1The CIFS VFS support for Linux supports many advanced network filesystem 
   2features such as hierarchical dfs like namespace, hardlinks, locking and more.  
   3It was designed to comply with the SNIA CIFS Technical Reference (which 
   4supersedes the 1992 X/Open SMB Standard) as well as to perform best practice 
   5practical interoperability with Windows 2000, Windows XP, Samba and equivalent 
   6servers.  This code was developed in participation with the Protocol Freedom
   7Information Foundation.
   9Please see
  10 and
  12for more details.
  15For questions or bug reports please contact:
  16 ( 
  18Build instructions:
  20For Linux 2.4:
  211) Get the kernel source (e.g.from
  22and download the cifs vfs source (see the project page
  24and change directory into the top of the kernel directory
  25then patch the kernel (e.g. "patch -p1 < cifs_24.patch") 
  26to add the cifs vfs to your kernel configure options if
  27it has not already been added (e.g. current SuSE and UL
  28users do not need to apply the cifs_24.patch since the cifs vfs is
  29already in the kernel configure menu) and then
  30mkdir linux/fs/cifs and then copy the current cifs vfs files from
  31the cifs download to your kernel build directory e.g.
  33        cp <cifs_download_dir>/fs/cifs/* to <kernel_download_dir>/fs/cifs
  352) make menuconfig (or make xconfig)
  363) select cifs from within the network filesystem choices
  374) save and exit
  385) make dep
  396) make modules (or "make" if CIFS VFS not to be built as a module)
  41For Linux 2.6:
  421) Download the kernel (e.g. from
  43and change directory into the top of the kernel directory tree
  44(e.g. /usr/src/linux-2.5.73)
  452) make menuconfig (or make xconfig)
  463) select cifs from within the network filesystem choices
  474) save and exit
  485) make
  51Installation instructions:
  53If you have built the CIFS vfs as module (successfully) simply
  54type "make modules_install" (or if you prefer, manually copy the file to
  55the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.o).
  57If you have built the CIFS vfs into the kernel itself, follow the instructions
  58for your distribution on how to install a new kernel (usually you
  59would simply type "make install").
  61If you do not have the utility mount.cifs (in the Samba 3.0 source tree and on 
  62the CIFS VFS web site) copy it to the same directory in which mount.smbfs and 
  63similar files reside (usually /sbin).  Although the helper software is not  
  64required, 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
  66users who are used to Windows e.g.
  67        net use <mount point> <UNC name or cifs URL>
  68Note that running the Winbind pam/nss module (logon service) on all of your
  69Linux clients is useful in mapping Uids and Gids consistently across the
  70domain to the proper network user.  The mount.cifs mount helper can be
  71trivially built from Samba 3.0 or later source e.g. by executing:
  73        gcc samba/source/client/mount.cifs.c -o mount.cifs
  75If cifs is built as a module, then the size and number of network buffers
  76and maximum number of simultaneous requests to one server can be configured.
  77Changing these from their defaults is not recommended. By executing modinfo
  78        modinfo kernel/fs/cifs/cifs.ko
  79on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
  80at module initialization time (by running insmod cifs.ko) can be seen.
  82Allowing User Mounts
  84To permit users to mount and unmount over directories they own is possible
  85with the cifs vfs.  A way to enable such mounting is to mark the mount.cifs
  86utility as suid (e.g. "chmod +s /sbin/mount.cifs). To enable users to 
  87umount shares they mount requires
  881) mount.cifs version 1.4 or later
  892) an entry for the share in /etc/fstab indicating that a user may
  90unmount it e.g.
  91//server/usersharename  /mnt/username cifs user 0 0
  93Note that when the mount.cifs utility is run suid (allowing user mounts), 
  94in order to reduce risks, the "nosuid" mount flag is passed in on mount to
  95disallow execution of an suid program mounted on the remote target.
  96When mount is executed as root, nosuid is not passed in by default,
  97and execution of suid programs on the remote target would be enabled
  98by default. This can be changed, as with nfs and other filesystems, 
  99by simply specifying "nosuid" among the mount options. For user mounts 
 100though to be able to pass the suid flag to mount requires rebuilding 
 101mount.cifs with the following flag: 
 103        gcc samba/source/client/mount.cifs.c -DCIFS_ALLOW_USR_SUID -o mount.cifs
 105There is a corresponding manual page for cifs mounting in the Samba 3.0 and
 106later source tree in docs/manpages/mount.cifs.8 
 108Allowing User Unmounts
 110To permit users to ummount directories that they have user mounted (see above),
 111the utility umount.cifs may be used.  It may be invoked directly, or if 
 112umount.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
 114mounts, unless umount is invoked with -i (which will avoid invoking a umount
 115helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
 116as suid (e.g. "chmod +s /sbin/umount.cifs") or equivalent (some distributions
 117allow adding entries to a file to the /etc/permissions file to achieve the
 118equivalent suid effect).  For this utility to succeed the target path
 119must be a cifs mount, and the uid of the current user must match the uid
 120of the user who mounted the resource.
 122Also 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
 124to the file /etc/fstab for each //server/share you wish to mount, but
 125this can become unwieldy when potential mount targets include many
 126or  unpredictable UNC names.
 128Samba Considerations 
 130To get the maximum benefit from the CIFS VFS, we recommend using a server that 
 131supports the SNIA CIFS Unix Extensions standard (e.g.  Samba 2.2.5 or later or 
 132Samba 3.0) but the CIFS vfs works fine with a wide variety of CIFS servers.  
 133Note that uid, gid and file permissions will display default values if you do 
 134not have a server that supports the Unix extensions for CIFS (such as Samba 
 1352.2.5 or later).  To enable the Unix CIFS Extensions in the Samba server, add 
 136the line: 
 138        unix extensions = yes
 140to your smb.conf file on the server.  Note that the following smb.conf settings 
 141are also useful (on the Samba server) when the majority of clients are Unix or 
 144        case sensitive = yes
 145        delete readonly = yes 
 146        ea support = yes
 148Note that server ea support is required for supporting xattrs from the Linux
 149cifs client, and that EA support is present in later versions of Samba (e.g. 
 1503.0.6 and later (also EA support works in all versions of Windows, at least to
 151shares on NTFS filesystems).  Extended Attribute (xattr) support is an optional
 152feature of most Linux filesystems which may require enabling via
 153make menuconfig. Client support for extended attributes (user xattr) can be
 154disabled on a per-mount basis by specifying "nouser_xattr" on mount.
 156The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
 157version 3.10 and later.  Setting POSIX ACLs requires enabling both XATTR and 
 158then POSIX support in the CIFS configuration options when building the cifs
 159module.  POSIX ACL support can be disabled on a per mount basic by specifying
 160"noacl" on mount.
 162Some 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
 164newly created files can end up with an unnecessarily restrictive default mode,
 165which may not be what you want, although if the CIFS Unix extensions are
 166enabled on the server and client, subsequent setattr calls (e.g. chmod) can
 167fix the mode.  Note that creating special devices (mknod) remotely 
 168may require specifying a mkdev function to Samba if you are not using 
 169Samba 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,
 171unlike 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).  
 173Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
 174open files (required for strict POSIX compliance).  Windows Servers already 
 175supported this feature. Samba server does not allow symlinks that refer to files
 176outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
 177files with absolute paths (ie beginning with slash) such as:
 178         ln -s /mnt/foo bar
 179would be forbidden. Samba 3.0.6 server or later includes the ability to create 
 180such symlinks safely by converting unsafe symlinks (ie symlinks to server 
 181files that are outside of the share) to a samba specific format on the server
 182that is ignored by local server applications and non-cifs clients and that will
 183not be traversed by the Samba server).  This is opaque to the Linux client
 184application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
 185later, but only for remote clients using the CIFS Unix extensions, and will
 186be invisbile to Windows clients and typically will not affect local
 187applications running on the same server as Samba.  
 189Use instructions:
 191Once 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 
 195  mount -t cifs //$ /mnt -o user=myname,pass=mypassword
 197Before -o the option -v may be specified to make the mount.cifs
 198mount helper display the mount steps more verbosely.  
 199After -o the following commonly used cifs vfs specific options
 200are supported:
 202  user=<username>
 203  pass=<password>
 204  domain=<domain name>
 206Other cifs mount options are described below.  Use of TCP names (in addition to
 207ip addresses) is available if the mount helper (mount.cifs) is installed. If
 208you do not trust the server to which are mounted, or if you do not have
 209cifs signing enabled (and the physical network is insecure), consider use
 210of the standard mount options "noexec" and "nosuid" to reduce the risk of 
 211running an altered binary on your local system (downloaded from a hostile server
 212or altered by a hostile router).
 214Although mounting using format corresponding to the CIFS URL specification is
 215not possible in mount.cifs yet, it is possible to use an alternate format
 216for the server and sharename (which is somewhat similar to NFS style mount
 217syntax) 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
 220When using the mount helper mount.cifs, passwords may be specified via alternate
 221mechanisms, instead of specifying it after -o using the normal "pass=" syntax
 222on the command line:
 2231) By including it in a credential file. Specify credentials=filename as one
 224of the mount options. Credential files contain two lines
 225        username=someuser
 226        password=your_password
 2272) By specifying the password in the PASSWD environment variable (similarly
 228the user name can be taken from the USER environment variable).
 2293) By specifying the password in a file by name via PASSWD_FILE
 2304) By specifying the password in a file by file descriptor via PASSWD_FD
 232If no password is provided, mount.cifs will prompt for password entry
 236Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC 
 2371001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a 
 238problem as most servers support this.
 240Valid filenames differ between Windows and Linux.  Windows typically restricts
 241filenames which contain certain reserved characters (e.g.the character : 
 242which is used to delimit the beginning of a stream name by Windows), while
 243Linux allows a slightly wider set of valid characters in filenames. Windows
 244servers can remap such characters when an explicit mapping is specified in
 245the Server's registry.  Samba starting with version 3.10 will allow such 
 246filenames (ie those which contain valid Linux characters, which normally
 247would be forbidden for Windows/CIFS semantics) as long as the server is
 248configured for Unix Extensions (and the client has not disabled
 252CIFS VFS Mount Options
 254A 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 specifed 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  acl           Allow setfacl and getfacl to manage posix ACLs if server
 461                supports them.  (default)
 462  noacl         Do not allow setfacl and getfacl calls on this mount
 463  user_xattr    Allow getting and setting user xattrs (those attributes whose
 464                name begins with "user." or "os2.") as OS/2 EAs (extended
 465                attributes) to the server.  This allows support of the
 466                setfattr and getfattr utilities. (default)
 467  nouser_xattr  Do not allow getfattr/setfattr to get/set/list xattrs 
 468  mapchars      Translate six of the seven reserved characters (not backslash)
 469                        *?<>|:
 470                to the remap range (above 0xF000), which also
 471                allows the CIFS client to recognize files created with
 472                such characters by Windows's POSIX emulation. This can
 473                also be useful when mounting to most versions of Samba
 474                (which also forbids creating and opening files
 475                whose names contain any of these seven characters).
 476                This has no effect if the server does not support
 477                Unicode on the wire.
 478 nomapchars     Do not translate any of these seven characters (default).
 479 nocase         Request case insensitive path name matching (case
 480                sensitive is the default if the server suports it).
 481                (mount option "ignorecase" is identical to "nocase")
 482 posixpaths     If CIFS Unix extensions are supported, attempt to
 483                negotiate posix path name support which allows certain
 484                characters forbidden in typical CIFS filenames, without
 485                requiring remapping. (default)
 486 noposixpaths   If CIFS Unix extensions are supported, do not request
 487                posix path name support (this may cause servers to
 488                reject creatingfile with certain reserved characters).
 489 nounix         Disable the CIFS Unix Extensions for this mount (tree
 490                connection). This is rarely needed, but it may be useful
 491                in order to turn off multiple settings all at once (ie
 492                posix acls, posix locks, posix paths, symlink support
 493                and retrieving uids/gids/mode from the server) or to
 494                work around a bug in server which implement the Unix
 495                Extensions.
 496 nobrl          Do not send byte range lock requests to the server.
 497                This is necessary for certain applications that break
 498                with cifs style mandatory byte range locks (and most
 499                cifs servers do not yet support requesting advisory
 500                byte range locks).
 501 forcemandatorylock Even if the server supports posix (advisory) byte range
 502                locking, send only mandatory lock requests.  For some
 503                (presumably rare) applications, originally coded for
 504                DOS/Windows, which require Windows style mandatory byte range
 505                locking, they may be able to take advantage of this option,
 506                forcing the cifs client to only send mandatory locks
 507                even if the cifs server would support posix advisory locks.
 508                "forcemand" is accepted as a shorter form of this mount
 509                option.
 510 nostrictsync   If this mount option is set, when an application does an
 511                fsync call then the cifs client does not send an SMB Flush
 512                to the server (to force the server to write all dirty data
 513                for this file immediately to disk), although cifs still sends
 514                all dirty (cached) file data to the server and waits for the
 515                server to respond to the write.  Since SMB Flush can be
 516                very slow, and some servers may be reliable enough (to risk
 517                delaying slightly flushing the data to disk on the server),
 518                turning on this option may be useful to improve performance for
 519                applications that fsync too much, at a small risk of server
 520                crash.  If this mount option is not set, by default cifs will
 521                send an SMB flush request (and wait for a response) on every
 522                fsync call.
 523 nodfs          Disable DFS (global name space support) even if the
 524                server claims to support it.  This can help work around
 525                a problem with parsing of DFS paths with Samba server
 526                versions 3.0.24 and 3.0.25.
 527 remount        remount the share (often used to change from ro to rw mounts
 528                or vice versa)
 529 cifsacl        Report mode bits (e.g. on stat) based on the Windows ACL for
 530                the file. (EXPERIMENTAL)
 531 servern        Specify the server 's netbios name (RFC1001 name) to use
 532                when attempting to setup a session to the server. 
 533                This is needed for mounting to some older servers (such
 534                as OS/2 or Windows 98 and Windows ME) since they do not
 535                support a default server name.  A server name can be up
 536                to 15 characters long and is usually uppercased.
 537 sfu            When the CIFS Unix Extensions are not negotiated, attempt to
 538                create device files and fifos in a format compatible with
 539                Services for Unix (SFU).  In addition retrieve bits 10-12
 540                of the mode via the SETFILEBITS extended attribute (as
 541                SFU does).  In the future the bottom 9 bits of the
 542                mode also will be emulated using queries of the security
 543                descriptor (ACL).
 544 mfsymlinks     Enable support for Minshall+French symlinks
 545                (see
 546                This option is ignored when specified together with the
 547                'sfu' option. Minshall+French symlinks are used even if
 548                the server supports the CIFS Unix Extensions.
 549 sign           Must use packet signing (helps avoid unwanted data modification
 550                by intermediate systems in the route).  Note that signing
 551                does not work with lanman or plaintext authentication.
 552 seal           Must seal (encrypt) all data on this mounted share before
 553                sending on the network.  Requires support for Unix Extensions.
 554                Note that this differs from the sign mount option in that it
 555                causes encryption of data sent over this mounted share but other
 556                shares mounted to the same server are unaffected.
 557 locallease     This option is rarely needed. Fcntl F_SETLEASE is
 558                used by some applications such as Samba and NFSv4 server to
 559                check to see whether a file is cacheable.  CIFS has no way
 560                to explicitly request a lease, but can check whether a file
 561                is cacheable (oplocked).  Unfortunately, even if a file
 562                is not oplocked, it could still be cacheable (ie cifs client
 563                could grant fcntl leases if no other local processes are using
 564                the file) for cases for example such as when the server does not
 565                support oplocks and the user is sure that the only updates to
 566                the file will be from this client. Specifying this mount option
 567                will allow the cifs client to check for leases (only) locally
 568                for files which are not oplocked instead of denying leases
 569                in that case. (EXPERIMENTAL)
 570 sec            Security mode.  Allowed values are:
 571                        none    attempt to connection as a null user (no name)
 572                        krb5    Use Kerberos version 5 authentication
 573                        krb5i   Use Kerberos authentication and packet signing
 574                        ntlm    Use NTLM password hashing (default)
 575                        ntlmi   Use NTLM password hashing with signing (if
 576                                /proc/fs/cifs/PacketSigningEnabled on or if
 577                                server requires signing also can be the default) 
 578                        ntlmv2  Use NTLMv2 password hashing      
 579                        ntlmv2i Use NTLMv2 password hashing with packet signing
 580                        lanman  (if configured in kernel config) use older
 581                                lanman hash
 582hard            Retry file operations if server is not responding
 583soft            Limit retries to unresponsive servers (usually only
 584                one retry) before returning an error.  (default)
 586The mount.cifs mount helper also accepts a few mount options before -o
 589        -S      take password from stdin (equivalent to setting the environment
 590                variable "PASSWD_FD=0"
 591        -V      print mount.cifs version
 592        -?      display simple usage information
 594With most 2.6 kernel versions of modutils, the version of the cifs kernel
 595module can be displayed via modinfo.
 597Misc /proc/fs/cifs Flags and Debug Info
 599Informational pseudo-files:
 600DebugData               Displays information about active CIFS sessions and
 601                        shares, features enabled as well as the cifs.ko
 602                        version.
 603Stats                   Lists summary resource usage information as well as per
 604                        share statistics, if CONFIG_CIFS_STATS in enabled
 605                        in the kernel configuration.
 607Configuration pseudo-files:
 608MultiuserMount          If set to one, more than one CIFS session to 
 609                        the same server ip address can be established
 610                        if more than one uid accesses the same mount
 611                        point and if the uids user/password mapping
 612                        information is available. (default is 0)
 613PacketSigningEnabled    If set to one, cifs packet signing is enabled
 614                        and will be used if the server requires 
 615                        it.  If set to two, cifs packet signing is
 616                        required even if the server considers packet
 617                        signing optional. (default 1)
 618SecurityFlags           Flags which control security negotiation and
 619                        also packet signing. Authentication (may/must)
 620                        flags (e.g. for NTLM and/or NTLMv2) may be combined with
 621                        the signing flags.  Specifying two different password
 622                        hashing mechanisms (as "must use") on the other hand 
 623                        does not make much sense. Default flags are 
 624                                0x07007 
 625                        (NTLM, NTLMv2 and packet signing allowed).  The maximum 
 626                        allowable flags if you want to allow mounts to servers
 627                        using weaker password hashes is 0x37037 (lanman,
 628                        plaintext, ntlm, ntlmv2, signing allowed).  Some
 629                        SecurityFlags require the corresponding menuconfig
 630                        options to be enabled (lanman and plaintext require
 631                        CONFIG_CIFS_WEAK_PW_HASH for example).  Enabling
 632                        plaintext authentication currently requires also
 633                        enabling lanman authentication in the security flags
 634                        because the cifs module only supports sending
 635                        laintext passwords using the older lanman dialect
 636                        form of the session setup SMB.  (e.g. for authentication
 637                        using plain text passwords, set the SecurityFlags
 638                        to 0x30030):
 640                        may use packet signing                          0x00001
 641                        must use packet signing                         0x01001
 642                        may use NTLM (most common password hash)        0x00002
 643                        must use NTLM                                   0x02002
 644                        may use NTLMv2                                  0x00004
 645                        must use NTLMv2                                 0x04004
 646                        may use Kerberos security                       0x00008
 647                        must use Kerberos                               0x08008
 648                        may use lanman (weak) password hash             0x00010
 649                        must use lanman password hash                   0x10010
 650                        may use plaintext passwords                     0x00020
 651                        must use plaintext passwords                    0x20020
 652                        (reserved for future packet encryption)         0x00040
 654cifsFYI                 If set to non-zero value, additional debug information
 655                        will be logged to the system error log.  This field
 656                        contains three flags controlling different classes of
 657                        debugging entries.  The maximum value it can be set
 658                        to is 7 which enables all debugging points (default 0).
 659                        Some debugging statements are not compiled into the
 660                        cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
 661                        kernel configuration. cifsFYI may be set to one or
 662                        nore of the following flags (7 sets them all):
 664                        log cifs informational messages                 0x01
 665                        log return codes from cifs entry points         0x02
 666                        log slow responses (ie which take longer than 1 second)
 667                          CONFIG_CIFS_STATS2 must be enabled in .config 0x04
 670traceSMB                If set to one, debug information is logged to the
 671                        system error log with the start of smb requests
 672                        and responses (default 0)
 673LookupCacheEnable       If set to one, inode information is kept cached
 674                        for one second improving performance of lookups
 675                        (default 1)
 676OplockEnabled           If set to one, safe distributed caching enabled.
 677                        (default 1)
 678LinuxExtensionsEnabled  If set to one then the client will attempt to
 679                        use the CIFS "UNIX" extensions which are optional
 680                        protocol enhancements that allow CIFS servers
 681                        to return accurate UID/GID information as well
 682                        as support symbolic links. If you use servers
 683                        such as Samba that support the CIFS Unix
 684                        extensions but do not want to use symbolic link
 685                        support and want to map the uid and gid fields 
 686                        to values supplied at mount (rather than the 
 687                        actual values, then set this to zero. (default 1)
 689These experimental features and tracing can be enabled by changing flags in 
 690/proc/fs/cifs (after the cifs module has been installed or built into the 
 691kernel, e.g.  insmod cifs).  To enable a feature set it to 1 e.g.  to enable 
 692tracing to the kernel message log type: 
 694        echo 7 > /proc/fs/cifs/cifsFYI
 696cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
 697logging of various informational messages.  2 enables logging of non-zero
 698SMB return codes while 4 enables logging of requests that take longer
 699than one second to complete (except for byte range lock requests). 
 700Setting it to 4 requires defining CONFIG_CIFS_STATS2 manually in the
 701source code (typically by setting it in the beginning of cifsglob.h),
 702and setting it to seven enables all three.  Finally, tracing
 703the start of smb requests and responses can be enabled via:
 705        echo 1 > /proc/fs/cifs/traceSMB
 707Two other experimental features are under development. To test these
 708requires enabling CONFIG_CIFS_EXPERIMENTAL
 710        cifsacl support needed to retrieve approximated mode bits based on
 711                the contents on the CIFS ACL.
 713        lease support: cifs will check the oplock state before calling into
 714        the vfs to see if we can grant a lease on a file.
 716        DNOTIFY fcntl: needed for support of directory change 
 717                            notification and perhaps later for file leases)
 719Per share (per client mount) statistics are available in /proc/fs/cifs/Stats
 720if the kernel was configured with cifs statistics enabled.  The statistics
 721represent the number of successful (ie non-zero return code from the server) 
 722SMB responses to some of the more common commands (open, delete, mkdir etc.).
 723Also recorded is the total bytes read and bytes written to the server for
 724that share.  Note that due to client caching effects this can be less than the
 725number of bytes read and written by the application running on the client.
 726The statistics for the number of total SMBs and oplock breaks are different in
 727that they represent all for that share, not just those for which the server
 728returned success.
 730Also note that "cat /proc/fs/cifs/DebugData" will display information about
 731the active sessions and the shares that are mounted.
 733Enabling Kerberos (extended security) works but requires version 1.2 or later
 734of the helper program cifs.upcall to be present and to be configured in the
 735/etc/request-key.conf file.  The cifs.upcall helper program is from the Samba
 736project( NTLM and NTLMv2 and LANMAN support do not
 737require this helper. Note that NTLMv2 security (which does not require the
 738cifs.upcall helper program), instead of using Kerberos, is sufficient for
 739some use cases.
 741DFS support allows transparent redirection to shares in an MS-DFS name space.
 742In addition, DFS support for target shares which are specified as UNC
 743names which begin with host names (rather than IP addresses) requires
 744a user space helper (such as cifs.upcall) to be present in order to
 745translate host names to ip address, and the user space helper must also
 746be configured in the file /etc/request-key.conf.  Samba, Windows servers and
 747many NAS appliances support DFS as a way of constructing a global name
 748space to ease network configuration and improve reliability.
 750To use cifs Kerberos and DFS support, the Linux keyutils package should be
 751installed and something like the following lines should be added to the
 752/etc/request-key.conf file:
 754create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
 755create dns_resolver * * /usr/local/sbin/cifs.upcall %k