<s>
anacron	B-Device
is	O
a	O
computer	B-Application
program	I-Application
that	O
performs	O
periodic	O
command	O
scheduling	O
,	O
which	O
is	O
traditionally	O
done	O
by	O
cron	B-General_Concept
,	O
but	O
without	O
assuming	O
that	O
the	O
system	O
is	O
running	O
continuously	O
.	O
</s>
<s>
anacron	B-Device
was	O
originally	O
conceived	O
and	O
implemented	O
by	O
Christian	O
Schwarz	O
in	O
Perl	B-Language
,	O
for	O
the	O
Unix	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
It	O
was	O
later	O
rewritten	O
in	O
C	B-Language
by	O
Itai	O
Tzur	O
;	O
maintainers	O
have	O
included	O
Sean	O
'	O
Shaleh	O
 '	O
Perry	O
and	O
Pascal	O
Hakim	O
.	O
</s>
<s>
It	O
is	O
a	O
dependency	O
of	O
cronie	O
which	O
is	O
maintained	O
by	O
Red	O
Hat	O
,	O
and	O
Red	O
Hat	O
updates	O
to	O
cronie	O
have	O
included	O
updates	O
to	O
anacron	B-Device
as	O
well	O
.	O
</s>
<s>
Unix	B-Application
systems	I-Application
commonly	O
run	O
"	O
housekeeping	O
chores	O
"	O
such	O
as	O
log	B-Application
rotation	I-Application
,	O
unused	O
files	O
deletion	O
,	O
indexing	O
local	O
files	O
for	O
the	O
search	O
engine	O
,	O
sending	O
disk	O
usage	O
reports	O
,	O
etc	O
.	O
</s>
<s>
A	O
program	O
called	O
cron	B-General_Concept
may	O
be	O
used	O
to	O
schedule	O
these	O
tasks	O
.	O
</s>
<s>
With	O
cron	B-General_Concept
,	O
tasks	O
are	O
commonly	O
scheduled	O
to	O
be	O
executed	O
when	O
the	O
system	O
is	O
expected	O
to	O
be	O
idle	O
.	O
</s>
<s>
If	O
the	O
system	O
is	O
off	O
at	B-Device
the	O
moment	O
a	O
task	O
should	O
be	O
run	O
,	O
it	O
will	O
not	O
be	O
executed	O
.	O
</s>
<s>
Anacron	B-Device
is	O
different	O
and	O
moves	O
tasks	O
to	O
different	O
moments	O
so	O
they	O
are	O
run	O
when	O
the	O
system	O
is	O
on	O
and	O
utilising	O
cron	B-General_Concept
.	O
</s>
<s>
Only	O
the	O
system	B-Application
administrator	I-Application
can	O
configure	O
anacron	B-Device
tasks	O
.	O
</s>
<s>
In	O
contrast	O
,	O
cron	B-General_Concept
allows	O
non-admin	O
users	O
to	O
configure	O
scheduled	O
tasks	O
.	O
</s>
<s>
If	O
necessary	O
,	O
a	O
non-admin	O
user	O
can	O
use	O
the	O
at	B-Device
Unix	B-Application
command	I-Application
to	O
request	O
a	O
scheduled	O
task	O
(	O
which	O
is	O
guaranteed	O
to	O
run	O
)	O
.	O
</s>
<s>
Upon	O
starting	O
,	O
this	O
command	O
can	O
then	O
automatically	O
request	O
to	O
run	O
itself	O
at	B-Device
a	O
future	O
date	O
,	O
thus	O
giving	O
the	O
appearance	O
of	O
a	O
regularly	O
scheduled	O
task	O
,	O
with	O
guaranteed	O
execution	O
.	O
</s>
<s>
anacron	B-Device
can	O
run	O
tasks	O
only	O
once	O
a	O
day	O
(	O
or	O
less	O
often	O
such	O
as	O
weekly	O
or	O
monthly	O
)	O
.	O
</s>
<s>
In	O
contrast	O
,	O
cron	B-General_Concept
allows	O
tasks	O
to	O
run	O
as	O
often	O
as	O
every	O
minute	O
(	O
but	O
does	O
not	O
guarantee	O
their	O
execution	O
if	O
the	O
system	O
goes	O
down	O
)	O
.	O
</s>
<s>
In	O
practice	O
,	O
this	O
is	O
not	O
usually	O
an	O
issue	O
,	O
since	O
it	O
is	O
rare	O
to	O
have	O
a	O
task	O
that	O
must	O
be	O
guaranteed	O
to	O
run	O
more	O
often	O
than	O
(	O
at	B-Device
least	O
)	O
once	O
a	O
day	O
—	O
especially	O
on	O
a	O
system	O
that	O
is	O
not	O
necessarily	O
running	O
at	B-Device
all	O
times	O
.	O
</s>
<s>
If	O
the	O
system	O
is	O
rebooted	O
or	O
started	O
after	O
midnight	O
,	O
the	O
daily	O
tasks	O
are	O
run	O
after	O
a	O
user-specified	O
delay	O
in	O
synchronized	O
fashion	O
(	O
sequential	O
order	O
)	O
,	O
so	O
only	O
one	O
anacron-task	O
is	O
running	O
at	B-Device
a	O
time	O
.	O
</s>
<s>
In	O
contrast	O
,	O
cron	B-General_Concept
will	O
only	O
run	O
daily	O
tasks	O
at	B-Device
the	O
time	O
set	O
(	O
e.g.	O
</s>
<s>
fcron	B-Device
is	O
another	O
implementation	O
of	O
cron	B-General_Concept
,	O
which	O
attempts	O
to	O
fulfill	O
the	O
roles	O
of	O
both	O
Vixiecron	O
and	O
anacron	B-Device
.	O
</s>
