0001 =====
0002 Usage
0003 =====
0004
0005 This module supports the SMB3 family of advanced network protocols (as well
0006 as older dialects, originally called "CIFS" or SMB1).
0007
0008 The CIFS VFS module for Linux supports many advanced network filesystem
0009 features such as hierarchical DFS like namespace, hardlinks, locking and more.
0010 It was designed to comply with the SNIA CIFS Technical Reference (which
0011 supersedes the 1992 X/Open SMB Standard) as well as to perform best practice
0012 practical interoperability with Windows 2000, Windows XP, Samba and equivalent
0013 servers. This code was developed in participation with the Protocol Freedom
0014 Information Foundation. CIFS and now SMB3 has now become a defacto
0015 standard for interoperating between Macs and Windows and major NAS appliances.
0016
0017 Please see
0018 MS-SMB2 (for detailed SMB2/SMB3/SMB3.1.1 protocol specification)
0019 or https://samba.org/samba/PFIF/
0020 for more details.
0021
0022
0023 For questions or bug reports please contact:
0024
0025 smfrench@gmail.com
0026
0027 See the project page at: https://wiki.samba.org/index.php/LinuxCIFS_utils
0028
0029 Build instructions
0030 ==================
0031
0032 For Linux:
0033
0034 1) Download the kernel (e.g. from https://www.kernel.org)
0035 and change directory into the top of the kernel directory tree
0036 (e.g. /usr/src/linux-2.5.73)
0037 2) make menuconfig (or make xconfig)
0038 3) select cifs from within the network filesystem choices
0039 4) save and exit
0040 5) make
0041
0042
0043 Installation instructions
0044 =========================
0045
0046 If you have built the CIFS vfs as module (successfully) simply
0047 type ``make modules_install`` (or if you prefer, manually copy the file to
0048 the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.ko).
0049
0050 If you have built the CIFS vfs into the kernel itself, follow the instructions
0051 for your distribution on how to install a new kernel (usually you
0052 would simply type ``make install``).
0053
0054 If you do not have the utility mount.cifs (in the Samba 4.x source tree and on
0055 the CIFS VFS web site) copy it to the same directory in which mount helpers
0056 reside (usually /sbin). Although the helper software is not
0057 required, mount.cifs is recommended. Most distros include a ``cifs-utils``
0058 package that includes this utility so it is recommended to install this.
0059
0060 Note that running the Winbind pam/nss module (logon service) on all of your
0061 Linux clients is useful in mapping Uids and Gids consistently across the
0062 domain to the proper network user. The mount.cifs mount helper can be
0063 found at cifs-utils.git on git.samba.org
0064
0065 If cifs is built as a module, then the size and number of network buffers
0066 and maximum number of simultaneous requests to one server can be configured.
0067 Changing these from their defaults is not recommended. By executing modinfo::
0068
0069 modinfo kernel/fs/cifs/cifs.ko
0070
0071 on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
0072 at module initialization time (by running insmod cifs.ko) can be seen.
0073
0074 Recommendations
0075 ===============
0076
0077 To improve security the SMB2.1 dialect or later (usually will get SMB3) is now
0078 the new default. To use old dialects (e.g. to mount Windows XP) use "vers=1.0"
0079 on mount (or vers=2.0 for Windows Vista). Note that the CIFS (vers=1.0) is
0080 much older and less secure than the default dialect SMB3 which includes
0081 many advanced security features such as downgrade attack detection
0082 and encrypted shares and stronger signing and authentication algorithms.
0083 There are additional mount options that may be helpful for SMB3 to get
0084 improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1):
0085
0086 ``mfsymlinks`` and either ``cifsacl`` or ``modefromsid`` (usually with ``idsfromsid``)
0087
0088 Allowing User Mounts
0089 ====================
0090
0091 To permit users to mount and unmount over directories they own is possible
0092 with the cifs vfs. A way to enable such mounting is to mark the mount.cifs
0093 utility as suid (e.g. ``chmod +s /sbin/mount.cifs``). To enable users to
0094 umount shares they mount requires
0095
0096 1) mount.cifs version 1.4 or later
0097 2) an entry for the share in /etc/fstab indicating that a user may
0098 unmount it e.g.::
0099
0100 //server/usersharename /mnt/username cifs user 0 0
0101
0102 Note that when the mount.cifs utility is run suid (allowing user mounts),
0103 in order to reduce risks, the ``nosuid`` mount flag is passed in on mount to
0104 disallow execution of an suid program mounted on the remote target.
0105 When mount is executed as root, nosuid is not passed in by default,
0106 and execution of suid programs on the remote target would be enabled
0107 by default. This can be changed, as with nfs and other filesystems,
0108 by simply specifying ``nosuid`` among the mount options. For user mounts
0109 though to be able to pass the suid flag to mount requires rebuilding
0110 mount.cifs with the following flag: CIFS_ALLOW_USR_SUID
0111
0112 There is a corresponding manual page for cifs mounting in the Samba 3.0 and
0113 later source tree in docs/manpages/mount.cifs.8
0114
0115 Allowing User Unmounts
0116 ======================
0117
0118 To permit users to unmount directories that they have user mounted (see above),
0119 the utility umount.cifs may be used. It may be invoked directly, or if
0120 umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
0121 (at least for most versions of the umount utility) for umount of cifs
0122 mounts, unless umount is invoked with -i (which will avoid invoking a umount
0123 helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
0124 as suid (e.g. ``chmod +s /sbin/umount.cifs``) or equivalent (some distributions
0125 allow adding entries to a file to the /etc/permissions file to achieve the
0126 equivalent suid effect). For this utility to succeed the target path
0127 must be a cifs mount, and the uid of the current user must match the uid
0128 of the user who mounted the resource.
0129
0130 Also note that the customary way of allowing user mounts and unmounts is
0131 (instead of using mount.cifs and unmount.cifs as suid) to add a line
0132 to the file /etc/fstab for each //server/share you wish to mount, but
0133 this can become unwieldy when potential mount targets include many
0134 or unpredictable UNC names.
0135
0136 Samba Considerations
0137 ====================
0138
0139 Most current servers support SMB2.1 and SMB3 which are more secure,
0140 but there are useful protocol extensions for the older less secure CIFS
0141 dialect, so to get the maximum benefit if mounting using the older dialect
0142 (CIFS/SMB1), we recommend using a server that supports the SNIA CIFS
0143 Unix Extensions standard (e.g. almost any version of Samba ie version
0144 2.2.5 or later) but the CIFS vfs works fine with a wide variety of CIFS servers.
0145 Note that uid, gid and file permissions will display default values if you do
0146 not have a server that supports the Unix extensions for CIFS (such as Samba
0147 2.2.5 or later). To enable the Unix CIFS Extensions in the Samba server, add
0148 the line::
0149
0150 unix extensions = yes
0151
0152 to your smb.conf file on the server. Note that the following smb.conf settings
0153 are also useful (on the Samba server) when the majority of clients are Unix or
0154 Linux::
0155
0156 case sensitive = yes
0157 delete readonly = yes
0158 ea support = yes
0159
0160 Note that server ea support is required for supporting xattrs from the Linux
0161 cifs client, and that EA support is present in later versions of Samba (e.g.
0162 3.0.6 and later (also EA support works in all versions of Windows, at least to
0163 shares on NTFS filesystems). Extended Attribute (xattr) support is an optional
0164 feature of most Linux filesystems which may require enabling via
0165 make menuconfig. Client support for extended attributes (user xattr) can be
0166 disabled on a per-mount basis by specifying ``nouser_xattr`` on mount.
0167
0168 The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
0169 version 3.10 and later. Setting POSIX ACLs requires enabling both XATTR and
0170 then POSIX support in the CIFS configuration options when building the cifs
0171 module. POSIX ACL support can be disabled on a per mount basic by specifying
0172 ``noacl`` on mount.
0173
0174 Some administrators may want to change Samba's smb.conf ``map archive`` and
0175 ``create mask`` parameters from the default. Unless the create mask is changed
0176 newly created files can end up with an unnecessarily restrictive default mode,
0177 which may not be what you want, although if the CIFS Unix extensions are
0178 enabled on the server and client, subsequent setattr calls (e.g. chmod) can
0179 fix the mode. Note that creating special devices (mknod) remotely
0180 may require specifying a mkdev function to Samba if you are not using
0181 Samba 3.0.6 or later. For more information on these see the manual pages
0182 (``man smb.conf``) on the Samba server system. Note that the cifs vfs,
0183 unlike the smbfs vfs, does not read the smb.conf on the client system
0184 (the few optional settings are passed in on mount via -o parameters instead).
0185 Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
0186 open files (required for strict POSIX compliance). Windows Servers already
0187 supported this feature. Samba server does not allow symlinks that refer to files
0188 outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
0189 files with absolute paths (ie beginning with slash) such as::
0190
0191 ln -s /mnt/foo bar
0192
0193 would be forbidden. Samba 3.0.6 server or later includes the ability to create
0194 such symlinks safely by converting unsafe symlinks (ie symlinks to server
0195 files that are outside of the share) to a samba specific format on the server
0196 that is ignored by local server applications and non-cifs clients and that will
0197 not be traversed by the Samba server). This is opaque to the Linux client
0198 application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
0199 later, but only for remote clients using the CIFS Unix extensions, and will
0200 be invisible to Windows clients and typically will not affect local
0201 applications running on the same server as Samba.
0202
0203 Use instructions
0204 ================
0205
0206 Once the CIFS VFS support is built into the kernel or installed as a module
0207 (cifs.ko), you can use mount syntax like the following to access Samba or
0208 Mac or Windows servers::
0209
0210 mount -t cifs //9.53.216.11/e$ /mnt -o username=myname,password=mypassword
0211
0212 Before -o the option -v may be specified to make the mount.cifs
0213 mount helper display the mount steps more verbosely.
0214 After -o the following commonly used cifs vfs specific options
0215 are supported::
0216
0217 username=<username>
0218 password=<password>
0219 domain=<domain name>
0220
0221 Other cifs mount options are described below. Use of TCP names (in addition to
0222 ip addresses) is available if the mount helper (mount.cifs) is installed. If
0223 you do not trust the server to which are mounted, or if you do not have
0224 cifs signing enabled (and the physical network is insecure), consider use
0225 of the standard mount options ``noexec`` and ``nosuid`` to reduce the risk of
0226 running an altered binary on your local system (downloaded from a hostile server
0227 or altered by a hostile router).
0228
0229 Although mounting using format corresponding to the CIFS URL specification is
0230 not possible in mount.cifs yet, it is possible to use an alternate format
0231 for the server and sharename (which is somewhat similar to NFS style mount
0232 syntax) instead of the more widely used UNC format (i.e. \\server\share)::
0233
0234 mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
0235
0236 When using the mount helper mount.cifs, passwords may be specified via alternate
0237 mechanisms, instead of specifying it after -o using the normal ``pass=`` syntax
0238 on the command line:
0239 1) By including it in a credential file. Specify credentials=filename as one
0240 of the mount options. Credential files contain two lines::
0241
0242 username=someuser
0243 password=your_password
0244
0245 2) By specifying the password in the PASSWD environment variable (similarly
0246 the user name can be taken from the USER environment variable).
0247 3) By specifying the password in a file by name via PASSWD_FILE
0248 4) By specifying the password in a file by file descriptor via PASSWD_FD
0249
0250 If no password is provided, mount.cifs will prompt for password entry
0251
0252 Restrictions
0253 ============
0254
0255 Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
0256 1001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a
0257 problem as most servers support this.
0258
0259 Valid filenames differ between Windows and Linux. Windows typically restricts
0260 filenames which contain certain reserved characters (e.g.the character :
0261 which is used to delimit the beginning of a stream name by Windows), while
0262 Linux allows a slightly wider set of valid characters in filenames. Windows
0263 servers can remap such characters when an explicit mapping is specified in
0264 the Server's registry. Samba starting with version 3.10 will allow such
0265 filenames (ie those which contain valid Linux characters, which normally
0266 would be forbidden for Windows/CIFS semantics) as long as the server is
0267 configured for Unix Extensions (and the client has not disabled
0268 /proc/fs/cifs/LinuxExtensionsEnabled). In addition the mount option
0269 ``mapposix`` can be used on CIFS (vers=1.0) to force the mapping of
0270 illegal Windows/NTFS/SMB characters to a remap range (this mount parameter
0271 is the default for SMB3). This remap (``mapposix``) range is also
0272 compatible with Mac (and "Services for Mac" on some older Windows).
0273
0274 CIFS VFS Mount Options
0275 ======================
0276 A partial list of the supported mount options follows:
0277
0278 username
0279 The user name to use when trying to establish
0280 the CIFS session.
0281 password
0282 The user password. If the mount helper is
0283 installed, the user will be prompted for password
0284 if not supplied.
0285 ip
0286 The ip address of the target server
0287 unc
0288 The target server Universal Network Name (export) to
0289 mount.
0290 domain
0291 Set the SMB/CIFS workgroup name prepended to the
0292 username during CIFS session establishment
0293 forceuid
0294 Set the default uid for inodes to the uid
0295 passed in on mount. For mounts to servers
0296 which do support the CIFS Unix extensions, such as a
0297 properly configured Samba server, the server provides
0298 the uid, gid and mode so this parameter should not be
0299 specified unless the server and clients uid and gid
0300 numbering differ. If the server and client are in the
0301 same domain (e.g. running winbind or nss_ldap) and
0302 the server supports the Unix Extensions then the uid
0303 and gid can be retrieved from the server (and uid
0304 and gid would not have to be specified on the mount.
0305 For servers which do not support the CIFS Unix
0306 extensions, the default uid (and gid) returned on lookup
0307 of existing files will be the uid (gid) of the person
0308 who executed the mount (root, except when mount.cifs
0309 is configured setuid for user mounts) unless the ``uid=``
0310 (gid) mount option is specified. Also note that permission
0311 checks (authorization checks) on accesses to a file occur
0312 at the server, but there are cases in which an administrator
0313 may want to restrict at the client as well. For those
0314 servers which do not report a uid/gid owner
0315 (such as Windows), permissions can also be checked at the
0316 client, and a crude form of client side permission checking
0317 can be enabled by specifying file_mode and dir_mode on
0318 the client. (default)
0319 forcegid
0320 (similar to above but for the groupid instead of uid) (default)
0321 noforceuid
0322 Fill in file owner information (uid) by requesting it from
0323 the server if possible. With this option, the value given in
0324 the uid= option (on mount) will only be used if the server
0325 can not support returning uids on inodes.
0326 noforcegid
0327 (similar to above but for the group owner, gid, instead of uid)
0328 uid
0329 Set the default uid for inodes, and indicate to the
0330 cifs kernel driver which local user mounted. If the server
0331 supports the unix extensions the default uid is
0332 not used to fill in the owner fields of inodes (files)
0333 unless the ``forceuid`` parameter is specified.
0334 gid
0335 Set the default gid for inodes (similar to above).
0336 file_mode
0337 If CIFS Unix extensions are not supported by the server
0338 this overrides the default mode for file inodes.
0339 fsc
0340 Enable local disk caching using FS-Cache (off by default). This
0341 option could be useful to improve performance on a slow link,
0342 heavily loaded server and/or network where reading from the
0343 disk is faster than reading from the server (over the network).
0344 This could also impact scalability positively as the
0345 number of calls to the server are reduced. However, local
0346 caching is not suitable for all workloads for e.g. read-once
0347 type workloads. So, you need to consider carefully your
0348 workload/scenario before using this option. Currently, local
0349 disk caching is functional for CIFS files opened as read-only.
0350 dir_mode
0351 If CIFS Unix extensions are not supported by the server
0352 this overrides the default mode for directory inodes.
0353 port
0354 attempt to contact the server on this tcp port, before
0355 trying the usual ports (port 445, then 139).
0356 iocharset
0357 Codepage used to convert local path names to and from
0358 Unicode. Unicode is used by default for network path
0359 names if the server supports it. If iocharset is
0360 not specified then the nls_default specified
0361 during the local client kernel build will be used.
0362 If server does not support Unicode, this parameter is
0363 unused.
0364 rsize
0365 default read size (usually 16K). The client currently
0366 can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
0367 defaults to 16K and may be changed (from 8K to the maximum
0368 kmalloc size allowed by your kernel) at module install time
0369 for cifs.ko. Setting CIFSMaxBufSize to a very large value
0370 will cause cifs to use more memory and may reduce performance
0371 in some cases. To use rsize greater than 127K (the original
0372 cifs protocol maximum) also requires that the server support
0373 a new Unix Capability flag (for very large read) which some
0374 newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
0375 set from a minimum of 2048 to a maximum of 130048 (127K or
0376 CIFSMaxBufSize, whichever is smaller)
0377 wsize
0378 default write size (default 57344)
0379 maximum wsize currently allowed by CIFS is 57344 (fourteen
0380 4096 byte pages)
0381 actimeo=n
0382 attribute cache timeout in seconds (default 1 second).
0383 After this timeout, the cifs client requests fresh attribute
0384 information from the server. This option allows to tune the
0385 attribute cache timeout to suit the workload needs. Shorter
0386 timeouts mean better the cache coherency, but increased number
0387 of calls to the server. Longer timeouts mean reduced number
0388 of calls to the server at the expense of less stricter cache
0389 coherency checks (i.e. incorrect attribute cache for a short
0390 period of time).
0391 rw
0392 mount the network share read-write (note that the
0393 server may still consider the share read-only)
0394 ro
0395 mount network share read-only
0396 version
0397 used to distinguish different versions of the
0398 mount helper utility (not typically needed)
0399 sep
0400 if first mount option (after the -o), overrides
0401 the comma as the separator between the mount
0402 parms. e.g.::
0403
0404 -o user=myname,password=mypassword,domain=mydom
0405
0406 could be passed instead with period as the separator by::
0407
0408 -o sep=.user=myname.password=mypassword.domain=mydom
0409
0410 this might be useful when comma is contained within username
0411 or password or domain. This option is less important
0412 when the cifs mount helper cifs.mount (version 1.1 or later)
0413 is used.
0414 nosuid
0415 Do not allow remote executables with the suid bit
0416 program to be executed. This is only meaningful for mounts
0417 to servers such as Samba which support the CIFS Unix Extensions.
0418 If you do not trust the servers in your network (your mount
0419 targets) it is recommended that you specify this option for
0420 greater security.
0421 exec
0422 Permit execution of binaries on the mount.
0423 noexec
0424 Do not permit execution of binaries on the mount.
0425 dev
0426 Recognize block devices on the remote mount.
0427 nodev
0428 Do not recognize devices on the remote mount.
0429 suid
0430 Allow remote files on this mountpoint with suid enabled to
0431 be executed (default for mounts when executed as root,
0432 nosuid is default for user mounts).
0433 credentials
0434 Although ignored by the cifs kernel component, it is used by
0435 the mount helper, mount.cifs. When mount.cifs is installed it
0436 opens and reads the credential file specified in order
0437 to obtain the userid and password arguments which are passed to
0438 the cifs vfs.
0439 guest
0440 Although ignored by the kernel component, the mount.cifs
0441 mount helper will not prompt the user for a password
0442 if guest is specified on the mount options. If no
0443 password is specified a null password will be used.
0444 perm
0445 Client does permission checks (vfs_permission check of uid
0446 and gid of the file against the mode and desired operation),
0447 Note that this is in addition to the normal ACL check on the
0448 target machine done by the server software.
0449 Client permission checking is enabled by default.
0450 noperm
0451 Client does not do permission checks. This can expose
0452 files on this mount to access by other users on the local
0453 client system. It is typically only needed when the server
0454 supports the CIFS Unix Extensions but the UIDs/GIDs on the
0455 client and server system do not match closely enough to allow
0456 access by the user doing the mount, but it may be useful with
0457 non CIFS Unix Extension mounts for cases in which the default
0458 mode is specified on the mount but is not to be enforced on the
0459 client (e.g. perhaps when MultiUserMount is enabled)
0460 Note that this does not affect the normal ACL check on the
0461 target machine done by the server software (of the server
0462 ACL against the user name provided at mount time).
0463 serverino
0464 Use server's inode numbers instead of generating automatically
0465 incrementing inode numbers on the client. Although this will
0466 make it easier to spot hardlinked files (as they will have
0467 the same inode numbers) and inode numbers may be persistent,
0468 note that the server does not guarantee that the inode numbers
0469 are unique if multiple server side mounts are exported under a
0470 single share (since inode numbers on the servers might not
0471 be unique if multiple filesystems are mounted under the same
0472 shared higher level directory). Note that some older
0473 (e.g. pre-Windows 2000) do not support returning UniqueIDs
0474 or the CIFS Unix Extensions equivalent and for those
0475 this mount option will have no effect. Exporting cifs mounts
0476 under nfsd requires this mount option on the cifs mount.
0477 This is now the default if server supports the
0478 required network operation.
0479 noserverino
0480 Client generates inode numbers (rather than using the actual one
0481 from the server). These inode numbers will vary after
0482 unmount or reboot which can confuse some applications,
0483 but not all server filesystems support unique inode
0484 numbers.
0485 setuids
0486 If the CIFS Unix extensions are negotiated with the server
0487 the client will attempt to set the effective uid and gid of
0488 the local process on newly created files, directories, and
0489 devices (create, mkdir, mknod). If the CIFS Unix Extensions
0490 are not negotiated, for newly created files and directories
0491 instead of using the default uid and gid specified on
0492 the mount, cache the new file's uid and gid locally which means
0493 that the uid for the file can change when the inode is
0494 reloaded (or the user remounts the share).
0495 nosetuids
0496 The client will not attempt to set the uid and gid on
0497 on newly created files, directories, and devices (create,
0498 mkdir, mknod) which will result in the server setting the
0499 uid and gid to the default (usually the server uid of the
0500 user who mounted the share). Letting the server (rather than
0501 the client) set the uid and gid is the default. If the CIFS
0502 Unix Extensions are not negotiated then the uid and gid for
0503 new files will appear to be the uid (gid) of the mounter or the
0504 uid (gid) parameter specified on the mount.
0505 netbiosname
0506 When mounting to servers via port 139, specifies the RFC1001
0507 source name to use to represent the client netbios machine
0508 name when doing the RFC1001 netbios session initialize.
0509 direct
0510 Do not do inode data caching on files opened on this mount.
0511 This precludes mmapping files on this mount. In some cases
0512 with fast networks and little or no caching benefits on the
0513 client (e.g. when the application is doing large sequential
0514 reads bigger than page size without rereading the same data)
0515 this can provide better performance than the default
0516 behavior which caches reads (readahead) and writes
0517 (writebehind) through the local Linux client pagecache
0518 if oplock (caching token) is granted and held. Note that
0519 direct allows write operations larger than page size
0520 to be sent to the server.
0521 strictcache
0522 Use for switching on strict cache mode. In this mode the
0523 client read from the cache all the time it has Oplock Level II,
0524 otherwise - read from the server. All written data are stored
0525 in the cache, but if the client doesn't have Exclusive Oplock,
0526 it writes the data to the server.
0527 rwpidforward
0528 Forward pid of a process who opened a file to any read or write
0529 operation on that file. This prevent applications like WINE
0530 from failing on read and write if we use mandatory brlock style.
0531 acl
0532 Allow setfacl and getfacl to manage posix ACLs if server
0533 supports them. (default)
0534 noacl
0535 Do not allow setfacl and getfacl calls on this mount
0536 user_xattr
0537 Allow getting and setting user xattrs (those attributes whose
0538 name begins with ``user.`` or ``os2.``) as OS/2 EAs (extended
0539 attributes) to the server. This allows support of the
0540 setfattr and getfattr utilities. (default)
0541 nouser_xattr
0542 Do not allow getfattr/setfattr to get/set/list xattrs
0543 mapchars
0544 Translate six of the seven reserved characters (not backslash)::
0545
0546 *?<>|:
0547
0548 to the remap range (above 0xF000), which also
0549 allows the CIFS client to recognize files created with
0550 such characters by Windows's POSIX emulation. This can
0551 also be useful when mounting to most versions of Samba
0552 (which also forbids creating and opening files
0553 whose names contain any of these seven characters).
0554 This has no effect if the server does not support
0555 Unicode on the wire.
0556 nomapchars
0557 Do not translate any of these seven characters (default).
0558 nocase
0559 Request case insensitive path name matching (case
0560 sensitive is the default if the server supports it).
0561 (mount option ``ignorecase`` is identical to ``nocase``)
0562 posixpaths
0563 If CIFS Unix extensions are supported, attempt to
0564 negotiate posix path name support which allows certain
0565 characters forbidden in typical CIFS filenames, without
0566 requiring remapping. (default)
0567 noposixpaths
0568 If CIFS Unix extensions are supported, do not request
0569 posix path name support (this may cause servers to
0570 reject creatingfile with certain reserved characters).
0571 nounix
0572 Disable the CIFS Unix Extensions for this mount (tree
0573 connection). This is rarely needed, but it may be useful
0574 in order to turn off multiple settings all at once (ie
0575 posix acls, posix locks, posix paths, symlink support
0576 and retrieving uids/gids/mode from the server) or to
0577 work around a bug in server which implement the Unix
0578 Extensions.
0579 nobrl
0580 Do not send byte range lock requests to the server.
0581 This is necessary for certain applications that break
0582 with cifs style mandatory byte range locks (and most
0583 cifs servers do not yet support requesting advisory
0584 byte range locks).
0585 forcemandatorylock
0586 Even if the server supports posix (advisory) byte range
0587 locking, send only mandatory lock requests. For some
0588 (presumably rare) applications, originally coded for
0589 DOS/Windows, which require Windows style mandatory byte range
0590 locking, they may be able to take advantage of this option,
0591 forcing the cifs client to only send mandatory locks
0592 even if the cifs server would support posix advisory locks.
0593 ``forcemand`` is accepted as a shorter form of this mount
0594 option.
0595 nostrictsync
0596 If this mount option is set, when an application does an
0597 fsync call then the cifs client does not send an SMB Flush
0598 to the server (to force the server to write all dirty data
0599 for this file immediately to disk), although cifs still sends
0600 all dirty (cached) file data to the server and waits for the
0601 server to respond to the write. Since SMB Flush can be
0602 very slow, and some servers may be reliable enough (to risk
0603 delaying slightly flushing the data to disk on the server),
0604 turning on this option may be useful to improve performance for
0605 applications that fsync too much, at a small risk of server
0606 crash. If this mount option is not set, by default cifs will
0607 send an SMB flush request (and wait for a response) on every
0608 fsync call.
0609 nodfs
0610 Disable DFS (global name space support) even if the
0611 server claims to support it. This can help work around
0612 a problem with parsing of DFS paths with Samba server
0613 versions 3.0.24 and 3.0.25.
0614 remount
0615 remount the share (often used to change from ro to rw mounts
0616 or vice versa)
0617 cifsacl
0618 Report mode bits (e.g. on stat) based on the Windows ACL for
0619 the file. (EXPERIMENTAL)
0620 servern
0621 Specify the server 's netbios name (RFC1001 name) to use
0622 when attempting to setup a session to the server.
0623 This is needed for mounting to some older servers (such
0624 as OS/2 or Windows 98 and Windows ME) since they do not
0625 support a default server name. A server name can be up
0626 to 15 characters long and is usually uppercased.
0627 sfu
0628 When the CIFS Unix Extensions are not negotiated, attempt to
0629 create device files and fifos in a format compatible with
0630 Services for Unix (SFU). In addition retrieve bits 10-12
0631 of the mode via the SETFILEBITS extended attribute (as
0632 SFU does). In the future the bottom 9 bits of the
0633 mode also will be emulated using queries of the security
0634 descriptor (ACL).
0635 mfsymlinks
0636 Enable support for Minshall+French symlinks
0637 (see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
0638 This option is ignored when specified together with the
0639 'sfu' option. Minshall+French symlinks are used even if
0640 the server supports the CIFS Unix Extensions.
0641 sign
0642 Must use packet signing (helps avoid unwanted data modification
0643 by intermediate systems in the route). Note that signing
0644 does not work with lanman or plaintext authentication.
0645 seal
0646 Must seal (encrypt) all data on this mounted share before
0647 sending on the network. Requires support for Unix Extensions.
0648 Note that this differs from the sign mount option in that it
0649 causes encryption of data sent over this mounted share but other
0650 shares mounted to the same server are unaffected.
0651 locallease
0652 This option is rarely needed. Fcntl F_SETLEASE is
0653 used by some applications such as Samba and NFSv4 server to
0654 check to see whether a file is cacheable. CIFS has no way
0655 to explicitly request a lease, but can check whether a file
0656 is cacheable (oplocked). Unfortunately, even if a file
0657 is not oplocked, it could still be cacheable (ie cifs client
0658 could grant fcntl leases if no other local processes are using
0659 the file) for cases for example such as when the server does not
0660 support oplocks and the user is sure that the only updates to
0661 the file will be from this client. Specifying this mount option
0662 will allow the cifs client to check for leases (only) locally
0663 for files which are not oplocked instead of denying leases
0664 in that case. (EXPERIMENTAL)
0665 sec
0666 Security mode. Allowed values are:
0667
0668 none
0669 attempt to connection as a null user (no name)
0670 krb5
0671 Use Kerberos version 5 authentication
0672 krb5i
0673 Use Kerberos authentication and packet signing
0674 ntlm
0675 Use NTLM password hashing (default)
0676 ntlmi
0677 Use NTLM password hashing with signing (if
0678 /proc/fs/cifs/PacketSigningEnabled on or if
0679 server requires signing also can be the default)
0680 ntlmv2
0681 Use NTLMv2 password hashing
0682 ntlmv2i
0683 Use NTLMv2 password hashing with packet signing
0684 lanman
0685 (if configured in kernel config) use older
0686 lanman hash
0687 hard
0688 Retry file operations if server is not responding
0689 soft
0690 Limit retries to unresponsive servers (usually only
0691 one retry) before returning an error. (default)
0692
0693 The mount.cifs mount helper also accepts a few mount options before -o
0694 including:
0695
0696 =============== ===============================================================
0697 -S take password from stdin (equivalent to setting the environment
0698 variable ``PASSWD_FD=0``
0699 -V print mount.cifs version
0700 -? display simple usage information
0701 =============== ===============================================================
0702
0703 With most 2.6 kernel versions of modutils, the version of the cifs kernel
0704 module can be displayed via modinfo.
0705
0706 Misc /proc/fs/cifs Flags and Debug Info
0707 =======================================
0708
0709 Informational pseudo-files:
0710
0711 ======================= =======================================================
0712 DebugData Displays information about active CIFS sessions and
0713 shares, features enabled as well as the cifs.ko
0714 version.
0715 Stats Lists summary resource usage information as well as per
0716 share statistics.
0717 open_files List all the open file handles on all active SMB sessions.
0718 ======================= =======================================================
0719
0720 Configuration pseudo-files:
0721
0722 ======================= =======================================================
0723 SecurityFlags Flags which control security negotiation and
0724 also packet signing. Authentication (may/must)
0725 flags (e.g. for NTLM and/or NTLMv2) may be combined with
0726 the signing flags. Specifying two different password
0727 hashing mechanisms (as "must use") on the other hand
0728 does not make much sense. Default flags are::
0729
0730 0x07007
0731
0732 (NTLM, NTLMv2 and packet signing allowed). The maximum
0733 allowable flags if you want to allow mounts to servers
0734 using weaker password hashes is 0x37037 (lanman,
0735 plaintext, ntlm, ntlmv2, signing allowed). Some
0736 SecurityFlags require the corresponding menuconfig
0737 options to be enabled. Enabling plaintext
0738 authentication currently requires also enabling
0739 lanman authentication in the security flags
0740 because the cifs module only supports sending
0741 laintext passwords using the older lanman dialect
0742 form of the session setup SMB. (e.g. for authentication
0743 using plain text passwords, set the SecurityFlags
0744 to 0x30030)::
0745
0746 may use packet signing 0x00001
0747 must use packet signing 0x01001
0748 may use NTLM (most common password hash) 0x00002
0749 must use NTLM 0x02002
0750 may use NTLMv2 0x00004
0751 must use NTLMv2 0x04004
0752 may use Kerberos security 0x00008
0753 must use Kerberos 0x08008
0754 may use lanman (weak) password hash 0x00010
0755 must use lanman password hash 0x10010
0756 may use plaintext passwords 0x00020
0757 must use plaintext passwords 0x20020
0758 (reserved for future packet encryption) 0x00040
0759
0760 cifsFYI If set to non-zero value, additional debug information
0761 will be logged to the system error log. This field
0762 contains three flags controlling different classes of
0763 debugging entries. The maximum value it can be set
0764 to is 7 which enables all debugging points (default 0).
0765 Some debugging statements are not compiled into the
0766 cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
0767 kernel configuration. cifsFYI may be set to one or
0768 nore of the following flags (7 sets them all)::
0769
0770 +-----------------------------------------------+------+
0771 | log cifs informational messages | 0x01 |
0772 +-----------------------------------------------+------+
0773 | log return codes from cifs entry points | 0x02 |
0774 +-----------------------------------------------+------+
0775 | log slow responses | 0x04 |
0776 | (ie which take longer than 1 second) | |
0777 | | |
0778 | CONFIG_CIFS_STATS2 must be enabled in .config | |
0779 +-----------------------------------------------+------+
0780
0781 traceSMB If set to one, debug information is logged to the
0782 system error log with the start of smb requests
0783 and responses (default 0)
0784 LookupCacheEnable If set to one, inode information is kept cached
0785 for one second improving performance of lookups
0786 (default 1)
0787 LinuxExtensionsEnabled If set to one then the client will attempt to
0788 use the CIFS "UNIX" extensions which are optional
0789 protocol enhancements that allow CIFS servers
0790 to return accurate UID/GID information as well
0791 as support symbolic links. If you use servers
0792 such as Samba that support the CIFS Unix
0793 extensions but do not want to use symbolic link
0794 support and want to map the uid and gid fields
0795 to values supplied at mount (rather than the
0796 actual values, then set this to zero. (default 1)
0797 dfscache List the content of the DFS cache.
0798 If set to 0, the client will clear the cache.
0799 ======================= =======================================================
0800
0801 These experimental features and tracing can be enabled by changing flags in
0802 /proc/fs/cifs (after the cifs module has been installed or built into the
0803 kernel, e.g. insmod cifs). To enable a feature set it to 1 e.g. to enable
0804 tracing to the kernel message log type::
0805
0806 echo 7 > /proc/fs/cifs/cifsFYI
0807
0808 cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
0809 logging of various informational messages. 2 enables logging of non-zero
0810 SMB return codes while 4 enables logging of requests that take longer
0811 than one second to complete (except for byte range lock requests).
0812 Setting it to 4 requires CONFIG_CIFS_STATS2 to be set in kernel configuration
0813 (.config). Setting it to seven enables all three. Finally, tracing
0814 the start of smb requests and responses can be enabled via::
0815
0816 echo 1 > /proc/fs/cifs/traceSMB
0817
0818 Per share (per client mount) statistics are available in /proc/fs/cifs/Stats.
0819 Additional information is available if CONFIG_CIFS_STATS2 is enabled in the
0820 kernel configuration (.config). The statistics returned include counters which
0821 represent the number of attempted and failed (ie non-zero return code from the
0822 server) SMB3 (or cifs) requests grouped by request type (read, write, close etc.).
0823 Also recorded is the total bytes read and bytes written to the server for
0824 that share. Note that due to client caching effects this can be less than the
0825 number of bytes read and written by the application running on the client.
0826 Statistics can be reset to zero by ``echo 0 > /proc/fs/cifs/Stats`` which may be
0827 useful if comparing performance of two different scenarios.
0828
0829 Also note that ``cat /proc/fs/cifs/DebugData`` will display information about
0830 the active sessions and the shares that are mounted.
0831
0832 Enabling Kerberos (extended security) works but requires version 1.2 or later
0833 of the helper program cifs.upcall to be present and to be configured in the
0834 /etc/request-key.conf file. The cifs.upcall helper program is from the Samba
0835 project(https://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
0836 require this helper. Note that NTLMv2 security (which does not require the
0837 cifs.upcall helper program), instead of using Kerberos, is sufficient for
0838 some use cases.
0839
0840 DFS support allows transparent redirection to shares in an MS-DFS name space.
0841 In addition, DFS support for target shares which are specified as UNC
0842 names which begin with host names (rather than IP addresses) requires
0843 a user space helper (such as cifs.upcall) to be present in order to
0844 translate host names to ip address, and the user space helper must also
0845 be configured in the file /etc/request-key.conf. Samba, Windows servers and
0846 many NAS appliances support DFS as a way of constructing a global name
0847 space to ease network configuration and improve reliability.
0848
0849 To use cifs Kerberos and DFS support, the Linux keyutils package should be
0850 installed and something like the following lines should be added to the
0851 /etc/request-key.conf file::
0852
0853 create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
0854 create dns_resolver * * /usr/local/sbin/cifs.upcall %k
0855
0856 CIFS kernel module parameters
0857 =============================
0858 These module parameters can be specified or modified either during the time of
0859 module loading or during the runtime by using the interface::
0860
0861 /proc/module/cifs/parameters/<param>
0862
0863 i.e.::
0864
0865 echo "value" > /sys/module/cifs/parameters/<param>
0866
0867 ================= ==========================================================
0868 1. enable_oplocks Enable or disable oplocks. Oplocks are enabled by default.
0869 [Y/y/1]. To disable use any of [N/n/0].
0870 ================= ==========================================================
