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 Release prepend support by Breno Leitao <leitao@debian.org>, Jul 7 2023
18 Please send bug reports to Matt Mackall <mpm@selenic.com>
19 Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
24 This module logs kernel printk messages over UDP allowing debugging of
25 problem where disk logging fails and serial consoles are impractical.
27 It can be used either built-in or as a module. As a built-in,
28 netconsole initializes immediately after NIC cards and will bring up
29 the specified interface as soon as possible. While this doesn't allow
30 capture of early kernel panics, it does capture most of the boot
33 Sender and receiver configuration:
34 ==================================
36 It takes a string configuration parameter "netconsole" in the
39 netconsole=[+][r][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
42 + if present, enable extended console support
43 r if present, prepend kernel version (release) to the message
44 src-port source for UDP packets (defaults to 6665)
45 src-ip source IP to use (interface address)
46 dev network interface (eth0)
47 tgt-port port for logging agent (6666)
48 tgt-ip IP address for logging agent
49 tgt-macaddr ethernet MAC address for logging agent (broadcast)
53 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
57 insmod netconsole netconsole=@/,@10.0.0.2/
61 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
63 It also supports logging to multiple remote agents by specifying
64 parameters for the multiple agents separated by semicolons and the
65 complete string enclosed in "quotes", thusly::
67 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
69 Built-in netconsole starts immediately after the TCP stack is
70 initialized and attempts to bring up the supplied dev at the supplied
73 The remote host has several options to receive the kernel messages,
80 On distributions using a BSD-based netcat version (e.g. Fedora,
81 openSUSE and Ubuntu) the listening port must be specified without
84 nc -u -l -p <port>' / 'nc -u -l <port>
88 netcat -u -l -p <port>' / 'netcat -u -l <port>
94 socat udp-recv:<port> -
96 Dynamic reconfiguration:
97 ========================
99 Dynamic reconfigurability is a useful addition to netconsole that enables
100 remote logging targets to be dynamically added, removed, or have their
101 parameters reconfigured at runtime from a configfs-based userspace interface.
102 [ Note that the parameters of netconsole targets that were specified/created
103 from the boot/module option are not exposed via this interface, and hence
104 cannot be modified dynamically. ]
106 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
107 netconsole module (or kernel, if netconsole is built-in).
109 Some examples follow (where configfs is mounted at the /sys/kernel/config
112 To add a remote logging target (target names can be arbitrary)::
114 cd /sys/kernel/config/netconsole/
117 Note that newly created targets have default parameter values (as mentioned
118 above) and are disabled by default -- they must first be enabled by writing
119 "1" to the "enabled" attribute (usually after setting parameters accordingly)
124 rmdir /sys/kernel/config/netconsole/othertarget/
126 The interface exposes these parameters of a netconsole target to userspace:
128 ============== ================================= ============
129 enabled Is this target currently enabled? (read-write)
130 extended Extended mode enabled (read-write)
131 release Prepend kernel release to message (read-write)
132 dev_name Local network interface name (read-write)
133 local_port Source UDP port to use (read-write)
134 remote_port Remote agent's UDP port (read-write)
135 local_ip Source IP address to use (read-write)
136 remote_ip Remote agent's IP address (read-write)
137 local_mac Local interface's MAC address (read-only)
138 remote_mac Remote agent's MAC address (read-write)
139 ============== ================================= ============
141 The "enabled" attribute is also used to control whether the parameters of
142 a target can be updated or not -- you can modify the parameters of only
143 disabled targets (i.e. if "enabled" is 0).
145 To update a target's parameters::
147 cat enabled # check if enabled is 1
148 echo 0 > enabled # disable the target (if required)
149 echo eth2 > dev_name # set local interface
150 echo 10.0.0.4 > remote_ip # update some parameter
151 echo cb:a9:87:65:43:21 > remote_mac # update more parameters
152 echo 1 > enabled # enable target again
154 You can also update the local interface dynamically. This is especially
155 useful if you want to use interfaces that have newly come up (and may not
156 have existed when netconsole was loaded / initialized).
161 If '+' is prefixed to the configuration line or "extended" config file
162 is set to 1, extended console support is enabled. An example boot
165 linux netconsole=+4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
167 Log messages are transmitted with extended metadata header in the
168 following format which is the same as /dev/kmsg::
170 <level>,<sequnum>,<timestamp>,<contflag>;<message text>
172 If 'r' (release) feature is enabled, the kernel release version is
173 prepended to the start of the message. Example::
175 6.4.0,6,444,501151268,-;netconsole: network logging started
177 Non printable characters in <message text> are escaped using "\xff"
178 notation. If the message contains optional dictionary, verbatim
179 newline is used as the delimiter.
181 If a message doesn't fit in certain number of bytes (currently 1000),
182 the message is split into multiple fragments by netconsole. These
183 fragments are transmitted with "ncfrag" header field added::
185 ncfrag=<byte-offset>/<total-bytes>
187 For example, assuming a lot smaller chunk size, a message "the first
188 chunk, the 2nd chunk." may be split as follows::
190 6,416,1758426,-,ncfrag=0/31;the first chunk,
191 6,416,1758426,-,ncfrag=16/31; the 2nd chunk.
198 the default target ethernet setting uses the broadcast
199 ethernet address to send packets, which can cause increased load on
200 other systems on the same ethernet segment.
204 some LAN switches may be configured to suppress ethernet broadcasts
205 so it is advised to explicitly specify the remote agents' MAC addresses
206 from the config parameters passed to netconsole.
210 to find out the MAC address of, say, 10.0.0.2, you may try using::
212 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
216 in case the remote logging agent is on a separate LAN subnet than
217 the sender, it is suggested to try specifying the MAC address of the
218 default gateway (you may use /sbin/route -n to find it out) as the
219 remote MAC address instead.
223 the network device (eth1 in the above case) can run any kind
224 of other network traffic, netconsole is not intrusive. Netconsole
225 might cause slight delays in other traffic if the volume of kernel
226 messages is high, but should have no other impact.
230 if you find that the remote logging agent is not receiving or
231 printing all messages from the sender, it is likely that you have set
232 the "console_loglevel" parameter (on the sender) to only send high
233 priority messages to the console. You can change this at runtime using::
237 or by specifying "debug" on the kernel command line at boot, to send
238 all kernel messages to the console. A specific value for this parameter
239 can also be set using the "loglevel" kernel boot option. See the
240 dmesg(8) man page and Documentation/admin-guide/kernel-parameters.rst
243 Netconsole was designed to be as instantaneous as possible, to
244 enable the logging of even the most critical kernel bugs. It works
245 from IRQ contexts as well, and does not enable interrupts while
246 sending packets. Due to these unique needs, configuration cannot
247 be more automatic, and some fundamental limitations will remain:
248 only IP networks, UDP packets and ethernet devices are supported.