utmp shows who is currently logged in user.
wtmp shows all the history of logged in and logout
both of them are binary so in order to see in human readilbe format we need to use last command
dmesg = print or control the kernel ring buffer.
kernel ring bufffer =
rsyslogd = reliable and extended syslogd , is a system utility providing support for message logging.
who writes these log file? rsylogd is responsilbe for listening those log message and write it on appropriate log file.
these are the lists of facilities that can be logged.
levels of priorities
whenever these daemon facility generates a log, irrespective of which priority the messages it will be logged. * means log every message
if priority is info than except debug level every other level of message will be logged.
oldest file will be deleted by logrotate.