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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2started by Ingo Molnar <mingo@redhat.com>, 2001.09.17
32.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003
Cong Wang7265a6b2013-01-07 20:52:42 +00004IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
Tejun Heoe2f15f92015-06-25 15:01:41 -07005Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015
Linus Torvalds1da177e2005-04-16 15:20:36 -07006
7Please send bug reports to Matt Mackall <mpm@selenic.com>
Cong Wang7265a6b2013-01-07 20:52:42 +00008Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
Satyam Sharma0bcc1812007-08-10 15:35:05 -07009
10Introduction:
11=============
Linus Torvalds1da177e2005-04-16 15:20:36 -070012
13This module logs kernel printk messages over UDP allowing debugging of
14problem where disk logging fails and serial consoles are impractical.
15
16It can be used either built-in or as a module. As a built-in,
17netconsole initializes immediately after NIC cards and will bring up
18the specified interface as soon as possible. While this doesn't allow
19capture of early kernel panics, it does capture most of the boot
20process.
21
Satyam Sharma0bcc1812007-08-10 15:35:05 -070022Sender and receiver configuration:
23==================================
24
Linus Torvalds1da177e2005-04-16 15:20:36 -070025It takes a string configuration parameter "netconsole" in the
26following format:
27
Tejun Heoe2f15f92015-06-25 15:01:41 -070028 netconsole=[+][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
Linus Torvalds1da177e2005-04-16 15:20:36 -070029
30 where
Tejun Heoe2f15f92015-06-25 15:01:41 -070031 + if present, enable extended console support
Linus Torvalds1da177e2005-04-16 15:20:36 -070032 src-port source for UDP packets (defaults to 6665)
33 src-ip source IP to use (interface address)
34 dev network interface (eth0)
35 tgt-port port for logging agent (6666)
36 tgt-ip IP address for logging agent
37 tgt-macaddr ethernet MAC address for logging agent (broadcast)
38
39Examples:
40
41 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
42
43 or
44
45 insmod netconsole netconsole=@/,@10.0.0.2/
46
Cong Wang7265a6b2013-01-07 20:52:42 +000047 or using IPv6
48
49 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
50
Satyam Sharmab5427c22007-08-10 15:33:40 -070051It also supports logging to multiple remote agents by specifying
52parameters for the multiple agents separated by semicolons and the
53complete string enclosed in "quotes", thusly:
54
55 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
56
Linus Torvalds1da177e2005-04-16 15:20:36 -070057Built-in netconsole starts immediately after the TCP stack is
58initialized and attempts to bring up the supplied dev at the supplied
59address.
60
Dirk Gouders6556bfd2012-08-10 01:24:51 +000061The remote host has several options to receive the kernel messages,
62for example:
63
641) syslogd
65
662) netcat
67
68 On distributions using a BSD-based netcat version (e.g. Fedora,
69 openSUSE and Ubuntu) the listening port must be specified without
70 the -p switch:
71
72 'nc -u -l -p <port>' / 'nc -u -l <port>' or
73 'netcat -u -l -p <port>' / 'netcat -u -l <port>'
74
753) socat
76
77 'socat udp-recv:<port> -'
Linus Torvalds1da177e2005-04-16 15:20:36 -070078
Satyam Sharma0bcc1812007-08-10 15:35:05 -070079Dynamic reconfiguration:
80========================
81
82Dynamic reconfigurability is a useful addition to netconsole that enables
83remote logging targets to be dynamically added, removed, or have their
84parameters reconfigured at runtime from a configfs-based userspace interface.
85[ Note that the parameters of netconsole targets that were specified/created
86from the boot/module option are not exposed via this interface, and hence
87cannot be modified dynamically. ]
88
89To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
90netconsole module (or kernel, if netconsole is built-in).
91
92Some examples follow (where configfs is mounted at the /sys/kernel/config
93mountpoint).
94
95To add a remote logging target (target names can be arbitrary):
96
97 cd /sys/kernel/config/netconsole/
98 mkdir target1
99
100Note that newly created targets have default parameter values (as mentioned
101above) and are disabled by default -- they must first be enabled by writing
102"1" to the "enabled" attribute (usually after setting parameters accordingly)
103as described below.
104
105To remove a target:
106
107 rmdir /sys/kernel/config/netconsole/othertarget/
108
109The interface exposes these parameters of a netconsole target to userspace:
110
111 enabled Is this target currently enabled? (read-write)
Tejun Heoe2f15f92015-06-25 15:01:41 -0700112 extended Extended mode enabled (read-write)
Satyam Sharma0bcc1812007-08-10 15:35:05 -0700113 dev_name Local network interface name (read-write)
114 local_port Source UDP port to use (read-write)
115 remote_port Remote agent's UDP port (read-write)
116 local_ip Source IP address to use (read-write)
117 remote_ip Remote agent's IP address (read-write)
118 local_mac Local interface's MAC address (read-only)
119 remote_mac Remote agent's MAC address (read-write)
120
121The "enabled" attribute is also used to control whether the parameters of
122a target can be updated or not -- you can modify the parameters of only
123disabled targets (i.e. if "enabled" is 0).
124
125To update a target's parameters:
126
127 cat enabled # check if enabled is 1
128 echo 0 > enabled # disable the target (if required)
129 echo eth2 > dev_name # set local interface
130 echo 10.0.0.4 > remote_ip # update some parameter
131 echo cb:a9:87:65:43:21 > remote_mac # update more parameters
132 echo 1 > enabled # enable target again
133
134You can also update the local interface dynamically. This is especially
135useful if you want to use interfaces that have newly come up (and may not
136have existed when netconsole was loaded / initialized).
137
Tejun Heoe2f15f92015-06-25 15:01:41 -0700138Extended console:
139=================
140
141If '+' is prefixed to the configuration line or "extended" config file
142is set to 1, extended console support is enabled. An example boot
143param follows.
144
145 linux netconsole=+4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
146
147Log messages are transmitted with extended metadata header in the
148following format which is the same as /dev/kmsg.
149
150 <level>,<sequnum>,<timestamp>,<contflag>;<message text>
151
152Non printable characters in <message text> are escaped using "\xff"
153notation. If the message contains optional dictionary, verbatim
154newline is used as the delimeter.
155
156If a message doesn't fit in certain number of bytes (currently 1000),
157the message is split into multiple fragments by netconsole. These
158fragments are transmitted with "ncfrag" header field added.
159
160 ncfrag=<byte-offset>/<total-bytes>
161
162For example, assuming a lot smaller chunk size, a message "the first
163chunk, the 2nd chunk." may be split as follows.
164
165 6,416,1758426,-,ncfrag=0/31;the first chunk,
166 6,416,1758426,-,ncfrag=16/31; the 2nd chunk.
167
Satyam Sharma0bcc1812007-08-10 15:35:05 -0700168Miscellaneous notes:
169====================
170
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171WARNING: the default target ethernet setting uses the broadcast
172ethernet address to send packets, which can cause increased load on
173other systems on the same ethernet segment.
174
Satyam Sharma8d4ef882007-08-10 15:31:19 -0700175TIP: some LAN switches may be configured to suppress ethernet broadcasts
176so it is advised to explicitly specify the remote agents' MAC addresses
177from the config parameters passed to netconsole.
178
179TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
180
181 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
182
183TIP: in case the remote logging agent is on a separate LAN subnet than
184the sender, it is suggested to try specifying the MAC address of the
185default gateway (you may use /sbin/route -n to find it out) as the
186remote MAC address instead.
187
Linus Torvalds1da177e2005-04-16 15:20:36 -0700188NOTE: the network device (eth1 in the above case) can run any kind
189of other network traffic, netconsole is not intrusive. Netconsole
190might cause slight delays in other traffic if the volume of kernel
191messages is high, but should have no other impact.
192
Satyam Sharma8d4ef882007-08-10 15:31:19 -0700193NOTE: if you find that the remote logging agent is not receiving or
194printing all messages from the sender, it is likely that you have set
195the "console_loglevel" parameter (on the sender) to only send high
196priority messages to the console. You can change this at runtime using:
197
198 dmesg -n 8
199
200or by specifying "debug" on the kernel command line at boot, to send
201all kernel messages to the console. A specific value for this parameter
202can also be set using the "loglevel" kernel boot option. See the
203dmesg(8) man page and Documentation/kernel-parameters.txt for details.
204
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205Netconsole was designed to be as instantaneous as possible, to
206enable the logging of even the most critical kernel bugs. It works
207from IRQ contexts as well, and does not enable interrupts while
Matt LaPlante84eb8d02006-10-03 22:53:09 +0200208sending packets. Due to these unique needs, configuration cannot
Linus Torvalds1da177e2005-04-16 15:20:36 -0700209be more automatic, and some fundamental limitations will remain:
210only IP networks, UDP packets and ethernet devices are supported.