<s>
gLite	B-Operating_System
(	O
pronounced	O
"	O
gee-lite	O
"	O
)	O
is	O
a	O
middleware	B-General_Concept
computer	O
software	O
project	O
for	O
grid	B-Architecture
computing	I-Architecture
used	O
by	O
the	O
CERN	O
LHC	O
experiments	O
and	O
other	O
scientific	O
domains	O
.	O
</s>
<s>
gLite	B-Operating_System
provides	O
a	O
framework	O
for	O
building	O
applications	O
tapping	O
into	O
distributed	O
computing	O
and	O
storage	O
resources	O
across	O
the	O
Internet	O
.	O
</s>
<s>
The	O
gLite	B-Operating_System
services	O
were	O
adopted	O
by	O
more	O
than	O
250	O
computing	O
centres	O
,	O
and	O
used	O
by	O
more	O
than	O
15000	O
researchers	O
in	O
Europe	O
and	O
around	O
the	O
world	O
.	O
</s>
<s>
After	O
prototyping	O
phases	O
in	O
2004	O
and	O
2005	O
,	O
convergence	O
with	O
the	O
LHC	O
Computing	B-Architecture
Grid	I-Architecture
(	O
LCG-2	O
)	O
distribution	O
was	O
reached	O
in	O
May	O
2006	O
,	O
when	O
gLite	B-Operating_System
3.0	O
was	O
released	O
,	O
and	O
became	O
the	O
official	O
middle-ware	O
of	O
the	O
Enabling	B-Operating_System
Grids	I-Operating_System
for	I-Operating_System
E-sciencE	I-Operating_System
(	O
EGEE	O
)	O
project	O
which	O
ended	O
in	O
2010	O
.	O
</s>
<s>
Development	O
of	O
the	O
gLite	B-Operating_System
middle-ware	O
was	O
then	O
taken	O
over	O
by	O
the	O
European	B-Operating_System
Middleware	I-Operating_System
Initiative	I-Operating_System
,	O
and	O
is	O
now	O
maintained	O
as	O
part	O
of	O
the	O
EMI	O
software	O
stack	O
.	O
</s>
<s>
It	O
runs	O
the	O
Grid	O
middle-ware	O
produced	O
by	O
the	O
"	O
European	B-Operating_System
Middleware	I-Operating_System
Initiative	I-Operating_System
"	O
,	O
many	O
components	O
of	O
which	O
came	O
from	O
the	O
gLite	B-Operating_System
middle-ware	O
.	O
</s>
<s>
The	O
gLite	B-Operating_System
user	O
community	O
is	O
grouped	O
into	O
Virtual	O
Organisations	O
(	O
VOs	O
)	O
.	O
</s>
<s>
A	O
user	O
must	O
join	O
a	O
VO	O
that	O
is	O
supported	O
by	O
the	O
infrastructure	O
running	O
gLite	B-Operating_System
to	O
be	O
authenticated	O
and	O
authorized	O
to	O
using	O
grid	O
resources	O
.	O
</s>
<s>
GSI	O
is	O
based	O
on	O
public	O
key	O
encryption	O
,	O
X.509	O
certificates	O
,	O
and	O
the	O
Secure	B-Protocol
Sockets	I-Protocol
Layer	I-Protocol
(	O
SSL	O
)	O
communication	O
protocol	O
,	O
with	O
extensions	O
for	O
single	O
sign-on	O
and	O
delegation	O
.	O
</s>
<s>
The	O
access	O
point	O
to	O
the	O
gLite	B-Operating_System
Grid	O
is	O
the	O
User	O
Interface	O
(	O
UI	O
)	O
.	O
</s>
<s>
list	O
all	O
the	O
resources	O
suitable	O
to	O
execute	O
a	O
given	O
job	B-General_Concept
;	O
</s>
<s>
There	O
are	O
two	O
CE	O
implementations	O
in	O
gLite	B-Operating_System
3.1	O
:	O
the	O
LCG	O
CE	O
,	O
developed	O
by	O
EDG	O
and	O
used	O
in	O
LCG-22	O
,	O
and	O
the	O
gLite	B-Operating_System
CE	O
,	O
developed	O
by	O
EGEE	O
.	O
</s>
<s>
In	O
gLite	B-Operating_System
3.1	O
supported	O
LRMS	O
types	O
were	O
OpenPBS/PBSPro	O
,	O
Platform	B-Operating_System
LSF	I-Operating_System
,	O
Maui/Torque	O
,	O
BQS	O
and	O
Condor	B-Operating_System
,	O
and	O
Sun	B-Operating_System
Grid	I-Operating_System
Engine	I-Operating_System
.	O
</s>
<s>
Most	O
storage	O
resources	O
are	O
managed	O
by	O
a	O
Storage	B-Application
Resource	I-Application
Manager	I-Application
(	O
SRM	O
)	O
,	O
a	O
middle-ware	O
service	O
providing	O
capabilities	O
like	O
transparent	O
file	O
migration	O
from	O
disk	O
to	O
tape	O
,	O
file	O
pinning	O
,	O
space	O
reservation	O
,	O
etc	O
.	O
</s>
<s>
The	O
Information	O
System	O
that	O
is	O
used	O
in	O
gLite	B-Operating_System
3.1	O
inherits	O
its	O
main	O
concepts	O
from	O
the	O
Globus	O
Monitoring	O
and	O
Discovery	O
Service	O
(	O
MDS	O
)	O
.	O
</s>
<s>
However	O
,	O
the	O
GRIS	O
and	O
GIIS	O
in	O
MDS	O
has	O
been	O
replaced	O
by	O
the	O
(	O
BDII	O
)	O
which	O
is	O
essentially	O
an	O
OpenLDAP	B-Language
server	O
that	O
is	O
updated	O
by	O
an	O
external	O
process	O
.	O
</s>
<s>
Jobs	O
to	O
be	O
submitted	O
are	O
described	O
using	O
the	O
Job	B-General_Concept
Description	O
Language	O
(	O
JDL	O
)	O
,	O
which	O
specifies	O
,	O
for	O
example	O
,	O
which	O
executable	O
to	O
run	O
and	O
its	O
parameters	O
,	O
files	O
to	O
be	O
moved	O
to	O
and	O
from	O
the	O
Worker	O
Node	O
on	O
which	O
the	O
job	B-General_Concept
is	O
run	O
,	O
input	O
Grid	O
files	O
needed	O
,	O
and	O
any	O
requirements	O
on	O
the	O
CE	O
and	O
the	O
Worker	O
Node	O
.	O
</s>
<s>
The	O
choice	O
of	O
CE	O
to	O
which	O
the	O
job	B-General_Concept
is	O
sent	O
is	O
made	O
in	O
a	O
process	O
called	O
match-making	O
,	O
which	O
first	O
selects	O
,	O
among	O
all	O
available	O
CEs	O
,	O
those	O
which	O
fulfill	O
the	O
requirements	O
expressed	O
by	O
the	O
user	O
and	O
which	O
are	O
close	O
to	O
specified	O
input	O
Grid	O
files	O
.	O
</s>
<s>
The	O
RB	O
locates	O
the	O
Grid	O
input	O
files	O
specified	O
in	O
the	O
job	B-General_Concept
description	O
using	O
a	O
service	O
called	O
the	O
Data	O
Location	O
Interface	O
(	O
DLI	O
)	O
,	O
which	O
provides	O
a	O
generic	O
interface	O
to	O
a	O
file	O
catalogue	O
.	O
</s>
<s>
It	O
collects	O
events	O
from	O
many	O
WMS	O
components	O
and	O
records	O
the	O
status	O
and	O
history	O
of	O
the	O
job	B-General_Concept
.	O
</s>
