/etc/rsyslog.conf

# local timestamp template
$template LocalTimeTraditionalFileFormat,"%timegenerated% %HOSTNAME% %syslogtag%%msg:::sp-if-no-1st-sp%%msg:::drop-last-lf%\n"
$template LocalTimeFileFormat,"%timegenerated:::date-rfc3339% %HOSTNAME% %syslogtag%%msg:::sp-if-no-1st-sp%%msg:::drop-last-lf%\n"

$ActionFileDefaultTemplate LocalTimeTraditionalFileFormat
#$ActionFileDefaultTemplate LocalTimeFileFormat