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1
2started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
32.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003
4IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
5
6Please send bug reports to Matt Mackall <mpm@selenic.com>
7Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
8
9Introduction:
10=============
11
12This module logs kernel printk messages over UDP allowing debugging of
13problem where disk logging fails and serial consoles are impractical.
14
15It can be used either built-in or as a module. As a built-in,
16netconsole initializes immediately after NIC cards and will bring up
17the specified interface as soon as possible. While this doesn't allow
18capture of early kernel panics, it does capture most of the boot
19process.
20
21Sender and receiver configuration:
22==================================
23
24It takes a string configuration parameter "netconsole" in the
25following format:
26
27 netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
28
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)
36
37Examples:
38
39 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
40
41 or
42
43 insmod netconsole netconsole=@/,@10.0.0.2/
44
45 or using IPv6
46
47 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
48
49It also supports logging to multiple remote agents by specifying
50parameters for the multiple agents separated by semicolons and the
51complete string enclosed in "quotes", thusly:
52
53 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
54
55Built-in netconsole starts immediately after the TCP stack is
56initialized and attempts to bring up the supplied dev at the supplied
57address.
58
59The remote host has several options to receive the kernel messages,
60for example:
61
621) syslogd
63
642) netcat
65
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:
69
70 'nc -u -l -p <port>' / 'nc -u -l <port>' or
71 'netcat -u -l -p <port>' / 'netcat -u -l <port>'
72
733) socat
74
75 'socat udp-recv:<port> -'
76
77Dynamic reconfiguration:
78========================
79
80Dynamic reconfigurability is a useful addition to netconsole that enables
81remote logging targets to be dynamically added, removed, or have their
82parameters reconfigured at runtime from a configfs-based userspace interface.
83[ Note that the parameters of netconsole targets that were specified/created
84from the boot/module option are not exposed via this interface, and hence
85cannot be modified dynamically. ]
86
87To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
88netconsole module (or kernel, if netconsole is built-in).
89
90Some examples follow (where configfs is mounted at the /sys/kernel/config
91mountpoint).
92
93To add a remote logging target (target names can be arbitrary):
94
95 cd /sys/kernel/config/netconsole/
96 mkdir target1
97
98Note that newly created targets have default parameter values (as mentioned
99above) and are disabled by default -- they must first be enabled by writing
100"1" to the "enabled" attribute (usually after setting parameters accordingly)
101as described below.
102
103To remove a target:
104
105 rmdir /sys/kernel/config/netconsole/othertarget/
106
107The interface exposes these parameters of a netconsole target to userspace:
108
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)
117
118The "enabled" attribute is also used to control whether the parameters of
119a target can be updated or not -- you can modify the parameters of only
120disabled targets (i.e. if "enabled" is 0).
121
122To update a target's parameters:
123
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 10.0.0.4 > 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
130
131You can also update the local interface dynamically. This is especially
132useful if you want to use interfaces that have newly come up (and may not
133have existed when netconsole was loaded / initialized).
134
135Miscellaneous notes:
136====================
137
138WARNING: the default target ethernet setting uses the broadcast
139ethernet address to send packets, which can cause increased load on
140other systems on the same ethernet segment.
141
142TIP: some LAN switches may be configured to suppress ethernet broadcasts
143so it is advised to explicitly specify the remote agents' MAC addresses
144from the config parameters passed to netconsole.
145
146TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
147
148 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
149
150TIP: in case the remote logging agent is on a separate LAN subnet than
151the sender, it is suggested to try specifying the MAC address of the
152default gateway (you may use /sbin/route -n to find it out) as the
153remote MAC address instead.
154
155NOTE: the network device (eth1 in the above case) can run any kind
156of other network traffic, netconsole is not intrusive. Netconsole
157might cause slight delays in other traffic if the volume of kernel
158messages is high, but should have no other impact.
159
160NOTE: if you find that the remote logging agent is not receiving or
161printing all messages from the sender, it is likely that you have set
162the "console_loglevel" parameter (on the sender) to only send high
163priority messages to the console. You can change this at runtime using:
164
165 dmesg -n 8
166
167or by specifying "debug" on the kernel command line at boot, to send
168all kernel messages to the console. A specific value for this parameter
169can also be set using the "loglevel" kernel boot option. See the
170dmesg(8) man page and Documentation/kernel-parameters.txt for details.
171
172Netconsole was designed to be as instantaneous as possible, to
173enable the logging of even the most critical kernel bugs. It works
174from IRQ contexts as well, and does not enable interrupts while
175sending packets. Due to these unique needs, configuration cannot
176be more automatic, and some fundamental limitations will remain:
177only IP networks, UDP packets and ethernet devices are supported.