<s>
These	O
events	O
may	O
occur	O
in	O
the	O
operating	B-General_Concept
system	I-General_Concept
or	O
in	O
other	O
software	O
.	O
</s>
<s>
Logging	O
is	O
particularly	O
important	O
in	O
multi-user	B-Operating_System
software	I-Operating_System
,	O
to	O
have	O
a	O
central	O
overview	O
of	O
the	O
operation	O
of	O
the	O
system	O
.	O
</s>
<s>
Alternatively	O
,	O
the	O
messages	O
may	O
be	O
written	O
to	O
a	O
dedicated	O
logging	O
system	O
or	O
to	O
a	O
log	B-Application
management	I-Application
software	I-Application
,	O
where	O
it	O
is	O
stored	O
in	O
a	O
database	O
or	O
on	O
a	O
different	O
computer	O
system	O
.	O
</s>
<s>
Many	O
operating	B-General_Concept
systems	I-General_Concept
,	O
software	O
frameworks	O
and	O
programs	O
include	O
a	O
logging	O
system	O
.	O
</s>
<s>
A	O
widely	O
used	O
logging	O
standard	O
is	O
Syslog	B-Protocol
,	O
defined	O
in	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
RFC	O
5424	O
)	O
.	O
</s>
<s>
The	O
Syslog	B-Protocol
standard	O
enables	O
a	O
dedicated	O
,	O
standardized	O
subsystem	O
to	O
generate	O
,	O
filter	O
,	O
record	O
,	O
and	O
analyze	O
log	O
messages	O
.	O
</s>
<s>
They	O
are	O
essential	O
to	O
understand	O
the	O
activities	O
of	O
complex	O
systems	O
,	O
particularly	O
in	O
the	O
case	O
of	O
applications	O
with	O
little	O
user	O
interaction	O
(	O
such	O
as	O
server	B-Application
applications	I-Application
)	O
.	O
</s>
<s>
Most	O
database	O
systems	O
maintain	O
some	O
kind	O
of	O
transaction	O
log	O
,	O
which	O
are	O
not	O
mainly	O
intended	O
as	O
an	O
audit	O
trail	O
for	O
later	O
analysis	O
,	O
and	O
are	O
not	O
intended	O
to	O
be	O
human-readable	B-General_Concept
.	O
</s>
<s>
These	O
logs	O
record	O
changes	O
to	O
the	O
stored	O
data	O
to	O
allow	O
the	O
database	O
to	O
recover	O
from	O
crashes	B-General_Concept
or	O
other	O
data	O
errors	O
and	O
maintain	O
the	O
stored	O
data	O
in	O
a	O
consistent	O
state	O
.	O
</s>
<s>
Internet	B-Protocol
Relay	I-Protocol
Chat	I-Protocol
(	O
IRC	B-Protocol
)	O
,	O
instant	B-Application
messaging	I-Application
(	O
IM	O
)	O
programs	O
,	O
peer-to-peer	O
file	O
sharing	O
clients	O
with	O
chat	O
functions	O
,	O
and	O
multiplayer	O
games	O
(	O
especially	O
MMORPGs	B-Protocol
)	O
commonly	O
have	O
the	O
ability	O
to	O
automatically	O
save	O
textual	O
communication	O
,	O
both	O
public	O
(	O
IRC	B-Protocol
channel/IM	O
conference/MMO	O
public/party	O
chat	O
messages	O
)	O
and	O
private	O
chat	O
between	O
users	O
,	O
as	O
message	O
logs	O
.	O
</s>
<s>
Message	O
logs	O
are	O
almost	O
universally	O
plain	O
text	O
files	O
,	O
but	O
IM	O
and	O
VoIP	B-Application
clients	O
(	O
which	O
support	O
textual	O
chat	O
,	O
e.g.	O
</s>
<s>
Skype	O
)	O
might	O
save	O
them	O
in	O
HTML	B-Language
files	I-Language
or	O
in	O
a	O
custom	O
format	O
to	O
ease	O
reading	O
or	O
enable	O
encryption	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
IRC	B-Protocol
software	O
,	O
message	O
logs	O
often	O
include	O
system/server	O
messages	O
and	O
entries	O
related	O
to	O
channel	O
and	O
user	O
changes	O
(	O
e.g.	O
</s>
<s>
topic	O
change	O
,	O
user	O
joins/exits/kicks/bans	O
,	O
nickname	O
changes	O
,	O
the	O
user	O
status	O
changes	O
)	O
,	O
making	O
them	O
more	O
like	O
a	O
combined	O
message/event	O
log	O
of	O
the	O
channel	O
in	O
question	O
,	O
but	O
such	O
a	O
log	O
is	O
n't	O
comparable	O
to	O
a	O
true	O
IRC	B-Protocol
server	B-Application
event	O
log	O
,	O
because	O
it	O
only	O
records	O
user-visible	O
events	O
for	O
the	O
time	O
frame	O
the	O
user	O
spent	O
being	O
connected	O
to	O
a	O
certain	O
channel	O
.	O
</s>
<s>
Instant	B-Application
messaging	I-Application
and	O
VoIP	B-Application
clients	O
often	O
offer	O
the	O
chance	O
to	O
store	O
encrypted	O
logs	O
to	O
enhance	O
the	O
user	O
's	O
privacy	O
.	O
</s>
<s>
Some	O
privacy	O
focused	O
messaging	O
services	O
,	O
such	O
as	O
Signal	B-Application
,	O
record	O
minimal	O
logs	O
about	O
users	O
,	O
limiting	O
their	O
information	O
to	O
connection	O
times	O
.	O
</s>
<s>
A	O
server	B-Application
log	I-Application
is	O
a	O
log	O
file	O
(	O
or	O
several	O
files	O
)	O
automatically	O
created	O
and	O
maintained	O
by	O
a	O
server	B-Application
consisting	O
of	O
a	O
list	O
of	O
activities	O
it	O
performed	O
.	O
</s>
<s>
A	O
typical	O
example	O
is	O
a	O
web	O
server	B-Application
log	I-Application
which	O
maintains	O
a	O
history	O
of	O
page	O
requests	O
.	O
</s>
<s>
The	O
W3C	O
maintains	O
a	O
standard	O
format	O
(	O
the	O
Common	O
Log	O
Format	O
)	O
for	O
web	O
server	B-Application
log	I-Application
files	O
,	O
but	O
other	O
proprietary	O
formats	O
exist	O
.	O
</s>
<s>
Some	O
servers	O
can	O
log	O
information	O
to	O
computer	O
readable	O
formats	O
(	O
such	O
as	O
JSON	B-General_Concept
)	O
versus	O
the	O
human	B-General_Concept
readable	I-General_Concept
standard	O
.	O
</s>
<s>
Information	O
about	O
the	O
request	O
,	O
including	O
client	B-Protocol
IP	B-Protocol
address	I-Protocol
,	O
request	O
date/time	O
,	O
page	O
requested	O
,	O
HTTP	B-Protocol
code	O
,	O
bytes	O
served	O
,	O
user	B-Protocol
agent	I-Protocol
,	O
and	O
referrer	B-Protocol
are	O
typically	O
added	O
.	O
</s>
<s>
This	O
data	O
can	O
be	O
combined	O
into	O
a	O
single	O
file	O
,	O
or	O
separated	O
into	O
distinct	O
logs	O
,	O
such	O
as	O
an	O
access	O
log	O
,	O
error	O
log	O
,	O
or	O
referrer	B-Protocol
log	O
.	O
</s>
<s>
However	O
,	O
server	B-Application
logs	I-Application
typically	O
do	O
not	O
collect	O
user-specific	O
information	O
.	O
</s>
<s>
A	O
statistical	O
analysis	O
of	O
the	O
server	B-Application
log	I-Application
may	O
be	O
used	O
to	O
examine	O
traffic	O
patterns	O
by	O
time	O
of	O
day	O
,	O
day	O
of	O
week	O
,	O
referrer	B-Protocol
,	O
or	O
user	B-Protocol
agent	I-Protocol
.	O
</s>
<s>
Efficient	O
web	O
site	O
administration	O
,	O
adequate	O
hosting	O
resources	O
and	O
the	O
fine	O
tuning	O
of	O
sales	O
efforts	O
can	O
be	O
aided	O
by	O
analysis	O
of	O
the	O
web	O
server	B-Application
logs	I-Application
.	O
</s>
