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1 | .. SPDX-License-Identifier: GPL-2.0 |
2 | ||
3 | ========== | |
4 | Netconsole | |
5 | ========== | |
6 | ||
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7 | |
8 | started by Ingo Molnar <mingo@redhat.com>, 2001.09.17 | |
d9d6ef25 | 9 | |
1da177e4 | 10 | 2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003 |
d9d6ef25 | 11 | |
7265a6bb | 12 | IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013 |
d9d6ef25 | 13 | |
e2f15f9a | 14 | Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015 |
1da177e4 LT |
15 | |
16 | Please send bug reports to Matt Mackall <mpm@selenic.com> | |
7265a6bb | 17 | Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com> |
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18 | |
19 | Introduction: | |
20 | ============= | |
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21 | |
22 | This module logs kernel printk messages over UDP allowing debugging of | |
23 | problem where disk logging fails and serial consoles are impractical. | |
24 | ||
25 | It can be used either built-in or as a module. As a built-in, | |
26 | netconsole initializes immediately after NIC cards and will bring up | |
27 | the specified interface as soon as possible. While this doesn't allow | |
28 | capture of early kernel panics, it does capture most of the boot | |
29 | process. | |
30 | ||
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31 | Sender and receiver configuration: |
32 | ================================== | |
33 | ||
1da177e4 | 34 | It takes a string configuration parameter "netconsole" in the |
d9d6ef25 | 35 | following format:: |
1da177e4 | 36 | |
e2f15f9a | 37 | netconsole=[+][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr] |
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38 | |
39 | where | |
d9d6ef25 MCC |
40 | + if present, enable extended console support |
41 | src-port source for UDP packets (defaults to 6665) | |
42 | src-ip source IP to use (interface address) | |
43 | dev network interface (eth0) | |
44 | tgt-port port for logging agent (6666) | |
45 | tgt-ip IP address for logging agent | |
46 | tgt-macaddr ethernet MAC address for logging agent (broadcast) | |
1da177e4 | 47 | |
d9d6ef25 | 48 | Examples:: |
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49 | |
50 | linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc | |
51 | ||
d9d6ef25 | 52 | or:: |
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53 | |
54 | insmod netconsole netconsole=@/,@10.0.0.2/ | |
55 | ||
d9d6ef25 | 56 | or using IPv6:: |
7265a6bb CW |
57 | |
58 | insmod netconsole netconsole=@/,@fd00:1:2:3::1/ | |
59 | ||
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60 | It also supports logging to multiple remote agents by specifying |
61 | parameters for the multiple agents separated by semicolons and the | |
d9d6ef25 | 62 | complete string enclosed in "quotes", thusly:: |
b5427c27 SS |
63 | |
64 | modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/" | |
65 | ||
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66 | Built-in netconsole starts immediately after the TCP stack is |
67 | initialized and attempts to bring up the supplied dev at the supplied | |
68 | address. | |
69 | ||
6556bfde DG |
70 | The remote host has several options to receive the kernel messages, |
71 | for example: | |
72 | ||
73 | 1) syslogd | |
74 | ||
75 | 2) netcat | |
76 | ||
77 | On distributions using a BSD-based netcat version (e.g. Fedora, | |
78 | openSUSE and Ubuntu) the listening port must be specified without | |
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79 | the -p switch:: |
80 | ||
81 | nc -u -l -p <port>' / 'nc -u -l <port> | |
82 | ||
83 | or:: | |
6556bfde | 84 | |
d9d6ef25 | 85 | netcat -u -l -p <port>' / 'netcat -u -l <port> |
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86 | |
87 | 3) socat | |
88 | ||
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89 | :: |
90 | ||
91 | socat udp-recv:<port> - | |
1da177e4 | 92 | |
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93 | Dynamic reconfiguration: |
94 | ======================== | |
95 | ||
96 | Dynamic reconfigurability is a useful addition to netconsole that enables | |
97 | remote logging targets to be dynamically added, removed, or have their | |
98 | parameters reconfigured at runtime from a configfs-based userspace interface. | |
99 | [ Note that the parameters of netconsole targets that were specified/created | |
100 | from the boot/module option are not exposed via this interface, and hence | |
101 | cannot be modified dynamically. ] | |
102 | ||
103 | To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the | |
104 | netconsole module (or kernel, if netconsole is built-in). | |
105 | ||
106 | Some examples follow (where configfs is mounted at the /sys/kernel/config | |
107 | mountpoint). | |
108 | ||
d9d6ef25 | 109 | To add a remote logging target (target names can be arbitrary):: |
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110 | |
111 | cd /sys/kernel/config/netconsole/ | |
112 | mkdir target1 | |
113 | ||
114 | Note that newly created targets have default parameter values (as mentioned | |
115 | above) and are disabled by default -- they must first be enabled by writing | |
116 | "1" to the "enabled" attribute (usually after setting parameters accordingly) | |
117 | as described below. | |
118 | ||
d9d6ef25 | 119 | To remove a target:: |
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120 | |
121 | rmdir /sys/kernel/config/netconsole/othertarget/ | |
122 | ||
123 | The interface exposes these parameters of a netconsole target to userspace: | |
124 | ||
d9d6ef25 | 125 | ============== ================================= ============ |
0bcc1816 | 126 | enabled Is this target currently enabled? (read-write) |
e2f15f9a | 127 | extended Extended mode enabled (read-write) |
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128 | dev_name Local network interface name (read-write) |
129 | local_port Source UDP port to use (read-write) | |
130 | remote_port Remote agent's UDP port (read-write) | |
131 | local_ip Source IP address to use (read-write) | |
132 | remote_ip Remote agent's IP address (read-write) | |
133 | local_mac Local interface's MAC address (read-only) | |
134 | remote_mac Remote agent's MAC address (read-write) | |
d9d6ef25 | 135 | ============== ================================= ============ |
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136 | |
137 | The "enabled" attribute is also used to control whether the parameters of | |
138 | a target can be updated or not -- you can modify the parameters of only | |
139 | disabled targets (i.e. if "enabled" is 0). | |
140 | ||
d9d6ef25 | 141 | To update a target's parameters:: |
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142 | |
143 | cat enabled # check if enabled is 1 | |
144 | echo 0 > enabled # disable the target (if required) | |
145 | echo eth2 > dev_name # set local interface | |
146 | echo 10.0.0.4 > remote_ip # update some parameter | |
147 | echo cb:a9:87:65:43:21 > remote_mac # update more parameters | |
148 | echo 1 > enabled # enable target again | |
149 | ||
150 | You can also update the local interface dynamically. This is especially | |
151 | useful if you want to use interfaces that have newly come up (and may not | |
152 | have existed when netconsole was loaded / initialized). | |
153 | ||
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154 | Extended console: |
155 | ================= | |
156 | ||
157 | If '+' is prefixed to the configuration line or "extended" config file | |
158 | is set to 1, extended console support is enabled. An example boot | |
d9d6ef25 | 159 | param follows:: |
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160 | |
161 | linux netconsole=+4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc | |
162 | ||
163 | Log messages are transmitted with extended metadata header in the | |
d9d6ef25 | 164 | following format which is the same as /dev/kmsg:: |
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165 | |
166 | <level>,<sequnum>,<timestamp>,<contflag>;<message text> | |
167 | ||
168 | Non printable characters in <message text> are escaped using "\xff" | |
169 | notation. If the message contains optional dictionary, verbatim | |
170 | newline is used as the delimeter. | |
171 | ||
172 | If a message doesn't fit in certain number of bytes (currently 1000), | |
173 | the message is split into multiple fragments by netconsole. These | |
d9d6ef25 | 174 | fragments are transmitted with "ncfrag" header field added:: |
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175 | |
176 | ncfrag=<byte-offset>/<total-bytes> | |
177 | ||
178 | For example, assuming a lot smaller chunk size, a message "the first | |
d9d6ef25 | 179 | chunk, the 2nd chunk." may be split as follows:: |
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180 | |
181 | 6,416,1758426,-,ncfrag=0/31;the first chunk, | |
182 | 6,416,1758426,-,ncfrag=16/31; the 2nd chunk. | |
183 | ||
0bcc1816 SS |
184 | Miscellaneous notes: |
185 | ==================== | |
186 | ||
d9d6ef25 MCC |
187 | .. Warning:: |
188 | ||
189 | the default target ethernet setting uses the broadcast | |
190 | ethernet address to send packets, which can cause increased load on | |
191 | other systems on the same ethernet segment. | |
192 | ||
193 | .. Tip:: | |
194 | ||
195 | some LAN switches may be configured to suppress ethernet broadcasts | |
196 | so it is advised to explicitly specify the remote agents' MAC addresses | |
197 | from the config parameters passed to netconsole. | |
198 | ||
199 | .. Tip:: | |
200 | ||
201 | to find out the MAC address of, say, 10.0.0.2, you may try using:: | |
202 | ||
203 | ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2 | |
1da177e4 | 204 | |
d9d6ef25 | 205 | .. Tip:: |
8d4ef88b | 206 | |
d9d6ef25 MCC |
207 | in case the remote logging agent is on a separate LAN subnet than |
208 | the sender, it is suggested to try specifying the MAC address of the | |
209 | default gateway (you may use /sbin/route -n to find it out) as the | |
210 | remote MAC address instead. | |
8d4ef88b | 211 | |
d9d6ef25 | 212 | .. note:: |
8d4ef88b | 213 | |
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214 | the network device (eth1 in the above case) can run any kind |
215 | of other network traffic, netconsole is not intrusive. Netconsole | |
216 | might cause slight delays in other traffic if the volume of kernel | |
217 | messages is high, but should have no other impact. | |
8d4ef88b | 218 | |
d9d6ef25 | 219 | .. note:: |
1da177e4 | 220 | |
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221 | if you find that the remote logging agent is not receiving or |
222 | printing all messages from the sender, it is likely that you have set | |
223 | the "console_loglevel" parameter (on the sender) to only send high | |
224 | priority messages to the console. You can change this at runtime using:: | |
8d4ef88b | 225 | |
d9d6ef25 | 226 | dmesg -n 8 |
8d4ef88b | 227 | |
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228 | or by specifying "debug" on the kernel command line at boot, to send |
229 | all kernel messages to the console. A specific value for this parameter | |
230 | can also be set using the "loglevel" kernel boot option. See the | |
231 | dmesg(8) man page and Documentation/admin-guide/kernel-parameters.rst | |
232 | for details. | |
8d4ef88b | 233 | |
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234 | Netconsole was designed to be as instantaneous as possible, to |
235 | enable the logging of even the most critical kernel bugs. It works | |
236 | from IRQ contexts as well, and does not enable interrupts while | |
84eb8d06 | 237 | sending packets. Due to these unique needs, configuration cannot |
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238 | be more automatic, and some fundamental limitations will remain: |
239 | only IP networks, UDP packets and ethernet devices are supported. |