How much diferrent and compatible is DragonFlyBSD to FreeBSD?

Freddie Cash fjwcash at
Fri Jan 28 08:56:37 PST 2022

On Fri, Jan 28, 2022 at 5:25 AM <rempas at> wrote:

> When it comes to the core of the operating systems themselves (mostly the
> kernel), how much difference these two operating systems have? I know that
> DragonFlyBSD was a fork of FreeBSD so I suppose that they have most things
> in common. But what are different? For example, has DragonFlyBSD changed
> the numbers (or even the functionality) for the basic system calls? Or
> maybe changed some other stuff? Hence I wonder if there is a lot of works
> that has to been done to port FreeBSD binaries to DragonFlyBSD. Sorry if
> this question sounds too n00by but I want to know how much compatibility
> there is with FreeBSD.

DragonFlyBSD is a fork/continuation of FreeBSD 4.x.  A lot has changed in
FreeBSD between 5.0 and 13.0, just as a lot has changed in DFly from 1.0 to

When it comes to porting userland binaries there's usually not a lot of
work required.  They're both POSIX-compatible and provide a lot of the same
functionality.  For example, the DFly ports tree is mostly a clone of the
FreeBSD ports tree, with just minor changes/patches here and there to make
certain things run on DFly.

When it comes to porting kernel level drivers and applications that user
kernel services directly, there's a lot of work required.  The biggest
differences are in the storage and network subsystems, as FreeBSD 5+ uses
GEOM for accessing devices and DFly uses something completely different.
Many of the locking primitives and multithreading support are very
different between the two, and the DFly methods appear to be better in many
cases.  The IPFW packet filter on DFly is very different from the IPFW
packet filter on FreeBSD (different syntax, different features, almost
entirely different codebases now).  And so on.  DF;y has the HAMMER1 and
HAMMER2 filesystems and volume managers, while FreeBSD has ZFS; they both
support UFS, although I'm not sure if DFly still supports SoftUpdates.

It really depends what you want to port, and how deep into the kernel it
goes.  The deeper you go, the more differences you'll find.
Freddie Cash
fjwcash at
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