From SambaWiki

Linux Kernel SMB3/CIFS Client

The Linux cifs kernel client has been included in the kernel since kernel version 2.5.42. For improved security and performance, SMB3 is the now the default dialect (SMB3.02/SMB3/SMB2.1 dialects are requested by default). CIFS protocol (and other old dialects) can be selected (by specifying "vers=1.0" or "vers=2.02" in the mount options for example). The newest, most secure dialect, SMB3.11 can also be requested (vers=3.1.1).

If you want to try current SMB3 support on an older kernel, full backports of all SMB3/CIFS fixes to earlier kernel versions can be found at:

Changes by release

5.3-rc kernel (module version will be 2.21, 45+ changesets)

Includes improved cross-mount server side copy (copy offload). Performance of large file I/O over encrypted shares increased dramatically (more than doubled in many cases for large reads and writes) with addition of "GCM" encryption support (and GCM is negotiated by default). Remove unneeded ifdef for CONFIG_CIFS_ACL (always enabled now). Performance of file open improved (reduced network roundtrips from three requests to two). New netname negotiate context sent when sessions are established with a server (may be useful for load balancers in the future). SMBDIRECT (SMB3 over RDMA) is no longer experimental.

5.2 kernel (module version 2.20 64 changesets)

Sparse file support improved (fiemap now can query allocated ranges which can help common Linux commands like "cp", and support added for SEEK_HOLE and SEEK_DATA). "FSCTL passthrough" improved - now can support cases where user space tools need to write data over an SMB3 fsctl. Improvements to smbdirect (SMB3 over RDMA) support.

5.1 kernel (86 changesets)

"FSCTL passthrough" improved allowing user space tools like smbinfo in cifs-utils to query any available info via SMB3 fsctl or SMB3 query info requests. Net mount parm "handletimeout" added to allow persistent/resilient handle timeouts to be configurable. Added ability for fallocate "zero range" to expand a file. Performance improved - FILE_ALL_INFO cached for shared root file handle. default inode block size report now as 1MB. Guest mounts now supported on SMB3.1.1 dialect. Many dynamic trace points added for easier debugging and analysis. Many important fixes for "crediting" (SMB3 flow control)

5.0 kernel (module version 2.17 82 changesets)

SMB3.1.1 dialect requested by default (added to the list of negotiated dialects) Reconnect possible to server even if its IP address changes (requires the user to install the updated cifs-utils package as well). Major improvements to DFS caching and reconnect (global name space). Failover is now possible to alternate targets. Performance improvements (compounding) for get/set extended attributes. Many critical bug fixes for 'crediting' (SMB3 flow and control) including reducing reconnects, and fixing large file copy in cases where the network connection is slow or interrupted. Add key for OFD lock support.

4.20 Kernel (70 changesets)

Large performance improvement in some common operations: stat, create, unlink, mkdir, rmdir, setinfo (due to adding more support for the SMB3 "compounding" feature). I/O size that client requests has increased (rsize/wsize) from 1MB to 4MB which improves performance to many servers. Fix Kerberos mounts to Azure (cloud). Improve performance of direct i/o read and write. Add passthrough ioctl to allow querying additional metadata information (ie send any SMB3 infolevel) from server (this features is needed for the newly updated smbinfo (see its man page in the cifs-utils package for more information) tool to allow it to query SMB3 metadata, ACLs, quotas better and display this information to users). Add additional tracepoints for improved debugging.

4.19 Kernel (69 changesets, module version 2.13)

Allow cifs.ko to be built with insecure dialects disabled (vers=1.0 and vers=2.0 not allowed). Add support for snapshot mounts (specifying "snapshot=

4.18 Kernel (90 changesets, module version 2.12)

Add "smb3" alias to cifs.ko ("insmod smb3" and "mount -t smb3 ...") and make it easier to disable less secure dialects, disable cifs dialect if mounting with "-t smb3" Add support for improved tracing (ftrace, trace-cmd) Cache root file handle (with a directory lease), reduce redundant opens, improving performance. RDMA improvements for direct i/o Experimental posix extensions for SMB3.1.1 (mount option "posix")

4.17 Kernel (56 changesets)

SMB3.1.1 support (most secure authentication) improved and no longer marked experimental. SMB3.1.1 Encryption. SMB3.1.1 Preauth integrity Add signing support for SMB Direct. Bug fixes.

4.16 Kernel (66 changesets)

RDMA support (SMB Direct, limited to one adapter). sendfile (and splice write) performance improvement. Bug fixes.

4.15 Kernel (6 changesets)

Bug fixes.

4.14 Kernel (37 changesets)

Add support for getting and setting xattrs over SMB3. Multidialect support now the default (SMB2.1 and later, SMB3, SMB3.02). Bugfixes (including more improvements to reconnection scenarios. Fixes for "validate negotiate" SMB3 security feature).

4.13 Kernel (24 changesets)

Default dialect changed to SMB3 (from CIFS). SMB3 support added for "cifsacl" mount option (and can now emulate retrieving mode from ACL in SMB3). Bug fixes.

4.12 Kernel (36 changesets)

SMB3 mapping of illegal (in SMB3/Windows but legal in POSIX) characters improved. Improved AIO support. Add support for enumerating snapshots. Misc. bug fixes.

4.11 Kernel (47 changesets) VERY IMPORTANT update

SMB3 Reconnect improvements (persistent and durable handle fixes). Much higher reliability when server crashes while I/O in flight or cached. Server side copy enabled in more cases (clone file range and "cp --reflink" now support the commonly implemented "copychunk" API not just servers which support "duplicate extents"). SMB3 DFS support added (global name space). SMB3 Encryption support added (can mount encrypted shares).

4.10 Kernel (14 changesets)

Misc. bug fixes

4.9 Kernel (32 changesets)

Various reconnect improvements (e.g. sends "echo" request sooner after socket reconnect to better tell when server comes back up). Add way to query file attributes (cifs.dosattrib) and creation time (cifs.creationtime) via Linux xattrs. New mount option "idsfromsid" to let cifs.ko retrieve the uid and gid owner fields from special sids (in the ACL). Can override number of credits (new mount option "max_credits"). Various bug fixes (including DFS fix).

4.8 Kernel (14 changesets)

Allow mounts with prefixpath where top of share unaccessible. Fix for file create when existing directory of the same name exists. Add mfsymlink support for SMB2.0 (symlink emulation, also used by the Mac). Various bug fixes.

4.7 Kernel (44 changesets)

Fix badlock regression for guest mounts (mount with -o guest can fail to Samba servers when patched for badlock). Cifs.ko version updated to 2.09. Minor fixes: including NetApp DFSpathname issue and SPNEGO fix. Persistent handle reconnect fixes

4.6 Kernel

Minor bug fixes

4.5 Kernel

Minor bug fixes. clone_file_range added to vfs, cifs support for clone_file_range changed ("cp --reflink ..." now requires duplicate_extents support in server e.g. Windows 2016 REFS, and the older ioct, used e.g. by the "cloner" tool, can use the more broadly supported "CopyChunk"). Allow file open O_DIRECT with cache=loose. Make echo interval tunable (to improve server failure detection in unusual network configurations). First phase of SMB3 per-share encryption support begun (not complete in 4.5).

4.4 Kernel

Allow copy offload across shares. Add resilient and persistent handle mount options ("-o resilienthandles" and "-o persistenthandles") and support for the create context (durable v2)

4.3 Kernel

Minor bug fixes (including Mac authentication issue when timestamps differ too much on server/client). Add krb5 support for smb3 (mount sec=krb5 for SMB3 e.g. vers=3.02, not just for cifs). Cifs.ko version updated to 2.08. Added ioctl to query detailed fs info on mounted share

4.2 Kernel

Partial support for SMB 3.1.1 (Windows 10) dialect support (will improve security when complete). Faster copy offload (REFLINK, duplicate_extents) added for Windows Server 2016 when target file system is REFS (cp --reflink to REFS exported shares is much faster).

4.1 Kernel

Mapchars fix, fix to allow Unicode surrogate pairs (improved character conversion for some Asian languages), DFS fix, inode number reuse fix

4.0 Kernel

Fix copy offload (clone range) bug, and find_writable_file bug

3.19 Kernel (cifs.ko module version 2.06)

Fix Oplock bug, inode caching bug and ioctl clone bug Fix conflicts between SecurityFlags (which allowed CONFIG_MUST_LANMAN and CONFIG_MUST_PLNTXT to get cleared when set to non-default values)

3.18 Kernel

Add mfsymlink (emulated symlink) support for SMB3 mounts Add optional support for "sfu" style FIFO and device file emulation for SMB3 (when "sfu" is specific on an SMB3 mount) By default support mapchars ('SFM' style remapping, ie the same way the Mac remaps them) for the seven reserved characters (*, ?, : etc.) when mounting with SMB3. Workaround Unix Extensions problem on cifs mounts to Mac servers.

3.17 Kernel

SMB3 large read/write support much faster (including SMB3 multicredit support) Many SMB3 stability fixes directio allowed on "cache=strict" mounts Added fallocate/sparse file support for SMB3 Fixed SMB2.1 mounts to MacOS servers

3.16 Kernel

Allow multiple mounts to the same server with different dialects Rewrote authentication support to improve GSSAPI support Fix mapchars (which allows use of reserved characters like ':' ion paths) to work over SMB3, not just cifs, mounts

3.15 Kernel

Bug fixes (aio/write, append, xattrs, metadata caching)


Bug Fixes (including SMB3 large write fix, and fix DFS refererals when mounted to Samba with Unix Extensions). Security fix for illegal aio write request


Added support for setting/getting per-file compression ("chattr +c /mnt/filename") CIFS and SMB2/SMB3 CopyChunk (server side copy offload support added) Support for O_DIRECT on "cache=none" mounts (specsfs support) Secure negotiate support (SMB3 downgrade attack protection)


Multiuser SMB3 signing now possible SMB2/SMB3 symlinks SMB2.1 Lease (client caching) == 3.11 SMB3 signing (not multiuser) Authentication overhaul SMB2 Durable handle (improved data integrity) SMB3.02 dialect added


cifs.ko module size reduced nosharesock mount option added


Bug fixes (rename fix, dfs security fix)


default authentication mechanism strengthened, moved to ntlmv2 (ntlmv2 in ntlmssp) smb2.02 support added


SMB2.1 support added


"cache=" mount option needed (making forcedirectio and strictcache mount options obsolete)


'Faster read ahead performance'. Also can allow many more requests in flight for cifs dialect (if server sets maximum multiplex requests above the default, client will now honor it even if more than 50 at one time). Support for "sloppy" mount option.