Curtis McEnroe

Sharing Files with macOS from FreeBSD with SMB and mDNS Service Discovery

This is an explanation of one way of sharing files with Mac OS X 10.11 El Capitan from FreeBSD 11.0. It uses Samba, an implementation of the SMB protocol, and Apple’s mDNSResponder for service discovery. Alternatives are listed at the end.

Background

SMB is the protocol used for file sharing between Windows systems. Mac systems previously used their own Apple Filing Protocol, but deprecated it in favour of SMB with Mac OS X 10.9 Mavericks.

mDNS, or multicast DNS, is a technology for resolving host names in a local network. On top of this, DNS service discovery, or DNS-SD, can be used to broadcast available services, such as SMB. This is how Finder discovers hosts to show in “Shared” or “Network.”

Samba

First, install Samba. There are two versions available in FreeBSD. This is the newer one.

pkg install samba42

Next, configure it with /usr/local/etc/smb4.conf. The manual page smb.conf(5) suggests a basic configuration allowing users to access their home directories.

[homes]
read only = no

Additional shared directories can be added, such as the downloads directory of the Transmission daemon.

[Downloads]
path = /usr/local/etc/transmission/home/Downloads
read only = yes

In order to allow users to log in over SMB, give them a password with smbpasswd as root.

smbpasswd -a curtis

Now, enable and start the Samba server.

echo 'samba_server_enable="YES"' >> /etc/rc.conf
service samba_service start

At this point, it should be possible to connect manually from Finder’s “Connect to Server…” by typing, for example, smb://192.168.0.101/Downloads and authenticating with username and password.

mDNSResponder

Install mDNSResponder, Apple’s implementation of mDNS and DNS-SD.

pkg install mDNSResponder

Unfortunately, this software is poorly documented and the mdnsd binary does not seem to work. However, the package also provides mDNSResponderPosix, which is targeted at embedded systems and is a bit less opaque.

Given no arguments, mDNSResponderPosix exits with an error, so configure /etc/rc.conf to pass it a configuration file.

mdnsresponderposix_enable="YES"
mdnsresponderposix_flags="-f /usr/local/etc/mdnsresponderposix.conf"

The format of the file does not seem to be documented, but it can be inferred by reading RegisterServicesInFile in mDNSPosix/Responder.c. The function reads newline-separated service name, type, port, and optional text records. Each service is separated by a blank line.

To broadcast the SMB service from a host named “thursday”, add the following to /usr/local/etc/mdnsresponderposix.conf.

thursday
_smb._tcp
445

Now start the service and Finder should find the shared directories. You may have to click “Connect As…” to enter your credentials the first time.1

service mdnsresponderposix start

Finder showing shared directories

As a bonus, it should now be possible to ssh thursday.local.

Alternatives

Samba alternatives:

mDNSResponder alternatives:

  1. I’m not sure why both curtis and homes appear in Finder.