Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.
1 The CIFS VFS support for Linux supports many advanced network filesystem 2 features such as hierarchical dfs like namespace, hardlinks, locking and more. 3 It was designed to comply with the SNIA CIFS Technical Reference (which 4 supersedes the 1992 X/Open SMB Standard) as well as to perform best practice 5 practical interoperability with Windows 2000, Windows XP, Samba and equivalent 6 servers. This code was developed in participation with the Protocol Freedom 7 Information Foundation. 8 9 Please see 10 http://protocolfreedom.org/ and 11 http://samba.org/samba/PFIF/ 12 for more details. 13 14 15 For questions or bug reports please contact: 16 firstname.lastname@example.org (email@example.com) 17 18 Build instructions: 19 ================== 20 For Linux 2.4: 21 1) Get the kernel source (e.g.from http://www.kernel.org) 22 and download the cifs vfs source (see the project page 23 at http://us1.samba.org/samba/Linux_CIFS_client.html) 24 and change directory into the top of the kernel directory 25 then patch the kernel (e.g. "patch -p1 < cifs_24.patch") 26 to add the cifs vfs to your kernel configure options if 27 it has not already been added (e.g. current SuSE and UL 28 users do not need to apply the cifs_24.patch since the cifs vfs is 29 already in the kernel configure menu) and then 30 mkdir linux/fs/cifs and then copy the current cifs vfs files from 31 the cifs download to your kernel build directory e.g. 32 33 cp <cifs_download_dir>/fs/cifs/* to <kernel_download_dir>/fs/cifs 34 35 2) make menuconfig (or make xconfig) 36 3) select cifs from within the network filesystem choices 37 4) save and exit 38 5) make dep 39 6) make modules (or "make" if CIFS VFS not to be built as a module) 40 41 For Linux 2.6: 42 1) Download the kernel (e.g. from http://www.kernel.org) 43 and change directory into the top of the kernel directory tree 44 (e.g. /usr/src/linux-2.5.73) 45 2) make menuconfig (or make xconfig) 46 3) select cifs from within the network filesystem choices 47 4) save and exit 48 5) make 49 50 51 Installation instructions: 52 ========================= 53 If you have built the CIFS vfs as module (successfully) simply 54 type "make modules_install" (or if you prefer, manually copy the file to 55 the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.o). 56 57 If you have built the CIFS vfs into the kernel itself, follow the instructions 58 for your distribution on how to install a new kernel (usually you 59 would simply type "make install"). 60 61 If you do not have the utility mount.cifs (in the Samba 3.0 source tree and on 62 the CIFS VFS web site) copy it to the same directory in which mount.smbfs and 63 similar files reside (usually /sbin). Although the helper software is not 64 required, 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 66 users who are used to Windows e.g. 67 net use <mount point> <UNC name or cifs URL> 68 Note that running the Winbind pam/nss module (logon service) on all of your 69 Linux clients is useful in mapping Uids and Gids consistently across the 70 domain to the proper network user. The mount.cifs mount helper can be 71 trivially built from Samba 3.0 or later source e.g. by executing: 72 73 gcc samba/source/client/mount.cifs.c -o mount.cifs 74 75 If cifs is built as a module, then the size and number of network buffers 76 and maximum number of simultaneous requests to one server can be configured. 77 Changing these from their defaults is not recommended. By executing modinfo 78 modinfo kernel/fs/cifs/cifs.ko 79 on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made 80 at module initialization time (by running insmod cifs.ko) can be seen. 81 82 Allowing User Mounts 83 ==================== 84 To permit users to mount and unmount over directories they own is possible 85 with the cifs vfs. A way to enable such mounting is to mark the mount.cifs 86 utility as suid (e.g. "chmod +s /sbin/mount.cifs). To enable users to 87 umount shares they mount requires 88 1) mount.cifs version 1.4 or later 89 2) an entry for the share in /etc/fstab indicating that a user may 90 unmount it e.g. 91 //server/usersharename /mnt/username cifs user 0 0 92 93 Note that when the mount.cifs utility is run suid (allowing user mounts), 94 in order to reduce risks, the "nosuid" mount flag is passed in on mount to 95 disallow execution of an suid program mounted on the remote target. 96 When mount is executed as root, nosuid is not passed in by default, 97 and execution of suid programs on the remote target would be enabled 98 by default. This can be changed, as with nfs and other filesystems, 99 by simply specifying "nosuid" among the mount options. For user mounts 100 though to be able to pass the suid flag to mount requires rebuilding 101 mount.cifs with the following flag: 102 103 gcc samba/source/client/mount.cifs.c -DCIFS_ALLOW_USR_SUID -o mount.cifs 104 105 There is a corresponding manual page for cifs mounting in the Samba 3.0 and 106 later source tree in docs/manpages/mount.cifs.8 107 108 Allowing User Unmounts 109 ====================== 110 To permit users to ummount directories that they have user mounted (see above), 111 the utility umount.cifs may be used. It may be invoked directly, or if 112 umount.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 114 mounts, unless umount is invoked with -i (which will avoid invoking a umount 115 helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked 116 as suid (e.g. "chmod +s /sbin/umount.cifs") or equivalent (some distributions 117 allow adding entries to a file to the /etc/permissions file to achieve the 118 equivalent suid effect). For this utility to succeed the target path 119 must be a cifs mount, and the uid of the current user must match the uid 120 of the user who mounted the resource. 121 122 Also 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 124 to the file /etc/fstab for each //server/share you wish to mount, but 125 this can become unwieldy when potential mount targets include many 126 or unpredictable UNC names. 127 128 Samba Considerations 129 ==================== 130 To get the maximum benefit from the CIFS VFS, we recommend using a server that 131 supports the SNIA CIFS Unix Extensions standard (e.g. Samba 2.2.5 or later or 132 Samba 3.0) but the CIFS vfs works fine with a wide variety of CIFS servers. 133 Note that uid, gid and file permissions will display default values if you do 134 not have a server that supports the Unix extensions for CIFS (such as Samba 135 2.2.5 or later). To enable the Unix CIFS Extensions in the Samba server, add 136 the line: 137 138 unix extensions = yes 139 140 to your smb.conf file on the server. Note that the following smb.conf settings 141 are also useful (on the Samba server) when the majority of clients are Unix or 142 Linux: 143 144 case sensitive = yes 145 delete readonly = yes 146 ea support = yes 147 148 Note that server ea support is required for supporting xattrs from the Linux 149 cifs client, and that EA support is present in later versions of Samba (e.g. 150 3.0.6 and later (also EA support works in all versions of Windows, at least to 151 shares on NTFS filesystems). Extended Attribute (xattr) support is an optional 152 feature of most Linux filesystems which may require enabling via 153 make menuconfig. Client support for extended attributes (user xattr) can be 154 disabled on a per-mount basis by specifying "nouser_xattr" on mount. 155 156 The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers 157 version 3.10 and later. Setting POSIX ACLs requires enabling both XATTR and 158 then POSIX support in the CIFS configuration options when building the cifs 159 module. POSIX ACL support can be disabled on a per mount basic by specifying 160 "noacl" on mount. 161 162 Some 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 164 newly created files can end up with an unnecessarily restrictive default mode, 165 which may not be what you want, although if the CIFS Unix extensions are 166 enabled on the server and client, subsequent setattr calls (e.g. chmod) can 167 fix the mode. Note that creating special devices (mknod) remotely 168 may require specifying a mkdev function to Samba if you are not using 169 Samba 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, 171 unlike 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). 173 Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete 174 open files (required for strict POSIX compliance). Windows Servers already 175 supported this feature. Samba server does not allow symlinks that refer to files 176 outside of the share, so in Samba versions prior to 3.0.6, most symlinks to 177 files with absolute paths (ie beginning with slash) such as: 178 ln -s /mnt/foo bar 179 would be forbidden. Samba 3.0.6 server or later includes the ability to create 180 such symlinks safely by converting unsafe symlinks (ie symlinks to server 181 files that are outside of the share) to a samba specific format on the server 182 that is ignored by local server applications and non-cifs clients and that will 183 not be traversed by the Samba server). This is opaque to the Linux client 184 application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or 185 later, but only for remote clients using the CIFS Unix extensions, and will 186 be invisbile to Windows clients and typically will not affect local 187 applications running on the same server as Samba. 188 189 Use instructions: 190 ================ 191 Once 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 193 servers: 194 195 mount -t cifs //188.8.131.52/e$ /mnt -o user=myname,pass=mypassword 196 197 Before -o the option -v may be specified to make the mount.cifs 198 mount helper display the mount steps more verbosely. 199 After -o the following commonly used cifs vfs specific options 200 are supported: 201 202 user=<username> 203 pass=<password> 204 domain=<domain name> 205 206 Other cifs mount options are described below. Use of TCP names (in addition to 207 ip addresses) is available if the mount helper (mount.cifs) is installed. If 208 you do not trust the server to which are mounted, or if you do not have 209 cifs signing enabled (and the physical network is insecure), consider use 210 of the standard mount options "noexec" and "nosuid" to reduce the risk of 211 running an altered binary on your local system (downloaded from a hostile server 212 or altered by a hostile router). 213 214 Although mounting using format corresponding to the CIFS URL specification is 215 not possible in mount.cifs yet, it is possible to use an alternate format 216 for the server and sharename (which is somewhat similar to NFS style mount 217 syntax) 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 219 220 When using the mount helper mount.cifs, passwords may be specified via alternate 221 mechanisms, instead of specifying it after -o using the normal "pass=" syntax 222 on the command line: 223 1) By including it in a credential file. Specify credentials=filename as one 224 of the mount options. Credential files contain two lines 225 username=someuser 226 password=your_password 227 2) By specifying the password in the PASSWD environment variable (similarly 228 the user name can be taken from the USER environment variable). 229 3) By specifying the password in a file by name via PASSWD_FILE 230 4) By specifying the password in a file by file descriptor via PASSWD_FD 231 232 If no password is provided, mount.cifs will prompt for password entry 233 234 Restrictions 235 ============ 236 Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC 237 1001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a 238 problem as most servers support this. 239 240 Valid filenames differ between Windows and Linux. Windows typically restricts 241 filenames which contain certain reserved characters (e.g.the character : 242 which is used to delimit the beginning of a stream name by Windows), while 243 Linux allows a slightly wider set of valid characters in filenames. Windows 244 servers can remap such characters when an explicit mapping is specified in 245 the Server's registry. Samba starting with version 3.10 will allow such 246 filenames (ie those which contain valid Linux characters, which normally 247 would be forbidden for Windows/CIFS semantics) as long as the server is 248 configured for Unix Extensions (and the client has not disabled 249 /proc/fs/cifs/LinuxExtensionsEnabled). 250 251 252 CIFS VFS Mount Options 253 ====================== 254 A 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 specified 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 rwpidforward Forward pid of a process who opened a file to any read or write 461 operation on that file. This prevent applications like WINE 462 from failing on read and write if we use mandatory brlock style. 463 acl Allow setfacl and getfacl to manage posix ACLs if server 464 supports them. (default) 465 noacl Do not allow setfacl and getfacl calls on this mount 466 user_xattr Allow getting and setting user xattrs (those attributes whose 467 name begins with "user." or "os2.") as OS/2 EAs (extended 468 attributes) to the server. This allows support of the 469 setfattr and getfattr utilities. (default) 470 nouser_xattr Do not allow getfattr/setfattr to get/set/list xattrs 471 mapchars Translate six of the seven reserved characters (not backslash) 472 *?<>|: 473 to the remap range (above 0xF000), which also 474 allows the CIFS client to recognize files created with 475 such characters by Windows's POSIX emulation. This can 476 also be useful when mounting to most versions of Samba 477 (which also forbids creating and opening files 478 whose names contain any of these seven characters). 479 This has no effect if the server does not support 480 Unicode on the wire. 481 nomapchars Do not translate any of these seven characters (default). 482 nocase Request case insensitive path name matching (case 483 sensitive is the default if the server supports it). 484 (mount option "ignorecase" is identical to "nocase") 485 posixpaths If CIFS Unix extensions are supported, attempt to 486 negotiate posix path name support which allows certain 487 characters forbidden in typical CIFS filenames, without 488 requiring remapping. (default) 489 noposixpaths If CIFS Unix extensions are supported, do not request 490 posix path name support (this may cause servers to 491 reject creatingfile with certain reserved characters). 492 nounix Disable the CIFS Unix Extensions for this mount (tree 493 connection). This is rarely needed, but it may be useful 494 in order to turn off multiple settings all at once (ie 495 posix acls, posix locks, posix paths, symlink support 496 and retrieving uids/gids/mode from the server) or to 497 work around a bug in server which implement the Unix 498 Extensions. 499 nobrl Do not send byte range lock requests to the server. 500 This is necessary for certain applications that break 501 with cifs style mandatory byte range locks (and most 502 cifs servers do not yet support requesting advisory 503 byte range locks). 504 forcemandatorylock Even if the server supports posix (advisory) byte range 505 locking, send only mandatory lock requests. For some 506 (presumably rare) applications, originally coded for 507 DOS/Windows, which require Windows style mandatory byte range 508 locking, they may be able to take advantage of this option, 509 forcing the cifs client to only send mandatory locks 510 even if the cifs server would support posix advisory locks. 511 "forcemand" is accepted as a shorter form of this mount 512 option. 513 nostrictsync If this mount option is set, when an application does an 514 fsync call then the cifs client does not send an SMB Flush 515 to the server (to force the server to write all dirty data 516 for this file immediately to disk), although cifs still sends 517 all dirty (cached) file data to the server and waits for the 518 server to respond to the write. Since SMB Flush can be 519 very slow, and some servers may be reliable enough (to risk 520 delaying slightly flushing the data to disk on the server), 521 turning on this option may be useful to improve performance for 522 applications that fsync too much, at a small risk of server 523 crash. If this mount option is not set, by default cifs will 524 send an SMB flush request (and wait for a response) on every 525 fsync call. 526 nodfs Disable DFS (global name space support) even if the 527 server claims to support it. This can help work around 528 a problem with parsing of DFS paths with Samba server 529 versions 3.0.24 and 3.0.25. 530 remount remount the share (often used to change from ro to rw mounts 531 or vice versa) 532 cifsacl Report mode bits (e.g. on stat) based on the Windows ACL for 533 the file. (EXPERIMENTAL) 534 servern Specify the server 's netbios name (RFC1001 name) to use 535 when attempting to setup a session to the server. 536 This is needed for mounting to some older servers (such 537 as OS/2 or Windows 98 and Windows ME) since they do not 538 support a default server name. A server name can be up 539 to 15 characters long and is usually uppercased. 540 sfu When the CIFS Unix Extensions are not negotiated, attempt to 541 create device files and fifos in a format compatible with 542 Services for Unix (SFU). In addition retrieve bits 10-12 543 of the mode via the SETFILEBITS extended attribute (as 544 SFU does). In the future the bottom 9 bits of the 545 mode also will be emulated using queries of the security 546 descriptor (ACL). 547 mfsymlinks Enable support for Minshall+French symlinks 548 (see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks) 549 This option is ignored when specified together with the 550 'sfu' option. Minshall+French symlinks are used even if 551 the server supports the CIFS Unix Extensions. 552 sign Must use packet signing (helps avoid unwanted data modification 553 by intermediate systems in the route). Note that signing 554 does not work with lanman or plaintext authentication. 555 seal Must seal (encrypt) all data on this mounted share before 556 sending on the network. Requires support for Unix Extensions. 557 Note that this differs from the sign mount option in that it 558 causes encryption of data sent over this mounted share but other 559 shares mounted to the same server are unaffected. 560 locallease This option is rarely needed. Fcntl F_SETLEASE is 561 used by some applications such as Samba and NFSv4 server to 562 check to see whether a file is cacheable. CIFS has no way 563 to explicitly request a lease, but can check whether a file 564 is cacheable (oplocked). Unfortunately, even if a file 565 is not oplocked, it could still be cacheable (ie cifs client 566 could grant fcntl leases if no other local processes are using 567 the file) for cases for example such as when the server does not 568 support oplocks and the user is sure that the only updates to 569 the file will be from this client. Specifying this mount option 570 will allow the cifs client to check for leases (only) locally 571 for files which are not oplocked instead of denying leases 572 in that case. (EXPERIMENTAL) 573 sec Security mode. Allowed values are: 574 none attempt to connection as a null user (no name) 575 krb5 Use Kerberos version 5 authentication 576 krb5i Use Kerberos authentication and packet signing 577 ntlm Use NTLM password hashing (default) 578 ntlmi Use NTLM password hashing with signing (if 579 /proc/fs/cifs/PacketSigningEnabled on or if 580 server requires signing also can be the default) 581 ntlmv2 Use NTLMv2 password hashing 582 ntlmv2i Use NTLMv2 password hashing with packet signing 583 lanman (if configured in kernel config) use older 584 lanman hash 585 hard Retry file operations if server is not responding 586 soft Limit retries to unresponsive servers (usually only 587 one retry) before returning an error. (default) 588 589 The mount.cifs mount helper also accepts a few mount options before -o 590 including: 591 592 -S take password from stdin (equivalent to setting the environment 593 variable "PASSWD_FD=0" 594 -V print mount.cifs version 595 -? display simple usage information 596 597 With most 2.6 kernel versions of modutils, the version of the cifs kernel 598 module can be displayed via modinfo. 599 600 Misc /proc/fs/cifs Flags and Debug Info 601 ======================================= 602 Informational pseudo-files: 603 DebugData Displays information about active CIFS sessions and 604 shares, features enabled as well as the cifs.ko 605 version. 606 Stats Lists summary resource usage information as well as per 607 share statistics, if CONFIG_CIFS_STATS in enabled 608 in the kernel configuration. 609 610 Configuration pseudo-files: 611 PacketSigningEnabled If set to one, cifs packet signing is enabled 612 and will be used if the server requires 613 it. If set to two, cifs packet signing is 614 required even if the server considers packet 615 signing optional. (default 1) 616 SecurityFlags Flags which control security negotiation and 617 also packet signing. Authentication (may/must) 618 flags (e.g. for NTLM and/or NTLMv2) may be combined with 619 the signing flags. Specifying two different password 620 hashing mechanisms (as "must use") on the other hand 621 does not make much sense. Default flags are 622 0x07007 623 (NTLM, NTLMv2 and packet signing allowed). The maximum 624 allowable flags if you want to allow mounts to servers 625 using weaker password hashes is 0x37037 (lanman, 626 plaintext, ntlm, ntlmv2, signing allowed). Some 627 SecurityFlags require the corresponding menuconfig 628 options to be enabled (lanman and plaintext require 629 CONFIG_CIFS_WEAK_PW_HASH for example). Enabling 630 plaintext authentication currently requires also 631 enabling lanman authentication in the security flags 632 because the cifs module only supports sending 633 laintext passwords using the older lanman dialect 634 form of the session setup SMB. (e.g. for authentication 635 using plain text passwords, set the SecurityFlags 636 to 0x30030): 637 638 may use packet signing 0x00001 639 must use packet signing 0x01001 640 may use NTLM (most common password hash) 0x00002 641 must use NTLM 0x02002 642 may use NTLMv2 0x00004 643 must use NTLMv2 0x04004 644 may use Kerberos security 0x00008 645 must use Kerberos 0x08008 646 may use lanman (weak) password hash 0x00010 647 must use lanman password hash 0x10010 648 may use plaintext passwords 0x00020 649 must use plaintext passwords 0x20020 650 (reserved for future packet encryption) 0x00040 651 652 cifsFYI If set to non-zero value, additional debug information 653 will be logged to the system error log. This field 654 contains three flags controlling different classes of 655 debugging entries. The maximum value it can be set 656 to is 7 which enables all debugging points (default 0). 657 Some debugging statements are not compiled into the 658 cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the 659 kernel configuration. cifsFYI may be set to one or 660 nore of the following flags (7 sets them all): 661 662 log cifs informational messages 0x01 663 log return codes from cifs entry points 0x02 664 log slow responses (ie which take longer than 1 second) 665 CONFIG_CIFS_STATS2 must be enabled in .config 0x04 666 667 668 traceSMB If set to one, debug information is logged to the 669 system error log with the start of smb requests 670 and responses (default 0) 671 LookupCacheEnable If set to one, inode information is kept cached 672 for one second improving performance of lookups 673 (default 1) 674 OplockEnabled If set to one, safe distributed caching enabled. 675 (default 1) 676 LinuxExtensionsEnabled If set to one then the client will attempt to 677 use the CIFS "UNIX" extensions which are optional 678 protocol enhancements that allow CIFS servers 679 to return accurate UID/GID information as well 680 as support symbolic links. If you use servers 681 such as Samba that support the CIFS Unix 682 extensions but do not want to use symbolic link 683 support and want to map the uid and gid fields 684 to values supplied at mount (rather than the 685 actual values, then set this to zero. (default 1) 686 687 These experimental features and tracing can be enabled by changing flags in 688 /proc/fs/cifs (after the cifs module has been installed or built into the 689 kernel, e.g. insmod cifs). To enable a feature set it to 1 e.g. to enable 690 tracing to the kernel message log type: 691 692 echo 7 > /proc/fs/cifs/cifsFYI 693 694 cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel 695 logging of various informational messages. 2 enables logging of non-zero 696 SMB return codes while 4 enables logging of requests that take longer 697 than one second to complete (except for byte range lock requests). 698 Setting it to 4 requires defining CONFIG_CIFS_STATS2 manually in the 699 source code (typically by setting it in the beginning of cifsglob.h), 700 and setting it to seven enables all three. Finally, tracing 701 the start of smb requests and responses can be enabled via: 702 703 echo 1 > /proc/fs/cifs/traceSMB 704 705 Per share (per client mount) statistics are available in /proc/fs/cifs/Stats 706 if the kernel was configured with cifs statistics enabled. The statistics 707 represent the number of successful (ie non-zero return code from the server) 708 SMB responses to some of the more common commands (open, delete, mkdir etc.). 709 Also recorded is the total bytes read and bytes written to the server for 710 that share. Note that due to client caching effects this can be less than the 711 number of bytes read and written by the application running on the client. 712 The statistics for the number of total SMBs and oplock breaks are different in 713 that they represent all for that share, not just those for which the server 714 returned success. 715 716 Also note that "cat /proc/fs/cifs/DebugData" will display information about 717 the active sessions and the shares that are mounted. 718 719 Enabling Kerberos (extended security) works but requires version 1.2 or later 720 of the helper program cifs.upcall to be present and to be configured in the 721 /etc/request-key.conf file. The cifs.upcall helper program is from the Samba 722 project(http://www.samba.org). NTLM and NTLMv2 and LANMAN support do not 723 require this helper. Note that NTLMv2 security (which does not require the 724 cifs.upcall helper program), instead of using Kerberos, is sufficient for 725 some use cases. 726 727 DFS support allows transparent redirection to shares in an MS-DFS name space. 728 In addition, DFS support for target shares which are specified as UNC 729 names which begin with host names (rather than IP addresses) requires 730 a user space helper (such as cifs.upcall) to be present in order to 731 translate host names to ip address, and the user space helper must also 732 be configured in the file /etc/request-key.conf. Samba, Windows servers and 733 many NAS appliances support DFS as a way of constructing a global name 734 space to ease network configuration and improve reliability. 735 736 To use cifs Kerberos and DFS support, the Linux keyutils package should be 737 installed and something like the following lines should be added to the 738 /etc/request-key.conf file: 739 740 create cifs.spnego * * /usr/local/sbin/cifs.upcall %k 741 create dns_resolver * * /usr/local/sbin/cifs.upcall %k 742 743 CIFS kernel module parameters 744 ============================= 745 These module parameters can be specified or modified either during the time of 746 module loading or during the runtime by using the interface 747 /proc/module/cifs/parameters/<param> 748 749 i.e. echo "value" > /sys/module/cifs/parameters/<param> 750 751 1. enable_oplocks - Enable or disable oplocks. Oplocks are enabled by default. 752 [Y/y/1]. To disable use any of [N/n/0].