Based on kernel version 4.0. Page generated on 2015-04-14 21:25 EST.
1 2 started by Ingo Molnar <firstname.lastname@example.org>, 2001.09.17 3 2.6 port and netpoll api by Matt Mackall <email@example.com>, Sep 9 2003 4 IPv6 support by Cong Wang <firstname.lastname@example.org>, Jan 1 2013 5 6 Please send bug reports to Matt Mackall <email@example.com> 7 Satyam Sharma <firstname.lastname@example.org>, and Cong Wang <email@example.com> 8 9 Introduction: 10 ============= 11 12 This module logs kernel printk messages over UDP allowing debugging of 13 problem where disk logging fails and serial consoles are impractical. 14 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 19 process. 20 21 Sender and receiver configuration: 22 ================================== 23 24 It takes a string configuration parameter "netconsole" in the 25 following 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 37 Examples: 38 39 linux firstname.lastname@example.org/eth1,email@example.com/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 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: 52 53 modprobe netconsole netconsole="@/,@10.0.0.2/;@/eth1,firstname.lastname@example.org/" 54 55 Built-in netconsole starts immediately after the TCP stack is 56 initialized and attempts to bring up the supplied dev at the supplied 57 address. 58 59 The remote host has several options to receive the kernel messages, 60 for example: 61 62 1) syslogd 63 64 2) 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 73 3) socat 74 75 'socat udp-recv:<port> -' 76 77 Dynamic reconfiguration: 78 ======================== 79 80 Dynamic reconfigurability is a useful addition to netconsole that enables 81 remote logging targets to be dynamically added, removed, or have their 82 parameters reconfigured at runtime from a configfs-based userspace interface. 83 [ Note that the parameters of netconsole targets that were specified/created 84 from the boot/module option are not exposed via this interface, and hence 85 cannot be modified dynamically. ] 86 87 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the 88 netconsole module (or kernel, if netconsole is built-in). 89 90 Some examples follow (where configfs is mounted at the /sys/kernel/config 91 mountpoint). 92 93 To add a remote logging target (target names can be arbitrary): 94 95 cd /sys/kernel/config/netconsole/ 96 mkdir target1 97 98 Note that newly created targets have default parameter values (as mentioned 99 above) and are disabled by default -- they must first be enabled by writing 100 "1" to the "enabled" attribute (usually after setting parameters accordingly) 101 as described below. 102 103 To remove a target: 104 105 rmdir /sys/kernel/config/netconsole/othertarget/ 106 107 The 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) 117 118 The "enabled" attribute is also used to control whether the parameters of 119 a target can be updated or not -- you can modify the parameters of only 120 disabled targets (i.e. if "enabled" is 0). 121 122 To 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 130 131 You can also update the local interface dynamically. This is especially 132 useful if you want to use interfaces that have newly come up (and may not 133 have existed when netconsole was loaded / initialized). 134 135 Miscellaneous notes: 136 ==================== 137 138 WARNING: the default target ethernet setting uses the broadcast 139 ethernet address to send packets, which can cause increased load on 140 other systems on the same ethernet segment. 141 142 TIP: some LAN switches may be configured to suppress ethernet broadcasts 143 so it is advised to explicitly specify the remote agents' MAC addresses 144 from the config parameters passed to netconsole. 145 146 TIP: 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 10.0.0.2 149 150 TIP: in case the remote logging agent is on a separate LAN subnet than 151 the sender, it is suggested to try specifying the MAC address of the 152 default gateway (you may use /sbin/route -n to find it out) as the 153 remote MAC address instead. 154 155 NOTE: the network device (eth1 in the above case) can run any kind 156 of other network traffic, netconsole is not intrusive. Netconsole 157 might cause slight delays in other traffic if the volume of kernel 158 messages is high, but should have no other impact. 159 160 NOTE: if you find that the remote logging agent is not receiving or 161 printing all messages from the sender, it is likely that you have set 162 the "console_loglevel" parameter (on the sender) to only send high 163 priority messages to the console. You can change this at runtime using: 164 165 dmesg -n 8 166 167 or by specifying "debug" on the kernel command line at boot, to send 168 all kernel messages to the console. A specific value for this parameter 169 can also be set using the "loglevel" kernel boot option. See the 170 dmesg(8) man page and Documentation/kernel-parameters.txt for details. 171 172 Netconsole was designed to be as instantaneous as possible, to 173 enable the logging of even the most critical kernel bugs. It works 174 from IRQ contexts as well, and does not enable interrupts while 175 sending packets. Due to these unique needs, configuration cannot 176 be more automatic, and some fundamental limitations will remain: 177 only IP networks, UDP packets and ethernet devices are supported.