Debugging by printing - Revision history

Tim Bird: /* Printk from userspace */

2013-03-21T21:39:39Z

‎Printk from userspace

2013-03-18T20:03:34Z

‎Using CONFIG_DEBUG_LL and printascii() (ARM only)

2012-06-21T16:20:09Z

‎Netconsole resources

2012-06-21T16:19:56Z

‎NetConsole: create netconsole resources section, and add link to Sarah Sharp blog entry

2012-04-03T21:30:21Z

2012-04-03T21:26:17Z

‎Internals

2012-04-03T21:25:30Z

‎Internals: added dmesg -s

2012-04-03T21:19:50Z

‎Dmesg

2012-04-03T21:17:24Z

Printk was consolidated with Debugging_by_printing - so can be removed

2012-04-03T21:14:15Z

Moved / Added section about other printk pages here

@@ Line 226: / Line 226: @@
 '''Note:''' Don't confuse this with printf - we are printing a kernel message
 from userspace here.
 == Internals / Changing the size of the printk buffer ==

@@ Line 336: / Line 336: @@
 === Using CONFIG_DEBUG_LL and printascii() (ARM only) ===
 If the kernel fails before the serial console is enabled, you can use CONFIG_DEBUG_LL to add extra debug output routines to the kernel.  These are printascii, printch and printhex. These routines print directly to the serial port, bypassing the console code, and are available earlier in machine initialization.
 Here is an e-mail exchange seen on the linux-embedded mailing list (with answer by George Davis):[http://www.mail-archive.com/linux-embedded@vger.kernel.org/msg00223.html]

@@ Line 392: / Line 392: @@
 === Netconsole resources ===
-see
+See
 [http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/networking/netconsole.txt;hb=HEAD Documentation/networking/netconsole.txt]
 for more details.

@@ Line 390: / Line 390: @@
   $ telnet 10.0.0.2 6666
 see
 [http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/networking/netconsole.txt;hb=HEAD Documentation/networking/netconsole.txt]
 for more details.
 == Misc ==

← Older revision		Revision as of 21:30, 3 April 2012
Line 1:		Line 1:
	Probably the simplest way to get some debug information from your kernel code is by printing out various information with the kernel's equivalent of printf - the printk function and its derivatives.		Probably the simplest way to get some debug information from your kernel code is by printing out various information with the kernel's equivalent of printf - the printk function and its derivatives.
		+	The k in printk is used to specifically remind kernel developers that the environment is different.

	== Usage ==		== Usage ==

@@ Line 242: / Line 242: @@
 Using a reasonably large buffer size should give you enough time to read your
 important messages before they are overwritten.
 The kernel log buffer is accessible for reading from userspace by ''/proc/kmsg''.

@@ Line 390: / Line 390: @@
 == Misc ==
-=== Dmesg ===
+=== Dmesg / Clearing the buffer ===
   dmesg -c
 clears the dmesg buffer.

@@ Line 457: / Line 457: @@
 * [http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=include/linux/printk.h;hb=HEAD include/linux/printk.h] printk header file
 * [http://www.embedded-bits.co.uk/2010/printk-format-specifiers/ Blog Entry about the different %p format specifiers]
 * [http://lwn.net/Articles/487437/ LWN.net: The perils of pr_info()]
 * [http://www.ibm.com/developerworks/linux/library/l-kernel-logging-apis/index.html Kernel logging: APIs and implementation, Tim Jones (for IBM)] (nice article)

@@ Line 449: / Line 449: @@
 * [[Linux Device Drivers]], Corbet, Rubini and Kroah-Hartmann, 3rd Edition, Chapter 4 Section 2
 * [[Essential Linux Device Drivers]]
 * [http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/printk-formats.txt;hb=HEAD Documentation/printk-formats.txt]
@@ Line 459: / Line 460: @@
 * [http://lwn.net/Articles/487437/ LWN.net: The perils of pr_info()]
 * [http://www.ibm.com/developerworks/linux/library/l-kernel-logging-apis/index.html Kernel logging: APIs and implementation, Tim Jones (for IBM)] (nice article)
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