mount.cifs(8)
NAME
mount.cifs - mount using the Common Internet File System (CIFS)
SYNOPSIS
mount.cifs {service} {mount-point} [-o options]
DESCRIPTION
This tool is part of the cifs-utils suite. mount.cifs mounts a Linux CIFS filesystem. It is usually invoked indirectly by the mount(8) command when using the "-t cifs" option. This command only works in Linux, and the kernel must support the cifs filesystem. The CIFS protocol is the successor to the SMB protocol and is supported by most Windows servers and many other commercial servers and Network Attached Storage appliances as well as by the popular Open Source server Samba. The mount.cifs utility attaches the UNC name (exported network resource) specified as service (using //server/share syntax, where "server" is the server name or IP address and "share" is the name of the share) to the local directory mount-point. Options to mount.cifs are specified as a comma-separated list of key=value pairs. It is possible to send options other than those listed here, assuming that the cifs filesystem kernel module (cifs.ko) supports them. Unrecognized cifs mount options passed to the cifs vfs kernel code will be logged to the kernel log. mount.cifs causes the cifs vfs to launch a thread named cifsd. After mounting it keeps running until the mounted resource is unmounted (usually via the umount utility). mount.cifs -V command displays the version of cifs mount helper. modinfo cifs command displays the version of cifs module.
OPTIONS
username=arg
specifies the username to connect as. If this is not given, then
the environment variable USER is used.
Earlier versions of mount.cifs also allowed one to specify the
username in a "user%password" or "workgroup/user" or
"workgroup/user%password" to allow the password and workgroup to be
specified as part of the username. Support for those alternate
username formats is now deprecated and should no longer be used.
Users should use the discrete "password=" and "domain=" to specify
those values. While some versions of the cifs kernel module accept
"user=" as an abbreviation for this option, its use can confuse the
standard mount program into thinking that this is a non-superuser
mount. It is therefore recommended to use the full "username="
option name.
password=arg
specifies the CIFS password. If this option is not given then the
environment variable PASSWD is used. If the password is not
specified directly or indirectly via an argument to mount,
mount.cifs will prompt for a password, unless the guest option is
specified.
Note that a password which contains the delimiter character (i.e. a
comma ,) will fail to be parsed correctly on the command line.
However, the same password defined in the PASSWD environment
variable or via a credentials file (see below) or entered at the
password prompt will be read correctly.
credentials=filename
specifies a file that contains a username and/or password and
optionally the name of the workgroup. The format of the file is:
username=value
password=value
domain=value
This is preferred over having passwords in plaintext in a shared
file, such as /etc/fstab. Be sure to protect any credentials file
properly.
uid=arg
sets the uid that will own all files or directories on the mounted
filesystem when the server does not provide ownership information.
It may be specified as either a username or a numeric uid. When not
specified, the default is uid 0. The mount.cifs helper must be at
version 1.10 or higher to support specifying the uid in non-numeric
form. See the section on FILE AND DIRECTORY OWNERSHIP AND
PERMISSIONS below for more information.
forceuid
instructs the client to ignore any uid provided by the server for
files and directories and to always assign the owner to be the
value of the uid= option. See the section on FILE AND DIRECTORY
OWNERSHIP AND PERMISSIONS below for more information.
cruid=arg
sets the uid of the owner of the credentials cache. This is
primarily useful with sec=krb5. The default is the real uid of the
process performing the mount. Setting this parameter directs the
upcall to look for a credentials cache owned by that user.
gid=arg
sets the gid that will own all files or directories on the mounted
filesystem when the server does not provide ownership information.
It may be specified as either a groupname or a numeric gid. When
not specified, the default is gid 0. The mount.cifs helper must be
at version 1.10 or higher to support specifying the gid in
non-numeric form. See the section on FILE AND DIRECTORY OWNERSHIP
AND PERMISSIONS below for more information.
forcegid
instructs the client to ignore any gid provided by the server for
files and directories and to always assign the owner to be the
value of the gid= option. See the section on FILE AND DIRECTORY
OWNERSHIP AND PERMISSIONS below for more information.
port=arg
sets the port number on which the client will attempt to contact
the CIFS server. If this value is specified, look for an existing
connection with this port, and use that if one exists. If one
doesn't exist, try to create a new connection on that port. If that
connection fails, return an error. If this value isn't specified,
look for an existing connection on port 445 or 139. If no such
connection exists, try to connect on port 445 first and then port
139 if that fails. Return an error if both fail.
servernetbiosname=arg
Specify the server netbios name (RFC1001 name) to use when
attempting to setup a session to the server. Although rarely needed
for mounting to newer servers, this option is needed for mounting
to some older servers (such as OS/2 or Windows 98 and Windows ME)
since when connecting over port 139 they, unlike most newer
servers, do not support a default server name. A server name can be
up to 15 characters long and is usually uppercased.
servern=arg
Synonym for servernetbiosname.
netbiosname=arg
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.
file_mode=arg
If the server does not support the CIFS Unix extensions this
overrides the default file mode.
dir_mode=arg
If the server does not support the CIFS Unix extensions this
overrides the default mode for directories.
ip=arg
sets the destination IP address. This option is set automatically
if the server name portion of the requested UNC name can be
resolved so rarely needs to be specified by the user.
domain=arg
sets the domain (workgroup) of the user
guest
dont prompt for a password
iocharset
Charset 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.
ro
mount read-only
rw
mount read-write
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 the mount, cache the new files 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.
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.
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).
dynperm
Instructs the server to maintain ownership and permissions in
memory that cant be stored on the server. This information can
disappear at any time (whenever the inode is flushed from the
cache), so while this may help make some applications work, its
behavior is somewhat unreliable. See the section below on FILE AND
DIRECTORY OWNERSHIP AND PERMISSIONS for more information.
cache=
Cache mode. See the section below on CACHE COHERENCY for details.
Allowed values are:
* none: do not cache file data at all
* strict: follow the CIFS/SMB2 protocol strictly
* loose: allow loose caching semantics
The default in kernels prior to 3.7 was "loose". As of kernel 3.7
the default is "strict".
directio
Do not do inode data caching on files opened on this mount. This
precludes mmaping 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. On some kernels this requires the cifs.ko module to be
built with the CIFS_EXPERIMENTAL configure option.
This option is will be deprecated in 3.7. Users should use
cache=none instead on more recent kernels.
strictcache
Use for switching on strict cache mode. In this mode the client
reads from the cache all the time it has Oplock Level II, otherwise
- read from the server. As for write - the client stores a data in
the cache in Exclusive Oplock case, otherwise - write directly to
the server.
This option is will be deprecated in 3.7. Users should use
cache=strict instead on more recent kernels.
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.
mapchars
Translate six of the seven reserved characters (not backslash, but
including the colon, question mark, pipe, asterik, greater than and
less than characters) to the remap range (above 0xF000), which also
allows the CIFS client to recognize files created with such
characters by Windowss 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. Please note that the files created with
mapchars mount option may not be accessible if the share is mounted
without that option.
nomapchars
Do not translate any of these seven characters (default)
intr
currently unimplemented
nointr
(default) currently unimplemented
hard
The program accessing a file on the cifs mounted file system will
hang when the server crashes.
soft
(default) The program accessing a file on the cifs mounted file
system will not hang when the server crashes and will return errors
to the user application.
noacl
Do not allow POSIX ACL operations even if server would support
them.
The CIFS client can get and set POSIX ACLs (getfacl, setfacl) to
Samba servers version 3.0.10 and later. Setting POSIX ACLs requires
enabling both CIFS_XATTR and then CIFS_POSIX support in the CIFS
configuration options when building the cifs module. POSIX ACL
support can be disabled on a per mount basis by specifying "noacl"
on mount.
cifsacl
This option is used to map CIFS/NTFS ACLs to/from Linux permission
bits, map SIDs to/from UIDs and GIDs, and get and set Security
Descriptors.
See sections on CIFS/NTFS ACL, SID/UID/GID MAPPING, SECURITY
DESCRIPTORS for more information.
backupuid=arg
File access by this user shall be done with the backup intent flag
set. Either a name or an id must be provided as an argument, there
are no default values.
See section ACCESSING FILES WITH BACKUP INTENT for more details
backupgid=arg
File access by users who are members of this group shall be done
with the backup intent flag set. Either a name or an id must be
provided as an argument, there are no default values.
See section ACCESSING FILES WITH BACKUP INTENT for more details
nocase
Request case insensitive path name matching (case sensitive is the
default if the server suports it).
ignorecase
Synonym for nocase.
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 forcibly enable packet
signing
* ntlm - Use NTLM password hashing
* ntlmi - Use NTLM password hashing and force packet signing
* ntlmv2 - Use NTLMv2 password hashing
* ntlmv2i - Use NTLMv2 password hashing and force packet signing
* ntlmssp - Use NTLMv2 password hashing encapsulated in Raw
NTLMSSP message
* ntlmsspi - Use NTLMv2 password hashing encapsulated in Raw
NTLMSSP message, and force packet signing
The default in mainline kernel versions prior to v3.8 was sec=ntlm.
In v3.8, the default was changed to sec=ntlmssp.
If the server requires signing during protocol negotiation, then it
may be enabled automatically. Packet signing may also be enabled
automatically if it's enabled in /proc/fs/cifs/SecurityFlags.
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).
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 mode also will be emulated using queries
of the security descriptor (ACL). [NB: requires version 1.39 or
later of the CIFS VFS. To recognize symlinks and be able to create
symlinks in an SFU interoperable form requires version 1.40 or
later of the CIFS VFS kernel module.
serverino
Use inode numbers (unique persistent file identifiers) returned by
the server instead of automatically generating temporary inode
numbers on the client. Although server inode numbers make it easier
to spot hardlinked files (as they will have the same inode numbers)
and inode numbers may be persistent (which is userful for some
sofware), 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 not all servers support returning server
inode numbers, although those that support the CIFS Unix
Extensions, and Windows 2000 and later servers typically do support
this (although not necessarily on every local server filesystem).
Parameter has no effect if the server lacks support for returning
inode numbers or equivalent. This behavior is enabled by default.
noserverino
Client generates inode numbers itself rather than using the actual
ones from the server.
See section INODE NUMBERS for more information.
nounix
Disable the CIFS Unix Extensions for this mount. This can be useful
in order to turn off multiple settings at once. This includes POSIX
acls, POSIX locks, POSIX paths, symlink support and retrieving
uids/gids/mode from the server. This can also be useful to work
around a bug in a server that supports Unix Extensions.
See section INODE NUMBERS for more information.
nouser_xattr
Do not allow getfattr/setfattr to get/set xattrs, even if server
would support it otherwise. The default is for xattr support to be
enabled.
rsize=bytes
Maximum amount of data that the kernel will request in a read
request in bytes. Prior to kernel 3.2.0, the default was 16k, and
the maximum size was limited by the CIFSMaxBufSize module
parameter. As of kernel 3.2.0, the behavior varies according to
whether POSIX extensions are enabled on the mount and the server
supports large POSIX reads. If they are, then the default is 1M,
and the maxmimum is 16M. If they are not supported by the server,
then the default is 60k and the maximum is around 127k. The reason
for the 60k is because it's the maximum size read that windows
servers can fill. Note that this value is a maximum, and the client
may settle on a smaller size to accomodate what the server
supports. In kernels prior to 3.2.0, no negotiation is performed.
wsize=bytes
Maximum amount of data that the kernel will send in a write request
in bytes. Prior to kernel 3.0.0, the default and maximum was 57344
(14 * 4096 pages). As of 3.0.0, the default depends on whether the
client and server negotiate large writes via POSIX extensions. If
they do, then the default is 1M, and the maximum allowed is 16M. If
they do not, then the default is 65536 and the maximum allowed is
131007.
Note that this value is just a starting point for negotiation in
3.0.0 and up. The client and server may negotiate this size
downward according to the server's capabilities. In kernels prior
to 3.0.0, no negotiation is performed. It can end up with an
existing superblock if this value isn't specified or it's greater
or equal than the existing one.
fsc
Enable local disk caching using FS-Cache for CIFS. 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 the scalability positively as the number of calls to the
server are reduced. But, be warned that local caching is not
suitable for all workloads, for e.g., read-once type workloads. So,
you need to consider carefully the situation/workload before using
this option. Currently, local disk caching is enabled for CIFS
files opened as read-only.
NOTE: This feature is available only in the recent kernels that
have been built with the kernel config option CONFIG_CIFS_FSCACHE.
You also need to have cachefilesd daemon installed and running to
make the cache operational.
multiuser
Map user accesses to individual credentials when accessing the
server. By default, CIFS mounts only use a single set of user
credentials (the mount credentials) when accessing a share. With
this option, the client instead creates a new session with the
server using the user's credentials whenever a new user accesses
the mount. Further accesses by that user will also use those
credentials. Because the kernel cannot prompt for passwords,
multiuser mounts are limited to mounts using sec= options that
don't require passwords.
With this change, it's feasible for the server to handle
permissions enforcement, so this option also implies "noperm".
Furthermore, when unix extensions aren't in use and the
administrator has not overriden ownership using the uid= or gid=
options, ownership of files is presented as the current user
accessing the share.
actimeo=arg
The time (in seconds) that the CIFS client caches attributes of a
file or directory before it requests attribute information from a
server. During this period the changes that occur on the server
remain undetected until the client checks the server again.
By default, the attribute cache timeout is set to 1 second. This
means more frequent on-the-wire calls to the server to check
whether attributes have changed which could impact performance.
With this option users can make a tradeoff between performance and
cache metadata correctness, depending on workload needs. Shorter
timeouts mean better cache coherency, but frequent increased number
of calls to the server. Longer timeouts mean a reduced number of
calls to the server but looser cache coherency. The actimeo value
is a positive integer that can hold values between 0 and a maximum
value of 2^30 * HZ (frequency of timer interrupt) setting.
noposixpaths
If unix extensions are enabled on a share, then the client will
typically allow filenames to include any character besides '/' in a
pathname component, and will use forward slashes as a pathname
delimiter. This option prevents the client from attempting to
negotiate the use of posix-style pathnames to the server.
posixpaths
Inverse of noposixpaths.
prefixpath=
It's possible to mount a subdirectory of a share. The preferred way
to do this is to append the path to the UNC when mounting. However,
it's also possible to do the same by setting this option and
providing the path there.
vers=
SMB protocol version. Allowed values are:
* 1.0 - The classic CIFS/SMBv1 protocol. This is the default.
* 2.0 - The SMBv2.002 protocol. This was initially introduced in
Windows Vista Service Pack 1, and Windows Server 2008. Note
that the initial release version of Windows Vista spoke a
slightly different dialect (2.000) that is not supported.
* 2.1 - The SMBv2.1 protocol that was introduced in Microsoft
Windows 7 and Windows Server 2008R2.
* 3.0 - The SMBv3.0 protocol that was introduced in Microsoft
Windows 8 and Windows Server 2012.
Note too that while this option governs the protocol version used,
not all features of each version are available.
--verbose
Print additional debugging information for the mount. Note that
this parameter must be specified before the -o. For example:
mount -t cifs //server/share /mnt --verbose -o user=username
SERVICE FORMATTING AND DELIMITERS
Its generally preferred to use forward slashes (/) as a delimiter in service names. They are considered to be the "universal delimiter" since they are generally not allowed to be embedded within path components on Windows machines and the client can convert them to blackslashes (\) unconditionally. Conversely, backslash characters are allowed by POSIX to be part of a path component, and cant be automatically converted in the same way. mount.cifs will attempt to convert backslashes to forward slashes where its able to do so, but it cannot do so in any path component following the sharename.
INODE NUMBERS
When Unix Extensions are enabled, we use the actual inode number provided by the server in response to the POSIX calls as an inode number. When Unix Extensions are disabled and "serverino" mount option is enabled there is no way to get the server inode number. The client typically maps the server-assigned "UniqueID" onto an inode number. Note that the UniqueID is a different value from the server inode number. The UniqueID value is unique over the scope of the entire server and is often greater than 2 power 32. This value often makes programs that are not compiled with LFS (Large File Support), to trigger a glibc EOVERFLOW error as this wont fit in the target structure field. It is strongly recommended to compile your programs with LFS support (i.e. with -D_FILE_OFFSET_BITS=64) to prevent this problem. You can also use "noserverino" mount option to generate inode numbers smaller than 2 power 32 on the client. But you may not be able to detect hardlinks properly.
CACHE COHERENCY
With a network filesystem such as CIFS or NFS, the client must contend with the fact that activity on other clients or the server could change the contents or attributes of a file without the client being aware of it. One way to deal with such a problem is to mandate that all file accesses go to the server directly. This is performance prohibitive however, so most protocols have some mechanism to allow the client to cache data locally. The CIFS protocol mandates (in effect) that the client should not cache file data unless it holds an opportunistic lock (aka oplock) or a lease. Both of these entities allow the client to guarantee certain types of exclusive access to a file so that it can access its contents without needing to continually interact with the server. The server will call back the client when it needs to revoke either of them and allow the client a certain amount of time to flush any cached data. The cifs client uses the kernel's pagecache to cache file data. Any I/O that's done through the pagecache is generally page-aligned. This can be problematic when combined with byte-range locks as Windows' locking is mandatory and can block reads and writes from occurring. cache=none means that the client never utilizes the cache for normal reads and writes. It always accesses the server directly to satisfy a read or write request. cache=strict means that the client will attempt to follow the CIFS/SMB2 protocol strictly. That is, the cache is only trusted when the client holds an oplock. When the client does not hold an oplock, then the client bypasses the cache and accesses the server directly to satisfy a read or write request. By doing this, the client avoids problems with byte range locks. Additionally, byte range locks are cached on the client when it holds an oplock and are "pushed" to the server when that oplock is recalled. cache=loose allows the client to use looser protocol semantics which can sometimes provide better performance at the expense of cache coherency. File access always involves the pagecache. When an oplock or lease is not held, then the client will attempt to flush the cache soon after a write to a file. Note that that flush does not necessarily occur before a write system call returns. In the case of a read without holding an oplock, the client will attempt to periodically check the attributes of the file in order to ascertain whether it has changed and the cache might no longer be valid. This mechanism is much like the one that NFSv2/3 use for cache coherency, but it particularly problematic with CIFS. Windows is quite "lazy" with respect to updating the "LastWriteTime" field that the client uses to verify this. The effect is that cache=loose can cause data corruption when multiple readers and writers are working on the same files. Because of this, when multiple clients are accessing the same set of files, then cache=strict is recommended. That helps eliminate problems with cache coherency by following the CIFS/SMB2 protocols more strictly. Note too that no matter what caching model is used, the client will always use the pagecache to handle mmap'ed files. Writes to mmap'ed files are only guaranteed to be flushed to the server when msync() is called, or on close(). The default in kernels prior to 3.7 was "loose". As of 3.7, the default is "strict".
CIFS/NTFS ACL, SID/UID/GID MAPPING, SECURITY DESCRIPTORS
This option is used to work with file objects which posses Security
Descriptors and CIFS/NTFS ACL instead of UID, GID, file permission
bits, and POSIX ACL as user authentication model. This is the most
common authentication model for CIFS servers and is the one used by
Windows.
Support for this requires both CIFS_XATTR and CIFS_ACL support in the
CIFS configuration options when building the cifs module.
A CIFS/NTFS ACL is mapped to file permission bits using an algorithm
specified in the following Microsoft TechNet document:
* http://technet.microsoft.com/en-us/library/bb463216.aspx
In order to map SIDs to/from UIDs and GIDs, the following is required:
* a kernel upcall to the cifs.idmap utility set up via request-
key.conf(5)
* winbind support configured via nsswitch.conf(5) and smb.conf(5)
Please refer to the respective manpages of cifs.idmap(8) and
winbindd(8) for more information.
Security descriptors for a file object can be retrieved and set
directly using extended attribute named system.cifs_acl. The security
descriptors presented via this interface are "raw" blobs of data and
need a userspace utility to either parse and format or to assemble it
such as getcifsacl(1) and setcifsacl(1) respectively.
Some of the things to consider while using this mount option:
* There may be an increased latency when handling metadata due to
additional requests to get and set security descriptors.
* The mapping between a CIFS/NTFS ACL and POSIX file permission bits
is imperfect and some ACL information may be lost in the
translation.
* If either upcall to cifs.idmap is not setup correctly or winbind is
not configured and running, ID mapping will fail. In that case uid
and gid will default to either to those values of the share or to
the values of uid and/or gid mount options if specified.
ACCESSING FILES WITH BACKUP INTENT
For an user on the server, desired access to a file is determined by the permissions and rights associated with that file. This is typically accomplished using owenrship and ACL. For a user who does not have access rights to a file, it is still possible to access that file for a specific or a targeted purpose by granting special rights. One of the specific purposes is to access a file with the intent to either backup or restore i.e. backup intent. The right to access a file with the backup intent can typically be granted by making that user a part of the built-in group Backup Operators. Thus, when this user attempts to open a file with the backup intent, open request is sent by setting the bit FILE_OPEN_FOR_BACKUP_INTENT as one of the CreateOptions. As an example, on a Windows server, a user named testuser, cannot open this file with such a security descriptor. REVISION:0x1 CONTROL:0x9404 OWNER:Administrator GROUP:Domain Users ACL:Administrator:ALLOWED/0x0/FULL But the user testuser, if it becomes part of the group Backup Operators, can open the file with the backup intent. Any user on the client side who can authenticate as such a user on the server, can access the files with the backup intent. But it is desirable and preferable for security reasons amongst many, to restrict this special right. The mount option backupuid is used to restrict this special right to a user which is specified by either a name or an id. The mount option backupgid is used to restrict this special right to the users in a group which is specified by either a name or an id. Only users maching either backupuid or backupgid shall attempt to access files with backup intent. These two mount options can be used together.
FILE AND DIRECTORY OWNERSHIP AND PERMISSIONS
The core CIFS protocol does not provide unix ownership information or mode for files and directories. Because of this, files and directories will generally appear to be owned by whatever values the uid= or gid= options are set, and will have permissions set to the default file_mode and dir_mode for the mount. Attempting to change these values via chmod/chown will return success but have no effect. When the client and server negotiate unix extensions, files and directories will be assigned the uid, gid, and mode provided by the server. Because CIFS mounts are generally single-user, and the same credentials are used no matter what user accesses the mount, newly created files and directories will generally be given ownership corresponding to whatever credentials were used to mount the share. If the uids and gids being used do not match on the client and server, the forceuid and forcegid options may be helpful. Note however, that there is no corresponding option to override the mode. Permissions assigned to a file when forceuid or forcegid are in effect may not reflect the the real permissions. When unix extensions are not negotiated, its also possible to emulate them locally on the server using the "dynperm" mount option. When this mount option is in effect, newly created files and directories will receive what appear to be proper permissions. These permissions are not stored on the server however and can disappear at any time in the future (subject to the whims of the kernel flushing out the inode cache). In general, this mount option is discouraged. Its also possible to override permission checking on the client altogether via the noperm option. Server-side permission checks cannot be overriden. The permission checks done by the server will always correspond to the credentials used to mount the share, and not necessarily to the user who is accessing the share.
ENVIRONMENT VARIABLES
The variable USER may contain the username of the person to be used to authenticate to the server. The variable can be used to set both username and password by using the format username%password. The variable PASSWD may contain the password of the person using the client. The variable PASSWD_FILE may contain the pathname of a file to read the password from. A single line of input is read and used as the password.
NOTES
This command may be used only by root, unless installed setuid, in which case the noeexec and nosuid mount flags are enabled. When installed as a setuid program, the program follows the conventions set forth by the mount program for user mounts, with the added restriction that users must be able to chdir() into the mountpoint prior to the mount in order to be able to mount onto it. Some samba client tools like smbclient(8) honour client-side configuration parameters present in smb.conf. Unlike those client tools, mount.cifs ignores smb.conf completely.
CONFIGURATION
The primary mechanism for making configuration changes and for reading debug information for the cifs vfs is via the Linux /proc filesystem. In the directory /proc/fs/cifs are various configuration files and pseudo files which can display debug information. There are additional startup options such as maximum buffer size and number of buffers which only may be set when the kernel cifs vfs (cifs.ko module) is loaded. These can be seen by running the modinfo utility against the file cifs.ko which will list the options that may be passed to cifs during module installation (device driver load). For more information see the kernel file fs/cifs/README.
BUGS
Mounting using the CIFS URL specification is currently not supported. The credentials file does not handle usernames or passwords with leading space. Note that the typical response to a bug report is a suggestion to try the latest version first. So please try doing that first, and always include which versions you use of relevant software when reporting bugs (minimum: mount.cifs (try mount.cifs -V), kernel (see /proc/version) and server type you are trying to contact.
VERSION
This man page is correct for version 1.74 of the cifs vfs filesystem (roughly Linux kernel 3.0).
SEE ALSO
cifs.upcall(8), getcifsacl(1), setcifsacl(1) Documentation/filesystems/cifs.txt and fs/cifs/README in the linux kernel source tree may contain additional options and information.
AUTHOR
Steve French The syntax and manpage were loosely based on that of smbmount. It was converted to Docbook/XML by Jelmer Vernooij. The maintainer of the Linux cifs vfs and the userspace tool mount.cifs is Steve French. The Linux CIFS Mailing list is the preferred place to ask questions regarding these programs.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
