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1 | |
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 | |
7265a6bb | 4 | IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013 |
1da177e4 LT |
5 | |
6 | Please send bug reports to Matt Mackall <mpm@selenic.com> | |
7265a6bb | 7 | Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com> |
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8 | |
9 | Introduction: | |
10 | ============= | |
1da177e4 LT |
11 | |
12 | This module logs kernel printk messages over UDP allowing debugging of | |
13 | problem where disk logging fails and serial consoles are impractical. | |
14 | ||
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. | |
20 | ||
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21 | Sender and receiver configuration: |
22 | ================================== | |
23 | ||
1da177e4 LT |
24 | It takes a string configuration parameter "netconsole" in the |
25 | following 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 | ||
37 | Examples: | |
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 | ||
7265a6bb CW |
45 | or using IPv6 |
46 | ||
47 | insmod netconsole netconsole=@/,@fd00:1:2:3::1/ | |
48 | ||
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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: | |
52 | ||
53 | modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/" | |
54 | ||
1da177e4 LT |
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. | |
58 | ||
6556bfde DG |
59 | The remote host has several options to receive the kernel messages, |
60 | for example: | |
61 | ||
62 | 1) syslogd | |
63 | ||
64 | 2) 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 | ||
73 | 3) socat | |
74 | ||
75 | 'socat udp-recv:<port> -' | |
1da177e4 | 76 | |
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77 | Dynamic reconfiguration: |
78 | ======================== | |
79 | ||
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. ] | |
86 | ||
87 | To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the | |
88 | netconsole module (or kernel, if netconsole is built-in). | |
89 | ||
90 | Some examples follow (where configfs is mounted at the /sys/kernel/config | |
91 | mountpoint). | |
92 | ||
93 | To add a remote logging target (target names can be arbitrary): | |
94 | ||
95 | cd /sys/kernel/config/netconsole/ | |
96 | mkdir target1 | |
97 | ||
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. | |
102 | ||
103 | To remove a target: | |
104 | ||
105 | rmdir /sys/kernel/config/netconsole/othertarget/ | |
106 | ||
107 | The 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 | ||
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). | |
121 | ||
122 | To 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 | ||
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). | |
134 | ||
135 | Miscellaneous notes: | |
136 | ==================== | |
137 | ||
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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. | |
141 | ||
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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. | |
145 | ||
146 | TIP: 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 | ||
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. | |
154 | ||
1da177e4 LT |
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. | |
159 | ||
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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: | |
164 | ||
165 | dmesg -n 8 | |
166 | ||
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. | |
171 | ||
1da177e4 LT |
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 | |
84eb8d06 | 175 | sending packets. Due to these unique needs, configuration cannot |
1da177e4 LT |
176 | be more automatic, and some fundamental limitations will remain: |
177 | only IP networks, UDP packets and ethernet devices are supported. |