1 .. SPDX-License-Identifier: GPL-2.0
8 started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
10 2.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003
12 IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
14 Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015
16 Please send bug reports to Matt Mackall <mpm@selenic.com>
17 Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
22 This module logs kernel printk messages over UDP allowing debugging of
23 problem where disk logging fails and serial consoles are impractical.
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
31 Sender and receiver configuration:
32 ==================================
34 It takes a string configuration parameter "netconsole" in the
37 netconsole=[+][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
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)
50 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
54 insmod netconsole netconsole=@/,@10.0.0.2/
58 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
60 It also supports logging to multiple remote agents by specifying
61 parameters for the multiple agents separated by semicolons and the
62 complete string enclosed in "quotes", thusly::
64 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
66 Built-in netconsole starts immediately after the TCP stack is
67 initialized and attempts to bring up the supplied dev at the supplied
70 The remote host has several options to receive the kernel messages,
77 On distributions using a BSD-based netcat version (e.g. Fedora,
78 openSUSE and Ubuntu) the listening port must be specified without
81 nc -u -l -p <port>' / 'nc -u -l <port>
85 netcat -u -l -p <port>' / 'netcat -u -l <port>
91 socat udp-recv:<port> -
93 Dynamic reconfiguration:
94 ========================
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. ]
103 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
104 netconsole module (or kernel, if netconsole is built-in).
106 Some examples follow (where configfs is mounted at the /sys/kernel/config
109 To add a remote logging target (target names can be arbitrary)::
111 cd /sys/kernel/config/netconsole/
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)
121 rmdir /sys/kernel/config/netconsole/othertarget/
123 The interface exposes these parameters of a netconsole target to userspace:
125 ============== ================================= ============
126 enabled Is this target currently enabled? (read-write)
127 extended Extended mode enabled (read-write)
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)
135 ============== ================================= ============
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).
141 To update a target's parameters::
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
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).
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
161 linux netconsole=+4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
163 Log messages are transmitted with extended metadata header in the
164 following format which is the same as /dev/kmsg::
166 <level>,<sequnum>,<timestamp>,<contflag>;<message text>
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.
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
174 fragments are transmitted with "ncfrag" header field added::
176 ncfrag=<byte-offset>/<total-bytes>
178 For example, assuming a lot smaller chunk size, a message "the first
179 chunk, the 2nd chunk." may be split as follows::
181 6,416,1758426,-,ncfrag=0/31;the first chunk,
182 6,416,1758426,-,ncfrag=16/31; the 2nd chunk.
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.
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.
201 to find out the MAC address of, say, 10.0.0.2, you may try using::
203 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
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.
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.
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::
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
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
237 sending packets. Due to these unique needs, configuration cannot
238 be more automatic, and some fundamental limitations will remain:
239 only IP networks, UDP packets and ethernet devices are supported.