For the purposes of kernel logging, why do I have three different, non-inclusive levels of logging amongst /var/log/messages, /var/log/syslog, and /var/log/kern.log?
Syslog is a standard logging facility. It collects messages of various programs and services including the kernel, and stores them, depending on setup, in a bunch of log files typically under /var/log. In some datacenter setups there are hundreds of devices each with its own log; syslog comes here handy too. One just sets up a dedicated syslog server which collects all the individual device logs over the network. Syslog can also save logs to databases, and other stuff.
According to my /etc/syslog.conf, default /var/log/kern.log captures only the kernel's messages of any loglevel; i.e. the output of dmesg.
/var/log/messages instead aims at storing valuable, non-debug and non-critical messages. This log should be considered the "general system activity" log.
/var/log/syslog in turn logs everything, except auth related messages.
Other insteresting standard logs managed by syslog are /var/log/auth.log, /var/log/mail.log.
Regarding your question: if you need solely kernel messages log, use the kern.log or call dmesg.
原文地址：http://askubuntu.com/questions/26237/difference-between-var-log-messages-var-log-syslog-and-var-l...