The CIFS VFS support for Linux supports many advanced network filesystem
features such as heirarchical 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.
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 <cifs_download_dir>/fs/cifs/* to <kernel_download_dir>/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 2.5:
1) Download the kernel (e.g. from http://www.kernel.org or from bitkeeper
at bk://linux.bkbits.net/linux-2.5) 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 <mount point> <UNC name or cifs URL>
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
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
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
Some administrators also change the "map archive" and the "create mask"
parameters from their default values. Creating special devices (mknod) remotely
may require specifying a mkdev function to Samba. 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.
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=<username>
pass=<password>
domain=<domain name>
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).
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).
If no password is provided, mount.cifs will prompt for password entry
Restrictions
============
Servers must support the NTLM SMB dialect (which is the most recent, supported
by Samba and Windows NT version 4, 2000 and XP and many other SMB/CIFS servers)
Servers must support either "pure-TCP" (port 445 TCP/IP CIFS connections) or RFC
1001/1002 support for "Netbios-Over-TCP/IP." Neither of these is likely to be a
problem as most servers support this. IPv6 support is planned for the future.
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 it is 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
uid If CIFS Unix extensions are not supported by the server
this overrides the default uid for inodes. 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. For servers which do not support
the Unix extensions, the default uid (and gid) returned on
lookup of existing files is 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. For the uid (gid) of newly
created files and directories, ie files created since
the last mount of the server share, the expected uid
(gid) is cached as as long as the inode remains in
memory on the client. 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
gid If CIFS Unix extensions are not supported by the server
this overrides the default gid for inodes.
file_mode If CIFS Unix extensions are not supported by the server
this overrides the default mode for file inodes.
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
wsize default write size
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.
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.
Misc /proc/fs/cifs Flags and Debug Info
=======================================
Informational pseudo-files:
DebugData Displays information about active CIFS sessions
SimultaneousOps Counter which holds maximum number of
simultaneous outstanding SMB/CIFS requests.
Stats Lists summary resource usage information
Configuration pseudo-files:
MultiuserMount If set to one, more than one CIFS session to
the same server ip address can be established
if more than one uid accesses the same mount
point and if the uids user/password mapping
information is available. (default is 0)
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)
cifsFYI If set to one, additional debug information is
logged to the system error log. (default 0)
ExtendedSecurity If set to one, SPNEGO session establishment
is allowed which enables more advanced
secure CIFS session establishment (default 0)
NTLMV2Enabled If set to one, more secure password hashes
are used when the server supports them and
when kerberos is not negotiated (default 0)
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 1 > /proc/fs/cifs/cifsFYI
and for more extensive tracing including the start of smb requests and responses
echo 1 > /proc/fs/cifs/traceSMB
Three other experimental features are under development and to test
require enabling an ifdef (e.g. by adding "#define CIFS_FCNTL" in cifsglob.h)
CIFS_QUOTA
CIFS_XATTR
CIFS_FCNTL (fcntl needed for support of directory change notification)
Also note that "cat /proc/fs/cifs/DebugData" will display some information about
the active sessions and the shares that are mounted. Note: NTLMv2 enablement
will not work since they its implementation is not quite complete yet.
Do not alter these configuration values unless you are doing specific testing.
Enabling extended security works to Windows 2000 Workstations and XP but not to
Windows 2000 server or Samba since it does not usually send "raw NTLMSSP"
(instead it sends NTLMSSP encapsulated in SPNEGO/GSSAPI, which support is not
complete in the CIFS VFS yet).