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1
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
4IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
5Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015
6
7Please send bug reports to Matt Mackall <mpm@selenic.com>
8Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
9
10Introduction:
11=============
12
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
22Sender and receiver configuration:
23==================================
24
25It takes a string configuration parameter "netconsole" in the
26following format:
27
28 netconsole=[+][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
29
30 where
31 + if present, enable extended console support
32 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
47 or using IPv6
48
49 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
50
51It 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
57Built-in netconsole starts immediately after the TCP stack is
58initialized and attempts to bring up the supplied dev at the supplied
59address.
60
61The 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> -'
78
79Dynamic 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)
112 extended Extended mode enabled (read-write)
113 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
138Extended 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
168Miscellaneous notes:
169====================
170
171WARNING: 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
175TIP: 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
188NOTE: 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
193NOTE: 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
205Netconsole 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
208sending packets. Due to these unique needs, configuration cannot
209be more automatic, and some fundamental limitations will remain:
210only IP networks, UDP packets and ethernet devices are supported.
1
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
4IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
5
6Please send bug reports to Matt Mackall <mpm@selenic.com>
7Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
8
9Introduction:
10=============
11
12This module logs kernel printk messages over UDP allowing debugging of
13problem where disk logging fails and serial consoles are impractical.
14
15It can be used either built-in or as a module. As a built-in,
16netconsole initializes immediately after NIC cards and will bring up
17the specified interface as soon as possible. While this doesn't allow
18capture of early kernel panics, it does capture most of the boot
19process.
20
21Sender and receiver configuration:
22==================================
23
24It takes a string configuration parameter "netconsole" in the
25following format:
26
27 netconsole=[src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
28
29 where
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)
36
37Examples:
38
39 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc
40
41 or
42
43 insmod netconsole netconsole=@/,@10.0.0.2/
44
45 or using IPv6
46
47 insmod netconsole netconsole=@/,@fd00:1:2:3::1/
48
49It also supports logging to multiple remote agents by specifying
50parameters for the multiple agents separated by semicolons and the
51complete string enclosed in "quotes", thusly:
52
53 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/"
54
55Built-in netconsole starts immediately after the TCP stack is
56initialized and attempts to bring up the supplied dev at the supplied
57address.
58
59The remote host has several options to receive the kernel messages,
60for example:
61
621) syslogd
63
642) netcat
65
66 On distributions using a BSD-based netcat version (e.g. Fedora,
67 openSUSE and Ubuntu) the listening port must be specified without
68 the -p switch:
69
70 'nc -u -l -p <port>' / 'nc -u -l <port>' or
71 'netcat -u -l -p <port>' / 'netcat -u -l <port>'
72
733) socat
74
75 'socat udp-recv:<port> -'
76
77Dynamic reconfiguration:
78========================
79
80Dynamic reconfigurability is a useful addition to netconsole that enables
81remote logging targets to be dynamically added, removed, or have their
82parameters reconfigured at runtime from a configfs-based userspace interface.
83[ Note that the parameters of netconsole targets that were specified/created
84from the boot/module option are not exposed via this interface, and hence
85cannot be modified dynamically. ]
86
87To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
88netconsole module (or kernel, if netconsole is built-in).
89
90Some examples follow (where configfs is mounted at the /sys/kernel/config
91mountpoint).
92
93To add a remote logging target (target names can be arbitrary):
94
95 cd /sys/kernel/config/netconsole/
96 mkdir target1
97
98Note that newly created targets have default parameter values (as mentioned
99above) and are disabled by default -- they must first be enabled by writing
100"1" to the "enabled" attribute (usually after setting parameters accordingly)
101as described below.
102
103To remove a target:
104
105 rmdir /sys/kernel/config/netconsole/othertarget/
106
107The interface exposes these parameters of a netconsole target to userspace:
108
109 enabled Is this target currently enabled? (read-write)
110 dev_name Local network interface name (read-write)
111 local_port Source UDP port to use (read-write)
112 remote_port Remote agent's UDP port (read-write)
113 local_ip Source IP address to use (read-write)
114 remote_ip Remote agent's IP address (read-write)
115 local_mac Local interface's MAC address (read-only)
116 remote_mac Remote agent's MAC address (read-write)
117
118The "enabled" attribute is also used to control whether the parameters of
119a target can be updated or not -- you can modify the parameters of only
120disabled targets (i.e. if "enabled" is 0).
121
122To update a target's parameters:
123
124 cat enabled # check if enabled is 1
125 echo 0 > enabled # disable the target (if required)
126 echo eth2 > dev_name # set local interface
127 echo 10.0.0.4 > remote_ip # update some parameter
128 echo cb:a9:87:65:43:21 > remote_mac # update more parameters
129 echo 1 > enabled # enable target again
130
131You can also update the local interface dynamically. This is especially
132useful if you want to use interfaces that have newly come up (and may not
133have existed when netconsole was loaded / initialized).
134
135Miscellaneous notes:
136====================
137
138WARNING: the default target ethernet setting uses the broadcast
139ethernet address to send packets, which can cause increased load on
140other systems on the same ethernet segment.
141
142TIP: some LAN switches may be configured to suppress ethernet broadcasts
143so it is advised to explicitly specify the remote agents' MAC addresses
144from the config parameters passed to netconsole.
145
146TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
147
148 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
149
150TIP: in case the remote logging agent is on a separate LAN subnet than
151the sender, it is suggested to try specifying the MAC address of the
152default gateway (you may use /sbin/route -n to find it out) as the
153remote MAC address instead.
154
155NOTE: the network device (eth1 in the above case) can run any kind
156of other network traffic, netconsole is not intrusive. Netconsole
157might cause slight delays in other traffic if the volume of kernel
158messages is high, but should have no other impact.
159
160NOTE: if you find that the remote logging agent is not receiving or
161printing all messages from the sender, it is likely that you have set
162the "console_loglevel" parameter (on the sender) to only send high
163priority messages to the console. You can change this at runtime using:
164
165 dmesg -n 8
166
167or by specifying "debug" on the kernel command line at boot, to send
168all kernel messages to the console. A specific value for this parameter
169can also be set using the "loglevel" kernel boot option. See the
170dmesg(8) man page and Documentation/kernel-parameters.txt for details.
171
172Netconsole was designed to be as instantaneous as possible, to
173enable the logging of even the most critical kernel bugs. It works
174from IRQ contexts as well, and does not enable interrupts while
175sending packets. Due to these unique needs, configuration cannot
176be more automatic, and some fundamental limitations will remain:
177only IP networks, UDP packets and ethernet devices are supported.