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Based on kernel version 4.1. Page generated on 2015-06-28 12:13 EST.

2	started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
3	2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003
4	IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
6	Please send bug reports to Matt Mackall <mpm@selenic.com>
7	Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
9	Introduction:
10	=============
12	This module logs kernel printk messages over UDP allowing debugging of
13	problem where disk logging fails and serial consoles are impractical.
15	It can be used either built-in or as a module. As a built-in,
16	netconsole initializes immediately after NIC cards and will bring up
17	the specified interface as soon as possible. While this doesn't allow
18	capture of early kernel panics, it does capture most of the boot
19	process.
21	Sender and receiver configuration:
22	==================================
24	It takes a string configuration parameter "netconsole" in the
25	following format:
27	 netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
29	   where
30	        src-port      source for UDP packets (defaults to 6665)
31	        src-ip        source IP to use (interface address)
32	        dev           network interface (eth0)
33	        tgt-port      port for logging agent (6666)
34	        tgt-ip        IP address for logging agent
35	        tgt-macaddr   ethernet MAC address for logging agent (broadcast)
37	Examples:
39	 linux netconsole=4444@,9353@
41	  or
43	 insmod netconsole netconsole=@/,@
45	  or using IPv6
47	 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
49	It also supports logging to multiple remote agents by specifying
50	parameters for the multiple agents separated by semicolons and the
51	complete string enclosed in "quotes", thusly:
53	 modprobe netconsole netconsole="@/,@;@/eth1,6892@"
55	Built-in netconsole starts immediately after the TCP stack is
56	initialized and attempts to bring up the supplied dev at the supplied
57	address.
59	The remote host has several options to receive the kernel messages,
60	for example:
62	1) syslogd
64	2) netcat
66	   On distributions using a BSD-based netcat version (e.g. Fedora,
67	   openSUSE and Ubuntu) the listening port must be specified without
68	   the -p switch:
70	   'nc -u -l -p <port>' / 'nc -u -l <port>' or
71	   'netcat -u -l -p <port>' / 'netcat -u -l <port>'
73	3) socat
75	   'socat udp-recv:<port> -'
77	Dynamic reconfiguration:
78	========================
80	Dynamic reconfigurability is a useful addition to netconsole that enables
81	remote logging targets to be dynamically added, removed, or have their
82	parameters reconfigured at runtime from a configfs-based userspace interface.
83	[ Note that the parameters of netconsole targets that were specified/created
84	from the boot/module option are not exposed via this interface, and hence
85	cannot be modified dynamically. ]
87	To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
88	netconsole module (or kernel, if netconsole is built-in).
90	Some examples follow (where configfs is mounted at the /sys/kernel/config
91	mountpoint).
93	To add a remote logging target (target names can be arbitrary):
95	 cd /sys/kernel/config/netconsole/
96	 mkdir target1
98	Note that newly created targets have default parameter values (as mentioned
99	above) and are disabled by default -- they must first be enabled by writing
100	"1" to the "enabled" attribute (usually after setting parameters accordingly)
101	as described below.
103	To remove a target:
105	 rmdir /sys/kernel/config/netconsole/othertarget/
107	The interface exposes these parameters of a netconsole target to userspace:
109		enabled		Is this target currently enabled?	(read-write)
110		dev_name	Local network interface name		(read-write)
111		local_port	Source UDP port to use			(read-write)
112		remote_port	Remote agent's UDP port			(read-write)
113		local_ip	Source IP address to use		(read-write)
114		remote_ip	Remote agent's IP address		(read-write)
115		local_mac	Local interface's MAC address		(read-only)
116		remote_mac	Remote agent's MAC address		(read-write)
118	The "enabled" attribute is also used to control whether the parameters of
119	a target can be updated or not -- you can modify the parameters of only
120	disabled targets (i.e. if "enabled" is 0).
122	To update a target's parameters:
124	 cat enabled				# check if enabled is 1
125	 echo 0 > enabled			# disable the target (if required)
126	 echo eth2 > dev_name			# set local interface
127	 echo > remote_ip		# update some parameter
128	 echo cb:a9:87:65:43:21 > remote_mac	# update more parameters
129	 echo 1 > enabled			# enable target again
131	You can also update the local interface dynamically. This is especially
132	useful if you want to use interfaces that have newly come up (and may not
133	have existed when netconsole was loaded / initialized).
135	Miscellaneous notes:
136	====================
138	WARNING: the default target ethernet setting uses the broadcast
139	ethernet address to send packets, which can cause increased load on
140	other systems on the same ethernet segment.
142	TIP: some LAN switches may be configured to suppress ethernet broadcasts
143	so it is advised to explicitly specify the remote agents' MAC addresses
144	from the config parameters passed to netconsole.
146	TIP: to find out the MAC address of, say,, you may try using:
148	 ping -c 1 ; /sbin/arp -n | grep
150	TIP: in case the remote logging agent is on a separate LAN subnet than
151	the sender, it is suggested to try specifying the MAC address of the
152	default gateway (you may use /sbin/route -n to find it out) as the
153	remote MAC address instead.
155	NOTE: the network device (eth1 in the above case) can run any kind
156	of other network traffic, netconsole is not intrusive. Netconsole
157	might cause slight delays in other traffic if the volume of kernel
158	messages is high, but should have no other impact.
160	NOTE: if you find that the remote logging agent is not receiving or
161	printing all messages from the sender, it is likely that you have set
162	the "console_loglevel" parameter (on the sender) to only send high
163	priority messages to the console. You can change this at runtime using:
165	 dmesg -n 8
167	or by specifying "debug" on the kernel command line at boot, to send
168	all kernel messages to the console. A specific value for this parameter
169	can also be set using the "loglevel" kernel boot option. See the
170	dmesg(8) man page and Documentation/kernel-parameters.txt for details.
172	Netconsole was designed to be as instantaneous as possible, to
173	enable the logging of even the most critical kernel bugs. It works
174	from IRQ contexts as well, and does not enable interrupts while
175	sending packets. Due to these unique needs, configuration cannot
176	be more automatic, and some fundamental limitations will remain:
177	only IP networks, UDP packets and ethernet devices are supported.
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