Linux D-Bus Clients for .NET

Typed .NET clients for the three Linux system daemons an embedded or appliance-style device usually has to talk to: NetworkManager, ModemManager, and avahi.

They are built on Tmds.DBus and target net10.0.

Dbus.Clients.NetworkManager    connection profiles, Wi-Fi scan/AP mode, interface state
Dbus.Clients.ModemManager      the full ModemManager interface set, typed
Dbus.Clients.Avahi             publish DNS-SD/mDNS services at runtime

Why these exist

Shelling out to nmcli, mmcli, and avahi-publish works right up until you need a return value. Then you are parsing human-readable output that changes between distro versions, you have no way to react to a property change, and every call costs a process spawn.

Going straight to D-Bus fixes all three, but the raw interfaces are wide, weakly typed (Dictionary<string, Dictionary<string, object>> for a connection profile), and full of behaviour that is not written down anywhere except mailing-list threads. These packages are the typed layer plus, more usefully, the accumulated knowledge of what those daemons actually do — see Things that will bite you.

Install

dotnet add package Dbus.Clients.NetworkManager
dotnet add package Dbus.Clients.ModemManager
dotnet add package Dbus.Clients.Avahi

Take only what you need — the three packages are independent and share no code.

Avahi — publish a service

Use this over a static file in /etc/avahi/services when the TXT records depend on runtime state (build version, hardware serial, which port you actually bound to).

await using var avahi = await AvahiClient.CreateAsync();

await avahi.PublishServiceAsync(
    serviceName: "My Device",
    serviceType: "_http._tcp",
    port: 8080,
    txtRecords: new Dictionary<string, string>
    {
        ["version"] = ThisAssembly.InformationalVersion,
        ["serial"]  = boardSerial,
        ["api"]     = "/api/v1",
    });

// Report THIS to the user, not Environment.MachineName — see below.
var hostName = await avahi.GetPublishedHostNameAsync();
Console.WriteLine($"Reachable at {hostName}.local:8080");

Creating an entry group is privileged. If your service does not run as root, add a D-Bus policy drop-in under /etc/dbus-1/system.d/ allowing your user to org.freedesktop.Avahi.Server.EntryGroupNew, or the call throws DBusException ("Access denied").

NetworkManager — connection profiles

UpsertEthernetProfilesAsync builds and applies a whole addressing profile in one call. The link-local fallback is the interesting part: a second, lower-priority profile that activates only when DHCP fails, which is what makes a device reachable over a direct ethernet cable with no DHCP server present.

await using var nm = await NetworkManagerClient.CreateAsync();

await nm.UpsertEthernetProfilesAsync(new EthernetProfileRequestDto
{
    InterfaceName = "eth0",
    BaseConnectionId = "eth0",
    Mode = EthernetAddressingMode.Dhcp,
    AddLinkLocalFallbackProfile = true,   // adds "eth0-ll" at a lower autoconnect priority
});

Wi-Fi, in either direction:

var aps = await nm.ListWifiAccessPointsAsync(requestScan: true);

await nm.ApplyWifiModeAsync(new WifiModeRequestDto
{
    Mode = WifiProfileMode.AccessPoint,
    AccessPoint = new WifiAccessPointProfileRequestDto { /* ssid, psk, band... */ },
});

Also available: ListConnectionSummariesAsync, GetConnectionConfigurationByIdAsync, ActivateConnectionByIdAsync, DeleteConnectionAsync, ReapplyDeviceConnectionAsync, GetInterfaceRuntimeStateAsync, SetWifiEnabledAsync, SetNetworkingEnabledAsync, and UpsertGsmProfileAsync for cellular.

ModemManager — enumerate and query

await using var mm = await ModemManagerClient.CreateAsync();

Console.WriteLine($"ModemManager {await mm.GetVersionAsync()}");

foreach (var modem in await mm.GetModemsAsync())
{
    // ModemClient, plus Modem3gppClient, ModemSignalClient, ModemLocationClient,
    // SmsClient, CallClient, BearerClient, SimClient, ... one per MM interface.
}

The enumerations (MMModemState, MMModemAccessTechnology, MMModem3gppRegistrationState, and the rest) are translated to C# enums rather than left as raw uint.

Things that will bite you

Documented here because each one cost real debugging time on real hardware.

Avahi renames your host on collision, silently. If another device on the link already publishes mydevice.local, avahi publishes you as mydevice-2.local instead — and never tells you. Environment.MachineName still reports mydevice. Any UI or log line that tells a user where to connect must use GetPublishedHostNameAsync(), or you will confidently print an address that resolves to a different machine. This happens the moment two boards ship with the same default hostname.

Restarting avahi-daemon drops D-Bus-published records permanently. The daemon discards every entry group it was holding. Services declared in /etc/avahi/services come straight back; yours does not, because nothing re-creates it. Worse, the host name is unchanged across the restart, so a watchdog that only compares host names concludes nothing happened. Poll GetEntryGroupStateAsync() and republish when it stops returning AvahiConstants.EntryGroupEstablished.

In practice you usually detect the restart by that call throwing rather than by its return value: the entry group object dies with the daemon, so the proxy call fails with UnknownObject: Method GetState ... doesn't exist before any state comes back. Both outcomes want the same recovery, so handle the exception as "republish" rather than letting it escape.

Don't filter interfaces in code. AvahiConstants.InterfaceUnspecified (AVAHI_IF_UNSPEC) looks broad but is already bounded by allow-interfaces in avahi-daemon.conf. Keep that policy in the daemon config only — implementing it in both places guarantees they drift.

Empty TXT values are dropped, not published as key=. A consumer cannot distinguish "present but empty" from "absent" in any useful way, and an empty field reads as real data when it is actually a gap.

A D-Bus connection is not free to leak. All three clients are IAsyncDisposable and own their Connection. If you create one per retry in a startup loop — or one per tick in a status poller — you leak a socket and a reader task per attempt. Create once, keep it, dispose on shutdown.

Leaking them takes down the whole process, not just your client. A bus caps one UID at max_connections_per_user, 256 by default. Cross it and every D-Bus consumer in the process starts failing with "The maximum number of active connections for UID … has been reached" — including clients that were never involved in the leak — and nothing recovers until the process restarts. A once-per-second poller reaches that ceiling in about four minutes, so this shows up as a service that works after a restart and mysteriously stops a few minutes later.

Platform

Linux with a D-Bus system bus, and the corresponding daemon installed. The packages compile on Windows and macOS — CI builds them there, and it keeps editor tooling working in a mixed team — but every call needs a real system bus at runtime.

Tested against NetworkManager 1.42+, ModemManager 1.20+, and avahi 0.8 on Debian 12/13 (including Raspberry Pi OS on arm64).

Contributing

Bug reports and PRs welcome. Two requests:

• If you add a workaround for daemon behaviour, write down what you observed in the doc comment, not just what the code does. That is the part of this repo worth having.
• Proxy interfaces under Dbus/Proxies.cs mirror the daemon's published introspection XML. Keep them faithful to it; put convenience on the *Client classes instead.

See AGENTS.md for repository layout and conventions.

License

MIT — see LICENSE.