<s>
A	O
background	B-Operating_System
process	I-Operating_System
is	O
a	O
computer	B-Operating_System
process	I-Operating_System
that	O
runs	O
behind	O
the	O
scenes	O
(	O
i.e.	O
,	O
in	O
the	O
background	O
)	O
and	O
without	O
user	O
intervention	O
.	O
</s>
<s>
The	O
background	B-Operating_System
process	I-Operating_System
usually	O
is	O
a	O
child	O
process	O
created	O
by	O
a	O
control	O
process	O
for	O
processing	O
a	O
computing	O
task	O
.	O
</s>
<s>
On	O
a	O
Windows	B-Application
system	O
,	O
a	O
background	B-Operating_System
process	I-Operating_System
is	O
either	O
a	O
computer	B-Application
program	I-Application
that	O
does	O
not	O
create	O
a	O
user	B-Application
interface	I-Application
,	O
or	O
a	O
Windows	B-Application
service	O
.	O
</s>
<s>
Windows	B-Application
services	O
,	O
on	O
the	O
other	O
hand	O
,	O
are	O
started	O
by	O
Service	O
Control	O
Manager	O
.	O
</s>
<s>
In	O
Windows	B-Application
Vista	I-Application
and	O
later	O
,	O
they	O
are	O
run	O
in	O
a	O
separate	O
session	O
.	O
</s>
<s>
There	O
is	O
no	O
limit	O
to	O
how	O
much	O
a	O
system	O
service	O
or	O
background	B-Operating_System
process	I-Operating_System
can	O
use	O
system	O
resources	O
.	O
</s>
<s>
Indeed	O
,	O
in	O
the	O
Windows	B-Device
Server	I-Device
family	O
of	O
Microsoft	O
operating	B-General_Concept
systems	I-General_Concept
,	O
background	B-Operating_System
processes	I-Operating_System
are	O
expected	O
to	O
be	O
the	O
principal	O
consumers	O
of	O
system	O
resources	O
.	O
</s>
<s>
On	O
a	O
Unix	B-Application
or	O
Unix-like	B-Operating_System
system	I-Operating_System
,	O
a	O
background	B-Operating_System
process	I-Operating_System
or	O
job	O
can	O
be	O
further	O
identified	O
as	O
one	O
whose	O
process	B-Operating_System
group	I-Operating_System
ID	I-Operating_System
differs	O
from	O
its	O
terminal	O
group	O
ID	O
(	O
TGID	O
)	O
.	O
</s>
<s>
(	O
The	O
TGID	O
of	O
a	O
process	O
is	O
the	O
process	O
ID	O
of	O
the	O
process	B-Operating_System
group	I-Operating_System
leader	I-Operating_System
that	O
opened	O
the	O
terminal	O
,	O
which	O
is	O
typically	O
the	O
login	O
shell	O
.	O
</s>
<s>
The	O
TGID	O
identifies	O
the	O
control	O
terminal	O
of	O
the	O
process	B-Operating_System
group	I-Operating_System
.	O
)	O
</s>
<s>
Although	O
background	B-Operating_System
processes	I-Operating_System
are	O
typically	O
used	O
for	O
purposes	O
needing	O
few	O
resources	O
,	O
any	O
process	O
can	O
be	O
run	O
in	O
the	O
background	O
,	O
and	O
such	O
a	O
process	O
will	O
behave	O
like	O
any	O
other	O
process	O
,	O
with	O
the	O
exceptions	O
given	O
above	O
.	O
</s>
<s>
In	O
Windows	B-Device
NT	I-Device
family	I-Device
of	O
operating	B-General_Concept
systems	I-General_Concept
,	O
a	O
Windows	B-Application
service	O
is	O
a	O
dedicated	O
background	B-Operating_System
process	I-Operating_System
.	O
</s>
<s>
A	O
Windows	B-Application
service	O
must	O
conform	O
to	O
the	O
interface	O
rules	O
and	O
protocols	O
of	O
the	O
Service	O
Control	O
Manager	O
,	O
the	O
component	O
responsible	O
for	O
managing	O
Windows	B-Application
services	O
.	O
</s>
<s>
Windows	B-Application
services	O
can	O
be	O
configured	O
to	O
start	O
when	O
the	O
operating	B-General_Concept
system	I-General_Concept
starts	O
,	O
and	O
to	O
run	O
in	O
the	O
background	O
as	O
long	O
as	O
Windows	B-Application
runs	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
operating	B-General_Concept
systems	I-General_Concept
include	O
numerous	O
services	O
which	O
run	O
in	O
context	O
of	O
three	O
user	O
accounts	O
:	O
System	O
,	O
Network	O
Service	O
and	O
Local	O
Service	O
.	O
</s>
<s>
These	O
Windows	B-Application
components	O
are	O
often	O
associated	O
with	O
Host	O
Process	O
for	O
Windows	B-Application
Services	O
:	O
svchost.exe	O
.	O
</s>
<s>
Since	O
Windows	B-Application
services	O
operate	O
in	O
the	O
context	O
of	O
their	O
own	O
dedicated	O
user	O
accounts	O
,	O
they	O
can	O
operate	O
when	O
a	O
user	O
is	O
not	O
logged	O
on	O
.	O
</s>
<s>
Before	O
Windows	B-Application
Vista	I-Application
,	O
services	O
installed	O
as	O
"	O
interactive	O
services	O
"	O
could	O
interact	O
with	O
Windows	B-Application
desktop	B-Application
and	O
show	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
With	O
Windows	B-Application
Vista	I-Application
,	O
however	O
,	O
interactive	O
services	O
became	O
deprecated	B-General_Concept
and	O
ceased	O
operating	O
properly	O
,	O
as	O
a	O
result	O
of	O
Windows	B-Application
Service	O
Hardening	O
.	O
</s>
<s>
The	O
three	O
principal	O
means	O
of	O
managing	O
Windows	B-Application
services	O
are	O
:	O
</s>
<s>
A	O
daemon	B-Operating_System
is	O
a	O
type	O
of	O
background	B-Operating_System
process	I-Operating_System
designed	O
to	O
run	O
continually	O
in	O
the	O
background	O
,	O
waiting	O
for	O
event(s )	O
to	O
occur	O
or	O
condition(s )	O
to	O
be	O
met	O
.	O
</s>
<s>
When	O
launched	O
with	O
the	O
daemon	B-Operating_System
function	O
,	O
daemons	B-Operating_System
are	O
disassociated	O
from	O
their	O
parent	O
terminal	O
.	O
</s>
<s>
From	O
a	O
Unix	B-Application
command	O
line	O
,	O
a	O
background	B-Operating_System
process	I-Operating_System
can	O
be	O
launched	O
using	O
the	O
"	O
&	O
"	O
operator	O
.	O
</s>
<s>
The	O
bg	B-Device
utility	O
can	O
resume	O
a	O
suspended	O
job	O
(	O
sending	O
SIGCONT	B-General_Concept
)	O
,	O
running	O
it	O
in	O
the	O
background	O
.	O
</s>
<s>
The	O
jobs	B-Operating_System
utility	O
will	O
list	O
all	O
processes	O
associated	O
with	O
the	O
current	O
terminal	O
and	O
can	O
be	O
used	O
to	O
bring	O
background	B-Operating_System
processes	I-Operating_System
into	O
the	O
foreground	O
.	O
</s>
<s>
When	O
a	O
login	B-Operating_System
session	I-Operating_System
ends	O
,	O
via	O
explicit	O
logout	O
or	O
network	O
disconnection	O
,	O
all	O
processes	O
,	O
including	O
background	B-Operating_System
processes	I-Operating_System
,	O
will	O
by	O
default	O
be	O
terminated	O
,	O
to	O
prevent	O
them	O
from	O
becoming	O
orphan	O
processes	O
.	O
</s>
<s>
Concretely	O
,	O
when	O
the	O
user	O
exits	O
the	O
launching	O
shell	O
process	O
,	O
as	O
part	O
of	O
shutdown	O
it	O
sends	O
a	O
hangup	O
signal	O
(	O
SIGHUP	B-General_Concept
)	O
to	O
all	O
its	O
jobs	B-Operating_System
,	O
to	O
terminate	O
all	O
the	O
processes	O
in	O
the	O
corresponding	O
process	B-Operating_System
group	I-Operating_System
.	O
</s>
<s>
Or	O
,	O
termination	O
can	O
be	O
prevented	O
by	O
either	O
starting	O
the	O
process	O
via	O
the	O
nohup	B-Device
command	O
(	O
telling	O
the	O
process	O
to	O
ignore	O
SIGHUP	B-General_Concept
)	O
,	O
or	O
by	O
subsequently	O
running	O
disown	B-Application
with	O
the	O
job	O
id	O
,	O
which	O
either	O
removes	O
the	O
job	O
from	O
the	O
job	O
list	O
entirely	O
,	O
or	O
simply	O
prevents	O
SIGHUP	B-General_Concept
from	O
being	O
sent	O
.	O
</s>
<s>
In	O
the	O
latter	O
case	O
when	O
the	O
session	O
ends	O
,	O
the	O
child	O
processes	O
are	O
not	O
terminated	O
,	O
either	O
because	O
they	O
are	O
not	O
sent	O
SIGHUP	B-General_Concept
or	O
because	O
they	O
ignore	O
it	O
,	O
and	O
thus	O
become	O
orphan	O
processes	O
,	O
which	O
are	O
then	O
adopted	O
by	O
the	O
init	B-Operating_System
process	O
(	O
the	O
kernel	O
sets	O
the	O
init	B-Operating_System
process	O
as	O
their	O
parent	O
)	O
,	O
and	O
they	O
continue	O
running	O
without	O
a	O
session	O
,	O
now	O
called	O
daemons	B-Operating_System
.	O
</s>
<s>
In	O
this	O
example	O
running	O
on	O
Unix	B-Application
,	O
the	O
sleep	O
utility	O
was	O
launched	O
into	O
the	O
background	O
.	O
</s>
<s>
Many	O
newer	O
versions	O
of	O
smartphone	B-Application
and	O
PDA	O
operating	B-General_Concept
systems	I-General_Concept
now	O
include	O
the	O
ability	O
to	O
start	O
background	B-Operating_System
processes	I-Operating_System
.	O
</s>
<s>
Due	O
to	O
hardware	O
limits	O
,	O
background	B-Operating_System
processes	I-Operating_System
on	O
mobile	O
operating	B-General_Concept
systems	I-General_Concept
are	O
often	O
restricted	O
to	O
certain	O
tasks	O
or	O
consumption	O
levels	O
.	O
</s>
<s>
On	O
Android	B-Application
,	O
CPU	O
use	O
for	O
background	B-Operating_System
processes	I-Operating_System
may	O
be	O
bounded	O
at	O
5	O
-	O
10%	O
.	O
</s>
<s>
Applications	O
on	O
Apple	O
's	O
iOS	B-Application
are	O
limited	O
to	O
a	O
subset	O
of	O
functions	O
while	O
running	O
in	O
the	O
background	O
.	O
</s>
<s>
On	O
both	O
iOS	B-Application
and	O
Android	B-Application
,	O
background	B-Operating_System
processes	I-Operating_System
can	O
be	O
killed	O
by	O
the	O
system	O
if	O
they	O
are	O
using	O
too	O
much	O
memory	O
.	O
</s>
