path: root/mount.cifs.rst

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

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

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

This tool is part of the cifs-utils suite.

``mount.cifs`` mounts a CIFS or SMB3 filesystem from Linux. 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 SMB3 protocol is the successor to the CIFS (SMB)
protocol and is supported by most Windows servers, Azure (cloud storage),
Macs 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|user=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|pass=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|cred=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.

idsfromsid
  Extract uid/gid from special SID instead of mapping it. 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.

netbiosname=arg
  When mounting to servers via port 139, specifies the RFC1001 source
  name to use to represent the client netbios machine during the netbios
  session initialization.

servern=arg
  Similar to ``netbiosname`` except it specifies the netbios name of
  the server instead of the client. 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.

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|addr=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|dom=arg|workgroup=arg
  Sets the domain (workgroup) of the user. If no domains are given,
  the empty domain will be used. Use ``domainauto`` to automatically
  guess the domain of the server you are connecting to.

domainauto
  When using NTLM authentication and not providing a domain via
  ``domain``, guess the domain from the server NTLM challenge.
  This behavior used to be the default on kernels older than 2.6.36.

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``.

nostrictsync
  Do not ask the server to flush on fsync().
  Some servers perform non-buffered writes by default in which case
  flushing is redundant. In workloads where a client is performing a
  lot of small write + fsync combinations and where network latency is
  much higher than the server latency, this brings a 2x performance
  improvement.
  This option is also a good candidate in scenarios where we want
  performance over consistency.

handlecache
  (default) In SMB2 and above, the client often has to open the root
  of the share (empty path) in various places during mount, path
  revalidation and the statfs(2) system call. This option cuts
  redundant round trip traffic (opens and closes) by simply keeping
  the directory handle for the root around once opened.

nohandlecache
  Disable caching of the share root directory handle.

handletimeout=arg
  The time (in milliseconds) for which the server should reserve the handle after
  a failover waiting for the client to reconnect.  When mounting with
  resilienthandles or persistenthandles mount option, or when their use is
  requested by the server (continuous availability shares) then this parameter
  overrides the server default handle timeout (which for most servers is 120 seconds).

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 Services for Mac. 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.

mapposix
  Translate reserved characters similarly to ``mapchars`` but use the
  mapping from Microsoft "Services For Unix".

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. The encryption algorithm used
  is AES-128-CCM. Requires SMB3 or above (see ``vers``).

rdma
  Connect directly to the server using SMB Direct via a RDMA
  adapter. Requires SMB3 or above (see ``vers``).

resilienthandles
  Enable resilient handles. If the server supports it, keep opened
  files across reconnections. Requires SMB2.1 (see ``vers``).

noresilienthandles
  (default) Disable resilient handles.

persistenthandles
  Enable persistent handles. If the server supports it, keep opened
  files across reconnections. Persistent handles are also valid across
  servers in a cluster and have stronger guarantees than resilient
  handles. Requires SMB3 or above (see ``vers``).

nopersistenthandles
  (default) Disable persistent handles.

snapshot=time
   Mount a specific snapshot of the remote share. ``time`` must be a
   positive integer identifying the snapshot requested (in 100-nanosecond
   units that have elapsed since January 1, 1601, or alternatively it can
   be specified in GMT format e.g. @GMT-2019.03.27-20.52.19). Supported
   in the Linux kernel starting from v4.19.

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
  Do not use POSIX locks even when available via unix
  extensions. Always use cifs style mandatory locks.

locallease
  Check cached leases locally instead of querying the server.

sfu
  When the CIFS or SMB3 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.

echo_interval=n
  sets the interval at which echo requests are sent to the server on an
  idling connection. This setting also affects the time required for a
  connection to an unresponsive server to timeout. Here n is the echo
  interval in seconds. The reconnection happens at twice the value of the
  echo_interval set for an unresponsive server.
  If this option is not given then the default value of 60 seconds is used.
  The minimum tunable value is 1 second and maximum can go up to 600 seconds.

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.

posix|unix|linux
  (default) Enable Unix Extensions for this mount. Requires CIFS
  (vers=1.0) or SMB3.1.1 (vers=3.1.1) and a server supporting them.

noposix|nounix|nolinux
  Disable the 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.

nodfs
  Do not follow Distributed FileSystem referrals. IO on a file not
  stored on the server will fail instead of connecting to the target
  server transparently.

noautotune
  Use fixed size for kernel recv/send socket buffers.

nosharesock
  Do not try to reuse sockets if the system is already connected to
  the server via an existing mount point. This will make the client
  always make a new connection to the server no matter what he is
  already connected to. This can be useful in simulating multiple
  clients connecting to the same server, as each mount point
  will use a different TCP socket.

noblocksend
  Send data on the socket using non blocking operations (MSG_DONTWAIT flag).

rsize=bytes
  Maximum amount of data that the kernel will request in a read request
  in bytes. Maximum size that servers will accept is typically 8MB for SMB3
  or later dialects. Default requested during mount is 4MB. Prior to the 4.20
  kernel the default requested was 1MB. Prior to the SMB2.1 dialect the
  maximum was usually 64K.

wsize=bytes
  Maximum amount of data that the kernel will send in a write request in
  bytes. Maximum size that servers will accept is typically 8MB for SMB3
  or later dialects. Default requested during mount is 4MB. Prior to the 4.20
  kernel the default requested was 1MB. Prior to the SMB2.1 dialect the
  maximum was usually 64K.

bsize=bytes
  Override the default blocksize (1MB) reported on SMB3 files (requires
  kernel version of 5.1 or later). Prior to kernel version 5.1, the
  blocksize was always reported as 16K instead of 1MB (and was not
  configurable) which can hurt the performance of tools like cp and scp
  (especially for uncached I/O) which decide on the read and write size
  to use for file copies based on the inode blocksize. bsize may not be
  less than 16K or greater than 16M.

max_credits=n
  Maximum credits the SMB2 client can have. Default is 32000. Must be
  set to a number between 20 and 60000.

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