What do the values in printk kernel parameter mean in linux?

africaele

$ sysctl kernel.printk
kernel.printk = 7       4       1       7

The text below says syslog but, most Linux systems now use rsyslog. The man page for syslog may not exist.

printk:

The four values in printk denote: console_loglevel,
default_message_loglevel, minimum_console_loglevel and
default_console_loglevel respectively.

These values influence printk() behavior when printing or
logging error messages. See 'man 2 syslog' for more info on
the different loglevels.

- console_loglevel: messages with a higher priority than
  this will be printed to the console

- default_message_loglevel: messages without an explicit priority
  will be printed with this priority

- minimum_console_loglevel: minimum (highest) value to which
  console_loglevel can be set

- default_console_loglevel: default value for console_loglevel

In the example this equates to the following, which is the default setting on redhat.

console_loglevel = 7
default_message_loglevel = 4
minimum_console_loglevel = 1
default_console_loglevel = 7

The numbers relate to the following:

Supported log levels (priorities):
0   emerg - system is unusable
1   alert - action must be taken immediately
2    crit - critical conditions
3     err - error conditions
4    warn - warning conditions
5  notice - normal but significant condition
6    info - informational
7   debug - debug-level messages

Redhat descriptions of the log levels.

The log-level values break down in this order:

0 — Kernel emergency. The system is unusable.
1 — Kernel alert. Action must be taken immediately.
2 — Condition of the kernel is considered critical.
3 — General kernel error condition.
4 — General kernel warning condition.
5 — Kernel notice of a normal but significant condition.
6 — Kernel informational message.
7 — Kernel debug-level messages.