Forgot what package(s) needed to be installed but this is the command:
$ sudo mount -t cifs -o username=<your-username> //<server>/<share> /mnt/<your-dir>
# ^^^^^^^^^^^^^
After installing the cifs-utils package:
# VVVVVVVVVV
sudo mount.cifs //<server>/<share> /run/mount/<your-dir> -o username=<your-username>
uid) and not rootWithout any extra options, the mounted CIFS shares
will take the permissons of the user the share is
mounted with (which is usually root via sudo).
Also, a reminder because I was an idiot:
Options to mount.cifs are specified as a comma-separated list of key=value pairs.
The man mount.cifs is not long (see at the very
end because this is the NixOS-specific command), and
mount.cifs provides the uid option:
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 informa‐ tion.
It does accept a string, but numeric uid are
always a safe bet to use instead. To look mine up
I simply used the -n switch for ls on any
directory/file my user owns.
Finally, the command is:
sudo mount.cifs //<server>/<share> <mountpoint> \
-o username=<cifs-user>,uid=<linux-user-uid>
Using sudo umount <mountpount> did the trick, but read about a lot of issues, and usually sudo umount -l <mountpoint> worked.
man mount.cifsCaptured with the Vim command
:r!MANWIDTH=72 man --ascii mount.cifs | col -band on how to capture
manpages without the annoying control characters, read this: Save a Unix manpage as plain text
MOUNT.CIFS(8) MOUNT.CIFS(8)
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 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 appli‐
ances 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 spec‐
ify the username in a user%password or workgroup/user or
workgroup/user%password to allow the password and work‐
group 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 dis‐
crete 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 recom‐
mended 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 pass‐
word, unless the guest option is specified.
Note that a password which contains the delimiter char‐
acter (i.e. a comma ',') will fail to be parsed cor‐
rectly on the command line. However, the same password
defined in the PASSWD environment variable or via a cre‐
dentials 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 pass‐
word and optionally the name of the workgroup. The for‐
mat 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 de‐
fault is uid 0troff: <standard input>:473: warning [p 8, 0.3i]: can't break line
. The mount.cifs helper must be at version
1.10 or higher to support specifying the uid in non-nu‐
meric form. See the section on FILE AND DIRECTORY OWNER‐
SHIP 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 creden‐
tials 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 de‐
fault is gid 0. The mount.cifs helper must be at version
1.10 or higher to support specifying the gid in non-nu‐
meric form. See the section on FILE AND DIRECTORY OWNER‐
SHIP 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 PER‐
MISSIONS 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 net‐
bios 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 au‐
tomatically 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 do‐
main via domain, guess the domain from the server NTLM
challenge. This behavior used to be the default on ker‐
nels 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 lo‐
cal 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, di‐
rectories, and devices (create, mkdir, mknod). If the
CIFS Unix Extensions are not negotiated, for newly cre‐
ated 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 de‐
fault. 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 op‐
eration), Note that this is in addition to the normal
ACL check on the target machine done by the server soft‐
ware. 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 lo‐
cal 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 permis‐
sions in memory that can't be stored on the server. This
information can disappear at any time (whenever the in‐
ode 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 la‐
tency, 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 traf‐
fic (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 resilien‐
thandles or persistenthandles mount option, or when
their use is requested by the server (continuous avail‐
ability 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 applica‐
tions 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 for‐
bids 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 charac‐
ters.
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. Set‐
ting POSIX ACLs requires enabling both CIFS_XATTR and
then CIFS_POSIX support in the CIFS configuration op‐
tions 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, SECU‐
RITY 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 sensi‐
tive 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 en‐
able 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 negotia‐
tion, then it may be enabled automatically. Packet sign‐
ing may also be enabled automatically if it's enabled in
/proc/fs/cifs/SecurityFlags.
seal Request encryption at the SMB layer. The encryption al‐
gorithm 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 han‐
dles 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 ex‐
tensions. 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 negoti‐
ated, attempt to create device files and fifos in a for‐
mat compatible with Services for Unix (SFU). In addition
retrieve bits 10-12 of the mode via the SETFILEBITS ex‐
tended 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 sym‐
links and be able to create symlinks in an SFU interop‐
erable 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 af‐
fects the time required for a connection to an unrespon‐
sive 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 generat‐
ing 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 in‐
ode 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 direc‐
tory). 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. Re‐
quires 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, sym‐
link 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 con‐
necting 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 con‐
necting 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. De‐
fault 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. De‐
fault 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 (espe‐
cially 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 scalabil‐
ity positively as the number of calls to the server are
reduced. But, be warned that local caching is not suit‐
able for all workloads, for e.g., read-once type work‐
loads. So, you need to consider carefully the situa‐
tion/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 ker‐
nels 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 opera‐
tional.
multiuser
Map user accesses to individual credentials when access‐
ing the server. By default, CIFS mounts only use a sin‐
gle 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 cre‐
dentials. Because the kernel cannot prompt for pass‐
words, 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 pre‐
sented as the current user accessing the share.
actimeo=arg
The time (in seconds) that the CIFS client caches at‐
tributes of a file or directory before it requests at‐
tribute 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 sec‐
ond. 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 time‐
outs 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 in‐
troduced 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 Mi‐
crosoft Windows 7 and Windows Server 2008R2.
• 3.0 - The SMBv3.0 protocol that was introduced in Mi‐
crosoft Windows 8 and Windows Server 2012.
• 3.02 or 3.0.2 - The SMBv3.0.2 protocol that was intro‐
duced in Microsoft Windows 8.1 and Windows Server
2012R2.
• 3.1.1 or 3.11 - The SMBv3.1.1 protocol that was intro‐
duced in Microsoft Windows 10 and Windows Server 2016.
• 3 - The SMBv3.0 protocol version and above.
• default - Tries to negotiate the highest SMB2+ version
supported by both the client and server.
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 de‐
fault 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 delim‐
iter 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 num‐
ber 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 in‐
ode number.
Note that the UniqueID is a different value from the server in‐
ode 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_OFF‐
SET_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 with‐
out 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 pro‐
tocols 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 in‐
teract 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. Addi‐
tionally, 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 at‐
tempt to flush the cache soon after a write to a file. Note
that that flush does not necessarily occur before a write sys‐
tem 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 prob‐
lematic with CIFS. Windows is quite "lazy" with respect to up‐
dating 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 Se‐
curity 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 mod‐
ule.
A CIFS/NTFS ACL is mapped to file permission bits using an al‐
gorithm 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 re‐
quest-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 setcif‐
sacl(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 win‐
bind 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 deter‐
mined 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 pur‐
pose 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 at‐
tempts 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, can‐
not 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 Opera‐
tors 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 back‐
upgid 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 informa‐
tion 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 permis‐
sions 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 permis‐
sions.
When unix extensions are not negotiated, it's also possible to
emulate them locally on the server using the dynperm mount op‐
tion. When this mount option is in effect, newly created files
and directories will receive what appear to be proper permis‐
sions. 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 user‐
name%password.
The variable PASSWD may contain the password of the person us‐
ing 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 and performance statistics. There are additional
startup options such as maximum buffer size and number of buf‐
fers 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. When configuring dynamic tracing (trace-cmd)
note that the list of SMB3 events which can be enabled can be
seen at: /sys/kernel/debug/tracing/events/cifs/.
SECURITY
The use of SMB2.1 or later (including the latest dialect
SMB3.1.1) is recommended for improved security and SMB1 is no
longer requested by default at mount time. Old dialects such as
CIFS (SMB1, ie vers=1.0) have much weaker security. Use of CIFS
(SMB1) can be disabled by modprobe cifs disable_legacy_di‐
alects=y.
BUGS
Mounting using the CIFS URL specification is currently not sup‐
ported.
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 2.18 of the cifs vfs
filesystem (roughly Linux kernel 5.0).
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 in‐
formation.
AUTHOR
Steve French
The maintainer of the Linux cifs vfs is Steve French. The main‐
tainer of the cifs-utils suite of user space tools is Pavel
Shilovsky. The Linux CIFS Mailing list is the preferred place
to ask questions regarding these programs.
MOUNT.CIFS(8)