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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
4
5Please send bug reports to Matt Mackall <mpm@selenic.com>
Satyam Sharma0bcc1812007-08-10 15:35:05 -07006and Satyam Sharma <satyam.sharma@gmail.com>
7
8Introduction:
9=============
Linus Torvalds1da177e2005-04-16 15:20:36 -070010
11This module logs kernel printk messages over UDP allowing debugging of
12problem where disk logging fails and serial consoles are impractical.
13
14It can be used either built-in or as a module. As a built-in,
15netconsole initializes immediately after NIC cards and will bring up
16the specified interface as soon as possible. While this doesn't allow
17capture of early kernel panics, it does capture most of the boot
18process.
19
Satyam Sharma0bcc1812007-08-10 15:35:05 -070020Sender and receiver configuration:
21==================================
22
Linus Torvalds1da177e2005-04-16 15:20:36 -070023It takes a string configuration parameter "netconsole" in the
24following format:
25
26 netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
27
28 where
29 src-port source for UDP packets (defaults to 6665)
30 src-ip source IP to use (interface address)
31 dev network interface (eth0)
32 tgt-port port for logging agent (6666)
33 tgt-ip IP address for logging agent
34 tgt-macaddr ethernet MAC address for logging agent (broadcast)
35
36Examples:
37
38 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
39
40 or
41
42 insmod netconsole netconsole=@/,@10.0.0.2/
43
Satyam Sharmab5427c22007-08-10 15:33:40 -070044It also supports logging to multiple remote agents by specifying
45parameters for the multiple agents separated by semicolons and the
46complete string enclosed in "quotes", thusly:
47
48 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
49
Linus Torvalds1da177e2005-04-16 15:20:36 -070050Built-in netconsole starts immediately after the TCP stack is
51initialized and attempts to bring up the supplied dev at the supplied
52address.
53
Dirk Gouders6556bfd2012-08-10 01:24:51 +000054The remote host has several options to receive the kernel messages,
55for example:
56
571) syslogd
58
592) netcat
60
61 On distributions using a BSD-based netcat version (e.g. Fedora,
62 openSUSE and Ubuntu) the listening port must be specified without
63 the -p switch:
64
65 'nc -u -l -p <port>' / 'nc -u -l <port>' or
66 'netcat -u -l -p <port>' / 'netcat -u -l <port>'
67
683) socat
69
70 'socat udp-recv:<port> -'
Linus Torvalds1da177e2005-04-16 15:20:36 -070071
Satyam Sharma0bcc1812007-08-10 15:35:05 -070072Dynamic reconfiguration:
73========================
74
75Dynamic reconfigurability is a useful addition to netconsole that enables
76remote logging targets to be dynamically added, removed, or have their
77parameters reconfigured at runtime from a configfs-based userspace interface.
78[ Note that the parameters of netconsole targets that were specified/created
79from the boot/module option are not exposed via this interface, and hence
80cannot be modified dynamically. ]
81
82To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
83netconsole module (or kernel, if netconsole is built-in).
84
85Some examples follow (where configfs is mounted at the /sys/kernel/config
86mountpoint).
87
88To add a remote logging target (target names can be arbitrary):
89
90 cd /sys/kernel/config/netconsole/
91 mkdir target1
92
93Note that newly created targets have default parameter values (as mentioned
94above) and are disabled by default -- they must first be enabled by writing
95"1" to the "enabled" attribute (usually after setting parameters accordingly)
96as described below.
97
98To remove a target:
99
100 rmdir /sys/kernel/config/netconsole/othertarget/
101
102The interface exposes these parameters of a netconsole target to userspace:
103
104 enabled Is this target currently enabled? (read-write)
105 dev_name Local network interface name (read-write)
106 local_port Source UDP port to use (read-write)
107 remote_port Remote agent's UDP port (read-write)
108 local_ip Source IP address to use (read-write)
109 remote_ip Remote agent's IP address (read-write)
110 local_mac Local interface's MAC address (read-only)
111 remote_mac Remote agent's MAC address (read-write)
112
113The "enabled" attribute is also used to control whether the parameters of
114a target can be updated or not -- you can modify the parameters of only
115disabled targets (i.e. if "enabled" is 0).
116
117To update a target's parameters:
118
119 cat enabled # check if enabled is 1
120 echo 0 > enabled # disable the target (if required)
121 echo eth2 > dev_name # set local interface
122 echo 10.0.0.4 > remote_ip # update some parameter
123 echo cb:a9:87:65:43:21 > remote_mac # update more parameters
124 echo 1 > enabled # enable target again
125
126You can also update the local interface dynamically. This is especially
127useful if you want to use interfaces that have newly come up (and may not
128have existed when netconsole was loaded / initialized).
129
130Miscellaneous notes:
131====================
132
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133WARNING: the default target ethernet setting uses the broadcast
134ethernet address to send packets, which can cause increased load on
135other systems on the same ethernet segment.
136
Satyam Sharma8d4ef882007-08-10 15:31:19 -0700137TIP: some LAN switches may be configured to suppress ethernet broadcasts
138so it is advised to explicitly specify the remote agents' MAC addresses
139from the config parameters passed to netconsole.
140
141TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
142
143 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
144
145TIP: in case the remote logging agent is on a separate LAN subnet than
146the sender, it is suggested to try specifying the MAC address of the
147default gateway (you may use /sbin/route -n to find it out) as the
148remote MAC address instead.
149
Linus Torvalds1da177e2005-04-16 15:20:36 -0700150NOTE: the network device (eth1 in the above case) can run any kind
151of other network traffic, netconsole is not intrusive. Netconsole
152might cause slight delays in other traffic if the volume of kernel
153messages is high, but should have no other impact.
154
Satyam Sharma8d4ef882007-08-10 15:31:19 -0700155NOTE: if you find that the remote logging agent is not receiving or
156printing all messages from the sender, it is likely that you have set
157the "console_loglevel" parameter (on the sender) to only send high
158priority messages to the console. You can change this at runtime using:
159
160 dmesg -n 8
161
162or by specifying "debug" on the kernel command line at boot, to send
163all kernel messages to the console. A specific value for this parameter
164can also be set using the "loglevel" kernel boot option. See the
165dmesg(8) man page and Documentation/kernel-parameters.txt for details.
166
Linus Torvalds1da177e2005-04-16 15:20:36 -0700167Netconsole was designed to be as instantaneous as possible, to
168enable the logging of even the most critical kernel bugs. It works
169from IRQ contexts as well, and does not enable interrupts while
Matt LaPlante84eb8d02006-10-03 22:53:09 +0200170sending packets. Due to these unique needs, configuration cannot
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171be more automatic, and some fundamental limitations will remain:
172only IP networks, UDP packets and ethernet devices are supported.