1.. SPDX-License-Identifier: GPL-2.0 2 3========== 4Netconsole 5========== 6 7 8started by Ingo Molnar <mingo@redhat.com>, 2001.09.17 9 102.6 port and netpoll api by Matt Mackall <mpm@selenic.com>, Sep 9 2003 11 12IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013 13 14Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015 15 16Please send bug reports to Matt Mackall <mpm@selenic.com> 17Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com> 18 19Introduction: 20============= 21 22This module logs kernel printk messages over UDP allowing debugging of 23problem where disk logging fails and serial consoles are impractical. 24 25It can be used either built-in or as a module. As a built-in, 26netconsole initializes immediately after NIC cards and will bring up 27the specified interface as soon as possible. While this doesn't allow 28capture of early kernel panics, it does capture most of the boot 29process. 30 31Sender and receiver configuration: 32================================== 33 34It takes a string configuration parameter "netconsole" in the 35following format:: 36 37 netconsole=[+][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr] 38 39 where 40 + if present, enable extended console support 41 src-port source for UDP packets (defaults to 6665) 42 src-ip source IP to use (interface address) 43 dev network interface (eth0) 44 tgt-port port for logging agent (6666) 45 tgt-ip IP address for logging agent 46 tgt-macaddr ethernet MAC address for logging agent (broadcast) 47 48Examples:: 49 50 linux netconsole=4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc 51 52or:: 53 54 insmod netconsole netconsole=@/,@10.0.0.2/ 55 56or using IPv6:: 57 58 insmod netconsole netconsole=@/,@fd00:1:2:3::1/ 59 60It also supports logging to multiple remote agents by specifying 61parameters for the multiple agents separated by semicolons and the 62complete string enclosed in "quotes", thusly:: 63 64 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,6892@10.0.0.3/" 65 66Built-in netconsole starts immediately after the TCP stack is 67initialized and attempts to bring up the supplied dev at the supplied 68address. 69 70The remote host has several options to receive the kernel messages, 71for example: 72 731) syslogd 74 752) netcat 76 77 On distributions using a BSD-based netcat version (e.g. Fedora, 78 openSUSE and Ubuntu) the listening port must be specified without 79 the -p switch:: 80 81 nc -u -l -p <port>' / 'nc -u -l <port> 82 83 or:: 84 85 netcat -u -l -p <port>' / 'netcat -u -l <port> 86 873) socat 88 89:: 90 91 socat udp-recv:<port> - 92 93Dynamic reconfiguration: 94======================== 95 96Dynamic reconfigurability is a useful addition to netconsole that enables 97remote logging targets to be dynamically added, removed, or have their 98parameters reconfigured at runtime from a configfs-based userspace interface. 99[ Note that the parameters of netconsole targets that were specified/created 100from the boot/module option are not exposed via this interface, and hence 101cannot be modified dynamically. ] 102 103To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the 104netconsole module (or kernel, if netconsole is built-in). 105 106Some examples follow (where configfs is mounted at the /sys/kernel/config 107mountpoint). 108 109To add a remote logging target (target names can be arbitrary):: 110 111 cd /sys/kernel/config/netconsole/ 112 mkdir target1 113 114Note that newly created targets have default parameter values (as mentioned 115above) and are disabled by default -- they must first be enabled by writing 116"1" to the "enabled" attribute (usually after setting parameters accordingly) 117as described below. 118 119To remove a target:: 120 121 rmdir /sys/kernel/config/netconsole/othertarget/ 122 123The interface exposes these parameters of a netconsole target to userspace: 124 125 ============== ================================= ============ 126 enabled Is this target currently enabled? (read-write) 127 extended Extended mode enabled (read-write) 128 dev_name Local network interface name (read-write) 129 local_port Source UDP port to use (read-write) 130 remote_port Remote agent's UDP port (read-write) 131 local_ip Source IP address to use (read-write) 132 remote_ip Remote agent's IP address (read-write) 133 local_mac Local interface's MAC address (read-only) 134 remote_mac Remote agent's MAC address (read-write) 135 ============== ================================= ============ 136 137The "enabled" attribute is also used to control whether the parameters of 138a target can be updated or not -- you can modify the parameters of only 139disabled targets (i.e. if "enabled" is 0). 140 141To update a target's parameters:: 142 143 cat enabled # check if enabled is 1 144 echo 0 > enabled # disable the target (if required) 145 echo eth2 > dev_name # set local interface 146 echo 10.0.0.4 > remote_ip # update some parameter 147 echo cb:a9:87:65:43:21 > remote_mac # update more parameters 148 echo 1 > enabled # enable target again 149 150You can also update the local interface dynamically. This is especially 151useful if you want to use interfaces that have newly come up (and may not 152have existed when netconsole was loaded / initialized). 153 154Extended console: 155================= 156 157If '+' is prefixed to the configuration line or "extended" config file 158is set to 1, extended console support is enabled. An example boot 159param follows:: 160 161 linux netconsole=+4444@10.0.0.1/eth1,9353@10.0.0.2/12:34:56:78:9a:bc 162 163Log messages are transmitted with extended metadata header in the 164following format which is the same as /dev/kmsg:: 165 166 <level>,<sequnum>,<timestamp>,<contflag>;<message text> 167 168Non printable characters in <message text> are escaped using "\xff" 169notation. If the message contains optional dictionary, verbatim 170newline is used as the delimiter. 171 172If a message doesn't fit in certain number of bytes (currently 1000), 173the message is split into multiple fragments by netconsole. These 174fragments are transmitted with "ncfrag" header field added:: 175 176 ncfrag=<byte-offset>/<total-bytes> 177 178For example, assuming a lot smaller chunk size, a message "the first 179chunk, the 2nd chunk." may be split as follows:: 180 181 6,416,1758426,-,ncfrag=0/31;the first chunk, 182 6,416,1758426,-,ncfrag=16/31; the 2nd chunk. 183 184Miscellaneous notes: 185==================== 186 187.. Warning:: 188 189 the default target ethernet setting uses the broadcast 190 ethernet address to send packets, which can cause increased load on 191 other systems on the same ethernet segment. 192 193.. Tip:: 194 195 some LAN switches may be configured to suppress ethernet broadcasts 196 so it is advised to explicitly specify the remote agents' MAC addresses 197 from the config parameters passed to netconsole. 198 199.. Tip:: 200 201 to find out the MAC address of, say, 10.0.0.2, you may try using:: 202 203 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2 204 205.. Tip:: 206 207 in case the remote logging agent is on a separate LAN subnet than 208 the sender, it is suggested to try specifying the MAC address of the 209 default gateway (you may use /sbin/route -n to find it out) as the 210 remote MAC address instead. 211 212.. note:: 213 214 the network device (eth1 in the above case) can run any kind 215 of other network traffic, netconsole is not intrusive. Netconsole 216 might cause slight delays in other traffic if the volume of kernel 217 messages is high, but should have no other impact. 218 219.. note:: 220 221 if you find that the remote logging agent is not receiving or 222 printing all messages from the sender, it is likely that you have set 223 the "console_loglevel" parameter (on the sender) to only send high 224 priority messages to the console. You can change this at runtime using:: 225 226 dmesg -n 8 227 228 or by specifying "debug" on the kernel command line at boot, to send 229 all kernel messages to the console. A specific value for this parameter 230 can also be set using the "loglevel" kernel boot option. See the 231 dmesg(8) man page and Documentation/admin-guide/kernel-parameters.rst 232 for details. 233 234Netconsole was designed to be as instantaneous as possible, to 235enable the logging of even the most critical kernel bugs. It works 236from IRQ contexts as well, and does not enable interrupts while 237sending packets. Due to these unique needs, configuration cannot 238be more automatic, and some fundamental limitations will remain: 239only IP networks, UDP packets and ethernet devices are supported. 240