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--- console_loglevel [2018/11/23 13:24] – [Files] rpjday
+++ console_loglevel [2018/11/23 15:33] (current) – [Overview] rpjday
@@ Line 1: / Line 1: @@
 ===== Overview =====
-How to mess with ''loglevel'' at boot time.
+Properties of console loglevel, and how to use it.
 ===== Files =====
@@ Line 9: / Line 9: @@
   * [[https://github.com/torvalds/linux/tree/master/include|include/]]
     * [[https://github.com/torvalds/linux/tree/master/include/linux|linux/]]
-      * https://github.com/torvalds/linux/blob/master/include/linux/printk.h|printk.h]]
+      * [[https://github.com/torvalds/linux/blob/master/include/linux/printk.h|printk.h]]
+  * [[https://github.com/torvalds/linux/tree/master/lib|lib/]]
+    * [[https://github.com/torvalds/linux/blob/master/lib/Kconfig.debug|Kconfig.debug]]
+  * [[https://github.com/torvalds/linux/tree/master/init|init/]]
+    * [[https://github.com/torvalds/linux/blob/master/init/main.c|main.c]]
+  * [[https://github.com/torvalds/linux/tree/master/kernel|kernel/]]
+    * [[https://github.com/torvalds/linux/blob/master/kernel/sysctl.c|sysctl.c]]
+    * [[https://github.com/torvalds/linux/tree/master/kernel/printk|printk/]]
+      * [[https://github.com/torvalds/linux/blob/master/kernel/printk/printk.c|printk.c]]
+  * [[https://github.com/torvalds/linux/tree/master/Documentation|Documentation/]]
+    * [[https://github.com/torvalds/linux/tree/master/Documentation/admin-guide|admin-guide/]]
+      * [[https://github.com/torvalds/linux/blob/master/Documentation/admin-guide/kernel-parameters.txt|parameters.txt]]
 ==== Running system files ====
-==== lib/Kconfig.debug ====
+  * /etc/sysctl.conf
+  * /sys/module/printk/parameters
+  * /proc/sys/kernel/printk/*
+===== Kernel parameters =====
 <code>
-config CONSOLE_LOGLEVEL_DEFAULT
+loglevel=       All Kernel Messages with a loglevel smaller than the
-        int "Default console loglevel (1-15)"
+                console loglevel will be printed to the console. It can
-        range 1 15
+                also be changed with klogd or other programs. The
-        default "7"
+                loglevels are defined as follows:
-        help
-          Default loglevel to determine what will be printed on the console.
-          Setting a default here is equivalent to passing in loglevel=<x> in
+(KERN_EMERG)          system is unusable
-          the kernel bootargs. loglevel=<x> continues to override whatever
+(KERN_ALERT)          action must be taken immediately
-          value is specified here as well.
+(KERN_CRIT)           critical conditions
+(KERN_ERR)            error conditions
+(KERN_WARNING)        warning conditions
+(KERN_NOTICE)         normal but significant condition
+(KERN_INFO)           informational
+(KERN_DEBUG)          debug-level messages
+</code>
-          Note: This does not affect the log level of un-prefixed printk()
+<code>
-          usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT
+ignore_loglevel [KNL]
-          option.
+                Ignore loglevel setting - this will print /all/
+                kernel messages to the console. Useful for debugging.
+                We also add it as printk module parameter, so users
+                could change it dynamically, usually by
+                /sys/module/printk/parameters/ignore_loglevel.
+</code>
-config MESSAGE_LOGLEVEL_DEFAULT
+===== Kernel source files =====
-        int "Default message log level (1-7)"
-        range 1 7
-        default "4"
-        help
-          Default log level for printk statements with no specified priority.
-          This was hard-coded to KERN_WARNING since at least 2.6.10 but folks
+==== kernel/printk/printk.c ====
-          that are auditing their logs closely may want to set it to a lower
-          priority.
-          Note: This does not affect what message level gets printed on the console
+<code>
-          by default. To change that, use loglevel=<x> in the kernel bootargs,
+int console_printk[4] = {
-          or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value.
+	CONSOLE_LOGLEVEL_DEFAULT,	/* console_loglevel */
+	MESSAGE_LOGLEVEL_DEFAULT,	/* default_message_loglevel */
+	CONSOLE_LOGLEVEL_MIN,		/* minimum_console_loglevel */
+	CONSOLE_LOGLEVEL_DEFAULT,	/* default_console_loglevel */
+};
 </code>
@@ Line 56: / Line 77: @@
 #define CONSOLE_LOGLEVEL_SILENT  0 /* Mum's the word */
 #define CONSOLE_LOGLEVEL_MIN	 1 /* Minimum loglevel we let people use */
-#define CONSOLE_LOGLEVEL_QUIET	 4 /* Shhh ..., when booted with "quiet" */
 #define CONSOLE_LOGLEVEL_DEBUG	10 /* issue debug messages */
 #define CONSOLE_LOGLEVEL_MOTORMOUTH 15	/* You can't shut this one up */
 /*
- * Default used to be hard-coded at 7, we're now allowing it to be set from
+ * Default used to be hard-coded at 7, quiet used to be hardcoded at 4,
- * kernel config.
+ * we're now allowing both to be set from kernel config.
  */
 #define CONSOLE_LOGLEVEL_DEFAULT CONFIG_CONSOLE_LOGLEVEL_DEFAULT
+#define CONSOLE_LOGLEVEL_QUIET	 CONFIG_CONSOLE_LOGLEVEL_QUIET
 extern int console_printk[];
@@ Line 83: / Line 104: @@
 		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
 }
+</code>
+==== lib/Kconfig.debug ====
+<code>
+config CONSOLE_LOGLEVEL_DEFAULT
+	int "Default console loglevel (1-15)"
+	range 1 15
+	default "7"
+	help
+	  Default loglevel to determine what will be printed on the console.
+	  Setting a default here is equivalent to passing in loglevel=<x> in
+	  the kernel bootargs. loglevel=<x> continues to override whatever
+	  value is specified here as well.
+	  Note: This does not affect the log level of un-prefixed printk()
+	  usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT
+	  option.
+config CONSOLE_LOGLEVEL_QUIET
+	int "quiet console loglevel (1-15)"
+	range 1 15
+	default "4"
+	help
+	  loglevel to use when "quiet" is passed on the kernel commandline.
+	  When "quiet" is passed on the kernel commandline this loglevel
+	  will be used as the loglevel. IOW passing "quiet" will be the
+	  equivalent of passing "loglevel=<CONSOLE_LOGLEVEL_QUIET>"
+config MESSAGE_LOGLEVEL_DEFAULT
+	int "Default message log level (1-7)"
+	range 1 7
+	default "4"
+	help
+	  Default log level for printk statements with no specified priority.
+	  This was hard-coded to KERN_WARNING since at least 2.6.10 but folks
+	  that are auditing their logs closely may want to set it to a lower
+	  priority.
+	  Note: This does not affect what message level gets printed on the console
+	  by default. To change that, use loglevel=<x> in the kernel bootargs,
+or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value.
 </code>