linux-libre/Documentation/filesystems/cifs

The CIFS VFS support for Linux supports many advanced network filesystem
features such as hierarchical dfs like namespace, hardlinks, locking and more.
It was designed to comply with the SNIA CIFS Technical Reference (which
supersedes the 1992 X/Open SMB Standard) as well as to perform best practice
practical interoperability with Windows 2000, Windows XP, Samba and equivalent
servers. This code was developed in participation with the Protocol Freedom
Information Foundation.

Please see
http://protocolfreedom.org/ and
http://samba.org/samba/PFIF/
for more details.


For questions or bug reports please contact:
sfrench@samba.org (sfrench@us.ibm.com)

Build instructions:
==================
For Linux 2.4:
1) Get the kernel source (e.g.from http://www.kernel.org)
and download the cifs vfs source (see the project page
at http://us1.samba.org/samba/Linux_CIFS_client.html)
and change directory into the top of the kernel directory
then patch the kernel (e.g. "patch -p1 < cifs_24.patch")
to add the cifs vfs to your kernel configure options if
it has not already been added (e.g. current SuSE and UL
users do not need to apply the cifs_24.patch since the cifs vfs is
already in the kernel configure menu) and then
mkdir linux/fs/cifs and then copy the current cifs vfs files from
the cifs download to your kernel build directory e.g.

cp /fs/cifs/* to /fs/cifs

2) make menuconfig (or make xconfig)
3) select cifs from within the network filesystem choices
4) save and exit
5) make dep
6) make modules (or "make" if CIFS VFS not to be built as a module)

For Linux 2.6:
1) Download the kernel (e.g. from http://www.kernel.org)
and change directory into the top of the kernel directory tree
(e.g. /usr/src/linux-2.5.73)
2) make menuconfig (or make xconfig)
3) select cifs from within the network filesystem choices
4) save and exit
5) make


Installation instructions:
=========================
If you have built the CIFS vfs as module (successfully) simply
type "make modules_install" (or if you prefer, manually copy the file to
the modules directory e.g. /lib/modules/2.4.10-4GB/kernel/fs/cifs/cifs.o).

If you have built the CIFS vfs into the kernel itself, follow the instructions
for your distribution on how to install a new kernel (usually you
would simply type "make install").

If you do not have the utility mount.cifs (in the Samba 3.0 source tree and on
the CIFS VFS web site) copy it to the same directory in which mount.smbfs and
similar files reside (usually /sbin). Although the helper software is not
required, mount.cifs is recommended. Eventually the Samba 3.0 utility program
"net" may also be helpful since it may someday provide easier mount syntax for
users who are used to Windows e.g.
net use
Note that running the Winbind pam/nss module (logon service) on all of your
Linux clients is useful in mapping Uids and Gids consistently across the
domain to the proper network user. The mount.cifs mount helper can be
trivially built from Samba 3.0 or later source e.g. by executing:

gcc samba/source/client/mount.cifs.c -o mount.cifs

If cifs is built as a module, then the size and number of network buffers
and maximum number of simultaneous requests to one server can be configured.
Changing these from their defaults is not recommended. By executing modinfo
modinfo kernel/fs/cifs/cifs.ko
on kernel/fs/cifs/cifs.ko the list of configuration changes that can be made
at module initialization time (by running insmod cifs.ko) can be seen.

Allowing User Mounts
====================
To permit users to mount and unmount over directories they own is possible
with the cifs vfs. A way to enable such mounting is to mark the mount.cifs
utility as suid (e.g. "chmod +s /sbin/mount.cifs). To enable users to
umount shares they mount requires
1) mount.cifs version 1.4 or later
2) an entry for the share in /etc/fstab indicating that a user may
unmount it e.g.
//server/usersharename /mnt/username cifs user 0 0

Note that when the mount.cifs utility is run suid (allowing user mounts),
in order to reduce risks, the "nosuid" mount flag is passed in on mount to
disallow execution of an suid program mounted on the remote target.
When mount is executed as root, nosuid is not passed in by default,
and execution of suid programs on the remote target would be enabled
by default. This can be changed, as with nfs and other filesystems,
by simply specifying "nosuid" among the mount options. For user mounts
though to be able to pass the suid flag to mount requires rebuilding
mount.cifs with the following flag:

gcc samba/source/client/mount.cifs.c -DCIFS_ALLOW_USR_SUID -o mount.cifs

There is a corresponding manual page for cifs mounting in the Samba 3.0 and
later source tree in docs/manpages/mount.cifs.8

Allowing User Unmounts
======================
To permit users to ummount directories that they have user mounted (see above),
the utility umount.cifs may be used. It may be invoked directly, or if
umount.cifs is placed in /sbin, umount can invoke the cifs umount helper
(at least for most versions of the umount utility) for umount of cifs
mounts, unless umount is invoked with -i (which will avoid invoking a umount
helper). As with mount.cifs, to enable user unmounts umount.cifs must be marked
as suid (e.g. "chmod +s /sbin/umount.cifs") or equivalent (some distributions
allow adding entries to a file to the /etc/permissions file to achieve the
equivalent suid effect). For this utility to succeed the target path
must be a cifs mount, and the uid of the current user must match the uid
of the user who mounted the resource.

Also note that the customary way of allowing user mounts and unmounts is
(instead of using mount.cifs and unmount.cifs as suid) to add a line
to the file /etc/fstab for each //server/share you wish to mount, but
this can become unwieldy when potential mount targets include many
or unpredictable UNC names.

Samba Considerations
====================
To get the maximum benefit from the CIFS VFS, we recommend using a server that
supports the SNIA CIFS Unix Extensions standard (e.g. Samba 2.2.5 or later or
Samba 3.0) but the CIFS vfs works fine with a wide variety of CIFS servers.
Note that uid, gid and file permissions will display default values if you do
not have a server that supports the Unix extensions for CIFS (such as Samba
2.2.5 or later). To enable the Unix CIFS Extensions in the Samba server, add
the line:

unix extensions = yes

to your smb.conf file on the server. Note that the following smb.conf settings
are also useful (on the Samba server) when the majority of clients are Unix or
Linux:

case sensitive = yes
delete readonly = yes
ea support = yes

Note that server ea support is required for supporting xattrs from the Linux
cifs client, and that EA support is present in later versions of Samba (e.g.
3.0.6 and later (also EA support works in all versions of Windows, at least to
shares on NTFS filesystems). Extended Attribute (xattr) support is an optional
feature of most Linux filesystems which may require enabling via
make menuconfig. Client support for extended attributes (user xattr) can be
disabled on a per-mount basis by specifying "nouser_xattr" on mount.

The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to Samba servers
version 3.10 and later. Setting POSIX ACLs requires enabling both XATTR and
then POSIX support in the CIFS configuration options when building the cifs
module. POSIX ACL support can be disabled on a per mount basic by specifying
"noacl" on mount.

Some administrators may want to change Samba's smb.conf "map archive" and
"create mask" parameters from the default. Unless the create mask is changed
newly created files can end up with an unnecessarily restrictive default mode,
which may not be what you want, although if the CIFS Unix extensions are
enabled on the server and client, subsequent setattr calls (e.g. chmod) can
fix the mode. Note that creating special devices (mknod) remotely
may require specifying a mkdev function to Samba if you are not using
Samba 3.0.6 or later. For more information on these see the manual pages
("man smb.conf") on the Samba server system. Note that the cifs vfs,
unlike the smbfs vfs, does not read the smb.conf on the client system
(the few optional settings are passed in on mount via -o parameters instead).
Note that Samba 2.2.7 or later includes a fix that allows the CIFS VFS to delete
open files (required for strict POSIX compliance). Windows Servers already
supported this feature. Samba server does not allow symlinks that refer to files
outside of the share, so in Samba versions prior to 3.0.6, most symlinks to
files with absolute paths (ie beginning with slash) such as:
ln -s /mnt/foo bar
would be forbidden. Samba 3.0.6 server or later includes the ability to create
such symlinks safely by converting unsafe symlinks (ie symlinks to server
files that are outside of the share) to a samba specific format on the server
that is ignored by local server applications and non-cifs clients and that will
not be traversed by the Samba server). This is opaque to the Linux client
application using the cifs vfs. Absolute symlinks will work to Samba 3.0.5 or
later, but only for remote clients using the CIFS Unix extensions, and will
be invisbile to Windows clients and typically will not affect local
applications running on the same server as Samba.

Use instructions:
================
Once the CIFS VFS support is built into the kernel or installed as a module
(cifs.o), you can use mount syntax like the following to access Samba or Windows
servers:

mount -t cifs //9.53.216.11/e$ /mnt -o user=myname,pass=mypassword

Before -o the option -v may be specified to make the mount.cifs
mount helper display the mount steps more verbosely.
After -o the following commonly used cifs vfs specific options
are supported:

user=
pass=
domain=

Other cifs mount options are described below. Use of TCP names (in addition to
ip addresses) is available if the mount helper (mount.cifs) is installed. If
you do not trust the server to which are mounted, or if you do not have
cifs signing enabled (and the physical network is insecure), consider use
of the standard mount options "noexec" and "nosuid" to reduce the risk of
running an altered binary on your local system (downloaded from a hostile server
or altered by a hostile router).

Although mounting using format corresponding to the CIFS URL specification is
not possible in mount.cifs yet, it is possible to use an alternate format
for the server and sharename (which is somewhat similar to NFS style mount
syntax) instead of the more widely used UNC format (i.e. \\server\share):
mount -t cifs tcp_name_of_server:share_name /mnt -o user=myname,pass=mypasswd

When using the mount helper mount.cifs, passwords may be specified via alternate
mechanisms, instead of specifying it after -o using the normal "pass=" syntax
on the command line:
1) By including it in a credential file. Specify credentials=filename as one
of the mount options. Credential files contain two lines
username=someuser
password=your_password
2) By specifying the password in the PASSWD environment variable (similarly
the user name can be taken from the USER environment variable).
3) By specifying the password in a file by name via PASSWD_FILE
4) By specifying the password in a file by file descriptor via PASSWD_FD

If no password is provided, mount.cifs will prompt for password entry

Restrictions
============
Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
1001/1002 support for "Netbios-Over-TCP/IP." This is not likely to be a
problem as most servers support this.

Valid filenames differ between Windows and Linux. Windows typically restricts
filenames which contain certain reserved characters (e.g.the character :
which is used to delimit the beginning of a stream name by Windows), while
Linux allows a slightly wider set of valid characters in filenames. Windows
servers can remap such characters when an explicit mapping is specified in
the Server's registry. Samba starting with version 3.10 will allow such
filenames (ie those which contain valid Linux characters, which normally
would be forbidden for Windows/CIFS semantics) as long as the server is
configured for Unix Extensions (and the client has not disabled
/proc/fs/cifs/LinuxExtensionsEnabled).


CIFS VFS Mount Options
======================
A partial list of the supported mount options follows:
user The user name to use when trying to establish
the CIFS session.
password The user password. If the mount helper is
installed, the user will be prompted for password
if not supplied.
ip The ip address of the target server
unc The target server Universal Network Name (export) to
mount.
domain Set the SMB/CIFS workgroup name prepended to the
username during CIFS session establishment
forceuid Set the default uid for inodes to the uid
passed in on mount. For mounts to servers
which do support the CIFS Unix extensions, such as a
properly configured Samba server, the server provides
the uid, gid and mode so this parameter should not be
specified unless the server and clients uid and gid
numbering differ. If the server and client are in the
same domain (e.g. running winbind or nss_ldap) and
the server supports the Unix Extensions then the uid
and gid can be retrieved from the server (and uid
and gid would not have to be specified on the mount.
For servers which do not support the CIFS Unix
extensions, the default uid (and gid) returned on lookup
of existing files will be the uid (gid) of the person
who executed the mount (root, except when mount.cifs
is configured setuid for user mounts) unless the "uid="
(gid) mount option is specified. Also note that permission
checks (authorization checks) on accesses to a file occur
at the server, but there are cases in which an administrator
may want to restrict at the client as well. For those
servers which do not report a uid/gid owner
(such as Windows), permissions can also be checked at the
client, and a crude form of client side permission checking
can be enabled by specifying file_mode and dir_mode on
the client. (default)
forcegid (similar to above but for the groupid instead of uid) (default)
noforceuid Fill in file owner information (uid) by requesting it from
the server if possible. With this option, the value given in
the uid= option (on mount) will only be used if the server
can not support returning uids on inodes.
noforcegid (similar to above but for the group owner, gid, instead of uid)
uid Set the default uid for inodes, and indicate to the
cifs kernel driver which local user mounted. If the server
supports the unix extensions the default uid is
not used to fill in the owner fields of inodes (files)
unless the "forceuid" parameter is specified.
gid Set the default gid for inodes (similar to above).
file_mode If CIFS Unix extensions are not supported by the server
this overrides the default mode for file inodes.
fsc Enable local disk caching using FS-Cache (off by default). This
option could be useful to improve performance on a slow link,
heavily loaded server and/or network where reading from the
disk is faster than reading from the server (over the network).
This could also impact scalability positively as the
number of calls to the server are reduced. However, local
caching is not suitable for all workloads for e.g. read-once
type workloads. So, you need to consider carefully your
workload/scenario before using this option. Currently, local
disk caching is functional for CIFS files opened as read-only.
dir_mode If CIFS Unix extensions are not supported by the server
this overrides the default mode for directory inodes.
port attempt to contact the server on this tcp port, before
trying the usual ports (port 445, then 139).
iocharset Codepage used to convert local path names to and from
Unicode. Unicode is used by default for network path
names if the server supports it. If iocharset is
not specified then the nls_default specified
during the local client kernel build will be used.
If server does not support Unicode, this parameter is
unused.
rsize default read size (usually 16K). The client currently
can not use rsize larger than CIFSMaxBufSize. CIFSMaxBufSize
defaults to 16K and may be changed (from 8K to the maximum
kmalloc size allowed by your kernel) at module install time
for cifs.ko. Setting CIFSMaxBufSize to a very large value
will cause cifs to use more memory and may reduce performance
in some cases. To use rsize greater than 127K (the original
cifs protocol maximum) also requires that the server support
a new Unix Capability flag (for very large read) which some
newer servers (e.g. Samba 3.0.26 or later) do. rsize can be
set from a minimum of 2048 to a maximum of 130048 (127K or
CIFSMaxBufSize, whichever is smaller)
wsize default write size (default 57344)
maximum wsize currently allowed by CIFS is 57344 (fourteen
4096 byte pages)
actimeo=n attribute cache timeout in seconds (default 1 second).
After this timeout, the cifs client requests fresh attribute
information from the server. This option allows to tune the
attribute cache timeout to suit the workload needs. Shorter
timeouts mean better the cache coherency, but increased number
of calls to the server. Longer timeouts mean reduced number
of calls to the server at the expense of less stricter cache
coherency checks (i.e. incorrect attribute cache for a short
period of time).
rw mount the network share read-write (note that the
server may still consider the share read-only)
ro mount network share read-only
version used to distinguish different versions of the
mount helper utility (not typically needed)
sep if first mount option (after the -o), overrides
the comma as the separator between the mount
parms. e.g.
-o user=myname,password=mypassword,domain=mydom
could be passed instead with period as the separator by
-o sep=.user=myname.password=mypassword.domain=mydom
this might be useful when comma is contained within username
or password or domain. This option is less important
when the cifs mount helper cifs.mount (version 1.1 or later)
is used.
nosuid Do not allow remote executables with the suid bit
program to be executed. This is only meaningful for mounts
to servers such as Samba which support the CIFS Unix Extensions.
If you do not trust the servers in your network (your mount
targets) it is recommended that you specify this option for
greater security.
exec Permit execution of binaries on the mount.
noexec Do not permit execution of binaries on the mount.
dev Recognize block devices on the remote mount.
nodev Do not recognize devices on the remote mount.
suid Allow remote files on this mountpoint with suid enabled to
be executed (default for mounts when executed as root,
nosuid is default for user mounts).
credentials Although ignored by the cifs kernel component, it is used by
the mount helper, mount.cifs. When mount.cifs is installed it
opens and reads the credential file specified in order
to obtain the userid and password arguments which are passed to
the cifs vfs.
guest Although ignored by the kernel component, the mount.cifs
mount helper will not prompt the user for a password
if guest is specified on the mount options. If no
password is specified a null password will be used.
perm Client does permission checks (vfs_permission check of uid
and gid of the file against the mode and desired operation),
Note that this is in addition to the normal ACL check on the
target machine done by the server software.
Client permission checking is enabled by default.
noperm Client does not do permission checks. This can expose
files on this mount to access by other users on the local
client system. It is typically only needed when the server
supports the CIFS Unix Extensions but the UIDs/GIDs on the
client and server system do not match closely enough to allow
access by the user doing the mount, but it may be useful with
non CIFS Unix Extension mounts for cases in which the default
mode is specified on the mount but is not to be enforced on the
client (e.g. perhaps when MultiUserMount is enabled)
Note that this does not affect the normal ACL check on the
target machine done by the server software (of the server
ACL against the user name provided at mount time).
serverino Use server's inode numbers instead of generating automatically
incrementing inode numbers on the client. Although this will
make it easier to spot hardlinked files (as they will have
the same inode numbers) and inode numbers may be persistent,
note that the server does not guarantee that the inode numbers
are unique if multiple server side mounts are exported under a
single share (since inode numbers on the servers might not
be unique if multiple filesystems are mounted under the same
shared higher level directory). Note that some older
(e.g. pre-Windows 2000) do not support returning UniqueIDs
or the CIFS Unix Extensions equivalent and for those
this mount option will have no effect. Exporting cifs mounts
under nfsd requires this mount option on the cifs mount.
This is now the default if server supports the
required network operation.
noserverino Client generates inode numbers (rather than using the actual one
from the server). These inode numbers will vary after
unmount or reboot which can confuse some applications,
but not all server filesystems support unique inode
numbers.
setuids If the CIFS Unix extensions are negotiated with the server
the client will attempt to set the effective uid and gid of
the local process on newly created files, directories, and
devices (create, mkdir, mknod). If the CIFS Unix Extensions
are not negotiated, for newly created files and directories
instead of using the default uid and gid specified on
the mount, cache the new file's uid and gid locally which means
that the uid for the file can change when the inode is
reloaded (or the user remounts the share).
nosetuids The client will not attempt to set the uid and gid on
on newly created files, directories, and devices (create,
mkdir, mknod) which will result in the server setting the
uid and gid to the default (usually the server uid of the
user who mounted the share). Letting the server (rather than
the client) set the uid and gid is the default. If the CIFS
Unix Extensions are not negotiated then the uid and gid for
new files will appear to be the uid (gid) of the mounter or the
uid (gid) parameter specified on the mount.
netbiosname When mounting to servers via port 139, specifies the RFC1001
source name to use to represent the client netbios machine
name when doing the RFC1001 netbios session initialize.
direct Do not do inode data caching on files opened on this mount.
This precludes mmapping files on this mount. In some cases
with fast networks and little or no caching benefits on the
client (e.g. when the application is doing large sequential
reads bigger than page size without rereading the same data)
this can provide better performance than the default
behavior which caches reads (readahead) and writes
(writebehind) through the local Linux client pagecache
if oplock (caching token) is granted and held. Note that
direct allows write operations larger than page size
to be sent to the server.
strictcache Use for switching on strict cache mode. In this mode the
client read from the cache all the time it has Oplock Level II,
otherwise - read from the server. All written data are stored
in the cache, but if the client doesn't have Exclusive Oplock,
it writes the data to the server.
rwpidforward Forward pid of a process who opened a file to any read or write
operation on that file. This prevent applications like WINE
from failing on read and write if we use mandatory brlock style.
acl Allow setfacl and getfacl to manage posix ACLs if server
supports them. (default)
noacl Do not allow setfacl and getfacl calls on this mount
user_xattr Allow getting and setting user xattrs (those attributes whose
name begins with "user." or "os2.") as OS/2 EAs (extended
attributes) to the server. This allows support of the
setfattr and getfattr utilities. (default)
nouser_xattr Do not allow getfattr/setfattr to get/set/list xattrs
mapchars Translate six of the seven reserved characters (not backslash)
*?<>|:
to the remap range (above 0xF000), which also
allows the CIFS client to recognize files created with
such characters by Windows's POSIX emulation. This can
also be useful when mounting to most versions of Samba
(which also forbids creating and opening files
whose names contain any of these seven characters).
This has no effect if the server does not support
Unicode on the wire.
nomapchars Do not translate any of these seven characters (default).
nocase Request case insensitive path name matching (case
sensitive is the default if the server supports it).
(mount option "ignorecase" is identical to "nocase")
posixpaths If CIFS Unix extensions are supported, attempt to
negotiate posix path name support which allows certain
characters forbidden in typical CIFS filenames, without
requiring remapping. (default)
noposixpaths If CIFS Unix extensions are supported, do not request
posix path name support (this may cause servers to
reject creatingfile with certain reserved characters).
nounix Disable the CIFS Unix Extensions for this mount (tree
connection). This is rarely needed, but it may be useful
in order to turn off multiple settings all at once (ie
posix acls, posix locks, posix paths, symlink support
and retrieving uids/gids/mode from the server) or to
work around a bug in server which implement the Unix
Extensions.
nobrl Do not send byte range lock requests to the server.
This is necessary for certain applications that break
with cifs style mandatory byte range locks (and most
cifs servers do not yet support requesting advisory
byte range locks).
forcemandatorylock Even if the server supports posix (advisory) byte range
locking, send only mandatory lock requests. For some
(presumably rare) applications, originally coded for
DOS/Windows, which require Windows style mandatory byte range
locking, they may be able to take advantage of this option,
forcing the cifs client to only send mandatory locks
even if the cifs server would support posix advisory locks.
"forcemand" is accepted as a shorter form of this mount
option.
nostrictsync If this mount option is set, when an application does an
fsync call then the cifs client does not send an SMB Flush
to the server (to force the server to write all dirty data
for this file immediately to disk), although cifs still sends
all dirty (cached) file data to the server and waits for the
server to respond to the write. Since SMB Flush can be
very slow, and some servers may be reliable enough (to risk
delaying slightly flushing the data to disk on the server),
turning on this option may be useful to improve performance for
applications that fsync too much, at a small risk of server
crash. If this mount option is not set, by default cifs will
send an SMB flush request (and wait for a response) on every
fsync call.
nodfs Disable DFS (global name space support) even if the
server claims to support it. This can help work around
a problem with parsing of DFS paths with Samba server
versions 3.0.24 and 3.0.25.
remount remount the share (often used to change from ro to rw mounts
or vice versa)
cifsacl Report mode bits (e.g. on stat) based on the Windows ACL for
the file. (EXPERIMENTAL)
servern Specify the server 's netbios name (RFC1001 name) to use
when attempting to setup a session to the server.
This is needed for mounting to some older servers (such
as OS/2 or Windows 98 and Windows ME) since they do not
support a default server name. A server name can be up
to 15 characters long and is usually uppercased.
sfu When the CIFS Unix Extensions are not negotiated, attempt to
create device files and fifos in a format compatible with
Services for Unix (SFU). In addition retrieve bits 10-12
of the mode via the SETFILEBITS extended attribute (as
SFU does). In the future the bottom 9 bits of the
mode also will be emulated using queries of the security
descriptor (ACL).
mfsymlinks Enable support for Minshall+French symlinks
(see http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks)
This option is ignored when specified together with the
'sfu' option. Minshall+French symlinks are used even if
the server supports the CIFS Unix Extensions.
sign Must use packet signing (helps avoid unwanted data modification
by intermediate systems in the route). Note that signing
does not work with lanman or plaintext authentication.
seal Must seal (encrypt) all data on this mounted share before
sending on the network. Requires support for Unix Extensions.
Note that this differs from the sign mount option in that it
causes encryption of data sent over this mounted share but other
shares mounted to the same server are unaffected.
locallease This option is rarely needed. Fcntl F_SETLEASE is
used by some applications such as Samba and NFSv4 server to
check to see whether a file is cacheable. CIFS has no way
to explicitly request a lease, but can check whether a file
is cacheable (oplocked). Unfortunately, even if a file
is not oplocked, it could still be cacheable (ie cifs client
could grant fcntl leases if no other local processes are using
the file) for cases for example such as when the server does not
support oplocks and the user is sure that the only updates to
the file will be from this client. Specifying this mount option
will allow the cifs client to check for leases (only) locally
for files which are not oplocked instead of denying leases
in that case. (EXPERIMENTAL)
sec Security mode. Allowed values are:
none attempt to connection as a null user (no name)
krb5 Use Kerberos version 5 authentication
krb5i Use Kerberos authentication and packet signing
ntlm Use NTLM password hashing (default)
ntlmi Use NTLM password hashing with signing (if
/proc/fs/cifs/PacketSigningEnabled on or if
server requires signing also can be the default)
ntlmv2 Use NTLMv2 password hashing
ntlmv2i Use NTLMv2 password hashing with packet signing
lanman (if configured in kernel config) use older
lanman hash
hard Retry file operations if server is not responding
soft Limit retries to unresponsive servers (usually only
one retry) before returning an error. (default)

The mount.cifs mount helper also accepts a few mount options before -o
including:

-S take password from stdin (equivalent to setting the environment
variable "PASSWD_FD=0"
-V print mount.cifs version
-? display simple usage information

With most 2.6 kernel versions of modutils, the version of the cifs kernel
module can be displayed via modinfo.

Misc /proc/fs/cifs Flags and Debug Info
=======================================
Informational pseudo-files:
DebugData Displays information about active CIFS sessions and
shares, features enabled as well as the cifs.ko
version.
Stats Lists summary resource usage information as well as per
share statistics, if CONFIG_CIFS_STATS in enabled
in the kernel configuration.

Configuration pseudo-files:
PacketSigningEnabled If set to one, cifs packet signing is enabled
and will be used if the server requires
it. If set to two, cifs packet signing is
required even if the server considers packet
signing optional. (default 1)
SecurityFlags Flags which control security negotiation and
also packet signing. Authentication (may/must)
flags (e.g. for NTLM and/or NTLMv2) may be combined with
the signing flags. Specifying two different password
hashing mechanisms (as "must use") on the other hand
does not make much sense. Default flags are
0x07007
(NTLM, NTLMv2 and packet signing allowed). The maximum
allowable flags if you want to allow mounts to servers
using weaker password hashes is 0x37037 (lanman,
plaintext, ntlm, ntlmv2, signing allowed). Some
SecurityFlags require the corresponding menuconfig
options to be enabled (lanman and plaintext require
CONFIG_CIFS_WEAK_PW_HASH for example). Enabling
plaintext authentication currently requires also
enabling lanman authentication in the security flags
because the cifs module only supports sending
laintext passwords using the older lanman dialect
form of the session setup SMB. (e.g. for authentication
using plain text passwords, set the SecurityFlags
to 0x30030):

may use packet signing 0x00001
must use packet signing 0x01001
may use NTLM (most common password hash) 0x00002
must use NTLM 0x02002
may use NTLMv2 0x00004
must use NTLMv2 0x04004
may use Kerberos security 0x00008
must use Kerberos 0x08008
may use lanman (weak) password hash 0x00010
must use lanman password hash 0x10010
may use plaintext passwords 0x00020
must use plaintext passwords 0x20020
(reserved for future packet encryption) 0x00040

cifsFYI If set to non-zero value, additional debug information
will be logged to the system error log. This field
contains three flags controlling different classes of
debugging entries. The maximum value it can be set
to is 7 which enables all debugging points (default 0).
Some debugging statements are not compiled into the
cifs kernel unless CONFIG_CIFS_DEBUG2 is enabled in the
kernel configuration. cifsFYI may be set to one or
nore of the following flags (7 sets them all):

log cifs informational messages 0x01
log return codes from cifs entry points 0x02
log slow responses (ie which take longer than 1 second)
CONFIG_CIFS_STATS2 must be enabled in .config 0x04


traceSMB If set to one, debug information is logged to the
system error log with the start of smb requests
and responses (default 0)
LookupCacheEnable If set to one, inode information is kept cached
for one second improving performance of lookups
(default 1)
OplockEnabled If set to one, safe distributed caching enabled.
(default 1)
LinuxExtensionsEnabled If set to one then the client will attempt to
use the CIFS "UNIX" extensions which are optional
protocol enhancements that allow CIFS servers
to return accurate UID/GID information as well
as support symbolic links. If you use servers
such as Samba that support the CIFS Unix
extensions but do not want to use symbolic link
support and want to map the uid and gid fields
to values supplied at mount (rather than the
actual values, then set this to zero. (default 1)

These experimental features and tracing can be enabled by changing flags in
/proc/fs/cifs (after the cifs module has been installed or built into the
kernel, e.g. insmod cifs). To enable a feature set it to 1 e.g. to enable
tracing to the kernel message log type:

echo 7 > /proc/fs/cifs/cifsFYI

cifsFYI functions as a bit mask. Setting it to 1 enables additional kernel
logging of various informational messages. 2 enables logging of non-zero
SMB return codes while 4 enables logging of requests that take longer
than one second to complete (except for byte range lock requests).
Setting it to 4 requires defining CONFIG_CIFS_STATS2 manually in the
source code (typically by setting it in the beginning of cifsglob.h),
and setting it to seven enables all three. Finally, tracing
the start of smb requests and responses can be enabled via:

echo 1 > /proc/fs/cifs/traceSMB

Per share (per client mount) statistics are available in /proc/fs/cifs/Stats
if the kernel was configured with cifs statistics enabled. The statistics
represent the number of successful (ie non-zero return code from the server)
SMB responses to some of the more common commands (open, delete, mkdir etc.).
Also recorded is the total bytes read and bytes written to the server for
that share. Note that due to client caching effects this can be less than the
number of bytes read and written by the application running on the client.
The statistics for the number of total SMBs and oplock breaks are different in
that they represent all for that share, not just those for which the server
returned success.

Also note that "cat /proc/fs/cifs/DebugData" will display information about
the active sessions and the shares that are mounted.

Enabling Kerberos (extended security) works but requires version 1.2 or later
of the helper program cifs.upcall to be present and to be configured in the
/etc/request-key.conf file. The cifs.upcall helper program is from the Samba
project(http://www.samba.org). NTLM and NTLMv2 and LANMAN support do not
require this helper. Note that NTLMv2 security (which does not require the
cifs.upcall helper program), instead of using Kerberos, is sufficient for
some use cases.

DFS support allows transparent redirection to shares in an MS-DFS name space.
In addition, DFS support for target shares which are specified as UNC
names which begin with host names (rather than IP addresses) requires
a user space helper (such as cifs.upcall) to be present in order to
translate host names to ip address, and the user space helper must also
be configured in the file /etc/request-key.conf. Samba, Windows servers and
many NAS appliances support DFS as a way of constructing a global name
space to ease network configuration and improve reliability.

To use cifs Kerberos and DFS support, the Linux keyutils package should be
installed and something like the following lines should be added to the
/etc/request-key.conf file:

create cifs.spnego * * /usr/local/sbin/cifs.upcall %k
create dns_resolver * * /usr/local/sbin/cifs.upcall %k

CIFS kernel module parameters
=============================
These module parameters can be specified or modified either during the time of
module loading or during the runtime by using the interface
/proc/module/cifs/parameters/

i.e. echo "value" > /sys/module/cifs/parameters/

1. enable_oplocks - Enable or disable oplocks. Oplocks are enabled by default.
[Y/y/1]. To disable use any of [N/n/0].