Based on kernel version 2.6.26. Page generated on 2008-07-16 21:13 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>' or syslogd. 55 56 Dynamic reconfiguration: 57 ======================== 58 59 Dynamic reconfigurability is a useful addition to netconsole that enables 60 remote logging targets to be dynamically added, removed, or have their 61 parameters reconfigured at runtime from a configfs-based userspace interface. 62 [ Note that the parameters of netconsole targets that were specified/created 63 from the boot/module option are not exposed via this interface, and hence 64 cannot be modified dynamically. ] 65 66 To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the 67 netconsole module (or kernel, if netconsole is built-in). 68 69 Some examples follow (where configfs is mounted at the /sys/kernel/config 70 mountpoint). 71 72 To add a remote logging target (target names can be arbitrary): 73 74 cd /sys/kernel/config/netconsole/ 75 mkdir target1 76 77 Note that newly created targets have default parameter values (as mentioned 78 above) and are disabled by default -- they must first be enabled by writing 79 "1" to the "enabled" attribute (usually after setting parameters accordingly) 80 as described below. 81 82 To remove a target: 83 84 rmdir /sys/kernel/config/netconsole/othertarget/ 85 86 The interface exposes these parameters of a netconsole target to userspace: 87 88 enabled Is this target currently enabled? (read-write) 89 dev_name Local network interface name (read-write) 90 local_port Source UDP port to use (read-write) 91 remote_port Remote agent's UDP port (read-write) 92 local_ip Source IP address to use (read-write) 93 remote_ip Remote agent's IP address (read-write) 94 local_mac Local interface's MAC address (read-only) 95 remote_mac Remote agent's MAC address (read-write) 96 97 The "enabled" attribute is also used to control whether the parameters of 98 a target can be updated or not -- you can modify the parameters of only 99 disabled targets (i.e. if "enabled" is 0). 100 101 To update a target's parameters: 102 103 cat enabled # check if enabled is 1 104 echo 0 > enabled # disable the target (if required) 105 echo eth2 > dev_name # set local interface 106 echo 10.0.0.4 > remote_ip # update some parameter 107 echo cb:a9:87:65:43:21 > remote_mac # update more parameters 108 echo 1 > enabled # enable target again 109 110 You can also update the local interface dynamically. This is especially 111 useful if you want to use interfaces that have newly come up (and may not 112 have existed when netconsole was loaded / initialized). 113 114 Miscellaneous notes: 115 ==================== 116 117 WARNING: the default target ethernet setting uses the broadcast 118 ethernet address to send packets, which can cause increased load on 119 other systems on the same ethernet segment. 120 121 TIP: some LAN switches may be configured to suppress ethernet broadcasts 122 so it is advised to explicitly specify the remote agents' MAC addresses 123 from the config parameters passed to netconsole. 124 125 TIP: to find out the MAC address of, say, 10.0.0.2, you may try using: 126 127 ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2 128 129 TIP: in case the remote logging agent is on a separate LAN subnet than 130 the sender, it is suggested to try specifying the MAC address of the 131 default gateway (you may use /sbin/route -n to find it out) as the 132 remote MAC address instead. 133 134 NOTE: the network device (eth1 in the above case) can run any kind 135 of other network traffic, netconsole is not intrusive. Netconsole 136 might cause slight delays in other traffic if the volume of kernel 137 messages is high, but should have no other impact. 138 139 NOTE: if you find that the remote logging agent is not receiving or 140 printing all messages from the sender, it is likely that you have set 141 the "console_loglevel" parameter (on the sender) to only send high 142 priority messages to the console. You can change this at runtime using: 143 144 dmesg -n 8 145 146 or by specifying "debug" on the kernel command line at boot, to send 147 all kernel messages to the console. A specific value for this parameter 148 can also be set using the "loglevel" kernel boot option. See the 149 dmesg(8) man page and Documentation/kernel-parameters.txt for details. 150 151 Netconsole was designed to be as instantaneous as possible, to 152 enable the logging of even the most critical kernel bugs. It works 153 from IRQ contexts as well, and does not enable interrupts while 154 sending packets. Due to these unique needs, configuration cannot 155 be more automatic, and some fundamental limitations will remain: 156 only IP networks, UDP packets and ethernet devices are supported.