File does not exist in v3.1.
1=====
2Usage
3=====
4
5This module supports the SMB3 family of advanced network protocols (as well
6as older dialects, originally called "CIFS" or SMB1).
7
8The CIFS VFS module for Linux supports many advanced network filesystem
9features such as hierarchical DFS like namespace, hardlinks, locking and more.
10It was designed to comply with the SNIA CIFS Technical Reference (which
11supersedes the 1992 X/Open SMB Standard) as well as to perform best practice
12practical interoperability with Windows 2000, Windows XP, Samba and equivalent
13servers. This code was developed in participation with the Protocol Freedom
14Information Foundation. CIFS and now SMB3 has now become a defacto
15standard for interoperating between Macs and Windows and major NAS appliances.
16
17Please see
18MS-SMB2 (for detailed SMB2/SMB3/SMB3.1.1 protocol specification)
19http://protocolfreedom.org/ and
20http://samba.org/samba/PFIF/
21for more details.
22
23
24For questions or bug reports please contact:
25
26 smfrench@gmail.com
27
28See the project page at: https://wiki.samba.org/index.php/LinuxCIFS_utils
29
30Build instructions
31==================
32
33For Linux:
34
351) Download the kernel (e.g. from http://www.kernel.org)
36 and change directory into the top of the kernel directory tree
37 (e.g. /usr/src/linux-2.5.73)
382) make menuconfig (or make xconfig)
393) select cifs from within the network filesystem choices
404) save and exit
415) make
42
43
44Installation instructions
45=========================
46
47If you have built the CIFS vfs as module (successfully) simply
48type ``make modules_install`` (or if you prefer, manually copy the file to
49the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.ko).
50
51If you have built the CIFS vfs into the kernel itself, follow the instructions
52for your distribution on how to install a new kernel (usually you
53would simply type ``make install``).
54
55If you do not have the utility mount.cifs (in the Samba 4.x source tree and on
56the CIFS VFS web site) copy it to the same directory in which mount helpers
57reside (usually /sbin). Although the helper software is not
58required, mount.cifs is recommended. Most distros include a ``cifs-utils``
59package that includes this utility so it is recommended to install this.
60
61Note that running the Winbind pam/nss module (logon service) on all of your
62Linux clients is useful in mapping Uids and Gids consistently across the
63domain to the proper network user. The mount.cifs mount helper can be
64found at cifs-utils.git on git.samba.org
65
66If cifs is built as a module, then the size and number of network buffers
67and maximum number of simultaneous requests to one server can be configured.
68Changing these from their defaults is not recommended. By executing modinfo::
69
70 modinfo kernel/fs/cifs/cifs.ko
71
72on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
73at module initialization time (by running insmod cifs.ko) can be seen.
74
75Recommendations
76===============
77
78To improve security the SMB2.1 dialect or later (usually will get SMB3) is now
79the new default. To use old dialects (e.g. to mount Windows XP) use "vers=1.0"
80on mount (or vers=2.0 for Windows Vista). Note that the CIFS (vers=1.0) is
81much older and less secure than the default dialect SMB3 which includes
82many advanced security features such as downgrade attack detection
83and encrypted shares and stronger signing and authentication algorithms.
84There are additional mount options that may be helpful for SMB3 to get
85improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1):
86
87 ``mfsymlinks`` and ``cifsacl`` and ``idsfromsid``
88
89Allowing User Mounts
90====================
91
92To permit users to mount and unmount over directories they own is possible
93with the cifs vfs. A way to enable such mounting is to mark the mount.cifs
94utility as suid (e.g. ``chmod +s /sbin/mount.cifs``). To enable users to
95umount shares they mount requires
96
971) mount.cifs version 1.4 or later
982) an entry for the share in /etc/fstab indicating that a user may
99 unmount it e.g.::
100
101 //server/usersharename /mnt/username cifs user 0 0
102
103Note that when the mount.cifs utility is run suid (allowing user mounts),
104in order to reduce risks, the ``nosuid`` mount flag is passed in on mount to
105disallow execution of an suid program mounted on the remote target.
106When mount is executed as root, nosuid is not passed in by default,
107and execution of suid programs on the remote target would be enabled
108by default. This can be changed, as with nfs and other filesystems,
109by simply specifying ``nosuid`` among the mount options. For user mounts
110though to be able to pass the suid flag to mount requires rebuilding
111mount.cifs with the following flag: CIFS_ALLOW_USR_SUID
112
113There is a corresponding manual page for cifs mounting in the Samba 3.0 and
114later source tree in docs/manpages/mount.cifs.8
115
116Allowing User Unmounts
117======================
118
119To permit users to ummount directories that they have user mounted (see above),
120the utility umount.cifs may be used. It may be invoked directly, or if
121umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
122(at least for most versions of the umount utility) for umount of cifs
123mounts, unless umount is invoked with -i (which will avoid invoking a umount
124helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
125as suid (e.g. ``chmod +s /sbin/umount.cifs``) or equivalent (some distributions
126allow adding entries to a file to the /etc/permissions file to achieve the
127equivalent suid effect). For this utility to succeed the target path
128must be a cifs mount, and the uid of the current user must match the uid
129of the user who mounted the resource.
130
131Also note that the customary way of allowing user mounts and unmounts is
132(instead of using mount.cifs and unmount.cifs as suid) to add a line
133to the file /etc/fstab for each //server/share you wish to mount, but
134this can become unwieldy when potential mount targets include many
135or unpredictable UNC names.
136
137Samba Considerations
138====================
139
140Most current servers support SMB2.1 and SMB3 which are more secure,
141but there are useful protocol extensions for the older less secure CIFS
142dialect, so to get the maximum benefit if mounting using the older dialect
143(CIFS/SMB1), we recommend using a server that supports the SNIA CIFS
144Unix Extensions standard (e.g. almost any version of Samba ie version
1452.2.5 or later) but the CIFS vfs works fine with a wide variety of CIFS servers.
146Note that uid, gid and file permissions will display default values if you do
147not have a server that supports the Unix extensions for CIFS (such as Samba
1482.2.5 or later). To enable the Unix CIFS Extensions in the Samba server, add
149the line::
150
151 unix extensions = yes
152
153to your smb.conf file on the server. Note that the following smb.conf settings
154are also useful (on the Samba server) when the majority of clients are Unix or
155Linux::
156
157 case sensitive = yes
158 delete readonly = yes
159 ea support = yes
160
161Note that server ea support is required for supporting xattrs from the Linux
162cifs client, and that EA support is present in later versions of Samba (e.g.
1633.0.6 and later (also EA support works in all versions of Windows, at least to
164shares on NTFS filesystems). Extended Attribute (xattr) support is an optional
165feature of most Linux filesystems which may require enabling via
166make menuconfig. Client support for extended attributes (user xattr) can be
167disabled on a per-mount basis by specifying ``nouser_xattr`` on mount.
168
169The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
170version 3.10 and later. Setting POSIX ACLs requires enabling both XATTR and
171then POSIX support in the CIFS configuration options when building the cifs
172module. POSIX ACL support can be disabled on a per mount basic by specifying
173``noacl`` on mount.
174
175Some administrators may want to change Samba's smb.conf ``map archive`` and
176``create mask`` parameters from the default. Unless the create mask is changed
177newly created files can end up with an unnecessarily restrictive default mode,
178which may not be what you want, although if the CIFS Unix extensions are
179enabled on the server and client, subsequent setattr calls (e.g. chmod) can
180fix the mode. Note that creating special devices (mknod) remotely
181may require specifying a mkdev function to Samba if you are not using
182Samba 3.0.6 or later. For more information on these see the manual pages
183(``man smb.conf``) on the Samba server system. Note that the cifs vfs,
184unlike the smbfs vfs, does not read the smb.conf on the client system
185(the few optional settings are passed in on mount via -o parameters instead).
186Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
187open files (required for strict POSIX compliance). Windows Servers already
188supported this feature. Samba server does not allow symlinks that refer to files
189outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
190files with absolute paths (ie beginning with slash) such as::
191
192 ln -s /mnt/foo bar
193
194would be forbidden. Samba 3.0.6 server or later includes the ability to create
195such symlinks safely by converting unsafe symlinks (ie symlinks to server
196files that are outside of the share) to a samba specific format on the server
197that is ignored by local server applications and non-cifs clients and that will
198not be traversed by the Samba server). This is opaque to the Linux client
199application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
200later, but only for remote clients using the CIFS Unix extensions, and will
201be invisbile to Windows clients and typically will not affect local
202applications running on the same server as Samba.
203
204Use instructions
205================
206
207Once the CIFS VFS support is built into the kernel or installed as a module
208(cifs.ko), you can use mount syntax like the following to access Samba or
209Mac or Windows servers::
210
211 mount -t cifs //9.53.216.11/e$ /mnt -o username=myname,password=mypassword
212
213Before -o the option -v may be specified to make the mount.cifs
214mount helper display the mount steps more verbosely.
215After -o the following commonly used cifs vfs specific options
216are supported::
217
218 username=<username>
219 password=<password>
220 domain=<domain name>
221
222Other cifs mount options are described below. Use of TCP names (in addition to
223ip addresses) is available if the mount helper (mount.cifs) is installed. If
224you do not trust the server to which are mounted, or if you do not have
225cifs signing enabled (and the physical network is insecure), consider use
226of the standard mount options ``noexec`` and ``nosuid`` to reduce the risk of
227running an altered binary on your local system (downloaded from a hostile server
228or altered by a hostile router).
229
230Although mounting using format corresponding to the CIFS URL specification is
231not possible in mount.cifs yet, it is possible to use an alternate format
232for the server and sharename (which is somewhat similar to NFS style mount
233syntax) instead of the more widely used UNC format (i.e. \\server\share)::
234
235 mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
236
237When using the mount helper mount.cifs, passwords may be specified via alternate
238mechanisms, instead of specifying it after -o using the normal ``pass=`` syntax
239on the command line:
2401) By including it in a credential file. Specify credentials=filename as one
241of the mount options. Credential files contain two lines::
242
243 username=someuser
244 password=your_password
245
2462) By specifying the password in the PASSWD environment variable (similarly
247 the user name can be taken from the USER environment variable).
2483) By specifying the password in a file by name via PASSWD_FILE
2494) By specifying the password in a file by file descriptor via PASSWD_FD
250
251If no password is provided, mount.cifs will prompt for password entry
252
253Restrictions
254============
255
256Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
2571001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a
258problem as most servers support this.
259
260Valid filenames differ between Windows and Linux. Windows typically restricts
261filenames which contain certain reserved characters (e.g.the character :
262which is used to delimit the beginning of a stream name by Windows), while
263Linux allows a slightly wider set of valid characters in filenames. Windows
264servers can remap such characters when an explicit mapping is specified in
265the Server's registry. Samba starting with version 3.10 will allow such
266filenames (ie those which contain valid Linux characters, which normally
267would be forbidden for Windows/CIFS semantics) as long as the server is
268configured for Unix Extensions (and the client has not disabled
269/proc/fs/cifs/LinuxExtensionsEnabled). In addition the mount option
270``mapposix`` can be used on CIFS (vers=1.0) to force the mapping of
271illegal Windows/NTFS/SMB characters to a remap range (this mount parm
272is the default for SMB3). This remap (``mapposix``) range is also
273compatible with Mac (and "Services for Mac" on some older Windows).
274
275CIFS VFS Mount Options
276======================
277A partial list of the supported mount options follows:
278
279 username
280 The user name to use when trying to establish
281 the CIFS session.
282 password
283 The user password. If the mount helper is
284 installed, the user will be prompted for password
285 if not supplied.
286 ip
287 The ip address of the target server
288 unc
289 The target server Universal Network Name (export) to
290 mount.
291 domain
292 Set the SMB/CIFS workgroup name prepended to the
293 username during CIFS session establishment
294 forceuid
295 Set the default uid for inodes to the uid
296 passed in on mount. For mounts to servers
297 which do support the CIFS Unix extensions, such as a
298 properly configured Samba server, the server provides
299 the uid, gid and mode so this parameter should not be
300 specified unless the server and clients uid and gid
301 numbering differ. If the server and client are in the
302 same domain (e.g. running winbind or nss_ldap) and
303 the server supports the Unix Extensions then the uid
304 and gid can be retrieved from the server (and uid
305 and gid would not have to be specified on the mount.
306 For servers which do not support the CIFS Unix
307 extensions, the default uid (and gid) returned on lookup
308 of existing files will be the uid (gid) of the person
309 who executed the mount (root, except when mount.cifs
310 is configured setuid for user mounts) unless the ``uid=``
311 (gid) mount option is specified. Also note that permission
312 checks (authorization checks) on accesses to a file occur
313 at the server, but there are cases in which an administrator
314 may want to restrict at the client as well. For those
315 servers which do not report a uid/gid owner
316 (such as Windows), permissions can also be checked at the
317 client, and a crude form of client side permission checking
318 can be enabled by specifying file_mode and dir_mode on
319 the client. (default)
320 forcegid
321 (similar to above but for the groupid instead of uid) (default)
322 noforceuid
323 Fill in file owner information (uid) by requesting it from
324 the server if possible. With this option, the value given in
325 the uid= option (on mount) will only be used if the server
326 can not support returning uids on inodes.
327 noforcegid
328 (similar to above but for the group owner, gid, instead of uid)
329 uid
330 Set the default uid for inodes, and indicate to the
331 cifs kernel driver which local user mounted. If the server
332 supports the unix extensions the default uid is
333 not used to fill in the owner fields of inodes (files)
334 unless the ``forceuid`` parameter is specified.
335 gid
336 Set the default gid for inodes (similar to above).
337 file_mode
338 If CIFS Unix extensions are not supported by the server
339 this overrides the default mode for file inodes.
340 fsc
341 Enable local disk caching using FS-Cache (off by default). This
342 option could be useful to improve performance on a slow link,
343 heavily loaded server and/or network where reading from the
344 disk is faster than reading from the server (over the network).
345 This could also impact scalability positively as the
346 number of calls to the server are reduced. However, local
347 caching is not suitable for all workloads for e.g. read-once
348 type workloads. So, you need to consider carefully your
349 workload/scenario before using this option. Currently, local
350 disk caching is functional for CIFS files opened as read-only.
351 dir_mode
352 If CIFS Unix extensions are not supported by the server
353 this overrides the default mode for directory inodes.
354 port
355 attempt to contact the server on this tcp port, before
356 trying the usual ports (port 445, then 139).
357 iocharset
358 Codepage used to convert local path names to and from
359 Unicode. Unicode is used by default for network path
360 names if the server supports it. If iocharset is
361 not specified then the nls_default specified
362 during the local client kernel build will be used.
363 If server does not support Unicode, this parameter is
364 unused.
365 rsize
366 default read size (usually 16K). The client currently
367 can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
368 defaults to 16K and may be changed (from 8K to the maximum
369 kmalloc size allowed by your kernel) at module install time
370 for cifs.ko. Setting CIFSMaxBufSize to a very large value
371 will cause cifs to use more memory and may reduce performance
372 in some cases. To use rsize greater than 127K (the original
373 cifs protocol maximum) also requires that the server support
374 a new Unix Capability flag (for very large read) which some
375 newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
376 set from a minimum of 2048 to a maximum of 130048 (127K or
377 CIFSMaxBufSize, whichever is smaller)
378 wsize
379 default write size (default 57344)
380 maximum wsize currently allowed by CIFS is 57344 (fourteen
381 4096 byte pages)
382 actimeo=n
383 attribute cache timeout in seconds (default 1 second).
384 After this timeout, the cifs client requests fresh attribute
385 information from the server. This option allows to tune the
386 attribute cache timeout to suit the workload needs. Shorter
387 timeouts mean better the cache coherency, but increased number
388 of calls to the server. Longer timeouts mean reduced number
389 of calls to the server at the expense of less stricter cache
390 coherency checks (i.e. incorrect attribute cache for a short
391 period of time).
392 rw
393 mount the network share read-write (note that the
394 server may still consider the share read-only)
395 ro
396 mount network share read-only
397 version
398 used to distinguish different versions of the
399 mount helper utility (not typically needed)
400 sep
401 if first mount option (after the -o), overrides
402 the comma as the separator between the mount
403 parms. e.g.::
404
405 -o user=myname,password=mypassword,domain=mydom
406
407 could be passed instead with period as the separator by::
408
409 -o sep=.user=myname.password=mypassword.domain=mydom
410
411 this might be useful when comma is contained within username
412 or password or domain. This option is less important
413 when the cifs mount helper cifs.mount (version 1.1 or later)
414 is used.
415 nosuid
416 Do not allow remote executables with the suid bit
417 program to be executed. This is only meaningful for mounts
418 to servers such as Samba which support the CIFS Unix Extensions.
419 If you do not trust the servers in your network (your mount
420 targets) it is recommended that you specify this option for
421 greater security.
422 exec
423 Permit execution of binaries on the mount.
424 noexec
425 Do not permit execution of binaries on the mount.
426 dev
427 Recognize block devices on the remote mount.
428 nodev
429 Do not recognize devices on the remote mount.
430 suid
431 Allow remote files on this mountpoint with suid enabled to
432 be executed (default for mounts when executed as root,
433 nosuid is default for user mounts).
434 credentials
435 Although ignored by the cifs kernel component, it is used by
436 the mount helper, mount.cifs. When mount.cifs is installed it
437 opens and reads the credential file specified in order
438 to obtain the userid and password arguments which are passed to
439 the cifs vfs.
440 guest
441 Although ignored by the kernel component, the mount.cifs
442 mount helper will not prompt the user for a password
443 if guest is specified on the mount options. If no
444 password is specified a null password will be used.
445 perm
446 Client does permission checks (vfs_permission check of uid
447 and gid of the file against the mode and desired operation),
448 Note that this is in addition to the normal ACL check on the
449 target machine done by the server software.
450 Client permission checking is enabled by default.
451 noperm
452 Client does not do permission checks. This can expose
453 files on this mount to access by other users on the local
454 client system. It is typically only needed when the server
455 supports the CIFS Unix Extensions but the UIDs/GIDs on the
456 client and server system do not match closely enough to allow
457 access by the user doing the mount, but it may be useful with
458 non CIFS Unix Extension mounts for cases in which the default
459 mode is specified on the mount but is not to be enforced on the
460 client (e.g. perhaps when MultiUserMount is enabled)
461 Note that this does not affect the normal ACL check on the
462 target machine done by the server software (of the server
463 ACL against the user name provided at mount time).
464 serverino
465 Use server's inode numbers instead of generating automatically
466 incrementing inode numbers on the client. Although this will
467 make it easier to spot hardlinked files (as they will have
468 the same inode numbers) and inode numbers may be persistent,
469 note that the server does not guarantee that the inode numbers
470 are unique if multiple server side mounts are exported under a
471 single share (since inode numbers on the servers might not
472 be unique if multiple filesystems are mounted under the same
473 shared higher level directory). Note that some older
474 (e.g. pre-Windows 2000) do not support returning UniqueIDs
475 or the CIFS Unix Extensions equivalent and for those
476 this mount option will have no effect. Exporting cifs mounts
477 under nfsd requires this mount option on the cifs mount.
478 This is now the default if server supports the
479 required network operation.
480 noserverino
481 Client generates inode numbers (rather than using the actual one
482 from the server). These inode numbers will vary after
483 unmount or reboot which can confuse some applications,
484 but not all server filesystems support unique inode
485 numbers.
486 setuids
487 If the CIFS Unix extensions are negotiated with the server
488 the client will attempt to set the effective uid and gid of
489 the local process on newly created files, directories, and
490 devices (create, mkdir, mknod). If the CIFS Unix Extensions
491 are not negotiated, for newly created files and directories
492 instead of using the default uid and gid specified on
493 the mount, cache the new file's uid and gid locally which means
494 that the uid for the file can change when the inode is
495 reloaded (or the user remounts the share).
496 nosetuids
497 The client will not attempt to set the uid and gid on
498 on newly created files, directories, and devices (create,
499 mkdir, mknod) which will result in the server setting the
500 uid and gid to the default (usually the server uid of the
501 user who mounted the share). Letting the server (rather than
502 the client) set the uid and gid is the default. If the CIFS
503 Unix Extensions are not negotiated then the uid and gid for
504 new files will appear to be the uid (gid) of the mounter or the
505 uid (gid) parameter specified on the mount.
506 netbiosname
507 When mounting to servers via port 139, specifies the RFC1001
508 source name to use to represent the client netbios machine
509 name when doing the RFC1001 netbios session initialize.
510 direct
511 Do not do inode data caching on files opened on this mount.
512 This precludes mmapping files on this mount. In some cases
513 with fast networks and little or no caching benefits on the
514 client (e.g. when the application is doing large sequential
515 reads bigger than page size without rereading the same data)
516 this can provide better performance than the default
517 behavior which caches reads (readahead) and writes
518 (writebehind) through the local Linux client pagecache
519 if oplock (caching token) is granted and held. Note that
520 direct allows write operations larger than page size
521 to be sent to the server.
522 strictcache
523 Use for switching on strict cache mode. In this mode the
524 client read from the cache all the time it has Oplock Level II,
525 otherwise - read from the server. All written data are stored
526 in the cache, but if the client doesn't have Exclusive Oplock,
527 it writes the data to the server.
528 rwpidforward
529 Forward pid of a process who opened a file to any read or write
530 operation on that file. This prevent applications like WINE
531 from failing on read and write if we use mandatory brlock style.
532 acl
533 Allow setfacl and getfacl to manage posix ACLs if server
534 supports them. (default)
535 noacl
536 Do not allow setfacl and getfacl calls on this mount
537 user_xattr
538 Allow getting and setting user xattrs (those attributes whose
539 name begins with ``user.`` or ``os2.``) as OS/2 EAs (extended
540 attributes) to the server. This allows support of the
541 setfattr and getfattr utilities. (default)
542 nouser_xattr
543 Do not allow getfattr/setfattr to get/set/list xattrs
544 mapchars
545 Translate six of the seven reserved characters (not backslash)::
546
547 *?<>|:
548
549 to the remap range (above 0xF000), which also
550 allows the CIFS client to recognize files created with
551 such characters by Windows's POSIX emulation. This can
552 also be useful when mounting to most versions of Samba
553 (which also forbids creating and opening files
554 whose names contain any of these seven characters).
555 This has no effect if the server does not support
556 Unicode on the wire.
557 nomapchars
558 Do not translate any of these seven characters (default).
559 nocase
560 Request case insensitive path name matching (case
561 sensitive is the default if the server supports it).
562 (mount option ``ignorecase`` is identical to ``nocase``)
563 posixpaths
564 If CIFS Unix extensions are supported, attempt to
565 negotiate posix path name support which allows certain
566 characters forbidden in typical CIFS filenames, without
567 requiring remapping. (default)
568 noposixpaths
569 If CIFS Unix extensions are supported, do not request
570 posix path name support (this may cause servers to
571 reject creatingfile with certain reserved characters).
572 nounix
573 Disable the CIFS Unix Extensions for this mount (tree
574 connection). This is rarely needed, but it may be useful
575 in order to turn off multiple settings all at once (ie
576 posix acls, posix locks, posix paths, symlink support
577 and retrieving uids/gids/mode from the server) or to
578 work around a bug in server which implement the Unix
579 Extensions.
580 nobrl
581 Do not send byte range lock requests to the server.
582 This is necessary for certain applications that break
583 with cifs style mandatory byte range locks (and most
584 cifs servers do not yet support requesting advisory
585 byte range locks).
586 forcemandatorylock
587 Even if the server supports posix (advisory) byte range
588 locking, send only mandatory lock requests. For some
589 (presumably rare) applications, originally coded for
590 DOS/Windows, which require Windows style mandatory byte range
591 locking, they may be able to take advantage of this option,
592 forcing the cifs client to only send mandatory locks
593 even if the cifs server would support posix advisory locks.
594 ``forcemand`` is accepted as a shorter form of this mount
595 option.
596 nostrictsync
597 If this mount option is set, when an application does an
598 fsync call then the cifs client does not send an SMB Flush
599 to the server (to force the server to write all dirty data
600 for this file immediately to disk), although cifs still sends
601 all dirty (cached) file data to the server and waits for the
602 server to respond to the write. Since SMB Flush can be
603 very slow, and some servers may be reliable enough (to risk
604 delaying slightly flushing the data to disk on the server),
605 turning on this option may be useful to improve performance for
606 applications that fsync too much, at a small risk of server
607 crash. If this mount option is not set, by default cifs will
608 send an SMB flush request (and wait for a response) on every
609 fsync call.
610 nodfs
611 Disable DFS (global name space support) even if the
612 server claims to support it. This can help work around
613 a problem with parsing of DFS paths with Samba server
614 versions 3.0.24 and 3.0.25.
615 remount
616 remount the share (often used to change from ro to rw mounts
617 or vice versa)
618 cifsacl
619 Report mode bits (e.g. on stat) based on the Windows ACL for
620 the file. (EXPERIMENTAL)
621 servern
622 Specify the server 's netbios name (RFC1001 name) to use
623 when attempting to setup a session to the server.
624 This is needed for mounting to some older servers (such
625 as OS/2 or Windows 98 and Windows ME) since they do not
626 support a default server name. A server name can be up
627 to 15 characters long and is usually uppercased.
628 sfu
629 When the CIFS Unix Extensions are not negotiated, attempt to
630 create device files and fifos in a format compatible with
631 Services for Unix (SFU). In addition retrieve bits 10-12
632 of the mode via the SETFILEBITS extended attribute (as
633 SFU does). In the future the bottom 9 bits of the
634 mode also will be emulated using queries of the security
635 descriptor (ACL).
636 mfsymlinks
637 Enable support for Minshall+French symlinks
638 (see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
639 This option is ignored when specified together with the
640 'sfu' option. Minshall+French symlinks are used even if
641 the server supports the CIFS Unix Extensions.
642 sign
643 Must use packet signing (helps avoid unwanted data modification
644 by intermediate systems in the route). Note that signing
645 does not work with lanman or plaintext authentication.
646 seal
647 Must seal (encrypt) all data on this mounted share before
648 sending on the network. Requires support for Unix Extensions.
649 Note that this differs from the sign mount option in that it
650 causes encryption of data sent over this mounted share but other
651 shares mounted to the same server are unaffected.
652 locallease
653 This option is rarely needed. Fcntl F_SETLEASE is
654 used by some applications such as Samba and NFSv4 server to
655 check to see whether a file is cacheable. CIFS has no way
656 to explicitly request a lease, but can check whether a file
657 is cacheable (oplocked). Unfortunately, even if a file
658 is not oplocked, it could still be cacheable (ie cifs client
659 could grant fcntl leases if no other local processes are using
660 the file) for cases for example such as when the server does not
661 support oplocks and the user is sure that the only updates to
662 the file will be from this client. Specifying this mount option
663 will allow the cifs client to check for leases (only) locally
664 for files which are not oplocked instead of denying leases
665 in that case. (EXPERIMENTAL)
666 sec
667 Security mode. Allowed values are:
668
669 none
670 attempt to connection as a null user (no name)
671 krb5
672 Use Kerberos version 5 authentication
673 krb5i
674 Use Kerberos authentication and packet signing
675 ntlm
676 Use NTLM password hashing (default)
677 ntlmi
678 Use NTLM password hashing with signing (if
679 /proc/fs/cifs/PacketSigningEnabled on or if
680 server requires signing also can be the default)
681 ntlmv2
682 Use NTLMv2 password hashing
683 ntlmv2i
684 Use NTLMv2 password hashing with packet signing
685 lanman
686 (if configured in kernel config) use older
687 lanman hash
688 hard
689 Retry file operations if server is not responding
690 soft
691 Limit retries to unresponsive servers (usually only
692 one retry) before returning an error. (default)
693
694The mount.cifs mount helper also accepts a few mount options before -o
695including:
696
697=============== ===============================================================
698 -S take password from stdin (equivalent to setting the environment
699 variable ``PASSWD_FD=0``
700 -V print mount.cifs version
701 -? display simple usage information
702=============== ===============================================================
703
704With most 2.6 kernel versions of modutils, the version of the cifs kernel
705module can be displayed via modinfo.
706
707Misc /proc/fs/cifs Flags and Debug Info
708=======================================
709
710Informational pseudo-files:
711
712======================= =======================================================
713DebugData Displays information about active CIFS sessions and
714 shares, features enabled as well as the cifs.ko
715 version.
716Stats Lists summary resource usage information as well as per
717 share statistics.
718======================= =======================================================
719
720Configuration pseudo-files:
721
722======================= =======================================================
723SecurityFlags Flags which control security negotiation and
724 also packet signing. Authentication (may/must)
725 flags (e.g. for NTLM and/or NTLMv2) may be combined with
726 the signing flags. Specifying two different password
727 hashing mechanisms (as "must use") on the other hand
728 does not make much sense. Default flags are::
729
730 0x07007
731
732 (NTLM, NTLMv2 and packet signing allowed). The maximum
733 allowable flags if you want to allow mounts to servers
734 using weaker password hashes is 0x37037 (lanman,
735 plaintext, ntlm, ntlmv2, signing allowed). Some
736 SecurityFlags require the corresponding menuconfig
737 options to be enabled (lanman and plaintext require
738 CONFIG_CIFS_WEAK_PW_HASH for example). Enabling
739 plaintext authentication currently requires also
740 enabling lanman authentication in the security flags
741 because the cifs module only supports sending
742 laintext passwords using the older lanman dialect
743 form of the session setup SMB. (e.g. for authentication
744 using plain text passwords, set the SecurityFlags
745 to 0x30030)::
746
747 may use packet signing 0x00001
748 must use packet signing 0x01001
749 may use NTLM (most common password hash) 0x00002
750 must use NTLM 0x02002
751 may use NTLMv2 0x00004
752 must use NTLMv2 0x04004
753 may use Kerberos security 0x00008
754 must use Kerberos 0x08008
755 may use lanman (weak) password hash 0x00010
756 must use lanman password hash 0x10010
757 may use plaintext passwords 0x00020
758 must use plaintext passwords 0x20020
759 (reserved for future packet encryption) 0x00040
760
761cifsFYI If set to non-zero value, additional debug information
762 will be logged to the system error log. This field
763 contains three flags controlling different classes of
764 debugging entries. The maximum value it can be set
765 to is 7 which enables all debugging points (default 0).
766 Some debugging statements are not compiled into the
767 cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
768 kernel configuration. cifsFYI may be set to one or
769 nore of the following flags (7 sets them all)::
770
771 +-----------------------------------------------+------+
772 | log cifs informational messages | 0x01 |
773 +-----------------------------------------------+------+
774 | log return codes from cifs entry points | 0x02 |
775 +-----------------------------------------------+------+
776 | log slow responses | 0x04 |
777 | (ie which take longer than 1 second) | |
778 | | |
779 | CONFIG_CIFS_STATS2 must be enabled in .config | |
780 +-----------------------------------------------+------+
781
782traceSMB If set to one, debug information is logged to the
783 system error log with the start of smb requests
784 and responses (default 0)
785LookupCacheEnable If set to one, inode information is kept cached
786 for one second improving performance of lookups
787 (default 1)
788LinuxExtensionsEnabled If set to one then the client will attempt to
789 use the CIFS "UNIX" extensions which are optional
790 protocol enhancements that allow CIFS servers
791 to return accurate UID/GID information as well
792 as support symbolic links. If you use servers
793 such as Samba that support the CIFS Unix
794 extensions but do not want to use symbolic link
795 support and want to map the uid and gid fields
796 to values supplied at mount (rather than the
797 actual values, then set this to zero. (default 1)
798======================= =======================================================
799
800These experimental features and tracing can be enabled by changing flags in
801/proc/fs/cifs (after the cifs module has been installed or built into the
802kernel, e.g. insmod cifs). To enable a feature set it to 1 e.g. to enable
803tracing to the kernel message log type::
804
805 echo 7 > /proc/fs/cifs/cifsFYI
806
807cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
808logging of various informational messages. 2 enables logging of non-zero
809SMB return codes while 4 enables logging of requests that take longer
810than one second to complete (except for byte range lock requests).
811Setting it to 4 requires CONFIG_CIFS_STATS2 to be set in kernel configuration
812(.config). Setting it to seven enables all three. Finally, tracing
813the start of smb requests and responses can be enabled via::
814
815 echo 1 > /proc/fs/cifs/traceSMB
816
817Per share (per client mount) statistics are available in /proc/fs/cifs/Stats.
818Additional information is available if CONFIG_CIFS_STATS2 is enabled in the
819kernel configuration (.config). The statistics returned include counters which
820represent the number of attempted and failed (ie non-zero return code from the
821server) SMB3 (or cifs) requests grouped by request type (read, write, close etc.).
822Also recorded is the total bytes read and bytes written to the server for
823that share. Note that due to client caching effects this can be less than the
824number of bytes read and written by the application running on the client.
825Statistics can be reset to zero by ``echo 0 > /proc/fs/cifs/Stats`` which may be
826useful if comparing performance of two different scenarios.
827
828Also note that ``cat /proc/fs/cifs/DebugData`` will display information about
829the active sessions and the shares that are mounted.
830
831Enabling Kerberos (extended security) works but requires version 1.2 or later
832of the helper program cifs.upcall to be present and to be configured in the
833/etc/request-key.conf file. The cifs.upcall helper program is from the Samba
834project(http://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
835require this helper. Note that NTLMv2 security (which does not require the
836cifs.upcall helper program), instead of using Kerberos, is sufficient for
837some use cases.
838
839DFS support allows transparent redirection to shares in an MS-DFS name space.
840In addition, DFS support for target shares which are specified as UNC
841names which begin with host names (rather than IP addresses) requires
842a user space helper (such as cifs.upcall) to be present in order to
843translate host names to ip address, and the user space helper must also
844be configured in the file /etc/request-key.conf. Samba, Windows servers and
845many NAS appliances support DFS as a way of constructing a global name
846space to ease network configuration and improve reliability.
847
848To use cifs Kerberos and DFS support, the Linux keyutils package should be
849installed and something like the following lines should be added to the
850/etc/request-key.conf file::
851
852 create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
853 create dns_resolver * * /usr/local/sbin/cifs.upcall %k
854
855CIFS kernel module parameters
856=============================
857These module parameters can be specified or modified either during the time of
858module loading or during the runtime by using the interface::
859
860 /proc/module/cifs/parameters/<param>
861
862i.e.::
863
864 echo "value" > /sys/module/cifs/parameters/<param>
865
866================= ==========================================================
8671. enable_oplocks Enable or disable oplocks. Oplocks are enabled by default.
868 [Y/y/1]. To disable use any of [N/n/0].
869================= ==========================================================