5 This module supports the SMB3 family of advanced network protocols (as well
6 as older dialects, originally called "CIFS" or SMB1).
8 The CIFS VFS module for Linux supports many advanced network filesystem
9 features such as hierarchical DFS like namespace, hardlinks, locking and more.
10 It was designed to comply with the SNIA CIFS Technical Reference (which
11 supersedes the 1992 X/Open SMB Standard) as well as to perform best practice
12 practical interoperability with Windows 2000, Windows XP, Samba and equivalent
13 servers. This code was developed in participation with the Protocol Freedom
14 Information Foundation. CIFS and now SMB3 has now become a defacto
15 standard for interoperating between Macs and Windows and major NAS appliances.
18 MS-SMB2 (for detailed SMB2/SMB3/SMB3.1.1 protocol specification)
19 or https://samba.org/samba/PFIF/
23 For questions or bug reports please contact:
27 See the project page at: https://wiki.samba.org/index.php/LinuxCIFS_utils
34 1) Download the kernel (e.g. from https://www.kernel.org)
35 and change directory into the top of the kernel directory tree
36 (e.g. /usr/src/linux-2.5.73)
37 2) make menuconfig (or make xconfig)
38 3) select cifs from within the network filesystem choices
43 Installation instructions
44 =========================
46 If you have built the CIFS vfs as module (successfully) simply
47 type ``make modules_install`` (or if you prefer, manually copy the file to
48 the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.ko).
50 If you have built the CIFS vfs into the kernel itself, follow the instructions
51 for your distribution on how to install a new kernel (usually you
52 would simply type ``make install``).
54 If you do not have the utility mount.cifs (in the Samba 4.x source tree and on
55 the CIFS VFS web site) copy it to the same directory in which mount helpers
56 reside (usually /sbin). Although the helper software is not
57 required, mount.cifs is recommended. Most distros include a ``cifs-utils``
58 package that includes this utility so it is recommended to install this.
60 Note that running the Winbind pam/nss module (logon service) on all of your
61 Linux clients is useful in mapping Uids and Gids consistently across the
62 domain to the proper network user. The mount.cifs mount helper can be
63 found at cifs-utils.git on git.samba.org
65 If cifs is built as a module, then the size and number of network buffers
66 and maximum number of simultaneous requests to one server can be configured.
67 Changing these from their defaults is not recommended. By executing modinfo::
69 modinfo kernel/fs/cifs/cifs.ko
71 on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
72 at module initialization time (by running insmod cifs.ko) can be seen.
77 To improve security the SMB2.1 dialect or later (usually will get SMB3) is now
78 the new default. To use old dialects (e.g. to mount Windows XP) use "vers=1.0"
79 on mount (or vers=2.0 for Windows Vista). Note that the CIFS (vers=1.0) is
80 much older and less secure than the default dialect SMB3 which includes
81 many advanced security features such as downgrade attack detection
82 and encrypted shares and stronger signing and authentication algorithms.
83 There are additional mount options that may be helpful for SMB3 to get
84 improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1):
86 ``mfsymlinks`` and ``cifsacl`` and ``idsfromsid``
91 To permit users to mount and unmount over directories they own is possible
92 with the cifs vfs. A way to enable such mounting is to mark the mount.cifs
93 utility as suid (e.g. ``chmod +s /sbin/mount.cifs``). To enable users to
94 umount shares they mount requires
96 1) mount.cifs version 1.4 or later
97 2) an entry for the share in /etc/fstab indicating that a user may
100 //server/usersharename /mnt/username cifs user 0 0
102 Note that when the mount.cifs utility is run suid (allowing user mounts),
103 in order to reduce risks, the ``nosuid`` mount flag is passed in on mount to
104 disallow execution of an suid program mounted on the remote target.
105 When mount is executed as root, nosuid is not passed in by default,
106 and execution of suid programs on the remote target would be enabled
107 by default. This can be changed, as with nfs and other filesystems,
108 by simply specifying ``nosuid`` among the mount options. For user mounts
109 though to be able to pass the suid flag to mount requires rebuilding
110 mount.cifs with the following flag: CIFS_ALLOW_USR_SUID
112 There is a corresponding manual page for cifs mounting in the Samba 3.0 and
113 later source tree in docs/manpages/mount.cifs.8
115 Allowing User Unmounts
116 ======================
118 To permit users to unmount directories that they have user mounted (see above),
119 the utility umount.cifs may be used. It may be invoked directly, or if
120 umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
121 (at least for most versions of the umount utility) for umount of cifs
122 mounts, unless umount is invoked with -i (which will avoid invoking a umount
123 helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
124 as suid (e.g. ``chmod +s /sbin/umount.cifs``) or equivalent (some distributions
125 allow adding entries to a file to the /etc/permissions file to achieve the
126 equivalent suid effect). For this utility to succeed the target path
127 must be a cifs mount, and the uid of the current user must match the uid
128 of the user who mounted the resource.
130 Also note that the customary way of allowing user mounts and unmounts is
131 (instead of using mount.cifs and unmount.cifs as suid) to add a line
132 to the file /etc/fstab for each //server/share you wish to mount, but
133 this can become unwieldy when potential mount targets include many
134 or unpredictable UNC names.
139 Most current servers support SMB2.1 and SMB3 which are more secure,
140 but there are useful protocol extensions for the older less secure CIFS
141 dialect, so to get the maximum benefit if mounting using the older dialect
142 (CIFS/SMB1), we recommend using a server that supports the SNIA CIFS
143 Unix Extensions standard (e.g. almost any version of Samba ie version
144 2.2.5 or later) but the CIFS vfs works fine with a wide variety of CIFS servers.
145 Note that uid, gid and file permissions will display default values if you do
146 not have a server that supports the Unix extensions for CIFS (such as Samba
147 2.2.5 or later). To enable the Unix CIFS Extensions in the Samba server, add
150 unix extensions = yes
152 to your smb.conf file on the server. Note that the following smb.conf settings
153 are also useful (on the Samba server) when the majority of clients are Unix or
157 delete readonly = yes
160 Note that server ea support is required for supporting xattrs from the Linux
161 cifs client, and that EA support is present in later versions of Samba (e.g.
162 3.0.6 and later (also EA support works in all versions of Windows, at least to
163 shares on NTFS filesystems). Extended Attribute (xattr) support is an optional
164 feature of most Linux filesystems which may require enabling via
165 make menuconfig. Client support for extended attributes (user xattr) can be
166 disabled on a per-mount basis by specifying ``nouser_xattr`` on mount.
168 The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
169 version 3.10 and later. Setting POSIX ACLs requires enabling both XATTR and
170 then POSIX support in the CIFS configuration options when building the cifs
171 module. POSIX ACL support can be disabled on a per mount basic by specifying
174 Some administrators may want to change Samba's smb.conf ``map archive`` and
175 ``create mask`` parameters from the default. Unless the create mask is changed
176 newly created files can end up with an unnecessarily restrictive default mode,
177 which may not be what you want, although if the CIFS Unix extensions are
178 enabled on the server and client, subsequent setattr calls (e.g. chmod) can
179 fix the mode. Note that creating special devices (mknod) remotely
180 may require specifying a mkdev function to Samba if you are not using
181 Samba 3.0.6 or later. For more information on these see the manual pages
182 (``man smb.conf``) on the Samba server system. Note that the cifs vfs,
183 unlike the smbfs vfs, does not read the smb.conf on the client system
184 (the few optional settings are passed in on mount via -o parameters instead).
185 Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
186 open files (required for strict POSIX compliance). Windows Servers already
187 supported this feature. Samba server does not allow symlinks that refer to files
188 outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
189 files with absolute paths (ie beginning with slash) such as::
193 would be forbidden. Samba 3.0.6 server or later includes the ability to create
194 such symlinks safely by converting unsafe symlinks (ie symlinks to server
195 files that are outside of the share) to a samba specific format on the server
196 that is ignored by local server applications and non-cifs clients and that will
197 not be traversed by the Samba server). This is opaque to the Linux client
198 application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
199 later, but only for remote clients using the CIFS Unix extensions, and will
200 be invisible to Windows clients and typically will not affect local
201 applications running on the same server as Samba.
206 Once the CIFS VFS support is built into the kernel or installed as a module
207 (cifs.ko), you can use mount syntax like the following to access Samba or
208 Mac or Windows servers::
210 mount -t cifs //9.53.216.11/e$ /mnt -o username=myname,password=mypassword
212 Before -o the option -v may be specified to make the mount.cifs
213 mount helper display the mount steps more verbosely.
214 After -o the following commonly used cifs vfs specific options
221 Other cifs mount options are described below. Use of TCP names (in addition to
222 ip addresses) is available if the mount helper (mount.cifs) is installed. If
223 you do not trust the server to which are mounted, or if you do not have
224 cifs signing enabled (and the physical network is insecure), consider use
225 of the standard mount options ``noexec`` and ``nosuid`` to reduce the risk of
226 running an altered binary on your local system (downloaded from a hostile server
227 or altered by a hostile router).
229 Although mounting using format corresponding to the CIFS URL specification is
230 not possible in mount.cifs yet, it is possible to use an alternate format
231 for the server and sharename (which is somewhat similar to NFS style mount
232 syntax) instead of the more widely used UNC format (i.e. \\server\share)::
234 mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
236 When using the mount helper mount.cifs, passwords may be specified via alternate
237 mechanisms, instead of specifying it after -o using the normal ``pass=`` syntax
239 1) By including it in a credential file. Specify credentials=filename as one
240 of the mount options. Credential files contain two lines::
243 password=your_password
245 2) By specifying the password in the PASSWD environment variable (similarly
246 the user name can be taken from the USER environment variable).
247 3) By specifying the password in a file by name via PASSWD_FILE
248 4) By specifying the password in a file by file descriptor via PASSWD_FD
250 If no password is provided, mount.cifs will prompt for password entry
255 Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
256 1001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a
257 problem as most servers support this.
259 Valid filenames differ between Windows and Linux. Windows typically restricts
260 filenames which contain certain reserved characters (e.g.the character :
261 which is used to delimit the beginning of a stream name by Windows), while
262 Linux allows a slightly wider set of valid characters in filenames. Windows
263 servers can remap such characters when an explicit mapping is specified in
264 the Server's registry. Samba starting with version 3.10 will allow such
265 filenames (ie those which contain valid Linux characters, which normally
266 would be forbidden for Windows/CIFS semantics) as long as the server is
267 configured for Unix Extensions (and the client has not disabled
268 /proc/fs/cifs/LinuxExtensionsEnabled). In addition the mount option
269 ``mapposix`` can be used on CIFS (vers=1.0) to force the mapping of
270 illegal Windows/NTFS/SMB characters to a remap range (this mount parameter
271 is the default for SMB3). This remap (``mapposix``) range is also
272 compatible with Mac (and "Services for Mac" on some older Windows).
274 CIFS VFS Mount Options
275 ======================
276 A partial list of the supported mount options follows:
279 The user name to use when trying to establish
282 The user password. If the mount helper is
283 installed, the user will be prompted for password
286 The ip address of the target server
288 The target server Universal Network Name (export) to
291 Set the SMB/CIFS workgroup name prepended to the
292 username during CIFS session establishment
294 Set the default uid for inodes to the uid
295 passed in on mount. For mounts to servers
296 which do support the CIFS Unix extensions, such as a
297 properly configured Samba server, the server provides
298 the uid, gid and mode so this parameter should not be
299 specified unless the server and clients uid and gid
300 numbering differ. If the server and client are in the
301 same domain (e.g. running winbind or nss_ldap) and
302 the server supports the Unix Extensions then the uid
303 and gid can be retrieved from the server (and uid
304 and gid would not have to be specified on the mount.
305 For servers which do not support the CIFS Unix
306 extensions, the default uid (and gid) returned on lookup
307 of existing files will be the uid (gid) of the person
308 who executed the mount (root, except when mount.cifs
309 is configured setuid for user mounts) unless the ``uid=``
310 (gid) mount option is specified. Also note that permission
311 checks (authorization checks) on accesses to a file occur
312 at the server, but there are cases in which an administrator
313 may want to restrict at the client as well. For those
314 servers which do not report a uid/gid owner
315 (such as Windows), permissions can also be checked at the
316 client, and a crude form of client side permission checking
317 can be enabled by specifying file_mode and dir_mode on
318 the client. (default)
320 (similar to above but for the groupid instead of uid) (default)
322 Fill in file owner information (uid) by requesting it from
323 the server if possible. With this option, the value given in
324 the uid= option (on mount) will only be used if the server
325 can not support returning uids on inodes.
327 (similar to above but for the group owner, gid, instead of uid)
329 Set the default uid for inodes, and indicate to the
330 cifs kernel driver which local user mounted. If the server
331 supports the unix extensions the default uid is
332 not used to fill in the owner fields of inodes (files)
333 unless the ``forceuid`` parameter is specified.
335 Set the default gid for inodes (similar to above).
337 If CIFS Unix extensions are not supported by the server
338 this overrides the default mode for file inodes.
340 Enable local disk caching using FS-Cache (off by default). This
341 option could be useful to improve performance on a slow link,
342 heavily loaded server and/or network where reading from the
343 disk is faster than reading from the server (over the network).
344 This could also impact scalability positively as the
345 number of calls to the server are reduced. However, local
346 caching is not suitable for all workloads for e.g. read-once
347 type workloads. So, you need to consider carefully your
348 workload/scenario before using this option. Currently, local
349 disk caching is functional for CIFS files opened as read-only.
351 If CIFS Unix extensions are not supported by the server
352 this overrides the default mode for directory inodes.
354 attempt to contact the server on this tcp port, before
355 trying the usual ports (port 445, then 139).
357 Codepage used to convert local path names to and from
358 Unicode. Unicode is used by default for network path
359 names if the server supports it. If iocharset is
360 not specified then the nls_default specified
361 during the local client kernel build will be used.
362 If server does not support Unicode, this parameter is
365 default read size (usually 16K). The client currently
366 can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
367 defaults to 16K and may be changed (from 8K to the maximum
368 kmalloc size allowed by your kernel) at module install time
369 for cifs.ko. Setting CIFSMaxBufSize to a very large value
370 will cause cifs to use more memory and may reduce performance
371 in some cases. To use rsize greater than 127K (the original
372 cifs protocol maximum) also requires that the server support
373 a new Unix Capability flag (for very large read) which some
374 newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
375 set from a minimum of 2048 to a maximum of 130048 (127K or
376 CIFSMaxBufSize, whichever is smaller)
378 default write size (default 57344)
379 maximum wsize currently allowed by CIFS is 57344 (fourteen
382 attribute cache timeout in seconds (default 1 second).
383 After this timeout, the cifs client requests fresh attribute
384 information from the server. This option allows to tune the
385 attribute cache timeout to suit the workload needs. Shorter
386 timeouts mean better the cache coherency, but increased number
387 of calls to the server. Longer timeouts mean reduced number
388 of calls to the server at the expense of less stricter cache
389 coherency checks (i.e. incorrect attribute cache for a short
392 mount the network share read-write (note that the
393 server may still consider the share read-only)
395 mount network share read-only
397 used to distinguish different versions of the
398 mount helper utility (not typically needed)
400 if first mount option (after the -o), overrides
401 the comma as the separator between the mount
404 -o user=myname,password=mypassword,domain=mydom
406 could be passed instead with period as the separator by::
408 -o sep=.user=myname.password=mypassword.domain=mydom
410 this might be useful when comma is contained within username
411 or password or domain. This option is less important
412 when the cifs mount helper cifs.mount (version 1.1 or later)
415 Do not allow remote executables with the suid bit
416 program to be executed. This is only meaningful for mounts
417 to servers such as Samba which support the CIFS Unix Extensions.
418 If you do not trust the servers in your network (your mount
419 targets) it is recommended that you specify this option for
422 Permit execution of binaries on the mount.
424 Do not permit execution of binaries on the mount.
426 Recognize block devices on the remote mount.
428 Do not recognize devices on the remote mount.
430 Allow remote files on this mountpoint with suid enabled to
431 be executed (default for mounts when executed as root,
432 nosuid is default for user mounts).
434 Although ignored by the cifs kernel component, it is used by
435 the mount helper, mount.cifs. When mount.cifs is installed it
436 opens and reads the credential file specified in order
437 to obtain the userid and password arguments which are passed to
440 Although ignored by the kernel component, the mount.cifs
441 mount helper will not prompt the user for a password
442 if guest is specified on the mount options. If no
443 password is specified a null password will be used.
445 Client does permission checks (vfs_permission check of uid
446 and gid of the file against the mode and desired operation),
447 Note that this is in addition to the normal ACL check on the
448 target machine done by the server software.
449 Client permission checking is enabled by default.
451 Client does not do permission checks. This can expose
452 files on this mount to access by other users on the local
453 client system. It is typically only needed when the server
454 supports the CIFS Unix Extensions but the UIDs/GIDs on the
455 client and server system do not match closely enough to allow
456 access by the user doing the mount, but it may be useful with
457 non CIFS Unix Extension mounts for cases in which the default
458 mode is specified on the mount but is not to be enforced on the
459 client (e.g. perhaps when MultiUserMount is enabled)
460 Note that this does not affect the normal ACL check on the
461 target machine done by the server software (of the server
462 ACL against the user name provided at mount time).
464 Use server's inode numbers instead of generating automatically
465 incrementing inode numbers on the client. Although this will
466 make it easier to spot hardlinked files (as they will have
467 the same inode numbers) and inode numbers may be persistent,
468 note that the server does not guarantee that the inode numbers
469 are unique if multiple server side mounts are exported under a
470 single share (since inode numbers on the servers might not
471 be unique if multiple filesystems are mounted under the same
472 shared higher level directory). Note that some older
473 (e.g. pre-Windows 2000) do not support returning UniqueIDs
474 or the CIFS Unix Extensions equivalent and for those
475 this mount option will have no effect. Exporting cifs mounts
476 under nfsd requires this mount option on the cifs mount.
477 This is now the default if server supports the
478 required network operation.
480 Client generates inode numbers (rather than using the actual one
481 from the server). These inode numbers will vary after
482 unmount or reboot which can confuse some applications,
483 but not all server filesystems support unique inode
486 If the CIFS Unix extensions are negotiated with the server
487 the client will attempt to set the effective uid and gid of
488 the local process on newly created files, directories, and
489 devices (create, mkdir, mknod). If the CIFS Unix Extensions
490 are not negotiated, for newly created files and directories
491 instead of using the default uid and gid specified on
492 the mount, cache the new file's uid and gid locally which means
493 that the uid for the file can change when the inode is
494 reloaded (or the user remounts the share).
496 The client will not attempt to set the uid and gid on
497 on newly created files, directories, and devices (create,
498 mkdir, mknod) which will result in the server setting the
499 uid and gid to the default (usually the server uid of the
500 user who mounted the share). Letting the server (rather than
501 the client) set the uid and gid is the default. If the CIFS
502 Unix Extensions are not negotiated then the uid and gid for
503 new files will appear to be the uid (gid) of the mounter or the
504 uid (gid) parameter specified on the mount.
506 When mounting to servers via port 139, specifies the RFC1001
507 source name to use to represent the client netbios machine
508 name when doing the RFC1001 netbios session initialize.
510 Do not do inode data caching on files opened on this mount.
511 This precludes mmapping files on this mount. In some cases
512 with fast networks and little or no caching benefits on the
513 client (e.g. when the application is doing large sequential
514 reads bigger than page size without rereading the same data)
515 this can provide better performance than the default
516 behavior which caches reads (readahead) and writes
517 (writebehind) through the local Linux client pagecache
518 if oplock (caching token) is granted and held. Note that
519 direct allows write operations larger than page size
520 to be sent to the server.
522 Use for switching on strict cache mode. In this mode the
523 client read from the cache all the time it has Oplock Level II,
524 otherwise - read from the server. All written data are stored
525 in the cache, but if the client doesn't have Exclusive Oplock,
526 it writes the data to the server.
528 Forward pid of a process who opened a file to any read or write
529 operation on that file. This prevent applications like WINE
530 from failing on read and write if we use mandatory brlock style.
532 Allow setfacl and getfacl to manage posix ACLs if server
533 supports them. (default)
535 Do not allow setfacl and getfacl calls on this mount
537 Allow getting and setting user xattrs (those attributes whose
538 name begins with ``user.`` or ``os2.``) as OS/2 EAs (extended
539 attributes) to the server. This allows support of the
540 setfattr and getfattr utilities. (default)
542 Do not allow getfattr/setfattr to get/set/list xattrs
544 Translate six of the seven reserved characters (not backslash)::
548 to the remap range (above 0xF000), which also
549 allows the CIFS client to recognize files created with
550 such characters by Windows's POSIX emulation. This can
551 also be useful when mounting to most versions of Samba
552 (which also forbids creating and opening files
553 whose names contain any of these seven characters).
554 This has no effect if the server does not support
557 Do not translate any of these seven characters (default).
559 Request case insensitive path name matching (case
560 sensitive is the default if the server supports it).
561 (mount option ``ignorecase`` is identical to ``nocase``)
563 If CIFS Unix extensions are supported, attempt to
564 negotiate posix path name support which allows certain
565 characters forbidden in typical CIFS filenames, without
566 requiring remapping. (default)
568 If CIFS Unix extensions are supported, do not request
569 posix path name support (this may cause servers to
570 reject creatingfile with certain reserved characters).
572 Disable the CIFS Unix Extensions for this mount (tree
573 connection). This is rarely needed, but it may be useful
574 in order to turn off multiple settings all at once (ie
575 posix acls, posix locks, posix paths, symlink support
576 and retrieving uids/gids/mode from the server) or to
577 work around a bug in server which implement the Unix
580 Do not send byte range lock requests to the server.
581 This is necessary for certain applications that break
582 with cifs style mandatory byte range locks (and most
583 cifs servers do not yet support requesting advisory
586 Even if the server supports posix (advisory) byte range
587 locking, send only mandatory lock requests. For some
588 (presumably rare) applications, originally coded for
589 DOS/Windows, which require Windows style mandatory byte range
590 locking, they may be able to take advantage of this option,
591 forcing the cifs client to only send mandatory locks
592 even if the cifs server would support posix advisory locks.
593 ``forcemand`` is accepted as a shorter form of this mount
596 If this mount option is set, when an application does an
597 fsync call then the cifs client does not send an SMB Flush
598 to the server (to force the server to write all dirty data
599 for this file immediately to disk), although cifs still sends
600 all dirty (cached) file data to the server and waits for the
601 server to respond to the write. Since SMB Flush can be
602 very slow, and some servers may be reliable enough (to risk
603 delaying slightly flushing the data to disk on the server),
604 turning on this option may be useful to improve performance for
605 applications that fsync too much, at a small risk of server
606 crash. If this mount option is not set, by default cifs will
607 send an SMB flush request (and wait for a response) on every
610 Disable DFS (global name space support) even if the
611 server claims to support it. This can help work around
612 a problem with parsing of DFS paths with Samba server
613 versions 3.0.24 and 3.0.25.
615 remount the share (often used to change from ro to rw mounts
618 Report mode bits (e.g. on stat) based on the Windows ACL for
619 the file. (EXPERIMENTAL)
621 Specify the server 's netbios name (RFC1001 name) to use
622 when attempting to setup a session to the server.
623 This is needed for mounting to some older servers (such
624 as OS/2 or Windows 98 and Windows ME) since they do not
625 support a default server name. A server name can be up
626 to 15 characters long and is usually uppercased.
628 When the CIFS Unix Extensions are not negotiated, attempt to
629 create device files and fifos in a format compatible with
630 Services for Unix (SFU). In addition retrieve bits 10-12
631 of the mode via the SETFILEBITS extended attribute (as
632 SFU does). In the future the bottom 9 bits of the
633 mode also will be emulated using queries of the security
636 Enable support for Minshall+French symlinks
637 (see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
638 This option is ignored when specified together with the
639 'sfu' option. Minshall+French symlinks are used even if
640 the server supports the CIFS Unix Extensions.
642 Must use packet signing (helps avoid unwanted data modification
643 by intermediate systems in the route). Note that signing
644 does not work with lanman or plaintext authentication.
646 Must seal (encrypt) all data on this mounted share before
647 sending on the network. Requires support for Unix Extensions.
648 Note that this differs from the sign mount option in that it
649 causes encryption of data sent over this mounted share but other
650 shares mounted to the same server are unaffected.
652 This option is rarely needed. Fcntl F_SETLEASE is
653 used by some applications such as Samba and NFSv4 server to
654 check to see whether a file is cacheable. CIFS has no way
655 to explicitly request a lease, but can check whether a file
656 is cacheable (oplocked). Unfortunately, even if a file
657 is not oplocked, it could still be cacheable (ie cifs client
658 could grant fcntl leases if no other local processes are using
659 the file) for cases for example such as when the server does not
660 support oplocks and the user is sure that the only updates to
661 the file will be from this client. Specifying this mount option
662 will allow the cifs client to check for leases (only) locally
663 for files which are not oplocked instead of denying leases
664 in that case. (EXPERIMENTAL)
666 Security mode. Allowed values are:
669 attempt to connection as a null user (no name)
671 Use Kerberos version 5 authentication
673 Use Kerberos authentication and packet signing
675 Use NTLM password hashing (default)
677 Use NTLM password hashing with signing (if
678 /proc/fs/cifs/PacketSigningEnabled on or if
679 server requires signing also can be the default)
681 Use NTLMv2 password hashing
683 Use NTLMv2 password hashing with packet signing
685 (if configured in kernel config) use older
688 Retry file operations if server is not responding
690 Limit retries to unresponsive servers (usually only
691 one retry) before returning an error. (default)
693 The mount.cifs mount helper also accepts a few mount options before -o
696 =============== ===============================================================
697 -S take password from stdin (equivalent to setting the environment
698 variable ``PASSWD_FD=0``
699 -V print mount.cifs version
700 -? display simple usage information
701 =============== ===============================================================
703 With most 2.6 kernel versions of modutils, the version of the cifs kernel
704 module can be displayed via modinfo.
706 Misc /proc/fs/cifs Flags and Debug Info
707 =======================================
709 Informational pseudo-files:
711 ======================= =======================================================
712 DebugData Displays information about active CIFS sessions and
713 shares, features enabled as well as the cifs.ko
715 Stats Lists summary resource usage information as well as per
717 ======================= =======================================================
719 Configuration pseudo-files:
721 ======================= =======================================================
722 SecurityFlags Flags which control security negotiation and
723 also packet signing. Authentication (may/must)
724 flags (e.g. for NTLM and/or NTLMv2) may be combined with
725 the signing flags. Specifying two different password
726 hashing mechanisms (as "must use") on the other hand
727 does not make much sense. Default flags are::
731 (NTLM, NTLMv2 and packet signing allowed). The maximum
732 allowable flags if you want to allow mounts to servers
733 using weaker password hashes is 0x37037 (lanman,
734 plaintext, ntlm, ntlmv2, signing allowed). Some
735 SecurityFlags require the corresponding menuconfig
736 options to be enabled (lanman and plaintext require
737 CONFIG_CIFS_WEAK_PW_HASH for example). Enabling
738 plaintext authentication currently requires also
739 enabling lanman authentication in the security flags
740 because the cifs module only supports sending
741 laintext passwords using the older lanman dialect
742 form of the session setup SMB. (e.g. for authentication
743 using plain text passwords, set the SecurityFlags
746 may use packet signing 0x00001
747 must use packet signing 0x01001
748 may use NTLM (most common password hash) 0x00002
749 must use NTLM 0x02002
750 may use NTLMv2 0x00004
751 must use NTLMv2 0x04004
752 may use Kerberos security 0x00008
753 must use Kerberos 0x08008
754 may use lanman (weak) password hash 0x00010
755 must use lanman password hash 0x10010
756 may use plaintext passwords 0x00020
757 must use plaintext passwords 0x20020
758 (reserved for future packet encryption) 0x00040
760 cifsFYI If set to non-zero value, additional debug information
761 will be logged to the system error log. This field
762 contains three flags controlling different classes of
763 debugging entries. The maximum value it can be set
764 to is 7 which enables all debugging points (default 0).
765 Some debugging statements are not compiled into the
766 cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
767 kernel configuration. cifsFYI may be set to one or
768 nore of the following flags (7 sets them all)::
770 +-----------------------------------------------+------+
771 | log cifs informational messages | 0x01 |
772 +-----------------------------------------------+------+
773 | log return codes from cifs entry points | 0x02 |
774 +-----------------------------------------------+------+
775 | log slow responses | 0x04 |
776 | (ie which take longer than 1 second) | |
778 | CONFIG_CIFS_STATS2 must be enabled in .config | |
779 +-----------------------------------------------+------+
781 traceSMB If set to one, debug information is logged to the
782 system error log with the start of smb requests
783 and responses (default 0)
784 LookupCacheEnable If set to one, inode information is kept cached
785 for one second improving performance of lookups
787 LinuxExtensionsEnabled If set to one then the client will attempt to
788 use the CIFS "UNIX" extensions which are optional
789 protocol enhancements that allow CIFS servers
790 to return accurate UID/GID information as well
791 as support symbolic links. If you use servers
792 such as Samba that support the CIFS Unix
793 extensions but do not want to use symbolic link
794 support and want to map the uid and gid fields
795 to values supplied at mount (rather than the
796 actual values, then set this to zero. (default 1)
797 ======================= =======================================================
799 These experimental features and tracing can be enabled by changing flags in
800 /proc/fs/cifs (after the cifs module has been installed or built into the
801 kernel, e.g. insmod cifs). To enable a feature set it to 1 e.g. to enable
802 tracing to the kernel message log type::
804 echo 7 > /proc/fs/cifs/cifsFYI
806 cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
807 logging of various informational messages. 2 enables logging of non-zero
808 SMB return codes while 4 enables logging of requests that take longer
809 than one second to complete (except for byte range lock requests).
810 Setting it to 4 requires CONFIG_CIFS_STATS2 to be set in kernel configuration
811 (.config). Setting it to seven enables all three. Finally, tracing
812 the start of smb requests and responses can be enabled via::
814 echo 1 > /proc/fs/cifs/traceSMB
816 Per share (per client mount) statistics are available in /proc/fs/cifs/Stats.
817 Additional information is available if CONFIG_CIFS_STATS2 is enabled in the
818 kernel configuration (.config). The statistics returned include counters which
819 represent the number of attempted and failed (ie non-zero return code from the
820 server) SMB3 (or cifs) requests grouped by request type (read, write, close etc.).
821 Also recorded is the total bytes read and bytes written to the server for
822 that share. Note that due to client caching effects this can be less than the
823 number of bytes read and written by the application running on the client.
824 Statistics can be reset to zero by ``echo 0 > /proc/fs/cifs/Stats`` which may be
825 useful if comparing performance of two different scenarios.
827 Also note that ``cat /proc/fs/cifs/DebugData`` will display information about
828 the active sessions and the shares that are mounted.
830 Enabling Kerberos (extended security) works but requires version 1.2 or later
831 of the helper program cifs.upcall to be present and to be configured in the
832 /etc/request-key.conf file. The cifs.upcall helper program is from the Samba
833 project(https://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
834 require this helper. Note that NTLMv2 security (which does not require the
835 cifs.upcall helper program), instead of using Kerberos, is sufficient for
838 DFS support allows transparent redirection to shares in an MS-DFS name space.
839 In addition, DFS support for target shares which are specified as UNC
840 names which begin with host names (rather than IP addresses) requires
841 a user space helper (such as cifs.upcall) to be present in order to
842 translate host names to ip address, and the user space helper must also
843 be configured in the file /etc/request-key.conf. Samba, Windows servers and
844 many NAS appliances support DFS as a way of constructing a global name
845 space to ease network configuration and improve reliability.
847 To use cifs Kerberos and DFS support, the Linux keyutils package should be
848 installed and something like the following lines should be added to the
849 /etc/request-key.conf file::
851 create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
852 create dns_resolver * * /usr/local/sbin/cifs.upcall %k
854 CIFS kernel module parameters
855 =============================
856 These module parameters can be specified or modified either during the time of
857 module loading or during the runtime by using the interface::
859 /proc/module/cifs/parameters/<param>
863 echo "value" > /sys/module/cifs/parameters/<param>
865 ================= ==========================================================
866 1. enable_oplocks Enable or disable oplocks. Oplocks are enabled by default.
867 [Y/y/1]. To disable use any of [N/n/0].
868 ================= ==========================================================