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List:       samba
Subject:    [Samba] SMB3 Unix Extensions - creating special files
From:       Matthew Richardson via samba <samba () lists ! samba ! org>
Date:       2025-07-29 14:21:39
Message-ID: 1124e7cd-6a46-40a6-9f44-b7664a66654b () ed ! ac ! uk
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Hi,

I'm currently investigating using the smb3 unix extensions. I can 
list/stat special files in the samba mount, and can create and delete 
'ordinary' files, but when I try to create special files I get an error:

$ ln -s b.txt sym_b
ln: failed to create symbolic link 'a.sym': Operation not supported

or

$ mkfifo b.fifo
mkfifo: cannot create fifo 'b.fifo': Operation not supported


My test setup is as follows:

Samba - Docker samba.org/samba-server:devbuilds-centos-amd64 (publishing 
to host port 445)
Host Ubuntu Noble with kernel 6.15.7 (cifs.ko v2.54)
cifs-utils v7.0


Samba config:

[global]
    workgroup = WORKGROUP
    security = user
    map to guest = never
    log level = 3
    guest ok = no
    smb3 unix extensions = yes

[myshare]
    path = /opt/smb
    browsable = yes
    writable = yes
    read only = no
    valid users = sambauser #uid/gid 1000
    create mask = 0777
    directory mask = 0777


I'm mounting the share as follows:

mount -t cifs //localhost/myshare /mnt -o 
user=sambauser,pass=samba,unix,uid=1000,gid=1000

Resulting in mount:
//localhost/myshare on /mnt type cifs 
(rw,relatime,vers=3.1.1,cache=strict,upcall_target=app,username=sambauser,uid=1000,for \
ceuid,gid=1000,forcegid,addr=127.0.0.1,file_mode=0755,dir_mode=0755,soft,posix,posixpa \
ths,serverino,mapposix,reparse=nfs,nativesocket,symlink=unix,rsize=4194304,wsize=4194304,bsize=1048576,retrans=1,echo_interval=60,actimeo=1,closetimeo=1)


There's nothing immediately obvious in the server logs which might add 
more information.

I'm not sure if I'm missing something in my config that is limiting the 
creation of special files, or if this is a limitation in the current 
development of the smb3 unix extensions code, and I just need to be patient.

Any advice appreciated!

Thanks,

Matthew


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