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  1. The CIFS VFS support for Linux supports many advanced network filesystem
  2. features such as heirarchical 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.
  7. For questions or bug reports please contact:
  8. sfrench@samba.org (sfrench@us.ibm.com)
  9. Build instructions:
  10. ==================
  11. For Linux 2.4:
  12. 1) Get the kernel source (e.g.from http://www.kernel.org)
  13. and download the cifs vfs source (see the project page
  14. at http://us1.samba.org/samba/Linux_CIFS_client.html)
  15. and change directory into the top of the kernel directory
  16. then patch the kernel (e.g. "patch -p1 < cifs_24.patch")
  17. to add the cifs vfs to your kernel configure options if
  18. it has not already been added (e.g. current SuSE and UL
  19. users do not need to apply the cifs_24.patch since the cifs vfs is
  20. already in the kernel configure menu) and then
  21. mkdir linux/fs/cifs and then copy the current cifs vfs files from
  22. the cifs download to your kernel build directory e.g.
  23. cp <cifs_download_dir>/fs/cifs/* to <kernel_download_dir>/fs/cifs
  24. 2) make menuconfig (or make xconfig)
  25. 3) select cifs from within the network filesystem choices
  26. 4) save and exit
  27. 5) make dep
  28. 6) make modules (or "make" if CIFS VFS not to be built as a module)
  29. For Linux 2.6:
  30. 1) Download the kernel (e.g. from http://www.kernel.org or from bitkeeper
  31. at bk://linux.bkbits.net/linux-2.5) and change directory into the top
  32. of the kernel directory tree (e.g. /usr/src/linux-2.5.73)
  33. 2) make menuconfig (or make xconfig)
  34. 3) select cifs from within the network filesystem choices
  35. 4) save and exit
  36. 5) make
  37. Installation instructions:
  38. =========================
  39. If you have built the CIFS vfs as module (successfully) simply
  40. type "make modules_install" (or if you prefer, manually copy the file to
  41. the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.o).
  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. If you do not have the utility mount.cifs (in the Samba 3.0 source tree and on
  46. the CIFS VFS web site) copy it to the same directory in which mount.smbfs and
  47. similar files reside (usually /sbin). Although the helper software is not
  48. required, mount.cifs is recommended. Eventually the Samba 3.0 utility program
  49. "net" may also be helpful since it may someday provide easier mount syntax for
  50. users who are used to Windows e.g. net use <mount point> <UNC name or cifs URL>
  51. Note that running the Winbind pam/nss module (logon service) on all of your
  52. Linux clients is useful in mapping Uids and Gids consistently across the
  53. domain to the proper network user. The mount.cifs mount helper can be
  54. trivially built from Samba 3.0 or later source e.g. by executing:
  55. gcc samba/source/client/mount.cifs.c -o mount.cifs
  56. If cifs is built as a module, then the size and number of network buffers
  57. and maximum number of simultaneous requests to one server can be configured.
  58. Changing these from their defaults is not recommended. By executing modinfo
  59. modinfo kernel/fs/cifs/cifs.ko
  60. on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
  61. at module initialization time (by running insmod cifs.ko) can be seen.
  62. Allowing User Mounts
  63. ====================
  64. To permit users to mount and unmount over directories they own is possible
  65. with the cifs vfs. A way to enable such mounting is to mark the mount.cifs
  66. utility as suid (e.g. "chmod +s /sbin/mount.cifs). To enable users to
  67. umount shares they mount requires
  68. 1) mount.cifs version 1.4 or later
  69. 2) an entry for the share in /etc/fstab indicating that a user may
  70. unmount it e.g.
  71. //server/usersharename /mnt/username cifs user 0 0
  72. Note that when the mount.cifs utility is run suid (allowing user mounts),
  73. in order to reduce risks, the "nosuid" mount flag is passed in on mount to
  74. disallow execution of an suid program mounted on the remote target.
  75. When mount is executed as root, nosuid is not passed in by default,
  76. and execution of suid programs on the remote target would be enabled
  77. by default. This can be changed, as with nfs and other filesystems,
  78. by simply specifying "nosuid" among the mount options. For user mounts
  79. though to be able to pass the suid flag to mount requires rebuilding
  80. mount.cifs with the following flag:
  81. gcc samba/source/client/mount.cifs.c -DCIFS_ALLOW_USR_SUID -o mount.cifs
  82. There is a corresponding manual page for cifs mounting in the Samba 3.0 and
  83. later source tree in docs/manpages/mount.cifs.8
  84. Allowing User Unmounts
  85. ======================
  86. To permit users to ummount directories that they have user mounted (see above),
  87. the utility umount.cifs may be used. It may be invoked directly, or if
  88. umount.cifs is placed in /sbin, umount -i can invoke the cifs umount helper
  89. (at least for most versions of the umount utility) for umount of cifs
  90. mounts. As with mount.cifs, to enable user unmounts umount.cifs must be marked
  91. as suid (e.g. "chmod +s /sbin/umount.cifs"). For this utility to succeed
  92. the target path must be a cifs mount, and the uid of the current user must
  93. match the uid of the user who mounted the resource.
  94. Also note that the customary way of allowing user mounts and unmounts is
  95. (instead of using mount.cifs and unmount.cifs as suid) to add a line
  96. to the file /etc/fstab for each //server/share you wish to mount, but
  97. this can become unwieldy when potential mount targets include many
  98. or unpredictable UNC names.
  99. Samba Considerations
  100. ====================
  101. To get the maximum benefit from the CIFS VFS, we recommend using a server that
  102. supports the SNIA CIFS Unix Extensions standard (e.g. Samba 2.2.5 or later or
  103. Samba 3.0) but the CIFS vfs works fine with a wide variety of CIFS servers.
  104. Note that uid, gid and file permissions will display default values if you do
  105. not have a server that supports the Unix extensions for CIFS (such as Samba
  106. 2.2.5 or later). To enable the Unix CIFS Extensions in the Samba server, add
  107. the line:
  108. unix extensions = yes
  109. to your smb.conf file on the server. Note that the following smb.conf settings
  110. are also useful (on the Samba server) when the majority of clients are Unix or
  111. Linux:
  112. case sensitive = yes
  113. delete readonly = yes
  114. ea support = yes
  115. Note that server ea support is required for supporting xattrs from the Linux
  116. cifs client, and that EA support is present in later versions of Samba (e.g.
  117. 3.0.6 and later (also EA support works in all versions of Windows, at least to
  118. shares on NTFS filesystems). Extended Attribute (xattr) support is an optional
  119. feature of most Linux filesystems which may require enabling via
  120. make menuconfig. Client support for extended attributes (user xattr) can be
  121. disabled on a per-mount basis by specifying "nouser_xattr" on mount.
  122. The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
  123. version 3.10 and later. Setting POSIX ACLs requires enabling both XATTR and
  124. then POSIX support in the CIFS configuration options when building the cifs
  125. module. POSIX ACL support can be disabled on a per mount basic by specifying
  126. "noacl" on mount.
  127. Some administrators may want to change Samba's smb.conf "map archive" and
  128. "create mask" parameters from the default. Unless the create mask is changed
  129. newly created files can end up with an unnecessarily restrictive default mode,
  130. which may not be what you want, although if the CIFS Unix extensions are
  131. enabled on the server and client, subsequent setattr calls (e.g. chmod) can
  132. fix the mode. Note that creating special devices (mknod) remotely
  133. may require specifying a mkdev function to Samba if you are not using
  134. Samba 3.0.6 or later. For more information on these see the manual pages
  135. ("man smb.conf") on the Samba server system. Note that the cifs vfs,
  136. unlike the smbfs vfs, does not read the smb.conf on the client system
  137. (the few optional settings are passed in on mount via -o parameters instead).
  138. Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
  139. open files (required for strict POSIX compliance). Windows Servers already
  140. supported this feature. Samba server does not allow symlinks that refer to files
  141. outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
  142. files with absolute paths (ie beginning with slash) such as:
  143. ln -s /mnt/foo bar
  144. would be forbidden. Samba 3.0.6 server or later includes the ability to create
  145. such symlinks safely by converting unsafe symlinks (ie symlinks to server
  146. files that are outside of the share) to a samba specific format on the server
  147. that is ignored by local server applications and non-cifs clients and that will
  148. not be traversed by the Samba server). This is opaque to the Linux client
  149. application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
  150. later, but only for remote clients using the CIFS Unix extensions, and will
  151. be invisbile to Windows clients and typically will not affect local
  152. applications running on the same server as Samba.
  153. Use instructions:
  154. ================
  155. Once the CIFS VFS support is built into the kernel or installed as a module
  156. (cifs.o), you can use mount syntax like the following to access Samba or Windows
  157. servers:
  158. mount -t cifs //9.53.216.11/e$ /mnt -o user=myname,pass=mypassword
  159. Before -o the option -v may be specified to make the mount.cifs
  160. mount helper display the mount steps more verbosely.
  161. After -o the following commonly used cifs vfs specific options
  162. are supported:
  163. user=<username>
  164. pass=<password>
  165. domain=<domain name>
  166. Other cifs mount options are described below. Use of TCP names (in addition to
  167. ip addresses) is available if the mount helper (mount.cifs) is installed. If
  168. you do not trust the server to which are mounted, or if you do not have
  169. cifs signing enabled (and the physical network is insecure), consider use
  170. of the standard mount options "noexec" and "nosuid" to reduce the risk of
  171. running an altered binary on your local system (downloaded from a hostile server
  172. or altered by a hostile router).
  173. Although mounting using format corresponding to the CIFS URL specification is
  174. not possible in mount.cifs yet, it is possible to use an alternate format
  175. for the server and sharename (which is somewhat similar to NFS style mount
  176. syntax) instead of the more widely used UNC format (i.e. \\server\share):
  177. mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd
  178. When using the mount helper mount.cifs, passwords may be specified via alternate
  179. mechanisms, instead of specifying it after -o using the normal "pass=" syntax
  180. on the command line:
  181. 1) By including it in a credential file. Specify credentials=filename as one
  182. of the mount options. Credential files contain two lines
  183. username=someuser
  184. password=your_password
  185. 2) By specifying the password in the PASSWD environment variable (similarly
  186. the user name can be taken from the USER environment variable).
  187. 3) By specifying the password in a file by name via PASSWD_FILE
  188. 4) By specifying the password in a file by file descriptor via PASSWD_FD
  189. If no password is provided, mount.cifs will prompt for password entry
  190. Restrictions
  191. ============
  192. Servers must support the NTLM SMB dialect (which is the most recent, supported
  193. by Samba and Windows NT version 4, 2000 and XP and many other SMB/CIFS servers)
  194. Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
  195. 1001/1002 support for "Netbios-Over-TCP/IP." Neither of these is likely to be a
  196. problem as most servers support this. IPv6 support is planned for the future,
  197. and is almost complete.
  198. Valid filenames differ between Windows and Linux. Windows typically restricts
  199. filenames which contain certain reserved characters (e.g.the character :
  200. which is used to delimit the beginning of a stream name by Windows), while
  201. Linux allows a slightly wider set of valid characters in filenames. Windows
  202. servers can remap such characters when an explicit mapping is specified in
  203. the Server's registry. Samba starting with version 3.10 will allow such
  204. filenames (ie those which contain valid Linux characters, which normally
  205. would be forbidden for Windows/CIFS semantics) as long as the server is
  206. configured for Unix Extensions (and the client has not disabled
  207. /proc/fs/cifs/LinuxExtensionsEnabled).
  208. CIFS VFS Mount Options
  209. ======================
  210. A partial list of the supported mount options follows:
  211. user The user name to use when trying to establish
  212. the CIFS session.
  213. password The user password. If the mount helper is
  214. installed, the user will be prompted for password
  215. if it is not supplied.
  216. ip The ip address of the target server
  217. unc The target server Universal Network Name (export) to
  218. mount.
  219. domain Set the SMB/CIFS workgroup name prepended to the
  220. username during CIFS session establishment
  221. uid If CIFS Unix extensions are not supported by the server
  222. this overrides the default uid for inodes. For mounts to
  223. servers which do support the CIFS Unix extensions, such
  224. as a properly configured Samba server, the server provides
  225. the uid, gid and mode. For servers which do not support
  226. the Unix extensions, the default uid (and gid) returned on
  227. lookup of existing files is the uid (gid) of the person
  228. who executed the mount (root, except when mount.cifs
  229. is configured setuid for user mounts) unless the "uid="
  230. (gid) mount option is specified. For the uid (gid) of newly
  231. created files and directories, ie files created since
  232. the last mount of the server share, the expected uid
  233. (gid) is cached as as long as the inode remains in
  234. memory on the client. Also note that permission
  235. checks (authorization checks) on accesses to a file occur
  236. at the server, but there are cases in which an administrator
  237. may want to restrict at the client as well. For those
  238. servers which do not report a uid/gid owner
  239. (such as Windows), permissions can also be checked at the
  240. client, and a crude form of client side permission checking
  241. can be enabled by specifying file_mode and dir_mode on
  242. the client
  243. gid If CIFS Unix extensions are not supported by the server
  244. this overrides the default gid for inodes.
  245. file_mode If CIFS Unix extensions are not supported by the server
  246. this overrides the default mode for file inodes.
  247. dir_mode If CIFS Unix extensions are not supported by the server
  248. this overrides the default mode for directory inodes.
  249. port attempt to contact the server on this tcp port, before
  250. trying the usual ports (port 445, then 139).
  251. iocharset Codepage used to convert local path names to and from
  252. Unicode. Unicode is used by default for network path
  253. names if the server supports it. If iocharset is
  254. not specified then the nls_default specified
  255. during the local client kernel build will be used.
  256. If server does not support Unicode, this parameter is
  257. unused.
  258. rsize default read size
  259. wsize default write size
  260. rw mount the network share read-write (note that the
  261. server may still consider the share read-only)
  262. ro mount network share read-only
  263. version used to distinguish different versions of the
  264. mount helper utility (not typically needed)
  265. sep if first mount option (after the -o), overrides
  266. the comma as the separator between the mount
  267. parms. e.g.
  268. -o user=myname,password=mypassword,domain=mydom
  269. could be passed instead with period as the separator by
  270. -o sep=.user=myname.password=mypassword.domain=mydom
  271. this might be useful when comma is contained within username
  272. or password or domain. This option is less important
  273. when the cifs mount helper cifs.mount (version 1.1 or later)
  274. is used.
  275. nosuid Do not allow remote executables with the suid bit
  276. program to be executed. This is only meaningful for mounts
  277. to servers such as Samba which support the CIFS Unix Extensions.
  278. If you do not trust the servers in your network (your mount
  279. targets) it is recommended that you specify this option for
  280. greater security.
  281. exec Permit execution of binaries on the mount.
  282. noexec Do not permit execution of binaries on the mount.
  283. dev Recognize block devices on the remote mount.
  284. nodev Do not recognize devices on the remote mount.
  285. suid Allow remote files on this mountpoint with suid enabled to
  286. be executed (default for mounts when executed as root,
  287. nosuid is default for user mounts).
  288. credentials Although ignored by the cifs kernel component, it is used by
  289. the mount helper, mount.cifs. When mount.cifs is installed it
  290. opens and reads the credential file specified in order
  291. to obtain the userid and password arguments which are passed to
  292. the cifs vfs.
  293. guest Although ignored by the kernel component, the mount.cifs
  294. mount helper will not prompt the user for a password
  295. if guest is specified on the mount options. If no
  296. password is specified a null password will be used.
  297. perm Client does permission checks (vfs_permission check of uid
  298. and gid of the file against the mode and desired operation),
  299. Note that this is in addition to the normal ACL check on the
  300. target machine done by the server software.
  301. Client permission checking is enabled by default.
  302. noperm Client does not do permission checks. This can expose
  303. files on this mount to access by other users on the local
  304. client system. It is typically only needed when the server
  305. supports the CIFS Unix Extensions but the UIDs/GIDs on the
  306. client and server system do not match closely enough to allow
  307. access by the user doing the mount.
  308. Note that this does not affect the normal ACL check on the
  309. target machine done by the server software (of the server
  310. ACL against the user name provided at mount time).
  311. serverino Use servers inode numbers instead of generating automatically
  312. incrementing inode numbers on the client. Although this will
  313. make it easier to spot hardlinked files (as they will have
  314. the same inode numbers) and inode numbers may be persistent,
  315. note that the server does not guarantee that the inode numbers
  316. are unique if multiple server side mounts are exported under a
  317. single share (since inode numbers on the servers might not
  318. be unique if multiple filesystems are mounted under the same
  319. shared higher level directory). Note that this requires that
  320. the server support the CIFS Unix Extensions as other servers
  321. do not return a unique IndexNumber on SMB FindFirst (most
  322. servers return zero as the IndexNumber). Parameter has no
  323. effect to Windows servers and others which do not support the
  324. CIFS Unix Extensions.
  325. noserverino Client generates inode numbers (rather than using the actual one
  326. from the server) by default.
  327. setuids If the CIFS Unix extensions are negotiated with the server
  328. the client will attempt to set the effective uid and gid of
  329. the local process on newly created files, directories, and
  330. devices (create, mkdir, mknod).
  331. nosetuids The client will not attempt to set the uid and gid on
  332. on newly created files, directories, and devices (create,
  333. mkdir, mknod) which will result in the server setting the
  334. uid and gid to the default (usually the server uid of the
  335. usern who mounted the share). Letting the server (rather than
  336. the client) set the uid and gid is the default. This
  337. parameter has no effect if the CIFS Unix Extensions are not
  338. negotiated.
  339. netbiosname When mounting to servers via port 139, specifies the RFC1001
  340. source name to use to represent the client netbios machine
  341. name when doing the RFC1001 netbios session initialize.
  342. direct Do not do inode data caching on files opened on this mount.
  343. This precludes mmaping files on this mount. In some cases
  344. with fast networks and little or no caching benefits on the
  345. client (e.g. when the application is doing large sequential
  346. reads bigger than page size without rereading the same data)
  347. this can provide better performance than the default
  348. behavior which caches reads (reaadahead) and writes
  349. (writebehind) through the local Linux client pagecache
  350. if oplock (caching token) is granted and held. Note that
  351. direct allows write operations larger than page size
  352. to be sent to the server.
  353. acl Allow setfacl and getfacl to manage posix ACLs if server
  354. supports them. (default)
  355. noacl Do not allow setfacl and getfacl calls on this mount
  356. user_xattr Allow getting and setting user xattrs as OS/2 EAs (extended
  357. attributes) to the server (default) e.g. via setfattr
  358. and getfattr utilities.
  359. nouser_xattr Do not allow getfattr/setfattr to get/set xattrs
  360. mapchars Translate six of the seven reserved characters (not backslash)
  361. *?<>|:
  362. to the remap range (above 0xF000), which also
  363. allows the CIFS client to recognize files created with
  364. such characters by Windows's POSIX emulation. This can
  365. also be useful when mounting to most versions of Samba
  366. (which also forbids creating and opening files
  367. whose names contain any of these seven characters).
  368. This has no effect if the server does not support
  369. Unicode on the wire.
  370. nomapchars Do not translate any of these seven characters (default).
  371. The mount.cifs mount helper also accepts a few mount options before -o
  372. including:
  373. -S take password from stdin (equivalent to setting the environment
  374. variable "PASSWD_FD=0"
  375. -V print mount.cifs version
  376. -? display simple usage information
  377. With recent 2.6 kernel versions of modutils, the version of the cifs kernel
  378. module can be displayed via modinfo.
  379. Misc /proc/fs/cifs Flags and Debug Info
  380. =======================================
  381. Informational pseudo-files:
  382. DebugData Displays information about active CIFS sessions
  383. and shares, as well as the cifs.ko version.
  384. Stats Lists summary resource usage information as well as per
  385. share statistics, if CONFIG_CIFS_STATS in enabled
  386. in the kernel configuration.
  387. Configuration pseudo-files:
  388. MultiuserMount If set to one, more than one CIFS session to
  389. the same server ip address can be established
  390. if more than one uid accesses the same mount
  391. point and if the uids user/password mapping
  392. information is available. (default is 0)
  393. PacketSigningEnabled If set to one, cifs packet signing is enabled
  394. and will be used if the server requires
  395. it. If set to two, cifs packet signing is
  396. required even if the server considers packet
  397. signing optional. (default 1)
  398. cifsFYI If set to one, additional debug information is
  399. logged to the system error log. (default 0)
  400. ExtendedSecurity If set to one, SPNEGO session establishment
  401. is allowed which enables more advanced
  402. secure CIFS session establishment (default 0)
  403. NTLMV2Enabled If set to one, more secure password hashes
  404. are used when the server supports them and
  405. when kerberos is not negotiated (default 0)
  406. traceSMB If set to one, debug information is logged to the
  407. system error log with the start of smb requests
  408. and responses (default 0)
  409. LookupCacheEnable If set to one, inode information is kept cached
  410. for one second improving performance of lookups
  411. (default 1)
  412. OplockEnabled If set to one, safe distributed caching enabled.
  413. (default 1)
  414. LinuxExtensionsEnabled If set to one then the client will attempt to
  415. use the CIFS "UNIX" extensions which are optional
  416. protocol enhancements that allow CIFS servers
  417. to return accurate UID/GID information as well
  418. as support symbolic links. If you use servers
  419. such as Samba that support the CIFS Unix
  420. extensions but do not want to use symbolic link
  421. support and want to map the uid and gid fields
  422. to values supplied at mount (rather than the
  423. actual values, then set this to zero. (default 1)
  424. These experimental features and tracing can be enabled by changing flags in
  425. /proc/fs/cifs (after the cifs module has been installed or built into the
  426. kernel, e.g. insmod cifs). To enable a feature set it to 1 e.g. to enable
  427. tracing to the kernel message log type:
  428. echo 1 > /proc/fs/cifs/cifsFYI
  429. and for more extensive tracing including the start of smb requests and responses
  430. echo 1 > /proc/fs/cifs/traceSMB
  431. Two other experimental features are under development and to test
  432. require enabling CONFIG_CIFS_EXPERIMENTAL
  433. More efficient write operations
  434. DNOTIFY fcntl: needed for support of directory change
  435. notification and perhaps later for file leases)
  436. Per share (per client mount) statistics are available in /proc/fs/cifs/Stats
  437. if the kernel was configured with cifs statistics enabled. The statistics
  438. represent the number of successful (ie non-zero return code from the server)
  439. SMB responses to some of the more common commands (open, delete, mkdir etc.).
  440. Also recorded is the total bytes read and bytes written to the server for
  441. that share. Note that due to client caching effects this can be less than the
  442. number of bytes read and written by the application running on the client.
  443. The statistics for the number of total SMBs and oplock breaks are different in
  444. that they represent all for that share, not just those for which the server
  445. returned success.
  446. Also note that "cat /proc/fs/cifs/DebugData" will display information about
  447. the active sessions and the shares that are mounted. Note: NTLMv2 enablement
  448. will not work since its implementation is not quite complete yet. Do not alter
  449. the ExtendedSecurity configuration value unless you are doing specific testing.
  450. Enabling extended security works to Windows 2000 Workstations and XP but not to
  451. Windows 2000 server or Samba since it does not usually send "raw NTLMSSP"
  452. (instead it sends NTLMSSP encapsulated in SPNEGO/GSSAPI, which support is not
  453. complete in the CIFS VFS yet).