<s>
DragonFly	O
BSD	B-Operating_System
is	O
a	O
free	B-License
and	I-License
open-source	I-License
Unix-like	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
forked	B-Application
from	O
FreeBSD	B-Operating_System
4.8	O
.	O
</s>
<s>
Matthew	O
Dillon	O
,	O
an	O
Amiga	B-Device
developer	O
in	O
the	O
late	O
1980s	O
and	O
early	O
1990s	O
and	O
FreeBSD	B-Operating_System
developer	O
between	O
1994	O
and	O
2003	O
,	O
began	O
working	O
on	O
DragonFly	O
BSD	B-Operating_System
in	O
June	O
2003	O
and	O
announced	O
it	O
on	O
the	O
FreeBSD	B-Operating_System
mailing	O
lists	O
on	O
16	O
July	O
2003	O
.	O
</s>
<s>
Dillon	O
started	O
DragonFly	O
in	O
the	O
belief	O
that	O
the	O
techniques	O
adopted	O
for	O
threading	B-Operating_System
and	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
in	O
FreeBSD	B-Operating_System
5	O
would	O
lead	O
to	O
poor	O
performance	O
and	O
maintenance	O
problems	O
.	O
</s>
<s>
He	O
sought	O
to	O
correct	O
these	O
anticipated	O
problems	O
within	O
the	O
FreeBSD	B-Operating_System
project	I-Operating_System
.	O
</s>
<s>
Due	O
to	O
conflicts	O
with	O
other	O
FreeBSD	B-Operating_System
developers	O
over	O
the	O
implementation	O
of	O
his	O
ideas	O
,	O
his	O
ability	O
to	O
directly	O
change	O
the	O
codebase	B-General_Concept
was	O
eventually	O
revoked	O
.	O
</s>
<s>
Despite	O
this	O
,	O
the	O
DragonFly	O
BSD	B-Operating_System
and	O
FreeBSD	B-Operating_System
projects	I-Operating_System
still	O
work	O
together	O
,	O
sharing	O
bug	O
fixes	O
,	O
driver	O
updates	O
,	O
and	O
other	O
improvements	O
.	O
</s>
<s>
Intended	O
as	O
the	O
logical	O
continuation	O
of	O
the	O
FreeBSD	B-Operating_System
4.x	O
series	O
,	O
DragonFly	O
has	O
diverged	O
significantly	O
from	O
FreeBSD	B-Operating_System
,	O
implementing	O
lightweight	B-Operating_System
kernel	I-Operating_System
threads	I-Operating_System
(	O
LWKT	B-Operating_System
)	O
,	O
an	O
in-kernel	O
message	B-Architecture
passing	I-Architecture
system	O
,	O
and	O
the	O
HAMMER	B-Application
file	I-Application
system	I-Application
.	O
</s>
<s>
Many	O
design	O
concepts	O
were	O
influenced	O
by	O
AmigaOS	B-Application
.	O
</s>
<s>
The	O
kernel	B-Operating_System
messaging	O
subsystem	O
being	O
developed	O
is	O
similar	O
to	O
those	O
found	O
in	O
microkernels	O
such	O
as	O
Mach	B-Operating_System
,	O
though	O
it	O
is	O
less	O
complex	O
by	O
design	O
.	O
</s>
<s>
According	O
to	O
developer	O
Matthew	O
Dillon	O
,	O
progress	O
is	O
being	O
made	O
to	O
provide	O
both	O
device	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
and	O
virtual	B-Application
file	I-Application
system	I-Application
(	O
VFS	O
)	O
messaging	O
capabilities	O
that	O
will	O
enable	O
the	O
remainder	O
of	O
the	O
project	O
goals	O
to	O
be	O
met	O
.	O
</s>
<s>
The	O
new	O
infrastructure	O
will	O
allow	O
many	O
parts	O
of	O
the	O
kernel	B-Operating_System
to	O
be	O
migrated	O
out	O
into	O
userspace	O
;	O
here	O
they	O
will	O
be	O
more	O
easily	O
debugged	O
as	O
they	O
will	O
be	O
smaller	O
,	O
isolated	O
programs	O
,	O
instead	O
of	O
being	O
small	O
parts	O
entwined	O
in	O
a	O
larger	O
chunk	O
of	O
code	O
.	O
</s>
<s>
Additionally	O
,	O
the	O
migration	O
of	O
select	O
kernel	B-Operating_System
code	O
into	O
userspace	O
has	O
the	O
benefit	O
of	O
making	O
the	O
system	O
more	O
robust	O
;	O
if	O
a	O
userspace	O
driver	O
crashes	O
,	O
it	O
will	O
not	O
crash	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
System	B-Operating_System
calls	I-Operating_System
are	O
being	O
split	O
into	O
userland	O
and	O
kernel	B-Operating_System
versions	O
and	O
being	O
encapsulated	O
into	O
messages	O
.	O
</s>
<s>
This	O
will	O
help	O
reduce	O
the	O
size	O
and	O
complexity	O
of	O
the	O
kernel	B-Operating_System
by	O
moving	O
variants	O
of	O
standard	O
system	B-Operating_System
calls	I-Operating_System
into	O
a	O
userland	O
compatibility	B-General_Concept
layer	I-General_Concept
,	O
and	O
help	O
maintain	O
forwards	O
and	O
backwards	O
compatibility	O
between	O
DragonFly	O
versions	O
.	O
</s>
<s>
Linux	B-Application
and	O
other	O
Unix-like	B-Operating_System
OS	I-Operating_System
compatibility	O
code	O
is	O
being	O
migrated	O
out	O
similarly	O
.	O
</s>
<s>
As	O
support	O
for	O
multiple	O
instruction	B-General_Concept
set	I-General_Concept
architectures	I-General_Concept
complicates	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
(	O
SMP	O
)	O
support	O
,	O
DragonFly	O
BSD	B-Operating_System
now	O
limits	O
its	O
support	O
to	O
the	O
x86-64	B-Device
platform	O
.	O
</s>
<s>
DragonFly	O
originally	O
ran	O
on	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
,	O
however	O
as	O
of	O
version	O
4.0	O
it	O
is	O
no	O
longer	O
supported	O
.	O
</s>
<s>
Since	O
version	O
1.10	O
,	O
DragonFly	O
supports	O
1:1	O
userland	O
threading	B-Operating_System
(	O
one	O
kernel	B-Operating_System
thread	B-Operating_System
per	O
userland	O
thread	B-Operating_System
)	O
,	O
which	O
is	O
regarded	O
as	O
a	O
relatively	O
simple	O
solution	O
that	O
is	O
also	O
easy	O
to	O
maintain	O
.	O
</s>
<s>
Inherited	O
from	O
FreeBSD	B-Operating_System
,	O
DragonFly	O
also	O
supports	O
multi-threading	O
.	O
</s>
<s>
In	O
DragonFly	O
,	O
each	O
CPU	B-General_Concept
has	O
its	O
own	O
thread	B-Operating_System
scheduler	O
.	O
</s>
<s>
Upon	O
creation	O
,	O
threads	B-Operating_System
are	O
assigned	O
to	O
processors	O
and	O
are	O
never	O
preemptively	O
switched	O
from	O
one	O
processor	O
to	O
another	O
;	O
they	O
are	O
only	O
migrated	O
by	O
the	O
passing	O
of	O
an	O
inter-processor	B-Device
interrupt	I-Device
(	O
IPI	O
)	O
message	O
between	O
the	O
CPUs	O
involved	O
.	O
</s>
<s>
Inter-processor	O
thread	B-Operating_System
scheduling	O
is	O
also	O
accomplished	O
by	O
sending	O
asynchronous	O
IPI	O
messages	O
.	O
</s>
<s>
One	O
advantage	O
to	O
this	O
clean	O
compartmentalization	O
of	O
the	O
threading	B-Operating_System
subsystem	O
is	O
that	O
the	O
processors	O
 '	O
on-board	O
caches	B-General_Concept
in	O
symmetric	B-Operating_System
multiprocessor	I-Operating_System
systems	I-Operating_System
do	O
not	O
contain	O
duplicated	O
data	O
,	O
allowing	O
for	O
higher	O
performance	O
by	O
giving	O
each	O
processor	O
in	O
the	O
system	O
the	O
ability	O
to	O
use	O
its	O
own	O
cache	O
to	O
store	O
different	O
things	O
to	O
work	O
on	O
.	O
</s>
<s>
The	O
LWKT	B-Operating_System
subsystem	O
is	O
being	O
employed	O
to	O
partition	O
work	O
among	O
multiple	O
kernel	B-Operating_System
threads	B-Operating_System
(	O
for	O
example	O
in	O
the	O
networking	O
code	O
there	O
is	O
one	O
thread	B-Operating_System
per	O
protocol	O
per	O
processor	O
)	O
,	O
reducing	O
competition	O
by	O
removing	O
the	O
need	O
to	O
share	O
certain	O
resources	O
among	O
various	O
kernel	B-Operating_System
tasks	O
.	O
</s>
<s>
In	O
order	O
to	O
run	O
safely	O
on	O
multiprocessor	B-Operating_System
machines	O
,	O
access	O
to	O
shared	O
resources	O
(	O
like	O
files	O
,	O
data	O
structures	O
)	O
must	O
be	O
serialized	B-Application
so	O
that	O
threads	B-Operating_System
or	O
processes	O
do	O
not	O
attempt	O
to	O
modify	O
the	O
same	O
resource	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
In	O
order	O
to	O
prevent	O
multiple	O
threads	B-Operating_System
from	O
accessing	O
or	O
modifying	O
a	O
shared	O
resource	O
simultaneously	O
,	O
DragonFly	O
employs	O
critical	B-Operating_System
sections	I-Operating_System
,	O
and	O
serializing	B-Operating_System
tokens	I-Operating_System
to	O
prevent	O
concurrent	O
access	O
.	O
</s>
<s>
While	O
both	O
Linux	B-Application
and	O
FreeBSD	B-Operating_System
5	O
employ	O
fine-grained	O
mutex	B-Operating_System
models	O
to	O
achieve	O
higher	O
performance	O
on	O
multiprocessor	B-Operating_System
systems	O
,	O
DragonFly	O
does	O
not	O
.	O
</s>
<s>
Until	O
recently	O
,	O
DragonFly	O
also	O
employed	O
spls	B-Operating_System
,	O
but	O
these	O
were	O
replaced	O
with	O
critical	B-Operating_System
sections	I-Operating_System
.	O
</s>
<s>
Much	O
of	O
the	O
system	O
's	O
core	O
,	O
including	O
the	O
LWKT	B-Operating_System
subsystem	O
,	O
the	O
IPI	O
messaging	O
subsystem	O
and	O
the	O
new	O
kernel	B-Operating_System
memory	O
allocator	O
,	O
are	O
lockless	O
,	O
meaning	O
that	O
they	O
work	O
without	O
using	O
mutexes	B-Operating_System
,	O
with	O
each	O
process	O
operating	O
on	O
a	O
single	O
CPU	B-General_Concept
.	O
</s>
<s>
Critical	B-Operating_System
sections	I-Operating_System
are	O
used	O
to	O
protect	O
against	O
local	O
interrupts	O
,	O
individually	O
for	O
each	O
CPU	B-General_Concept
,	O
guaranteeing	O
that	O
a	O
thread	B-Operating_System
currently	O
being	O
executed	O
will	O
not	O
be	O
preempted	O
.	O
</s>
<s>
Serializing	B-Operating_System
tokens	I-Operating_System
are	O
used	O
to	O
prevent	O
concurrent	O
accesses	O
from	O
other	O
CPUs	O
and	O
may	O
be	O
held	O
simultaneously	O
by	O
multiple	O
threads	B-Operating_System
,	O
ensuring	O
that	O
only	O
one	O
of	O
those	O
threads	B-Operating_System
is	O
running	O
at	O
any	O
given	O
time	O
.	O
</s>
<s>
Blocked	O
or	O
sleeping	O
threads	B-Operating_System
therefore	O
do	O
not	O
prevent	O
other	O
threads	B-Operating_System
from	O
accessing	O
the	O
shared	O
resource	O
unlike	O
a	O
thread	B-Operating_System
that	O
is	O
holding	O
a	O
mutex	B-Operating_System
.	O
</s>
<s>
Among	O
other	O
things	O
,	O
the	O
use	O
of	O
serializing	B-Operating_System
tokens	I-Operating_System
prevents	O
many	O
of	O
the	O
situations	O
that	O
could	O
result	O
in	O
deadlocks	B-Operating_System
and	O
priority	B-Operating_System
inversions	I-Operating_System
when	O
using	O
mutexes	B-Operating_System
,	O
as	O
well	O
as	O
greatly	O
simplifying	O
the	O
design	O
and	O
implementation	O
of	O
a	O
many-step	O
procedure	O
that	O
would	O
require	O
a	O
resource	O
to	O
be	O
shared	O
among	O
multiple	O
threads	B-Operating_System
.	O
</s>
<s>
The	O
serializing	B-Application
token	O
code	O
is	O
evolving	O
into	O
something	O
quite	O
similar	O
to	O
the	O
"	O
Read-copy-update	B-Operating_System
"	O
feature	O
now	O
available	O
in	O
Linux	B-Application
.	O
</s>
<s>
Unlike	O
Linux	B-Application
's	O
current	O
RCU	O
implementation	O
,	O
DragonFly	O
's	O
is	O
being	O
implemented	O
such	O
that	O
only	O
processors	O
competing	O
for	O
the	O
same	O
token	O
are	O
affected	O
rather	O
than	O
all	O
processors	O
in	O
the	O
computer	O
.	O
</s>
<s>
DragonFly	O
switched	O
to	O
multiprocessor	B-Operating_System
safe	O
slab	B-General_Concept
allocator	I-General_Concept
,	O
which	O
requires	O
neither	O
mutexes	B-Operating_System
nor	O
blocking	O
operations	O
for	O
memory	O
assignment	O
tasks	O
.	O
</s>
<s>
It	O
was	O
eventually	O
ported	O
into	O
standard	B-Language
C	I-Language
library	I-Language
in	O
the	O
userland	O
,	O
where	O
it	O
replaced	O
FreeBSD	B-Operating_System
's	O
malloc	O
implementation	O
.	O
</s>
<s>
Since	O
release	O
1.8	O
DragonFly	O
has	O
a	O
virtualization	O
mechanism	O
similar	O
to	O
User-mode	B-Application
Linux	I-Application
,	O
allowing	O
a	O
user	O
to	O
run	O
another	O
kernel	B-Operating_System
in	O
the	O
userland	O
.	O
</s>
<s>
The	O
virtual	B-Language
kernel	I-Language
(	O
vkernel	B-Language
)	O
is	O
run	O
in	O
completely	O
isolated	O
environment	O
with	O
emulated	O
network	O
and	O
storage	O
interfaces	O
,	O
thus	O
simplifying	O
testing	O
kernel	B-Operating_System
subsystems	O
and	O
clustering	O
features	O
.	O
</s>
<s>
The	O
vkernel	B-Language
has	O
two	O
important	O
differences	O
from	O
the	O
real	O
kernel	B-Operating_System
:	O
it	O
lacks	O
many	O
routines	O
for	O
dealing	O
with	O
the	O
low-level	O
hardware	O
management	O
and	O
it	O
uses	O
C	B-Language
standard	I-Language
library	I-Language
(	O
libc	B-Language
)	O
functions	O
in	O
place	O
of	O
in-kernel	O
implementations	O
wherever	O
possible	O
.	O
</s>
<s>
As	O
both	O
real	O
and	O
virtual	B-Language
kernel	I-Language
are	O
compiled	O
from	O
the	O
same	O
code	B-General_Concept
base	I-General_Concept
,	O
this	O
effectively	O
means	O
that	O
platform-dependent	O
routines	O
and	O
re-implementations	O
of	O
libc	B-Language
functions	O
are	O
clearly	O
separated	O
in	O
a	O
source	O
tree	O
.	O
</s>
<s>
The	O
vkernel	B-Language
runs	O
on	O
top	O
of	O
hardware	O
abstractions	O
provided	O
by	O
the	O
real	O
kernel	B-Operating_System
.	O
</s>
<s>
These	O
include	O
the	O
kqueue-based	O
timer	O
,	O
the	O
console	O
(	O
mapped	O
to	O
the	O
virtual	B-Application
terminal	I-Application
where	O
vkernel	B-Language
is	O
executed	O
)	O
,	O
the	O
disk	O
image	O
and	O
virtual	B-Language
kernel	I-Language
Ethernet	O
device	O
(	O
VKE	O
)	O
,	O
tunneling	O
all	O
packets	O
to	O
the	O
host	O
's	O
tap	B-Protocol
interface	O
.	O
</s>
<s>
Third-party	O
software	O
is	O
available	O
on	O
DragonFly	O
as	O
binary	O
packages	O
via	O
pkgng	O
or	O
from	O
a	O
native	O
ports	B-Application
collection	I-Application
–	O
DPorts	O
.	O
</s>
<s>
DragonFly	O
originally	O
used	O
the	O
FreeBSD	B-Application
Ports	I-Application
collection	I-Application
as	O
its	O
official	O
package	B-Application
management	I-Application
system	I-Application
,	O
but	O
starting	O
with	O
the	O
1.4	O
release	O
switched	O
to	O
NetBSD	B-Device
's	O
pkgsrc	B-Application
system	O
,	O
which	O
was	O
perceived	O
as	O
a	O
way	O
of	O
lessening	O
the	O
amount	O
of	O
work	O
needed	O
for	O
third-party	O
software	O
availability	O
.	O
</s>
<s>
Eventually	O
,	O
maintaining	O
compatibility	O
with	O
pkgsrc	B-Application
proved	O
to	O
require	O
more	O
effort	O
than	O
was	O
initially	O
anticipated	O
,	O
so	O
the	O
project	O
created	O
DPorts	O
,	O
an	O
overlay	O
on	O
top	O
of	O
the	O
FreeBSD	B-Application
Ports	I-Application
collection	I-Application
.	O
</s>
<s>
The	O
initial	O
implementation	O
of	O
Common	B-Application
Address	I-Application
Redundancy	I-Application
Protocol	I-Application
(	O
commonly	O
referred	O
to	O
as	O
CARP	O
)	O
was	O
finished	O
in	O
March	O
2007	O
.	O
</s>
<s>
As	O
of	O
2011	O
,	O
CARP	O
support	O
is	O
integrated	O
into	O
DragonFly	O
BSD	B-Operating_System
.	O
</s>
<s>
Alongside	O
the	O
Unix	B-Operating_System
File	I-Operating_System
System	I-Operating_System
,	O
which	O
is	O
typically	O
the	O
default	O
file	B-Application
system	I-Application
on	O
BSDs	B-Operating_System
,	O
DragonFly	O
BSD	B-Operating_System
supports	O
the	O
HAMMER	B-Application
and	O
HAMMER2	B-Application
file	B-Application
systems	I-Application
.	O
</s>
<s>
HAMMER2	B-Application
is	O
the	O
default	O
file	B-Application
system	I-Application
as	O
of	O
version	O
5.2.0	O
.	O
</s>
<s>
HAMMER	B-Application
was	O
developed	O
specifically	O
for	O
DragonFly	O
BSD	B-Operating_System
to	O
provide	O
a	O
feature-rich	O
yet	O
better	O
designed	O
analogue	O
of	O
the	O
increasingly	O
popular	O
ZFS	B-Application
.	O
</s>
<s>
HAMMER	B-Application
supports	O
configurable	O
file	B-Application
system	I-Application
history	O
,	O
snapshots	B-Application
,	O
checksumming	O
,	O
data	B-General_Concept
deduplication	I-General_Concept
and	O
other	O
features	O
typical	O
for	O
file	B-Application
systems	I-Application
of	O
its	O
kind	O
.	O
</s>
<s>
HAMMER2	B-Application
,	O
the	O
successor	O
of	O
the	O
HAMMER	B-Application
file	I-Application
system	I-Application
,	O
is	O
now	O
considered	O
stable	O
,	O
used	O
by	O
default	O
,	O
and	O
the	O
focus	O
of	O
further	O
development	O
.	O
</s>
<s>
In	O
2017	O
,	O
Dillon	O
announced	O
that	O
the	O
next	O
DragonFly	O
BSD	B-Operating_System
version	O
(	O
5.0.0	O
)	O
would	O
include	O
a	O
usable	O
,	O
though	O
still	O
experimental	O
,	O
version	O
of	O
HAMMER2	B-Application
,	O
and	O
described	O
features	O
of	O
the	O
design	O
.	O
</s>
<s>
With	O
the	O
release	O
after	O
5.0.0	O
,	O
version	O
5.2.0	O
,	O
HAMMER2	B-Application
became	O
the	O
new	O
default	O
file	B-Application
system	I-Application
.	O
</s>
<s>
In	O
2007	O
DragonFly	O
BSD	B-Operating_System
received	O
a	O
new	O
device	O
file	B-Application
system	I-Application
(	O
devfs	O
)	O
,	O
which	O
dynamically	O
adds	O
and	O
removes	O
device	O
nodes	O
,	O
allows	O
accessing	O
devices	O
by	O
connection	O
paths	O
,	O
recognises	O
drives	O
by	O
serial	O
numbers	O
and	O
removes	O
the	O
need	O
for	O
pre-populated	O
/dev	O
file	B-Application
system	I-Application
hierarchy	O
.	O
</s>
<s>
It	O
was	O
implemented	O
as	O
a	O
Google	B-Application
Summer	I-Application
of	I-Application
Code	I-Application
2009	O
project	O
.	O
</s>
<s>
DragonFly	O
BSD	B-Operating_System
supports	O
Amiga-style	O
resident	O
applications	O
feature	O
:	O
it	O
takes	O
a	O
snapshot	B-Application
of	O
a	O
large	O
,	O
dynamically	O
linked	O
program	O
's	O
virtual	B-Architecture
memory	I-Architecture
space	O
after	O
loading	O
,	O
allowing	O
future	O
instances	O
of	O
the	O
program	O
to	O
start	O
much	O
more	O
quickly	O
than	O
it	O
otherwise	O
would	O
have	O
.	O
</s>
<s>
This	O
replaces	O
the	O
prelinking	B-Library
capability	O
that	O
was	O
being	O
worked	O
on	O
earlier	O
in	O
the	O
project	O
's	O
history	O
,	O
as	O
the	O
resident	O
support	O
is	O
much	O
more	O
efficient	O
.	O
</s>
<s>
Large	O
programs	O
like	O
those	O
found	O
in	O
KDE	B-Language
Software	I-Language
Compilation	I-Language
with	O
many	O
shared	B-Library
libraries	I-Library
will	O
benefit	O
the	O
most	O
from	O
this	O
support	O
.	O
</s>
<s>
As	O
with	O
FreeBSD	B-Operating_System
and	O
OpenBSD	B-Operating_System
,	O
the	O
developers	O
of	O
DragonFly	O
BSD	B-Operating_System
are	O
slowly	O
replacing	O
pre-function	O
prototype-style	O
C	B-Language
code	O
with	O
more	O
modern	O
,	O
ANSI	O
equivalents	O
.	O
</s>
<s>
Similar	O
to	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
DragonFly	O
's	O
version	O
of	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
has	O
an	O
enhancement	O
called	O
the	O
Stack-Smashing	O
Protector	O
(	O
ProPolice	O
)	O
enabled	O
by	O
default	O
,	O
providing	O
some	O
additional	O
protection	O
against	O
buffer	B-General_Concept
overflow	I-General_Concept
based	O
attacks	O
.	O
</s>
<s>
,	O
the	O
kernel	B-Operating_System
is	O
no	O
longer	O
built	O
with	O
this	O
protection	O
by	O
default	O
.	O
</s>
<s>
Being	O
a	O
derivative	O
of	O
FreeBSD	B-Operating_System
,	O
DragonFly	O
has	O
inherited	O
an	O
easy-to-use	O
integrated	O
build	O
system	O
that	O
can	O
rebuild	O
the	O
entire	O
base	O
system	O
from	O
source	O
with	O
only	O
a	O
few	O
commands	O
.	O
</s>
<s>
The	O
DragonFly	O
developers	O
use	O
the	O
Git	B-Application
version	I-Application
control	I-Application
system	I-Application
to	O
manage	O
changes	O
to	O
the	O
DragonFly	O
source	O
code	O
.	O
</s>
<s>
Unlike	O
its	O
parent	O
FreeBSD	B-Operating_System
,	O
DragonFly	O
has	O
both	O
stable	O
and	O
unstable	O
releases	O
in	O
a	O
single	O
source	O
tree	O
,	O
due	O
to	O
a	O
smaller	O
developer	O
base	O
.	O
</s>
<s>
Like	O
the	O
other	O
BSD	B-Operating_System
kernels	B-Operating_System
(	O
and	O
those	O
of	O
most	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
)	O
,	O
DragonFly	O
employs	O
a	O
built-in	O
kernel	B-Operating_System
debugger	I-Operating_System
to	O
help	O
the	O
developers	O
find	O
kernel	B-Operating_System
bugs	O
.	O
</s>
<s>
Furthermore	O
,	O
,	O
a	O
debug	O
kernel	B-Operating_System
,	O
which	O
makes	O
bug	O
reports	O
more	O
useful	O
for	O
tracking	O
down	O
kernel-related	O
problems	O
,	O
is	O
installed	O
by	O
default	O
,	O
at	O
the	O
expense	O
of	O
a	O
relatively	O
small	O
quantity	O
of	O
disk	O
space	O
.	O
</s>
<s>
When	O
a	O
new	O
kernel	B-Operating_System
is	O
installed	O
,	O
the	O
backup	O
copy	O
of	O
the	O
previous	O
kernel	B-Operating_System
and	O
its	O
modules	O
are	O
stripped	O
of	O
their	O
debugging	O
symbols	O
to	O
further	O
minimize	O
disk	O
space	O
usage	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
is	O
distributed	O
as	O
a	O
Live	O
CD	O
and	O
Live	O
USB	O
that	O
boots	O
into	O
a	O
complete	O
DragonFly	O
system	O
.	O
</s>
<s>
Daily	O
snapshots	B-Application
are	O
available	O
from	O
the	O
master	O
site	O
for	O
those	O
who	O
want	O
to	O
install	O
the	O
most	O
recent	O
versions	O
of	O
DragonFly	O
without	O
building	O
from	O
source	O
.	O
</s>
<s>
Like	O
the	O
other	O
free	B-License
and	I-License
open-source	I-License
BSDs	B-Operating_System
,	O
DragonFly	O
is	O
distributed	O
under	O
the	O
terms	O
of	O
the	O
modern	O
version	O
of	O
the	O
BSD	B-Operating_System
license	I-Operating_System
.	O
</s>
<s>
Added	O
support	O
for	O
growfs	O
to	O
changing	O
the	O
size	O
of	O
an	O
existing	O
HAMMER2	B-Application
volume	O
.	O
</s>
<s>
Imported	O
amdgpu	B-Application
driver	O
,	O
matches	O
Linux	B-Application
4.19	O
support	O
.	O
</s>
<s>
Improved	O
CPU	B-General_Concept
usage	O
and	O
tmpfs	B-Application
performance	O
under	O
extreme	O
load	O
3.2	O
Multiprocessor-capable	O
kernel	B-Operating_System
became	O
mandatory	O
.	O
</s>
<s>
USB4BSD	O
imported	O
from	O
FreeBSD	B-Operating_System
.	O
</s>
<s>
PUFFS	B-Application
imported	O
from	O
NetBSD	B-Device
.	O
</s>
<s>
Application	B-General_Concept
checkpointing	I-General_Concept
support	O
.	O
</s>
