[daemon.log]Every   daemon  without  a   separate  facility   logs  to
daemon.log.  The  priority of  log events is  not relevent.[debug]File
debug has messages useful for debugging.The priority of log events are
not relevent.[dmesg] After the  kernel has booted, all kernel messages
are written to dmesg for  later reference.This file is not rotated and
only exists for a single boot cycle before being overwritten.Note that
the choice of  the name is a little unfortunate,  as the dmesg command
prints  the  current  kernel  log ring  buffer,which  is  continuously
updated and new kernel events are logged.These messages are written to
kern.log; The dmesg file is not modified until the next restart of the
system.[kern.log] Log messages  with the kern facility end  up in this
file.The  contents are mostly  what the  kernel spits  out,after being
formatted by klogd.[lpr.log]Log messages  with the lpr facility end up
in this file.

[mail.log]  Log entries  related  to the  mail  system(using the  mail
facility) go into  this file.  For easier parsing  by scripts,mail log
entries    are    also    written    to    mail.info,    mail.warn,and
mail.err,according to  their priority.  Unfortunately,Debian's default
MTA,exim4,  does not  use this  file.[messages]Pretty  much everything
that  is not  an  error or  a  trivial log  entry,and  not related  to
authentication,daemons  ,cron(or other  automatic schedulers),mail,and
news goes here.

btmp auth.log syslog boot

btmp shows a log of the file /var/log/btmp, which contains all the bad
login   attempts.    auth.log   receives   log  entries   related   to
authentication,and  other  events  that  are critical  to  privacy  or
security issues.   everything not related to authentication  end up in
syslog file.   syslog is  the catch-all log  file on a  debian system.
log  messages  produced during  the  initialization  sequence will  be
logged to boot.