For the purposes of kernel logging, why do I have three different, non-inclusive levels of logging amongst
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 in handy here 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 clients.
According to my
/var/log/kern.log captures only the kernel's messages of any loglevel; i.e. the output of
/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
You may still stumble upon syslog; but the defaults have changed.
journald has replaced syslog, in quite a big portion of systems, including Ubuntu.
This is relevant because you won't be finding
/var/log/messages that often anymore.
journald doesn't write plaintext logs — it uses its own, compressed and partially authenticated format.
Search online for e.g. journalctl cheatsheet, or just study
man 8 systemd-journald,
man 1 journalctl yourself.
Syslog and journald are, to a degree, cross-compatible; you can transport logs between them in either direction. However, you won't get plaintext logs a-la
/var/log/messages with journald; and you won't get structured (
journalctl -o json-pretty) and authenticated logging with syslog.
- syslog contains all the messages except of type auth.
- messages contains only generic non-critical messages. The category is
- For complete log look at
/var/log/kern.logcontains kernel messages.
- log files are just a convention spelled out in /etc/syslog.conf
syslog(3)for more information
Check this page about differences between messages and syslog