mount.smb3 error 0xc00000bb STATUS_NOT_SUPPORTED

mount.smb3 error 0xc00000bb STATUS_NOT_SUPPORTED

[John Kendall]

I hope this is a quick one. Thanks in advance.
John



kernel
5.14.0-611.30.1.el9_7.x86_64

= = = = = = = = = = = =

smbclient command (v4.22.4)
smbclient -A /etc/silomountuserpw //silo-azwest-fs.verqhaus.com/Invoices <http://cai-azwest-fs.capps.com/Invoices>

works!

= = = = = = = = = = = =


mount command (v7.2)
mount --verbose -t smb3 //silo-azwest-fs.verqhaus.com/Invoices /mnt -o cred=/etc/silomountuserpw

returns:
Host "silo-azwest-fs.verqhaus.com" resolved to the following IP addresses: 10.4.0.37
mount.smb3 kernel mount options: ip=10.4.0.37,unc=\\silo-azwest-fs.verqhaus.com\Invoices,user=silomountuser@verqhaus.com,domain=verqhaus.com,pass=********
mount error(95): Operation not supported
Refer to the mount.smb3(8) manual page (e.g. man mount.smb3) and kernel log messages (dmesg)


dmesg output with debuggin turned on:

[ 9733.032860] CIFS: fs/smb/client/fs_context.c: CIFS: parsing cifs mount option 'source'
[ 9733.032902] CIFS: fs/smb/client/fs_context.c: CIFS: parsing cifs mount option 'ip'
[ 9733.032914] CIFS: fs/smb/client/fs_context.c: CIFS: parsing cifs mount option 'unc'
[ 9733.032919] CIFS: fs/smb/client/fs_context.c: CIFS: parsing cifs mount option 'user'
[ 9733.032922] CIFS: fs/smb/client/fs_context.c: CIFS: parsing cifs mount option 'domain'
[ 9733.032925] CIFS: fs/smb/client/fs_context.c: Domain name set
[ 9733.032928] CIFS: fs/smb/client/fs_context.c: CIFS: parsing cifs mount option 'pass'
[ 9733.032931] CIFS: fs/smb/client/cifsfs.c: cifs_smb3_do_mount: devname=//silo-azwest-fs.verqhaus.com/Invoices flags=0x0
[ 9733.032937] CIFS: fs/smb/client/connect.c: file mode: 0755  dir mode: 0755
[ 9733.032942] CIFS: fs/smb/client/connect.c: VFS: in cifs_mount_get_session as Xid: 105 with uid: 0
[ 9733.032947] CIFS: fs/smb/client/connect.c: UNC: \\silo-azwest-fs.verqhaus.com\Invoices
[ 9733.032951] CIFS: fs/smb/client/connect.c: generic_ip_connect: connecting to 10.4.0.37:445
[ 9733.032963] CIFS: fs/smb/client/connect.c: Socket created
[ 9733.032966] CIFS: fs/smb/client/connect.c: sndbuf 16384 rcvbuf 131072 rcvtimeo 0x1b58
[ 9733.035235] CIFS: fs/smb/client/connect.c: VFS: in cifs_get_smb_ses as Xid: 106 with uid: 0
[ 9733.035241] CIFS: fs/smb/client/connect.c: Existing smb sess not found
[ 9733.035244] CIFS: fs/smb/client/connect.c: Demultiplex PID: 97842
[ 9733.035251] CIFS: fs/smb/client/smb2pdu.c: Negotiate protocol
[ 9733.035259] CIFS: fs/smb/client/transport.c: wait_for_free_credits: remove 1 credits total=0
[ 9733.035271] CIFS: fs/smb/client/transport.c: Sending smb: smb_len=260
[ 9733.035925] CIFS: fs/smb/client/connect.c: RFC1002 header 0x134
[ 9733.035937] CIFS: fs/smb/client/smb2misc.c: SMB2 data length 120 offset 128
[ 9733.035940] CIFS: fs/smb/client/smb2misc.c: SMB2 len 248
[ 9733.035944] CIFS: fs/smb/client/smb2misc.c: length of negcontexts 60 pad 0
[ 9733.035948] CIFS: fs/smb/client/smb2ops.c: smb2_add_credits: added 1 credits total=1
[ 9733.035973] CIFS: fs/smb/client/transport.c: cifs_sync_mid_result: cmd=0 mid=0 state=64
[ 9733.035986] CIFS: fs/smb/client/misc.c: Null buffer passed to cifs_small_buf_release
[ 9733.035995] CIFS: fs/smb/client/smb2pdu.c: mode 0x3
[ 9733.035997] CIFS: fs/smb/client/smb2pdu.c: negotiated smb3.1.1 dialect
[ 9733.036006] CIFS: fs/smb/client/asn1.c: Decoding negTokenInit: unsupported OID 1.3.6.1.4.1.311.2.2.30
[ 9733.036015] CIFS: fs/smb/client/smb2pdu.c: decoding 2 negotiate contexts
[ 9733.036020] CIFS: fs/smb/client/smb2pdu.c: decode SMB3.11 encryption neg context of len 4
[ 9733.036034] CIFS: fs/smb/client/smb2pdu.c: SMB311 cipher type:2
[ 9733.036046] CIFS: fs/smb/client/connect.c: cifs_setup_session: channel connect bitmap: 0x1
[ 9733.036052] CIFS: fs/smb/client/connect.c: Security Mode: 0x3 Capabilities: 0x300067 TimeAdjust: 0
[ 9733.036055] CIFS: fs/smb/client/smb2pdu.c: Session Setup
[ 9733.036060] CIFS: fs/smb/client/smb2pdu.c: sess setup type 2
[ 9733.036064] CIFS: fs/smb/client/smb2pdu.c: Fresh session. Previous: 0
[ 9733.036068] CIFS: fs/smb/client/transport.c: wait_for_free_credits: remove 1 credits total=0
[ 9733.036076] CIFS: fs/smb/client/transport.c: Sending smb: smb_len=136
[ 9733.036557] CIFS: fs/smb/client/connect.c: RFC1002 header 0x11c
[ 9733.036581] CIFS: fs/smb/client/smb2misc.c: SMB2 data length 212 offset 72
[ 9733.036597] CIFS: fs/smb/client/smb2misc.c: SMB2 len 284
[ 9733.036613] CIFS: fs/smb/client/smb2ops.c: smb2_add_credits: added 1 credits total=1
[ 9733.036655] CIFS: fs/smb/client/transport.c: cifs_sync_mid_result: cmd=1 mid=1 state=64
[ 9733.036678] CIFS: Status code returned 0xc0000016 STATUS_MORE_PROCESSING_REQUIRED
[ 9733.036694] CIFS: fs/smb/client/smb2maperror.c: Mapping SMB2 status code 0xc0000016 to POSIX err -5
[ 9733.036704] CIFS: fs/smb/client/misc.c: Null buffer passed to cifs_small_buf_release
[ 9733.036709] CIFS: fs/smb/client/sess.c: decode_ntlmssp_challenge: negotiate=0xe2088235 challenge=0xe2898235
[ 9733.036715] CIFS: fs/smb/client/smb2pdu.c: rawntlmssp session setup challenge phase
[ 9733.036719] CIFS: fs/smb/client/smb2pdu.c: Fresh session. Previous: 0
[ 9733.036762] CIFS: fs/smb/client/transport.c: wait_for_free_credits: remove 1 credits total=0
[ 9733.036777] CIFS: fs/smb/client/transport.c: Sending smb: smb_len=508
[ 9733.041144] CIFS: fs/smb/client/connect.c: RFC1002 header 0x48
[ 9733.041219] CIFS: fs/smb/client/smb2misc.c: SMB2 data length 0 offset 0
[ 9733.041224] CIFS: fs/smb/client/smb2misc.c: SMB2 len 73
[ 9733.041249] CIFS: fs/smb/client/smb2ops.c: smb2_add_credits: added 1 credits total=1
[ 9733.041294] CIFS: fs/smb/client/transport.c: cifs_sync_mid_result: cmd=1 mid=2 state=64
[ 9733.041315] CIFS: Status code returned 0xc00000bb STATUS_NOT_SUPPORTED
[ 9733.041330] CIFS: fs/smb/client/smb2maperror.c: Mapping SMB2 status code 0xc00000bb to POSIX err -95
[ 9733.041334] CIFS: fs/smb/client/misc.c: Null buffer passed to cifs_small_buf_release
[ 9733.041339] CIFS: VFS: \\silo-azwest-fs.verqhaus.com Send error in SessSetup = -95
[ 9733.041345] CIFS: fs/smb/client/connect.c: VFS: leaving cifs_get_smb_ses (xid = 106) rc = -95
[ 9733.041367] CIFS: fs/smb/client/connect.c: VFS: leaving cifs_mount_put_conns (xid = 105) rc = 0
[ 9733.041371] CIFS: VFS: cifs_mount failed w/return code = -95

Re: mount.smb3 error 0xc00000bb STATUS_NOT_SUPPORTED

[John Kendall]

Steve,
The server is Windows Server 2019. I was able to determine, with a lot of help from Paulo, that the server was (suddenly) not accepting any version of NTLM, leaving kerberos as the only option. I was not aware of new efforts to harden AD that includes shutting down all NTLM and allowing only kerberos.

So my mount.cifs issue is solved.

Thanks,
John





> On Feb 23, 2026, at 4:53 PM, Steve French <smfrench@gmail.com> wrote:
> 
> What is server type? Is it possible that it is failing because of Kerberos vs ntlmv2? Have you compared the Wireshark trace of success vs failure? Does it work fine to your server with a modern client (5.14 kernel is five years old)? Did it used to work on your client and recent stable kernel patch regress it?
> 
> Thanks,
> 
> Steve