Based on kernel version 2.6.33. Page generated on 2010-02-24 15:36 EST.
1 2 started by Ingo Molnar <mingo[AT]redhat.com>, 2001.09[DOT]17 3 2.6 port and netpoll api by Matt Mackall <mpm[AT]selenic[DOT]com>, Sep 9 2003 4 5 Please send bug reports to Matt Mackall <mpm[AT]selenic[DOT]com> 6 and Satyam Sharma <satyam.sharma[AT]gmail[DOT]com> 7 8 Introduction: 9 ============= 10 11 This module logs kernel printk messages over UDP allowing debugging of 12 problem where disk logging fails and serial consoles are impractical. 13 14 It can be used either built-in or as a module. As a built-in, 15 netconsole initializes immediately after NIC cards and will bring up 16 the specified interface as soon as possible. While this doesn't allow 17 capture of early kernel panics, it does capture most of the boot 18 process. 19 20 Sender and receiver configuration: 21 ================================== 22 23 It takes a string configuration parameter "netconsole" in the 24 following 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 36 Examples: 37 38 linux netconsole=4444[AT]10.0.0.1/eth1,9353@10.0.0[DOT]2/12:34:56:78:9a:bc 39 40 or 41 42 insmod netconsole netconsole=[AT]/,@10.0.0[DOT]2/ 43 44 It also supports logging to multiple remote agents by specifying 45 parameters for the multiple agents separated by semicolons and the 46 complete string enclosed in "quotes", thusly: 47 48 modprobe netconsole netconsole="[AT]/,@10.0.0.2/;@/eth1,6892@10.0.0[DOT]3/" 49 50 Built-in netconsole starts immediately after the TCP stack is 51 initialized and attempts to bring up the supplied dev at the supplied 52 address. 53 54 The remote host can run either 'netcat -u -l -p <port>', 55 'nc -l -u <port>' or syslogd. 56 57 Dynamic reconfiguration: 58 ======================== 59 60 Dynamic reconfigurability is a useful addition to netconsole that enables 61 remote logging targets to be dynamically added, removed, or have their 62 parameters reconfigured at runtime from a configfs-based userspace interface. 63 [ Note that the parameters of netconsole targets that were specified/created 64 from the boot/module option are not exposed via this interface, and hence 65 cannot be modified dynamically. ] 66 67 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the 68 netconsole module (or kernel, if netconsole is built-in). 69 70 Some examples follow (where configfs is mounted at the /sys/kernel/config 71 mountpoint). 72 73 To add a remote logging target (target names can be arbitrary): 74 75 cd /sys/kernel/config/netconsole/ 76 mkdir target1 77 78 Note that newly created targets have default parameter values (as mentioned 79 above) and are disabled by default -- they must first be enabled by writing 80 "1" to the "enabled" attribute (usually after setting parameters accordingly) 81 as described below. 82 83 To remove a target: 84 85 rmdir /sys/kernel/config/netconsole/othertarget/ 86 87 The interface exposes these parameters of a netconsole target to userspace: 88 89 enabled Is this target currently enabled? (read-write) 90 dev_name Local network interface name (read-write) 91 local_port Source UDP port to use (read-write) 92 remote_port Remote agent's UDP port (read-write) 93 local_ip Source IP address to use (read-write) 94 remote_ip Remote agent's IP address (read-write) 95 local_mac Local interface's MAC address (read-only) 96 remote_mac Remote agent's MAC address (read-write) 97 98 The "enabled" attribute is also used to control whether the parameters of 99 a target can be updated or not -- you can modify the parameters of only 100 disabled targets (i.e. if "enabled" is 0). 101 102 To update a target's parameters: 103 104 cat enabled # check if enabled is 1 105 echo 0 > enabled # disable the target (if required) 106 echo eth2 > dev_name # set local interface 107 echo 10.0.0.4 > remote_ip # update some parameter 108 echo cb:a9:87:65:43:21 > remote_mac # update more parameters 109 echo 1 > enabled # enable target again 110 111 You can also update the local interface dynamically. This is especially 112 useful if you want to use interfaces that have newly come up (and may not 113 have existed when netconsole was loaded / initialized). 114 115 Miscellaneous notes: 116 ==================== 117 118 WARNING: the default target ethernet setting uses the broadcast 119 ethernet address to send packets, which can cause increased load on 120 other systems on the same ethernet segment. 121 122 TIP: some LAN switches may be configured to suppress ethernet broadcasts 123 so it is advised to explicitly specify the remote agents' MAC addresses 124 from the config parameters passed to netconsole. 125 126 TIP: to find out the MAC address of, say, 10.0.0.2, you may try using: 127 128 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2 129 130 TIP: in case the remote logging agent is on a separate LAN subnet than 131 the sender, it is suggested to try specifying the MAC address of the 132 default gateway (you may use /sbin/route -n to find it out) as the 133 remote MAC address instead. 134 135 NOTE: the network device (eth1 in the above case) can run any kind 136 of other network traffic, netconsole is not intrusive. Netconsole 137 might cause slight delays in other traffic if the volume of kernel 138 messages is high, but should have no other impact. 139 140 NOTE: if you find that the remote logging agent is not receiving or 141 printing all messages from the sender, it is likely that you have set 142 the "console_loglevel" parameter (on the sender) to only send high 143 priority messages to the console. You can change this at runtime using: 144 145 dmesg -n 8 146 147 or by specifying "debug" on the kernel command line at boot, to send 148 all kernel messages to the console. A specific value for this parameter 149 can also be set using the "loglevel" kernel boot option. See the 150 dmesg(8) man page and Documentation/kernel-parameters.txt for details. 151 152 Netconsole was designed to be as instantaneous as possible, to 153 enable the logging of even the most critical kernel bugs. It works 154 from IRQ contexts as well, and does not enable interrupts while 155 sending packets. Due to these unique needs, configuration cannot 156 be more automatic, and some fundamental limitations will remain: 157 only IP networks, UDP packets and ethernet devices are supported.