<s>
The	O
Name	B-Protocol
Service	I-Protocol
Switch	I-Protocol
(	O
NSS	O
)	O
connects	O
the	O
computer	O
with	O
a	O
variety	O
of	O
sources	O
of	O
common	O
configuration	O
databases	O
and	O
name	O
resolution	O
mechanisms	O
.	O
</s>
<s>
These	O
sources	O
include	O
local	O
operating	B-General_Concept
system	I-General_Concept
files	O
(	O
such	O
as	O
,	O
,	O
and	O
)	O
,	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
,	O
the	O
Network	B-Operating_System
Information	I-Operating_System
Service	I-Operating_System
(	O
NIS	B-Operating_System
,	O
NIS+	O
)	O
,	O
and	O
LDAP	B-Protocol
.	O
</s>
<s>
This	O
operating	B-General_Concept
system	I-General_Concept
mechanism	O
,	O
used	O
in	O
billions	O
of	O
computers	O
,	O
including	O
all	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
is	O
indispensable	O
to	O
functioning	O
as	O
part	O
of	O
the	O
networked	O
organization	B-General_Concept
and	O
the	O
Internet	O
.	O
</s>
<s>
Among	O
other	O
things	O
,	O
it	O
is	O
invoked	O
every	O
time	O
a	O
computer	O
user	O
clicks	O
on	O
or	O
types	O
a	O
website	O
address	O
in	O
the	O
web	B-Application
browser	I-Application
or	O
responds	O
to	O
the	O
password	O
challenge	O
to	O
be	O
authorized	O
access	O
to	O
the	O
computer	O
and	O
the	O
Internet	O
.	O
</s>
<s>
A	O
system	B-Application
administrator	I-Application
usually	O
configures	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
name	O
services	O
using	O
the	O
file	O
.	O
</s>
<s>
This	O
file	O
lists	O
databases	O
(	O
such	O
as	O
passwd	B-Protocol
,	O
shadow	O
and	O
group	B-Operating_System
)	O
,	O
and	O
one	O
or	O
more	O
sources	O
for	O
obtaining	O
that	O
information	O
.	O
</s>
<s>
Examples	O
for	O
sources	O
are	O
files	O
for	O
local	O
files	O
,	O
ldap	B-Protocol
for	O
the	O
Lightweight	B-Protocol
Directory	I-Protocol
Access	I-Protocol
Protocol	I-Protocol
,	O
nis	B-Operating_System
for	O
the	O
Network	B-Operating_System
Information	I-Operating_System
Service	I-Operating_System
,	O
nisplus	O
for	O
NIS+	O
,	O
dns	B-Protocol
for	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
,	O
and	O
wins	O
for	O
Windows	B-Device
Internet	I-Device
Name	I-Device
Service	I-Device
.	O
</s>
<s>
Earlier	O
Unix-like	B-Operating_System
systems	I-Operating_System
either	O
accessed	O
only	O
local	O
files	O
or	O
had	O
hard-coded	O
rules	O
for	O
accessing	O
files	O
or	O
network-stored	O
databases	O
.	O
</s>
<s>
Ultrix	B-Operating_System
was	O
a	O
notable	O
exception	O
with	O
its	O
nearly	O
identical	O
functionality	O
of	O
the	O
NSS	O
configuration	O
file	O
in	O
.	O
</s>
<s>
Sun	O
Microsystems	O
first	O
developed	O
the	O
NSS	O
for	O
their	O
Solaris	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
Solaris	B-Application
 '	O
compliance	O
with	O
SVR4	O
,	O
which	O
Sun	O
Microsystems	O
and	O
AT&T	B-Operating_System
Unix	I-Operating_System
System	O
Laboratories	O
jointly	O
developed	O
by	O
merging	O
UNIX	B-Operating_System
System	I-Operating_System
V	I-Operating_System
,	O
BSD	B-Operating_System
and	O
Xenix	B-Application
,	O
required	O
that	O
third	O
parties	O
be	O
able	O
to	O
plug	O
in	O
name	O
service	O
implementations	O
for	O
the	O
transport	B-Architecture
layer	I-Architecture
of	O
their	O
choosing	O
(	O
OSI	O
or	O
IP	B-Protocol
)	O
without	O
rewriting	O
SVR4-compliant	O
Transport-Independent	O
RPC	B-Operating_System
(	O
TI-RPC	O
)	O
applications	O
or	O
rebuilding	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Sun	O
introduced	O
the	O
NIS+	O
directory	O
service	O
in	O
Solaris	B-Application
to	O
supersede	O
NIS	B-Operating_System
,	O
which	O
required	O
co-existence	O
of	O
the	O
two	O
directory	O
services	O
within	O
an	O
enterprise	O
to	O
ease	O
migration	O
.	O
</s>
<s>
Sun	O
engineers	O
Thomas	O
Maslen	O
and	O
Sanjay	O
Dani	O
were	O
the	O
first	O
to	O
design	O
and	O
implement	O
the	O
Name	B-Protocol
Service	I-Protocol
Switch	I-Protocol
.	O
</s>
<s>
They	O
fulfilled	O
Solaris	B-Application
requirements	O
with	O
the	O
nsswitch.conf	O
file	O
specification	O
and	O
the	O
implementation	O
choice	O
to	O
load	O
database	O
access	O
modules	O
as	O
dynamically	O
loaded	O
libraries	O
,	O
which	O
Sun	O
was	O
also	O
the	O
first	O
to	O
introduce	O
.	O
</s>
<s>
Sun	O
engineers	O
 '	O
original	O
design	O
of	O
the	O
configuration	O
file	O
and	O
runtime	O
loading	O
of	O
name	O
service	O
back-end	O
libraries	O
has	O
withstood	O
the	O
test	O
of	O
time	O
as	O
operating	B-General_Concept
systems	I-General_Concept
have	O
evolved	O
and	O
new	O
name	O
services	O
are	O
introduced	O
.	O
</s>
<s>
Over	O
the	O
years	O
,	O
programmers	O
ported	O
the	O
NSS	O
configuration	O
file	O
with	O
nearly	O
identical	O
implementations	O
to	O
many	O
other	O
operating	B-General_Concept
systems	I-General_Concept
including	O
FreeBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
Linux	B-Application
,	O
HP-UX	B-Application
,	O
IRIX	B-Operating_System
and	O
AIX	B-Application
.	O
</s>
<s>
More	O
than	O
two	O
decades	O
after	O
the	O
NSS	O
was	O
invented	O
,	O
GNU	B-Language
libc	I-Language
implements	O
it	O
almost	O
identically	O
.	O
</s>
