<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
xinetd	B-Operating_System
(	O
Extended	O
Internet	O
Service	B-General_Concept
Daemon	B-Operating_System
)	O
is	O
an	O
open-source	B-Application
super-server	B-Protocol
daemon	B-Operating_System
which	O
runs	O
on	O
many	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
and	O
manages	O
Internet-based	O
connectivity	O
.	O
</s>
<s>
It	O
offers	O
a	O
more	O
secure	O
alternative	O
to	O
the	O
older	O
inetd	B-Protocol
(	O
"	O
the	O
Internet	O
daemon	B-Operating_System
"	O
)	O
,	O
which	O
most	O
modern	O
Linux	B-Application
distributions	I-Application
have	O
deprecated	O
.	O
</s>
<s>
xinetd	B-Operating_System
listens	O
for	O
incoming	O
requests	O
over	O
a	O
network	O
and	O
launches	O
the	O
appropriate	O
service	B-General_Concept
for	O
that	O
request	O
.	O
</s>
<s>
Requests	O
are	O
made	O
using	O
port	B-Protocol
numbers	I-Protocol
as	O
identifiers	O
and	O
xinetd	B-Operating_System
usually	O
launches	O
another	O
daemon	B-Operating_System
to	O
handle	O
the	O
request	O
.	O
</s>
<s>
It	O
can	O
be	O
used	O
to	O
start	O
services	O
with	O
both	O
privileged	O
and	O
non-privileged	O
port	B-Protocol
numbers	I-Protocol
.	O
</s>
<s>
xinetd	B-Operating_System
features	O
access	O
control	O
mechanisms	O
such	O
as	O
TCP	B-Protocol
Wrapper	I-Protocol
ACLs	O
,	O
extensive	O
logging	O
capabilities	O
,	O
and	O
the	O
ability	O
to	O
make	O
services	O
available	O
based	O
on	O
time	O
.	O
</s>
<s>
On	O
some	O
implementations	O
of	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
,	O
this	O
daemon	B-Operating_System
starts	O
and	O
maintains	O
various	O
Internet-related	O
services	O
,	O
including	O
FTP	B-Protocol
and	O
telnet	B-Protocol
.	O
</s>
<s>
As	O
an	O
extended	O
form	O
of	O
inetd	B-Protocol
,	O
it	O
offers	O
enhanced	O
security	O
.	O
</s>
<s>
It	O
replaced	O
inetd	B-Protocol
in	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
v10.3	I-Operating_System
,	O
and	O
subsequently	O
launchd	B-Application
replaced	O
it	O
in	O
Mac	B-Application
OS	I-Application
X	I-Application
v10.4	I-Application
.	O
</s>
<s>
However	O
,	O
Apple	O
has	O
retained	O
inetd	B-Protocol
for	O
compatibility	O
purposes	O
.	O
</s>
<s>
Configuration	O
of	O
xinetd	B-Operating_System
resides	O
in	O
the	O
default	O
configuration	O
file	O
/etc/xinetd.conf	O
,	O
and	O
configuration	O
of	O
the	O
services	O
it	O
supports	O
resides	O
in	O
configuration	O
files	O
stored	O
in	O
the	O
/etc/xinetd.d	O
directory	O
.	O
</s>
<s>
The	O
configuration	O
for	O
each	O
service	B-General_Concept
usually	O
includes	O
a	O
switch	O
to	O
control	O
whether	O
xinetd	B-Operating_System
should	O
enable	O
or	O
disable	O
the	O
service	B-General_Concept
.	O
</s>
<s>
An	O
example	O
configuration	O
file	O
for	O
the	O
RFC	B-Protocol
868	I-Protocol
time	I-Protocol
server	I-Protocol
:	O
</s>
<s>
The	O
lines	O
with	O
the	O
"	O
#	O
"	O
character	O
at	O
the	O
beginning	O
are	O
comments	O
without	O
any	O
effect	O
on	O
the	O
service	B-General_Concept
.	O
</s>
<s>
There	O
are	O
two	O
service	B-General_Concept
versions	O
:	O
the	O
first	O
one	O
is	O
based	O
on	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
,	O
the	O
second	O
one	O
is	O
based	O
on	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
The	O
type	O
and	O
planned	O
usage	O
of	O
a	O
service	B-General_Concept
determines	O
the	O
necessary	O
core	O
protocol	O
.	O
</s>
<s>
The	O
disable	O
option	O
is	O
a	O
switch	O
to	O
run	O
a	O
service	B-General_Concept
or	O
not	O
.	O
</s>
<s>
To	O
activate	O
the	O
service	B-General_Concept
,	O
change	O
it	O
to	O
no	O
.	O
</s>
<s>
The	O
type	O
is	O
INTERNAL	O
if	O
the	O
service	B-General_Concept
is	O
provided	O
by	O
xinetd	B-Operating_System
,	O
RPC	O
when	O
it	O
based	O
on	O
Remote	B-Operating_System
procedure	I-Operating_System
call	I-Operating_System
(	O
commonly	O
listed	O
in	O
the	O
/etc/rpc	O
file	O
)	O
,	O
or	O
it	O
can	O
be	O
UNLISTED	O
when	O
the	O
service	B-General_Concept
is	O
neither	O
in	O
the	O
/etc/services	O
nor	O
in	O
the	O
/etc/rpc	O
files	O
.	O
</s>
<s>
The	O
id	O
is	O
the	O
unique	O
identifier	O
of	O
the	O
service	B-General_Concept
.	O
</s>
<s>
The	O
socket_type	O
determines	O
the	O
way	O
of	O
data	O
transmission	O
through	O
the	O
service	B-General_Concept
.	O
</s>
<s>
This	O
last	O
one	O
is	O
useful	O
when	O
we	O
want	O
to	O
establish	O
a	O
service	B-General_Concept
based	O
on	O
a	O
non-standard	O
protocol	O
.	O
</s>
<s>
With	O
the	O
user	O
option	O
,	O
it	O
is	O
possible	O
to	O
choose	O
a	O
user	O
to	O
be	O
the	O
owner	O
of	O
the	O
running	O
service	B-General_Concept
.	O
</s>
<s>
When	O
the	O
wait	O
is	O
on	O
yes	O
,	O
the	O
xinetd	B-Operating_System
will	O
not	O
receive	O
a	O
request	O
for	O
the	O
service	B-General_Concept
if	O
it	O
has	O
a	O
connection	O
.	O
</s>
<s>
There	O
are	O
many	O
more	O
options	O
available	O
for	O
xinetd	B-Operating_System
.	O
</s>
<s>
In	O
most	O
Linux	B-Application
distributions	I-Application
,	O
the	O
full	O
list	O
of	O
possible	O
options	O
and	O
their	O
description	O
is	O
accessible	O
with	O
a	O
"	O
man	O
xinetd.conf	O
"	O
command	O
.	O
</s>
<s>
To	O
apply	O
the	O
new	O
configuration	O
,	O
a	O
SIGHUP	B-General_Concept
signal	O
must	O
be	O
sent	O
to	O
the	O
xinetd	B-Operating_System
process	O
to	O
make	O
it	O
re-read	O
the	O
configuration	O
files	O
.	O
</s>
<s>
This	O
can	O
be	O
achieved	O
with	O
the	O
following	O
command	O
:	O
kill	O
-SIGHUP	O
"	O
PID	O
"	O
.	O
</s>
<s>
PID	O
is	O
the	O
actual	O
process	O
identifier	O
number	O
of	O
the	O
xinetd	B-Operating_System
,	O
which	O
can	O
be	O
obtained	O
with	O
the	O
command	O
pgrep	O
xinetd	B-Operating_System
.	O
</s>
