Provided by: cifs-utils_6.8-1_amd64 bug

NAME

       mount.cifs - mount using the Common Internet File System (CIFS)

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|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.

       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|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.

       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).   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.

       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.

              · 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.

              The default since v4.13.5 is for the client and server  to  negotiate  the  highest
              possible  version  greater  than  or  equal  to 2.1. In kernels prior to v4.13, the
              default was 1.0. For kernels between v4.13 and v4.13.5 the default is 3.0.

       --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.

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 ownership 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 Backup Operators group, 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 matching 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 uid's and gid's 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, it's 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.

       It's also possible to override permission checking on the client altogether via the noperm
       option. Server-side permission checks cannot be overridden. 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 noexec
       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 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.

                                                                                    MOUNT.CIFS(8)