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:

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 CONFIG_CIFS_XATTR and then CONFIG_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:

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.

nolease

Do not request lease/oplock when openning a file on the server. This turns off local caching of IO, byte-range lock and read metadata operations (see actimeo for more details about metadata caching). Requires SMB2 and above (see vers).

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). 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 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.

acregmax=arg

The maximum time (in seconds) that the CIFS client caches attributes of a regular file before it requests fresh attribute information from a server. If this option is not specified, then acregmax value will be set to actimeo value, see actimeo for more details.

acdirmax=arg

The maximum time (in seconds) that the CIFS client caches attributes of a directory before it requests fresh attribute information from a server. If this option is not specified, then acdirmax value will be set to actimeo value, see actimeo for more details.

multichannel

This option enables multichannel feature. Multichannel is an SMB3 protocol feature that allows client to establish multiple transport connections to an SMB server and bind them into a single authenticated SMB session. This feature enhances fault tolerance and increases throughput by distributing traffic across several connections. With this mount option default is to use two channels if the server supports multichannel. The max_channels parameter can be specified if you desire to use more than two channels.

max_channels=arg

This option is applicable while using multichannel feature. max_channels option allows the user to specify the number of transport connections that should be establised between client and server up to a limit of 16. Using this option implicitly enables the multichannel feature. If max_channels option not specified, multichannel feature defaults to using 2 connections.

closetimeo=arg

The maximum time (in seconds) that the CIFS client defers sending the final SMB3 close when the client has a handle lease on the file.

By default, closetimeo is set to 1 second and can hold values between 0 and a maximum value of 2^30 * HZ.

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 .

compress

EXPERIMENTAL FEATURE Enables over-the-wire message compression for SMB 3.1.1 or higher mounts. Mount fails when compress is on and vers is set to a version lower than 3.1.1.

vers=arg

SMB protocol version. Allowed values are:

If no dialect is specified on mount vers=default is used. To check Dialect refer to /proc/fs/cifs/DebugData

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.

sloppy

Allows the system to ignore any unrecognized mount options that follow this option instead of failing to mount altogether.

--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

• a kernel upcall to the cifs.idmap utility set up via request-key.conf(5)
• winbind or sssd support configured via nsswitch.conf(5)

• 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 or sssd 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.