Documentation/networking/netconsole.txt - kernel/mindspeed - Git at Google


 started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
 2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003

 Please send bug reports to Matt Mackall <mpm@selenic.com>
 and Satyam Sharma <satyam.sharma@gmail.com>

 Introduction:
 =============

 This module logs kernel printk messages over UDP allowing debugging of
 problem where disk logging fails and serial consoles are impractical.

 It can be used either built-in or as a module. As a built-in,
 netconsole initializes immediately after NIC cards and will bring up
 the specified interface as soon as possible. While this doesn't allow
 capture of early kernel panics, it does capture most of the boot
 process.

 Sender and receiver configuration:
 ==================================

 It takes a string configuration parameter "netconsole" in the
 following format:

  netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]

    where
         src-port      source for UDP packets (defaults to 6665)
         src-ip        source IP to use (interface address)
         dev           network interface (eth0)
         tgt-port      port for logging agent (6666)
         tgt-ip        IP address for logging agent
         tgt-macaddr   ethernet MAC address for logging agent (broadcast)

 Examples:

  linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc

   or

  insmod netconsole netconsole=@/,@10.0.0.2/

 It also supports logging to multiple remote agents by specifying
 parameters for the multiple agents separated by semicolons and the
 complete string enclosed in "quotes", thusly:

  modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"

 Built-in netconsole starts immediately after the TCP stack is
 initialized and attempts to bring up the supplied dev at the supplied
 address.

 The remote host can run either 'netcat -u -l -p <port>',
 'nc -l -u <port>' or syslogd.

 Dynamic reconfiguration:
 ========================

 Dynamic reconfigurability is a useful addition to netconsole that enables
 remote logging targets to be dynamically added, removed, or have their
 parameters reconfigured at runtime from a configfs-based userspace interface.
 [ Note that the parameters of netconsole targets that were specified/created
 from the boot/module option are not exposed via this interface, and hence
 cannot be modified dynamically. ]

 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
 netconsole module (or kernel, if netconsole is built-in).

 Some examples follow (where configfs is mounted at the /sys/kernel/config
 mountpoint).

 To add a remote logging target (target names can be arbitrary):

  cd /sys/kernel/config/netconsole/
  mkdir target1

 Note that newly created targets have default parameter values (as mentioned
 above) and are disabled by default -- they must first be enabled by writing
 "1" to the "enabled" attribute (usually after setting parameters accordingly)
 as described below.

 To remove a target:

  rmdir /sys/kernel/config/netconsole/othertarget/

 The interface exposes these parameters of a netconsole target to userspace:

 	enabled		Is this target currently enabled?	(read-write)
 	dev_name	Local network interface name		(read-write)
 	local_port	Source UDP port to use			(read-write)
 	remote_port	Remote agent's UDP port			(read-write)
 	local_ip	Source IP address to use		(read-write)
 	remote_ip	Remote agent's IP address		(read-write)
 	local_mac	Local interface's MAC address		(read-only)
 	remote_mac	Remote agent's MAC address		(read-write)

 The "enabled" attribute is also used to control whether the parameters of
 a target can be updated or not -- you can modify the parameters of only
 disabled targets (i.e. if "enabled" is 0).

 To update a target's parameters:

  cat enabled				# check if enabled is 1
  echo 0 > enabled			# disable the target (if required)
  echo eth2 > dev_name			# set local interface
  echo 10.0.0.4 > remote_ip		# update some parameter
  echo cb:a9:87:65:43:21 > remote_mac	# update more parameters
  echo 1 > enabled			# enable target again

 You can also update the local interface dynamically. This is especially
 useful if you want to use interfaces that have newly come up (and may not
 have existed when netconsole was loaded / initialized).

 Miscellaneous notes:
 ====================

 WARNING: the default target ethernet setting uses the broadcast
 ethernet address to send packets, which can cause increased load on
 other systems on the same ethernet segment.

 TIP: some LAN switches may be configured to suppress ethernet broadcasts
 so it is advised to explicitly specify the remote agents' MAC addresses
 from the config parameters passed to netconsole.

 TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:

  ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2

 TIP: in case the remote logging agent is on a separate LAN subnet than
 the sender, it is suggested to try specifying the MAC address of the
 default gateway (you may use /sbin/route -n to find it out) as the
 remote MAC address instead.

 NOTE: the network device (eth1 in the above case) can run any kind
 of other network traffic, netconsole is not intrusive. Netconsole
 might cause slight delays in other traffic if the volume of kernel
 messages is high, but should have no other impact.

 NOTE: if you find that the remote logging agent is not receiving or
 printing all messages from the sender, it is likely that you have set
 the "console_loglevel" parameter (on the sender) to only send high
 priority messages to the console. You can change this at runtime using:

  dmesg -n 8

 or by specifying "debug" on the kernel command line at boot, to send
 all kernel messages to the console. A specific value for this parameter
 can also be set using the "loglevel" kernel boot option. See the
 dmesg(8) man page and Documentation/kernel-parameters.txt for details.

 Netconsole was designed to be as instantaneous as possible, to
 enable the logging of even the most critical kernel bugs. It works
 from IRQ contexts as well, and does not enable interrupts while
 sending packets. Due to these unique needs, configuration cannot
 be more automatic, and some fundamental limitations will remain:
 only IP networks, UDP packets and ethernet devices are supported.

	started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
	2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003

	Please send bug reports to Matt Mackall <mpm@selenic.com>
	and Satyam Sharma <satyam.sharma@gmail.com>

	Introduction:
	=============

	This module logs kernel printk messages over UDP allowing debugging of
	problem where disk logging fails and serial consoles are impractical.

	It can be used either built-in or as a module. As a built-in,
	netconsole initializes immediately after NIC cards and will bring up
	the specified interface as soon as possible. While this doesn't allow
	capture of early kernel panics, it does capture most of the boot
	process.

	Sender and receiver configuration:
	==================================

	It takes a string configuration parameter "netconsole" in the
	following format:

	netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]

	where
	src-port source for UDP packets (defaults to 6665)
	src-ip source IP to use (interface address)
	dev network interface (eth0)
	tgt-port port for logging agent (6666)
	tgt-ip IP address for logging agent
	tgt-macaddr ethernet MAC address for logging agent (broadcast)

	Examples:

	linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc

	or

	insmod netconsole netconsole=@/,@10.0.0.2/

	It also supports logging to multiple remote agents by specifying
	parameters for the multiple agents separated by semicolons and the
	complete string enclosed in "quotes", thusly:

	modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"

	Built-in netconsole starts immediately after the TCP stack is
	initialized and attempts to bring up the supplied dev at the supplied
	address.

	The remote host can run either 'netcat -u -l -p <port>',
	'nc -l -u <port>' or syslogd.

	Dynamic reconfiguration:
	========================

	Dynamic reconfigurability is a useful addition to netconsole that enables
	remote logging targets to be dynamically added, removed, or have their
	parameters reconfigured at runtime from a configfs-based userspace interface.
	[ Note that the parameters of netconsole targets that were specified/created
	from the boot/module option are not exposed via this interface, and hence
	cannot be modified dynamically. ]

	To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
	netconsole module (or kernel, if netconsole is built-in).

	Some examples follow (where configfs is mounted at the /sys/kernel/config
	mountpoint).

	To add a remote logging target (target names can be arbitrary):

	cd /sys/kernel/config/netconsole/
	mkdir target1

	Note that newly created targets have default parameter values (as mentioned
	above) and are disabled by default -- they must first be enabled by writing
	"1" to the "enabled" attribute (usually after setting parameters accordingly)
	as described below.

	To remove a target:

	rmdir /sys/kernel/config/netconsole/othertarget/

	The interface exposes these parameters of a netconsole target to userspace:

	enabled Is this target currently enabled? (read-write)
	dev_name Local network interface name (read-write)
	local_port Source UDP port to use (read-write)
	remote_port Remote agent's UDP port (read-write)
	local_ip Source IP address to use (read-write)
	remote_ip Remote agent's IP address (read-write)
	local_mac Local interface's MAC address (read-only)
	remote_mac Remote agent's MAC address (read-write)

	The "enabled" attribute is also used to control whether the parameters of
	a target can be updated or not -- you can modify the parameters of only
	disabled targets (i.e. if "enabled" is 0).

	To update a target's parameters:

	cat enabled # check if enabled is 1
	echo 0 > enabled # disable the target (if required)
	echo eth2 > dev_name # set local interface
	echo 10.0.0.4 > remote_ip # update some parameter
	echo cb:a9:87:65:43:21 > remote_mac # update more parameters
	echo 1 > enabled # enable target again

	You can also update the local interface dynamically. This is especially
	useful if you want to use interfaces that have newly come up (and may not
	have existed when netconsole was loaded / initialized).

	Miscellaneous notes:
	====================

	WARNING: the default target ethernet setting uses the broadcast
	ethernet address to send packets, which can cause increased load on
	other systems on the same ethernet segment.

	TIP: some LAN switches may be configured to suppress ethernet broadcasts
	so it is advised to explicitly specify the remote agents' MAC addresses
	from the config parameters passed to netconsole.

	TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:

	ping -c 1 10.0.0.2 ; /sbin/arp -n \| grep 10.0.0.2

	TIP: in case the remote logging agent is on a separate LAN subnet than
	the sender, it is suggested to try specifying the MAC address of the
	default gateway (you may use /sbin/route -n to find it out) as the
	remote MAC address instead.

	NOTE: the network device (eth1 in the above case) can run any kind
	of other network traffic, netconsole is not intrusive. Netconsole
	might cause slight delays in other traffic if the volume of kernel
	messages is high, but should have no other impact.

	NOTE: if you find that the remote logging agent is not receiving or
	printing all messages from the sender, it is likely that you have set
	the "console_loglevel" parameter (on the sender) to only send high
	priority messages to the console. You can change this at runtime using:

	dmesg -n 8

	or by specifying "debug" on the kernel command line at boot, to send
	all kernel messages to the console. A specific value for this parameter
	can also be set using the "loglevel" kernel boot option. See the
	dmesg(8) man page and Documentation/kernel-parameters.txt for details.

	Netconsole was designed to be as instantaneous as possible, to
	enable the logging of even the most critical kernel bugs. It works
	from IRQ contexts as well, and does not enable interrupts while
	sending packets. Due to these unique needs, configuration cannot
	be more automatic, and some fundamental limitations will remain:
	only IP networks, UDP packets and ethernet devices are supported.