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
4 IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
6 Please send bug reports to Matt Mackall <mpm@selenic.com>
7 Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
12 This module logs kernel printk messages over UDP allowing debugging of
13 problem where disk logging fails and serial consoles are impractical.
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
21 Sender and receiver configuration:
22 ==================================
24 It takes a string configuration parameter "netconsole" in the
27 netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
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)
39 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
43 insmod netconsole netconsole=@/,@10.0.0.2/
47 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
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:
53 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
55 Built-in netconsole starts immediately after the TCP stack is
56 initialized and attempts to bring up the supplied dev at the supplied
59 The remote host has several options to receive the kernel messages,
64 On distributions using a BSD-based netcat version (e.g. Fedora,
65 openSUSE and Ubuntu) the listening port must be specified without
68 'nc -u -l -p <port>' / 'nc -u -l <port>' or
69 'netcat -u -l -p <port>' / 'netcat -u -l <port>'
73 'socat udp-recv:<port> -'
77 A daemon written specifically for netconsole that is good at capturing
78 output from many machines. Using netcat for several machines either
79 interleaves output from all machines or requires the use of per-machine
82 https://git.kernel.org/cgit/linux/kernel/git/joern/cancd.git/
83 https://oss.oracle.com/projects/cancd/
85 Dynamic reconfiguration:
86 ========================
88 Dynamic reconfigurability is a useful addition to netconsole that enables
89 remote logging targets to be dynamically added, removed, or have their
90 parameters reconfigured at runtime from a configfs-based userspace interface.
91 [ Note that the parameters of netconsole targets that were specified/created
92 from the boot/module option are not exposed via this interface, and hence
93 cannot be modified dynamically. ]
95 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
96 netconsole module (or kernel, if netconsole is built-in).
98 Some examples follow (where configfs is mounted at the /sys/kernel/config
101 To add a remote logging target (target names can be arbitrary):
103 cd /sys/kernel/config/netconsole/
106 Note that newly created targets have default parameter values (as mentioned
107 above) and are disabled by default -- they must first be enabled by writing
108 "1" to the "enabled" attribute (usually after setting parameters accordingly)
113 rmdir /sys/kernel/config/netconsole/othertarget/
115 The interface exposes these parameters of a netconsole target to userspace:
117 enabled Is this target currently enabled? (read-write)
118 dev_name Local network interface name (read-write)
119 local_port Source UDP port to use (read-write)
120 remote_port Remote agent's UDP port (read-write)
121 local_ip Source IP address to use (read-write)
122 remote_ip Remote agent's IP address (read-write)
123 local_mac Local interface's MAC address (read-only)
124 remote_mac Remote agent's MAC address (read-write)
126 The "enabled" attribute is also used to control whether the parameters of
127 a target can be updated or not -- you can modify the parameters of only
128 disabled targets (i.e. if "enabled" is 0).
130 To update a target's parameters:
132 cat enabled # check if enabled is 1
133 echo 0 > enabled # disable the target (if required)
134 echo eth2 > dev_name # set local interface
135 echo 10.0.0.4 > remote_ip # update some parameter
136 echo cb:a9:87:65:43:21 > remote_mac # update more parameters
137 echo 1 > enabled # enable target again
139 You can also update the local interface dynamically. This is especially
140 useful if you want to use interfaces that have newly come up (and may not
141 have existed when netconsole was loaded / initialized).
146 WARNING: the default target ethernet setting uses the broadcast
147 ethernet address to send packets, which can cause increased load on
148 other systems on the same ethernet segment.
150 TIP: some LAN switches may be configured to suppress ethernet broadcasts
151 so it is advised to explicitly specify the remote agents' MAC addresses
152 from the config parameters passed to netconsole.
154 TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
156 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
158 TIP: in case the remote logging agent is on a separate LAN subnet than
159 the sender, it is suggested to try specifying the MAC address of the
160 default gateway (you may use /sbin/route -n to find it out) as the
161 remote MAC address instead.
163 NOTE: the network device (eth1 in the above case) can run any kind
164 of other network traffic, netconsole is not intrusive. Netconsole
165 might cause slight delays in other traffic if the volume of kernel
166 messages is high, but should have no other impact.
168 NOTE: if you find that the remote logging agent is not receiving or
169 printing all messages from the sender, it is likely that you have set
170 the "console_loglevel" parameter (on the sender) to only send high
171 priority messages to the console. You can change this at runtime using:
175 or by specifying "debug" on the kernel command line at boot, to send
176 all kernel messages to the console. A specific value for this parameter
177 can also be set using the "loglevel" kernel boot option. See the
178 dmesg(8) man page and Documentation/kernel-parameters.txt for details.
180 Netconsole was designed to be as instantaneous as possible, to
181 enable the logging of even the most critical kernel bugs. It works
182 from IRQ contexts as well, and does not enable interrupts while
183 sending packets. Due to these unique needs, configuration cannot
184 be more automatic, and some fundamental limitations will remain:
185 only IP networks, UDP packets and ethernet devices are supported.