Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 This module supports the SMB3 family of advanced network protocols (as well 2 as older dialects, originally called "CIFS" or SMB1). 3 4 The CIFS VFS module for Linux supports many advanced network filesystem 5 features such as hierarchical DFS like namespace, hardlinks, locking and more. 6 It was designed to comply with the SNIA CIFS Technical Reference (which 7 supersedes the 1992 X/Open SMB Standard) as well as to perform best practice 8 practical interoperability with Windows 2000, Windows XP, Samba and equivalent 9 servers. This code was developed in participation with the Protocol Freedom 10 Information Foundation. CIFS and now SMB3 has now become a defacto 11 standard for interoperating between Macs and Windows and major NAS appliances. 12 13 Please see 14 http://protocolfreedom.org/ and 15 http://samba.org/samba/PFIF/ 16 for more details. 17 18 19 For questions or bug reports please contact: 20 email@example.com (firstname.lastname@example.org) 21 22 See the project page at: https://wiki.samba.org/index.php/LinuxCIFS_utils 23 24 Build instructions: 25 ================== 26 For Linux: 27 1) Download the kernel (e.g. from http://www.kernel.org) 28 and change directory into the top of the kernel directory tree 29 (e.g. /usr/src/linux-2.5.73) 30 2) make menuconfig (or make xconfig) 31 3) select cifs from within the network filesystem choices 32 4) save and exit 33 5) make 34 35 36 Installation instructions: 37 ========================= 38 If you have built the CIFS vfs as module (successfully) simply 39 type "make modules_install" (or if you prefer, manually copy the file to 40 the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.o). 41 42 If you have built the CIFS vfs into the kernel itself, follow the instructions 43 for your distribution on how to install a new kernel (usually you 44 would simply type "make install"). 45 46 If you do not have the utility mount.cifs (in the Samba 3.0 source tree and on 47 the CIFS VFS web site) copy it to the same directory in which mount.smbfs and 48 similar files reside (usually /sbin). Although the helper software is not 49 required, mount.cifs is recommended. Most distros include a "cifs-utils" 50 package that includes this utility so it is recommended to install this. 51 52 Note that running the Winbind pam/nss module (logon service) on all of your 53 Linux clients is useful in mapping Uids and Gids consistently across the 54 domain to the proper network user. The mount.cifs mount helper can be 55 found at cifs-utils.git on git.samba.org 56 57 If cifs is built as a module, then the size and number of network buffers 58 and maximum number of simultaneous requests to one server can be configured. 59 Changing these from their defaults is not recommended. By executing modinfo 60 modinfo kernel/fs/cifs/cifs.ko 61 on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made 62 at module initialization time (by running insmod cifs.ko) can be seen. 63 64 Recommendations 65 =============== 66 To improve security the SMB2.1 dialect or later (usually will get SMB3) is now 67 the new default. To use old dialects (e.g. to mount Windows XP) use "vers=1.0" 68 on mount (or vers=2.0 for Windows Vista). Note that the CIFS (vers=1.0) is 69 much older and less secure than the default dialect SMB3 which includes 70 many advanced security features such as downgrade attack detection 71 and encrypted shares and stronger signing and authentication algorithms. 72 There are additional mount options that may be helpful for SMB3 to get 73 improved POSIX behavior (NB: can use vers=3.0 to force only SMB3, never 2.1): 74 "mfsymlinks" and "cifsacl" and "idsfromsid" 75 76 Allowing User Mounts 77 ==================== 78 To permit users to mount and unmount over directories they own is possible 79 with the cifs vfs. A way to enable such mounting is to mark the mount.cifs 80 utility as suid (e.g. "chmod +s /sbin/mount.cifs). To enable users to 81 umount shares they mount requires 82 1) mount.cifs version 1.4 or later 83 2) an entry for the share in /etc/fstab indicating that a user may 84 unmount it e.g. 85 //server/usersharename /mnt/username cifs user 0 0 86 87 Note that when the mount.cifs utility is run suid (allowing user mounts), 88 in order to reduce risks, the "nosuid" mount flag is passed in on mount to 89 disallow execution of an suid program mounted on the remote target. 90 When mount is executed as root, nosuid is not passed in by default, 91 and execution of suid programs on the remote target would be enabled 92 by default. This can be changed, as with nfs and other filesystems, 93 by simply specifying "nosuid" among the mount options. For user mounts 94 though to be able to pass the suid flag to mount requires rebuilding 95 mount.cifs with the following flag: CIFS_ALLOW_USR_SUID 96 97 There is a corresponding manual page for cifs mounting in the Samba 3.0 and 98 later source tree in docs/manpages/mount.cifs.8 99 100 Allowing User Unmounts 101 ====================== 102 To permit users to ummount directories that they have user mounted (see above), 103 the utility umount.cifs may be used. It may be invoked directly, or if 104 umount.cifs is placed in /sbin, umount can invoke the cifs umount helper 105 (at least for most versions of the umount utility) for umount of cifs 106 mounts, unless umount is invoked with -i (which will avoid invoking a umount 107 helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked 108 as suid (e.g. "chmod +s /sbin/umount.cifs") or equivalent (some distributions 109 allow adding entries to a file to the /etc/permissions file to achieve the 110 equivalent suid effect). For this utility to succeed the target path 111 must be a cifs mount, and the uid of the current user must match the uid 112 of the user who mounted the resource. 113 114 Also note that the customary way of allowing user mounts and unmounts is 115 (instead of using mount.cifs and unmount.cifs as suid) to add a line 116 to the file /etc/fstab for each //server/share you wish to mount, but 117 this can become unwieldy when potential mount targets include many 118 or unpredictable UNC names. 119 120 Samba Considerations 121 ==================== 122 To get the maximum benefit from the CIFS VFS, we recommend using a server that 123 supports the SNIA CIFS Unix Extensions standard (e.g. Samba 2.2.5 or later or 124 Samba 3.0) but the CIFS vfs works fine with a wide variety of CIFS servers. 125 Note that uid, gid and file permissions will display default values if you do 126 not have a server that supports the Unix extensions for CIFS (such as Samba 127 2.2.5 or later). To enable the Unix CIFS Extensions in the Samba server, add 128 the line: 129 130 unix extensions = yes 131 132 to your smb.conf file on the server. Note that the following smb.conf settings 133 are also useful (on the Samba server) when the majority of clients are Unix or 134 Linux: 135 136 case sensitive = yes 137 delete readonly = yes 138 ea support = yes 139 140 Note that server ea support is required for supporting xattrs from the Linux 141 cifs client, and that EA support is present in later versions of Samba (e.g. 142 3.0.6 and later (also EA support works in all versions of Windows, at least to 143 shares on NTFS filesystems). Extended Attribute (xattr) support is an optional 144 feature of most Linux filesystems which may require enabling via 145 make menuconfig. Client support for extended attributes (user xattr) can be 146 disabled on a per-mount basis by specifying "nouser_xattr" on mount. 147 148 The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers 149 version 3.10 and later. Setting POSIX ACLs requires enabling both XATTR and 150 then POSIX support in the CIFS configuration options when building the cifs 151 module. POSIX ACL support can be disabled on a per mount basic by specifying 152 "noacl" on mount. 153 154 Some administrators may want to change Samba's smb.conf "map archive" and 155 "create mask" parameters from the default. Unless the create mask is changed 156 newly created files can end up with an unnecessarily restrictive default mode, 157 which may not be what you want, although if the CIFS Unix extensions are 158 enabled on the server and client, subsequent setattr calls (e.g. chmod) can 159 fix the mode. Note that creating special devices (mknod) remotely 160 may require specifying a mkdev function to Samba if you are not using 161 Samba 3.0.6 or later. For more information on these see the manual pages 162 ("man smb.conf") on the Samba server system. Note that the cifs vfs, 163 unlike the smbfs vfs, does not read the smb.conf on the client system 164 (the few optional settings are passed in on mount via -o parameters instead). 165 Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete 166 open files (required for strict POSIX compliance). Windows Servers already 167 supported this feature. Samba server does not allow symlinks that refer to files 168 outside of the share, so in Samba versions prior to 3.0.6, most symlinks to 169 files with absolute paths (ie beginning with slash) such as: 170 ln -s /mnt/foo bar 171 would be forbidden. Samba 3.0.6 server or later includes the ability to create 172 such symlinks safely by converting unsafe symlinks (ie symlinks to server 173 files that are outside of the share) to a samba specific format on the server 174 that is ignored by local server applications and non-cifs clients and that will 175 not be traversed by the Samba server). This is opaque to the Linux client 176 application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or 177 later, but only for remote clients using the CIFS Unix extensions, and will 178 be invisbile to Windows clients and typically will not affect local 179 applications running on the same server as Samba. 180 181 Use instructions: 182 ================ 183 Once the CIFS VFS support is built into the kernel or installed as a module 184 (cifs.ko), you can use mount syntax like the following to access Samba or 185 Mac or Windows servers: 186 187 mount -t cifs //126.96.36.199/e$ /mnt -o username=myname,password=mypassword 188 189 Before -o the option -v may be specified to make the mount.cifs 190 mount helper display the mount steps more verbosely. 191 After -o the following commonly used cifs vfs specific options 192 are supported: 193 194 username=<username> 195 password=<password> 196 domain=<domain name> 197 198 Other cifs mount options are described below. Use of TCP names (in addition to 199 ip addresses) is available if the mount helper (mount.cifs) is installed. If 200 you do not trust the server to which are mounted, or if you do not have 201 cifs signing enabled (and the physical network is insecure), consider use 202 of the standard mount options "noexec" and "nosuid" to reduce the risk of 203 running an altered binary on your local system (downloaded from a hostile server 204 or altered by a hostile router). 205 206 Although mounting using format corresponding to the CIFS URL specification is 207 not possible in mount.cifs yet, it is possible to use an alternate format 208 for the server and sharename (which is somewhat similar to NFS style mount 209 syntax) instead of the more widely used UNC format (i.e. \\server\share): 210 mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd 211 212 When using the mount helper mount.cifs, passwords may be specified via alternate 213 mechanisms, instead of specifying it after -o using the normal "pass=" syntax 214 on the command line: 215 1) By including it in a credential file. Specify credentials=filename as one 216 of the mount options. Credential files contain two lines 217 username=someuser 218 password=your_password 219 2) By specifying the password in the PASSWD environment variable (similarly 220 the user name can be taken from the USER environment variable). 221 3) By specifying the password in a file by name via PASSWD_FILE 222 4) By specifying the password in a file by file descriptor via PASSWD_FD 223 224 If no password is provided, mount.cifs will prompt for password entry 225 226 Restrictions 227 ============ 228 Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC 229 1001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a 230 problem as most servers support this. 231 232 Valid filenames differ between Windows and Linux. Windows typically restricts 233 filenames which contain certain reserved characters (e.g.the character : 234 which is used to delimit the beginning of a stream name by Windows), while 235 Linux allows a slightly wider set of valid characters in filenames. Windows 236 servers can remap such characters when an explicit mapping is specified in 237 the Server's registry. Samba starting with version 3.10 will allow such 238 filenames (ie those which contain valid Linux characters, which normally 239 would be forbidden for Windows/CIFS semantics) as long as the server is 240 configured for Unix Extensions (and the client has not disabled 241 /proc/fs/cifs/LinuxExtensionsEnabled). In addition the mount option 242 "mapposix" can be used on CIFS (vers=1.0) to force the mapping of 243 illegal Windows/NTFS/SMB characters to a remap range (this mount parm 244 is the default for SMB3). This remap ("mapposix") range is also 245 compatible with Mac (and "Services for Mac" on some older Windows). 246 247 CIFS VFS Mount Options 248 ====================== 249 A partial list of the supported mount options follows: 250 username The user name to use when trying to establish 251 the CIFS session. 252 password The user password. If the mount helper is 253 installed, the user will be prompted for password 254 if not supplied. 255 ip The ip address of the target server 256 unc The target server Universal Network Name (export) to 257 mount. 258 domain Set the SMB/CIFS workgroup name prepended to the 259 username during CIFS session establishment 260 forceuid Set the default uid for inodes to the uid 261 passed in on mount. For mounts to servers 262 which do support the CIFS Unix extensions, such as a 263 properly configured Samba server, the server provides 264 the uid, gid and mode so this parameter should not be 265 specified unless the server and clients uid and gid 266 numbering differ. If the server and client are in the 267 same domain (e.g. running winbind or nss_ldap) and 268 the server supports the Unix Extensions then the uid 269 and gid can be retrieved from the server (and uid 270 and gid would not have to be specified on the mount. 271 For servers which do not support the CIFS Unix 272 extensions, the default uid (and gid) returned on lookup 273 of existing files will be the uid (gid) of the person 274 who executed the mount (root, except when mount.cifs 275 is configured setuid for user mounts) unless the "uid=" 276 (gid) mount option is specified. Also note that permission 277 checks (authorization checks) on accesses to a file occur 278 at the server, but there are cases in which an administrator 279 may want to restrict at the client as well. For those 280 servers which do not report a uid/gid owner 281 (such as Windows), permissions can also be checked at the 282 client, and a crude form of client side permission checking 283 can be enabled by specifying file_mode and dir_mode on 284 the client. (default) 285 forcegid (similar to above but for the groupid instead of uid) (default) 286 noforceuid Fill in file owner information (uid) by requesting it from 287 the server if possible. With this option, the value given in 288 the uid= option (on mount) will only be used if the server 289 can not support returning uids on inodes. 290 noforcegid (similar to above but for the group owner, gid, instead of uid) 291 uid Set the default uid for inodes, and indicate to the 292 cifs kernel driver which local user mounted. If the server 293 supports the unix extensions the default uid is 294 not used to fill in the owner fields of inodes (files) 295 unless the "forceuid" parameter is specified. 296 gid Set the default gid for inodes (similar to above). 297 file_mode If CIFS Unix extensions are not supported by the server 298 this overrides the default mode for file inodes. 299 fsc Enable local disk caching using FS-Cache (off by default). This 300 option could be useful to improve performance on a slow link, 301 heavily loaded server and/or network where reading from the 302 disk is faster than reading from the server (over the network). 303 This could also impact scalability positively as the 304 number of calls to the server are reduced. However, local 305 caching is not suitable for all workloads for e.g. read-once 306 type workloads. So, you need to consider carefully your 307 workload/scenario before using this option. Currently, local 308 disk caching is functional for CIFS files opened as read-only. 309 dir_mode If CIFS Unix extensions are not supported by the server 310 this overrides the default mode for directory inodes. 311 port attempt to contact the server on this tcp port, before 312 trying the usual ports (port 445, then 139). 313 iocharset Codepage used to convert local path names to and from 314 Unicode. Unicode is used by default for network path 315 names if the server supports it. If iocharset is 316 not specified then the nls_default specified 317 during the local client kernel build will be used. 318 If server does not support Unicode, this parameter is 319 unused. 320 rsize default read size (usually 16K). The client currently 321 can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize 322 defaults to 16K and may be changed (from 8K to the maximum 323 kmalloc size allowed by your kernel) at module install time 324 for cifs.ko. Setting CIFSMaxBufSize to a very large value 325 will cause cifs to use more memory and may reduce performance 326 in some cases. To use rsize greater than 127K (the original 327 cifs protocol maximum) also requires that the server support 328 a new Unix Capability flag (for very large read) which some 329 newer servers (e.g. Samba 3.0.26 or later) do. rsize can be 330 set from a minimum of 2048 to a maximum of 130048 (127K or 331 CIFSMaxBufSize, whichever is smaller) 332 wsize default write size (default 57344) 333 maximum wsize currently allowed by CIFS is 57344 (fourteen 334 4096 byte pages) 335 actimeo=n attribute cache timeout in seconds (default 1 second). 336 After this timeout, the cifs client requests fresh attribute 337 information from the server. This option allows to tune the 338 attribute cache timeout to suit the workload needs. Shorter 339 timeouts mean better the cache coherency, but increased number 340 of calls to the server. Longer timeouts mean reduced number 341 of calls to the server at the expense of less stricter cache 342 coherency checks (i.e. incorrect attribute cache for a short 343 period of time). 344 rw mount the network share read-write (note that the 345 server may still consider the share read-only) 346 ro mount network share read-only 347 version used to distinguish different versions of the 348 mount helper utility (not typically needed) 349 sep if first mount option (after the -o), overrides 350 the comma as the separator between the mount 351 parms. e.g. 352 -o user=myname,password=mypassword,domain=mydom 353 could be passed instead with period as the separator by 354 -o sep=.user=myname.password=mypassword.domain=mydom 355 this might be useful when comma is contained within username 356 or password or domain. This option is less important 357 when the cifs mount helper cifs.mount (version 1.1 or later) 358 is used. 359 nosuid Do not allow remote executables with the suid bit 360 program to be executed. This is only meaningful for mounts 361 to servers such as Samba which support the CIFS Unix Extensions. 362 If you do not trust the servers in your network (your mount 363 targets) it is recommended that you specify this option for 364 greater security. 365 exec Permit execution of binaries on the mount. 366 noexec Do not permit execution of binaries on the mount. 367 dev Recognize block devices on the remote mount. 368 nodev Do not recognize devices on the remote mount. 369 suid Allow remote files on this mountpoint with suid enabled to 370 be executed (default for mounts when executed as root, 371 nosuid is default for user mounts). 372 credentials Although ignored by the cifs kernel component, it is used by 373 the mount helper, mount.cifs. When mount.cifs is installed it 374 opens and reads the credential file specified in order 375 to obtain the userid and password arguments which are passed to 376 the cifs vfs. 377 guest Although ignored by the kernel component, the mount.cifs 378 mount helper will not prompt the user for a password 379 if guest is specified on the mount options. If no 380 password is specified a null password will be used. 381 perm Client does permission checks (vfs_permission check of uid 382 and gid of the file against the mode and desired operation), 383 Note that this is in addition to the normal ACL check on the 384 target machine done by the server software. 385 Client permission checking is enabled by default. 386 noperm Client does not do permission checks. This can expose 387 files on this mount to access by other users on the local 388 client system. It is typically only needed when the server 389 supports the CIFS Unix Extensions but the UIDs/GIDs on the 390 client and server system do not match closely enough to allow 391 access by the user doing the mount, but it may be useful with 392 non CIFS Unix Extension mounts for cases in which the default 393 mode is specified on the mount but is not to be enforced on the 394 client (e.g. perhaps when MultiUserMount is enabled) 395 Note that this does not affect the normal ACL check on the 396 target machine done by the server software (of the server 397 ACL against the user name provided at mount time). 398 serverino Use server's inode numbers instead of generating automatically 399 incrementing inode numbers on the client. Although this will 400 make it easier to spot hardlinked files (as they will have 401 the same inode numbers) and inode numbers may be persistent, 402 note that the server does not guarantee that the inode numbers 403 are unique if multiple server side mounts are exported under a 404 single share (since inode numbers on the servers might not 405 be unique if multiple filesystems are mounted under the same 406 shared higher level directory). Note that some older 407 (e.g. pre-Windows 2000) do not support returning UniqueIDs 408 or the CIFS Unix Extensions equivalent and for those 409 this mount option will have no effect. Exporting cifs mounts 410 under nfsd requires this mount option on the cifs mount. 411 This is now the default if server supports the 412 required network operation. 413 noserverino Client generates inode numbers (rather than using the actual one 414 from the server). These inode numbers will vary after 415 unmount or reboot which can confuse some applications, 416 but not all server filesystems support unique inode 417 numbers. 418 setuids If the CIFS Unix extensions are negotiated with the server 419 the client will attempt to set the effective uid and gid of 420 the local process on newly created files, directories, and 421 devices (create, mkdir, mknod). If the CIFS Unix Extensions 422 are not negotiated, for newly created files and directories 423 instead of using the default uid and gid specified on 424 the mount, cache the new file's uid and gid locally which means 425 that the uid for the file can change when the inode is 426 reloaded (or the user remounts the share). 427 nosetuids The client will not attempt to set the uid and gid on 428 on newly created files, directories, and devices (create, 429 mkdir, mknod) which will result in the server setting the 430 uid and gid to the default (usually the server uid of the 431 user who mounted the share). Letting the server (rather than 432 the client) set the uid and gid is the default. If the CIFS 433 Unix Extensions are not negotiated then the uid and gid for 434 new files will appear to be the uid (gid) of the mounter or the 435 uid (gid) parameter specified on the mount. 436 netbiosname When mounting to servers via port 139, specifies the RFC1001 437 source name to use to represent the client netbios machine 438 name when doing the RFC1001 netbios session initialize. 439 direct Do not do inode data caching on files opened on this mount. 440 This precludes mmapping files on this mount. In some cases 441 with fast networks and little or no caching benefits on the 442 client (e.g. when the application is doing large sequential 443 reads bigger than page size without rereading the same data) 444 this can provide better performance than the default 445 behavior which caches reads (readahead) and writes 446 (writebehind) through the local Linux client pagecache 447 if oplock (caching token) is granted and held. Note that 448 direct allows write operations larger than page size 449 to be sent to the server. 450 strictcache Use for switching on strict cache mode. In this mode the 451 client read from the cache all the time it has Oplock Level II, 452 otherwise - read from the server. All written data are stored 453 in the cache, but if the client doesn't have Exclusive Oplock, 454 it writes the data to the server. 455 rwpidforward Forward pid of a process who opened a file to any read or write 456 operation on that file. This prevent applications like WINE 457 from failing on read and write if we use mandatory brlock style. 458 acl Allow setfacl and getfacl to manage posix ACLs if server 459 supports them. (default) 460 noacl Do not allow setfacl and getfacl calls on this mount 461 user_xattr Allow getting and setting user xattrs (those attributes whose 462 name begins with "user." or "os2.") as OS/2 EAs (extended 463 attributes) to the server. This allows support of the 464 setfattr and getfattr utilities. (default) 465 nouser_xattr Do not allow getfattr/setfattr to get/set/list xattrs 466 mapchars Translate six of the seven reserved characters (not backslash) 467 *?<>|: 468 to the remap range (above 0xF000), which also 469 allows the CIFS client to recognize files created with 470 such characters by Windows's POSIX emulation. This can 471 also be useful when mounting to most versions of Samba 472 (which also forbids creating and opening files 473 whose names contain any of these seven characters). 474 This has no effect if the server does not support 475 Unicode on the wire. 476 nomapchars Do not translate any of these seven characters (default). 477 nocase Request case insensitive path name matching (case 478 sensitive is the default if the server supports it). 479 (mount option "ignorecase" is identical to "nocase") 480 posixpaths If CIFS Unix extensions are supported, attempt to 481 negotiate posix path name support which allows certain 482 characters forbidden in typical CIFS filenames, without 483 requiring remapping. (default) 484 noposixpaths If CIFS Unix extensions are supported, do not request 485 posix path name support (this may cause servers to 486 reject creatingfile with certain reserved characters). 487 nounix Disable the CIFS Unix Extensions for this mount (tree 488 connection). This is rarely needed, but it may be useful 489 in order to turn off multiple settings all at once (ie 490 posix acls, posix locks, posix paths, symlink support 491 and retrieving uids/gids/mode from the server) or to 492 work around a bug in server which implement the Unix 493 Extensions. 494 nobrl Do not send byte range lock requests to the server. 495 This is necessary for certain applications that break 496 with cifs style mandatory byte range locks (and most 497 cifs servers do not yet support requesting advisory 498 byte range locks). 499 forcemandatorylock Even if the server supports posix (advisory) byte range 500 locking, send only mandatory lock requests. For some 501 (presumably rare) applications, originally coded for 502 DOS/Windows, which require Windows style mandatory byte range 503 locking, they may be able to take advantage of this option, 504 forcing the cifs client to only send mandatory locks 505 even if the cifs server would support posix advisory locks. 506 "forcemand" is accepted as a shorter form of this mount 507 option. 508 nostrictsync If this mount option is set, when an application does an 509 fsync call then the cifs client does not send an SMB Flush 510 to the server (to force the server to write all dirty data 511 for this file immediately to disk), although cifs still sends 512 all dirty (cached) file data to the server and waits for the 513 server to respond to the write. Since SMB Flush can be 514 very slow, and some servers may be reliable enough (to risk 515 delaying slightly flushing the data to disk on the server), 516 turning on this option may be useful to improve performance for 517 applications that fsync too much, at a small risk of server 518 crash. If this mount option is not set, by default cifs will 519 send an SMB flush request (and wait for a response) on every 520 fsync call. 521 nodfs Disable DFS (global name space support) even if the 522 server claims to support it. This can help work around 523 a problem with parsing of DFS paths with Samba server 524 versions 3.0.24 and 3.0.25. 525 remount remount the share (often used to change from ro to rw mounts 526 or vice versa) 527 cifsacl Report mode bits (e.g. on stat) based on the Windows ACL for 528 the file. (EXPERIMENTAL) 529 servern Specify the server 's netbios name (RFC1001 name) to use 530 when attempting to setup a session to the server. 531 This is needed for mounting to some older servers (such 532 as OS/2 or Windows 98 and Windows ME) since they do not 533 support a default server name. A server name can be up 534 to 15 characters long and is usually uppercased. 535 sfu When the CIFS Unix Extensions are not negotiated, attempt to 536 create device files and fifos in a format compatible with 537 Services for Unix (SFU). In addition retrieve bits 10-12 538 of the mode via the SETFILEBITS extended attribute (as 539 SFU does). In the future the bottom 9 bits of the 540 mode also will be emulated using queries of the security 541 descriptor (ACL). 542 mfsymlinks Enable support for Minshall+French symlinks 543 (see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks) 544 This option is ignored when specified together with the 545 'sfu' option. Minshall+French symlinks are used even if 546 the server supports the CIFS Unix Extensions. 547 sign Must use packet signing (helps avoid unwanted data modification 548 by intermediate systems in the route). Note that signing 549 does not work with lanman or plaintext authentication. 550 seal Must seal (encrypt) all data on this mounted share before 551 sending on the network. Requires support for Unix Extensions. 552 Note that this differs from the sign mount option in that it 553 causes encryption of data sent over this mounted share but other 554 shares mounted to the same server are unaffected. 555 locallease This option is rarely needed. Fcntl F_SETLEASE is 556 used by some applications such as Samba and NFSv4 server to 557 check to see whether a file is cacheable. CIFS has no way 558 to explicitly request a lease, but can check whether a file 559 is cacheable (oplocked). Unfortunately, even if a file 560 is not oplocked, it could still be cacheable (ie cifs client 561 could grant fcntl leases if no other local processes are using 562 the file) for cases for example such as when the server does not 563 support oplocks and the user is sure that the only updates to 564 the file will be from this client. Specifying this mount option 565 will allow the cifs client to check for leases (only) locally 566 for files which are not oplocked instead of denying leases 567 in that case. (EXPERIMENTAL) 568 sec Security mode. Allowed values are: 569 none attempt to connection as a null user (no name) 570 krb5 Use Kerberos version 5 authentication 571 krb5i Use Kerberos authentication and packet signing 572 ntlm Use NTLM password hashing (default) 573 ntlmi Use NTLM password hashing with signing (if 574 /proc/fs/cifs/PacketSigningEnabled on or if 575 server requires signing also can be the default) 576 ntlmv2 Use NTLMv2 password hashing 577 ntlmv2i Use NTLMv2 password hashing with packet signing 578 lanman (if configured in kernel config) use older 579 lanman hash 580 hard Retry file operations if server is not responding 581 soft Limit retries to unresponsive servers (usually only 582 one retry) before returning an error. (default) 583 584 The mount.cifs mount helper also accepts a few mount options before -o 585 including: 586 587 -S take password from stdin (equivalent to setting the environment 588 variable "PASSWD_FD=0" 589 -V print mount.cifs version 590 -? display simple usage information 591 592 With most 2.6 kernel versions of modutils, the version of the cifs kernel 593 module can be displayed via modinfo. 594 595 Misc /proc/fs/cifs Flags and Debug Info 596 ======================================= 597 Informational pseudo-files: 598 DebugData Displays information about active CIFS sessions and 599 shares, features enabled as well as the cifs.ko 600 version. 601 Stats Lists summary resource usage information as well as per 602 share statistics, if CONFIG_CIFS_STATS in enabled 603 in the kernel configuration. 604 605 Configuration pseudo-files: 606 PacketSigningEnabled If set to one, cifs packet signing is enabled 607 and will be used if the server requires 608 it. If set to two, cifs packet signing is 609 required even if the server considers packet 610 signing optional. (default 1) 611 SecurityFlags Flags which control security negotiation and 612 also packet signing. Authentication (may/must) 613 flags (e.g. for NTLM and/or NTLMv2) may be combined with 614 the signing flags. Specifying two different password 615 hashing mechanisms (as "must use") on the other hand 616 does not make much sense. Default flags are 617 0x07007 618 (NTLM, NTLMv2 and packet signing allowed). The maximum 619 allowable flags if you want to allow mounts to servers 620 using weaker password hashes is 0x37037 (lanman, 621 plaintext, ntlm, ntlmv2, signing allowed). Some 622 SecurityFlags require the corresponding menuconfig 623 options to be enabled (lanman and plaintext require 624 CONFIG_CIFS_WEAK_PW_HASH for example). Enabling 625 plaintext authentication currently requires also 626 enabling lanman authentication in the security flags 627 because the cifs module only supports sending 628 laintext passwords using the older lanman dialect 629 form of the session setup SMB. (e.g. for authentication 630 using plain text passwords, set the SecurityFlags 631 to 0x30030): 632 633 may use packet signing 0x00001 634 must use packet signing 0x01001 635 may use NTLM (most common password hash) 0x00002 636 must use NTLM 0x02002 637 may use NTLMv2 0x00004 638 must use NTLMv2 0x04004 639 may use Kerberos security 0x00008 640 must use Kerberos 0x08008 641 may use lanman (weak) password hash 0x00010 642 must use lanman password hash 0x10010 643 may use plaintext passwords 0x00020 644 must use plaintext passwords 0x20020 645 (reserved for future packet encryption) 0x00040 646 647 cifsFYI If set to non-zero value, additional debug information 648 will be logged to the system error log. This field 649 contains three flags controlling different classes of 650 debugging entries. The maximum value it can be set 651 to is 7 which enables all debugging points (default 0). 652 Some debugging statements are not compiled into the 653 cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the 654 kernel configuration. cifsFYI may be set to one or 655 nore of the following flags (7 sets them all): 656 657 log cifs informational messages 0x01 658 log return codes from cifs entry points 0x02 659 log slow responses (ie which take longer than 1 second) 660 CONFIG_CIFS_STATS2 must be enabled in .config 0x04 661 662 663 traceSMB If set to one, debug information is logged to the 664 system error log with the start of smb requests 665 and responses (default 0) 666 LookupCacheEnable If set to one, inode information is kept cached 667 for one second improving performance of lookups 668 (default 1) 669 OplockEnabled If set to one, safe distributed caching enabled. 670 (default 1) 671 LinuxExtensionsEnabled If set to one then the client will attempt to 672 use the CIFS "UNIX" extensions which are optional 673 protocol enhancements that allow CIFS servers 674 to return accurate UID/GID information as well 675 as support symbolic links. If you use servers 676 such as Samba that support the CIFS Unix 677 extensions but do not want to use symbolic link 678 support and want to map the uid and gid fields 679 to values supplied at mount (rather than the 680 actual values, then set this to zero. (default 1) 681 682 These experimental features and tracing can be enabled by changing flags in 683 /proc/fs/cifs (after the cifs module has been installed or built into the 684 kernel, e.g. insmod cifs). To enable a feature set it to 1 e.g. to enable 685 tracing to the kernel message log type: 686 687 echo 7 > /proc/fs/cifs/cifsFYI 688 689 cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel 690 logging of various informational messages. 2 enables logging of non-zero 691 SMB return codes while 4 enables logging of requests that take longer 692 than one second to complete (except for byte range lock requests). 693 Setting it to 4 requires defining CONFIG_CIFS_STATS2 manually in the 694 source code (typically by setting it in the beginning of cifsglob.h), 695 and setting it to seven enables all three. Finally, tracing 696 the start of smb requests and responses can be enabled via: 697 698 echo 1 > /proc/fs/cifs/traceSMB 699 700 Per share (per client mount) statistics are available in /proc/fs/cifs/Stats 701 if the kernel was configured with cifs statistics enabled. The statistics 702 represent the number of successful (ie non-zero return code from the server) 703 SMB responses to some of the more common commands (open, delete, mkdir etc.). 704 Also recorded is the total bytes read and bytes written to the server for 705 that share. Note that due to client caching effects this can be less than the 706 number of bytes read and written by the application running on the client. 707 The statistics for the number of total SMBs and oplock breaks are different in 708 that they represent all for that share, not just those for which the server 709 returned success. 710 711 Also note that "cat /proc/fs/cifs/DebugData" will display information about 712 the active sessions and the shares that are mounted. 713 714 Enabling Kerberos (extended security) works but requires version 1.2 or later 715 of the helper program cifs.upcall to be present and to be configured in the 716 /etc/request-key.conf file. The cifs.upcall helper program is from the Samba 717 project(http://www.samba.org). NTLM and NTLMv2 and LANMAN support do not 718 require this helper. Note that NTLMv2 security (which does not require the 719 cifs.upcall helper program), instead of using Kerberos, is sufficient for 720 some use cases. 721 722 DFS support allows transparent redirection to shares in an MS-DFS name space. 723 In addition, DFS support for target shares which are specified as UNC 724 names which begin with host names (rather than IP addresses) requires 725 a user space helper (such as cifs.upcall) to be present in order to 726 translate host names to ip address, and the user space helper must also 727 be configured in the file /etc/request-key.conf. Samba, Windows servers and 728 many NAS appliances support DFS as a way of constructing a global name 729 space to ease network configuration and improve reliability. 730 731 To use cifs Kerberos and DFS support, the Linux keyutils package should be 732 installed and something like the following lines should be added to the 733 /etc/request-key.conf file: 734 735 create cifs.spnego * * /usr/local/sbin/cifs.upcall %k 736 create dns_resolver * * /usr/local/sbin/cifs.upcall %k 737 738 CIFS kernel module parameters 739 ============================= 740 These module parameters can be specified or modified either during the time of 741 module loading or during the runtime by using the interface 742 /proc/module/cifs/parameters/<param> 743 744 i.e. echo "value" > /sys/module/cifs/parameters/<param> 745 746 1. enable_oplocks - Enable or disable oplocks. Oplocks are enabled by default. 747 [Y/y/1]. To disable use any of [N/n/0].