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Documentation / networking / netconsole.txt

Based on kernel version 2.6.26. Page generated on 2008-07-16 21:13 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>' or syslogd.
55	
56	Dynamic reconfiguration:
57	========================
58	
59	Dynamic reconfigurability is a useful addition to netconsole that enables
60	remote logging targets to be dynamically added, removed, or have their
61	parameters reconfigured at runtime from a configfs-based userspace interface.
62	[ Note that the parameters of netconsole targets that were specified/created
63	from the boot/module option are not exposed via this interface, and hence
64	cannot be modified dynamically. ]
65	
66	To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
67	netconsole module (or kernel, if netconsole is built-in).
68	
69	Some examples follow (where configfs is mounted at the /sys/kernel/config
70	mountpoint).
71	
72	To add a remote logging target (target names can be arbitrary):
73	
74	 cd /sys/kernel/config/netconsole/
75	 mkdir target1
76	
77	Note that newly created targets have default parameter values (as mentioned
78	above) and are disabled by default -- they must first be enabled by writing
79	"1" to the "enabled" attribute (usually after setting parameters accordingly)
80	as described below.
81	
82	To remove a target:
83	
84	 rmdir /sys/kernel/config/netconsole/othertarget/
85	
86	The interface exposes these parameters of a netconsole target to userspace:
87	
88		enabled		Is this target currently enabled?	(read-write)
89		dev_name	Local network interface name		(read-write)
90		local_port	Source UDP port to use			(read-write)
91		remote_port	Remote agent's UDP port			(read-write)
92		local_ip	Source IP address to use		(read-write)
93		remote_ip	Remote agent's IP address		(read-write)
94		local_mac	Local interface's MAC address		(read-only)
95		remote_mac	Remote agent's MAC address		(read-write)
96	
97	The "enabled" attribute is also used to control whether the parameters of
98	a target can be updated or not -- you can modify the parameters of only
99	disabled targets (i.e. if "enabled" is 0).
100	
101	To update a target's parameters:
102	
103	 cat enabled				# check if enabled is 1
104	 echo 0 > enabled			# disable the target (if required)
105	 echo eth2 > dev_name			# set local interface
106	 echo 10.0.0.4 > remote_ip		# update some parameter
107	 echo cb:a9:87:65:43:21 > remote_mac	# update more parameters
108	 echo 1 > enabled			# enable target again
109	
110	You can also update the local interface dynamically. This is especially
111	useful if you want to use interfaces that have newly come up (and may not
112	have existed when netconsole was loaded / initialized).
113	
114	Miscellaneous notes:
115	====================
116	
117	WARNING: the default target ethernet setting uses the broadcast
118	ethernet address to send packets, which can cause increased load on
119	other systems on the same ethernet segment.
120	
121	TIP: some LAN switches may be configured to suppress ethernet broadcasts
122	so it is advised to explicitly specify the remote agents' MAC addresses
123	from the config parameters passed to netconsole.
124	
125	TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
126	
127	 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
128	
129	TIP: in case the remote logging agent is on a separate LAN subnet than
130	the sender, it is suggested to try specifying the MAC address of the
131	default gateway (you may use /sbin/route -n to find it out) as the
132	remote MAC address instead.
133	
134	NOTE: the network device (eth1 in the above case) can run any kind
135	of other network traffic, netconsole is not intrusive. Netconsole
136	might cause slight delays in other traffic if the volume of kernel
137	messages is high, but should have no other impact.
138	
139	NOTE: if you find that the remote logging agent is not receiving or
140	printing all messages from the sender, it is likely that you have set
141	the "console_loglevel" parameter (on the sender) to only send high
142	priority messages to the console. You can change this at runtime using:
143	
144	 dmesg -n 8
145	
146	or by specifying "debug" on the kernel command line at boot, to send
147	all kernel messages to the console. A specific value for this parameter
148	can also be set using the "loglevel" kernel boot option. See the
149	dmesg(8) man page and Documentation/kernel-parameters.txt for details.
150	
151	Netconsole was designed to be as instantaneous as possible, to
152	enable the logging of even the most critical kernel bugs. It works
153	from IRQ contexts as well, and does not enable interrupts while
154	sending packets. Due to these unique needs, configuration cannot
155	be more automatic, and some fundamental limitations will remain:
156	only IP networks, UDP packets and ethernet devices are supported.
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