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Based on kernel version 2.6.33. Page generated on 2010-02-24 15:36 EST.

1	
2	started by Ingo Molnar <mingo[AT]redhat.com>, 2001.09[DOT]17
3	2.6 port and netpoll api by Matt Mackall <mpm[AT]selenic[DOT]com>, Sep 9 2003
4	
5	Please send bug reports to Matt Mackall <mpm[AT]selenic[DOT]com>
6	and Satyam Sharma <satyam.sharma[AT]gmail[DOT]com>
7	
8	Introduction:
9	=============
10	
11	This module logs kernel printk messages over UDP allowing debugging of
12	problem where disk logging fails and serial consoles are impractical.
13	
14	It can be used either built-in or as a module. As a built-in,
15	netconsole initializes immediately after NIC cards and will bring up
16	the specified interface as soon as possible. While this doesn't allow
17	capture of early kernel panics, it does capture most of the boot
18	process.
19	
20	Sender and receiver configuration:
21	==================================
22	
23	It takes a string configuration parameter "netconsole" in the
24	following format:
25	
26	 netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
27	
28	   where
29	        src-port      source for UDP packets (defaults to 6665)
30	        src-ip        source IP to use (interface address)
31	        dev           network interface (eth0)
32	        tgt-port      port for logging agent (6666)
33	        tgt-ip        IP address for logging agent
34	        tgt-macaddr   ethernet MAC address for logging agent (broadcast)
35	
36	Examples:
37	
38	 linux netconsole=4444[AT]10.0.0.1/eth1,9353@10.0.0[DOT]2/12:34:56:78:9a:bc
39	
40	  or
41	
42	 insmod netconsole netconsole=[AT]/,@10.0.0[DOT]2/
43	
44	It also supports logging to multiple remote agents by specifying
45	parameters for the multiple agents separated by semicolons and the
46	complete string enclosed in "quotes", thusly:
47	
48	 modprobe netconsole netconsole="[AT]/,@10.0.0.2/;@/eth1,6892@10.0.0[DOT]3/"
49	
50	Built-in netconsole starts immediately after the TCP stack is
51	initialized and attempts to bring up the supplied dev at the supplied
52	address.
53	
54	The remote host can run either 'netcat -u -l -p <port>',
55	'nc -l -u <port>' or syslogd.
56	
57	Dynamic reconfiguration:
58	========================
59	
60	Dynamic reconfigurability is a useful addition to netconsole that enables
61	remote logging targets to be dynamically added, removed, or have their
62	parameters reconfigured at runtime from a configfs-based userspace interface.
63	[ Note that the parameters of netconsole targets that were specified/created
64	from the boot/module option are not exposed via this interface, and hence
65	cannot be modified dynamically. ]
66	
67	To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
68	netconsole module (or kernel, if netconsole is built-in).
69	
70	Some examples follow (where configfs is mounted at the /sys/kernel/config
71	mountpoint).
72	
73	To add a remote logging target (target names can be arbitrary):
74	
75	 cd /sys/kernel/config/netconsole/
76	 mkdir target1
77	
78	Note that newly created targets have default parameter values (as mentioned
79	above) and are disabled by default -- they must first be enabled by writing
80	"1" to the "enabled" attribute (usually after setting parameters accordingly)
81	as described below.
82	
83	To remove a target:
84	
85	 rmdir /sys/kernel/config/netconsole/othertarget/
86	
87	The interface exposes these parameters of a netconsole target to userspace:
88	
89		enabled		Is this target currently enabled?	(read-write)
90		dev_name	Local network interface name		(read-write)
91		local_port	Source UDP port to use			(read-write)
92		remote_port	Remote agent's UDP port			(read-write)
93		local_ip	Source IP address to use		(read-write)
94		remote_ip	Remote agent's IP address		(read-write)
95		local_mac	Local interface's MAC address		(read-only)
96		remote_mac	Remote agent's MAC address		(read-write)
97	
98	The "enabled" attribute is also used to control whether the parameters of
99	a target can be updated or not -- you can modify the parameters of only
100	disabled targets (i.e. if "enabled" is 0).
101	
102	To update a target's parameters:
103	
104	 cat enabled				# check if enabled is 1
105	 echo 0 > enabled			# disable the target (if required)
106	 echo eth2 > dev_name			# set local interface
107	 echo 10.0.0.4 > remote_ip		# update some parameter
108	 echo cb:a9:87:65:43:21 > remote_mac	# update more parameters
109	 echo 1 > enabled			# enable target again
110	
111	You can also update the local interface dynamically. This is especially
112	useful if you want to use interfaces that have newly come up (and may not
113	have existed when netconsole was loaded / initialized).
114	
115	Miscellaneous notes:
116	====================
117	
118	WARNING: the default target ethernet setting uses the broadcast
119	ethernet address to send packets, which can cause increased load on
120	other systems on the same ethernet segment.
121	
122	TIP: some LAN switches may be configured to suppress ethernet broadcasts
123	so it is advised to explicitly specify the remote agents' MAC addresses
124	from the config parameters passed to netconsole.
125	
126	TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
127	
128	 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
129	
130	TIP: in case the remote logging agent is on a separate LAN subnet than
131	the sender, it is suggested to try specifying the MAC address of the
132	default gateway (you may use /sbin/route -n to find it out) as the
133	remote MAC address instead.
134	
135	NOTE: the network device (eth1 in the above case) can run any kind
136	of other network traffic, netconsole is not intrusive. Netconsole
137	might cause slight delays in other traffic if the volume of kernel
138	messages is high, but should have no other impact.
139	
140	NOTE: if you find that the remote logging agent is not receiving or
141	printing all messages from the sender, it is likely that you have set
142	the "console_loglevel" parameter (on the sender) to only send high
143	priority messages to the console. You can change this at runtime using:
144	
145	 dmesg -n 8
146	
147	or by specifying "debug" on the kernel command line at boot, to send
148	all kernel messages to the console. A specific value for this parameter
149	can also be set using the "loglevel" kernel boot option. See the
150	dmesg(8) man page and Documentation/kernel-parameters.txt for details.
151	
152	Netconsole was designed to be as instantaneous as possible, to
153	enable the logging of even the most critical kernel bugs. It works
154	from IRQ contexts as well, and does not enable interrupts while
155	sending packets. Due to these unique needs, configuration cannot
156	be more automatic, and some fundamental limitations will remain:
157	only IP networks, UDP packets and ethernet devices are supported.
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