path: root/mount.cifs.rst

==========
mount.cifs
==========

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mount using the Common Internet File System (CIFS)
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:Manual section: 8

********
SYNOPSIS
********

  mount.cifs {service} {mount-point} [-o options]

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
  don't 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 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.

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 can't 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, it's behavior is somewhat
  unreliable. See the section below on `FILE AND DIRECTORY OWNERSHIP
  AND PERMISSIONS`_ for more information.

cache=arg
  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(1) 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 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. Please note that
  the files created with ``mapchars`` mount option may not be accessible
  if the share is mounted without that option.

nomapchars
  (default) Do not translate any of these seven characters.

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 section 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 supports it).

ignorecase
  Synonym for ``nocase``.

sec=arg
  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*.

seal
  Request encryption at the SMB layer. Encryption is only supported in
  SMBv3 and above. The encryption algorithm used is AES-128-CCM.

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.

mfsymlinks
  Enable support for Minshall+French symlinks (see
  `http://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks <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.

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 useful for some software), 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 maximum 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
  accommodate 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 overridden
  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=arg
  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=arg
  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.
  - 3.1.1 or 3.11 - The SMBv3.1.1 protocol that was introduced in Microsoft Windows Server 2016.

  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
*********************************

It's 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
backslashes (\) unconditionally. Conversely, backslash characters are
allowed by POSIX to be part of a path component, and can't be
automatically converted in the same way.

``mount.cifs`` will attempt to convert backslashes to forward slashes
where it's 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 won't 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.