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Subject[PATCH -mm 8/9] netconsole: Update documentation for dynamic reconfigurability
From: Satyam Sharma <>

[8/9] netconsole: Update documentation for dynamic reconfigurability

Add myself to parties interested in receiving bug reports, and give lots
of examples. Also fix some whitespace inconsistencies I introduced earlier.

Signed-off-by: Satyam Sharma <>
Cc: Keiichi Kii <>
Cc: Takayoshi Kochi <>


Documentation/networking/netconsole.txt | 70 +++++++++++++++++++++++++++++++-
1 file changed, 68 insertions(+), 2 deletions(-)


diff -ruNp a/Documentation/networking/netconsole.txt b/Documentation/networking/netconsole.txt
--- a/Documentation/networking/netconsole.txt 2007-07-04 03:12:25.000000000 +0530
+++ b/Documentation/networking/netconsole.txt 2007-07-04 12:24:44.000000000 +0530
@@ -3,6 +3,10 @@ started by Ingo Molnar <
2.6 port and netpoll api by Matt Mackall <>, Sep 9 2003

Please send bug reports to Matt Mackall <>
+and Satyam Sharma <>

This module logs kernel printk messages over UDP allowing debugging of
problem where disk logging fails and serial consoles are impractical.
@@ -13,6 +17,9 @@ the specified interface as soon as possi
capture of early kernel panics, it does capture most of the boot

+Sender and receiver configuration:
It takes a string configuration parameter "netconsole" in the
following format:

@@ -38,7 +45,7 @@ It also supports logging to multiple rem
parameters for the multiple agents separated by semicolons and the
complete string enclosed in "quotes", thusly:

-modprobe netconsole netconsole="@/,@;@/eth1,6892@"
+ modprobe netconsole netconsole="@/,@;@/eth1,6892@"

Built-in netconsole starts immediately after the TCP stack is
initialized and attempts to bring up the supplied dev at the supplied
@@ -46,6 +53,64 @@ address.

The remote host can run either 'netcat -u -l -p <port>' or syslogd.

+Dynamic reconfiguration:
+Dynamic reconfigurability is a useful addition to netconsole that enables
+remote logging targets to be dynamically added, removed, or have their
+parameters reconfigured at runtime from a configfs-based userspace interface.
+To include this feature, select CONFIG_NETCONSOLE_DYNAMIC when building the
+netconsole module (or kernel, if netconsole is built-in).
+Some examples follow (configfs is mounted at the /config mountpoint, say).
+To add a remote logging target (target names can be arbitrary):
+ cd /config/netconsole/
+ mkdir target1
+Note that newly created targets have default parameter values (as mentioned
+above) and are disabled by default -- they must first be enabled by writing
+"1" to the "enabled" attribute (usually after setting parameters accordingly)
+as described below.
+To remove a target:
+ rmdir /config/netconsole/othertarget/
+The interface exposes these parameters of a netconsole target to userspace:
+ id Unique identifier for this target (read-only)
+ enabled Is this target currently enabled? (read-write)
+ dev_name Local network interface name (read-only)
+ local_ip Source IP address to use (read-write)
+ remote_ip Remote agent's IP address (read-write)
+ local_port Source UDP port to use (read-write)
+ remote_port Remote agent's UDP port (read-write)
+ local_mac Local interface's MAC address (read-only)
+ remote_mac Remote agent's MAC address (read-write)
+The "enabled" attribute is also used to control whether the parameters of
+a target can be updated or not -- you can modify the parameters of only
+disabled targets (i.e. if "enabled" is 0).
+To update a target's parameters:
+ cat enabled # check if enabled is 1
+ echo 0 > enabled # disable the target (if required)
+ echo eth2 > dev_name # set local interface
+ echo > remote_ip # update some parameter
+ echo cb:a9:87:65:43:21 > remote_mac # update more parameters
+ echo 1 > enabled # enable target again
+Note that you can even update the local interface dynamically. This is
+especially useful if you want to use interfaces that have newly come up
+and didn't even exist when netconsole was loaded / initialized.
+Miscellaneous notes:
WARNING: the default target ethernet setting uses the broadcast
ethernet address to send packets, which can cause increased load on
other systems on the same ethernet segment.
@@ -55,7 +120,8 @@ so it is advised to explicitly specify t
from the config parameters passed to netconsole.

TIP: to find out the MAC address of, you may try using:
-ping -c 1 ; /sbin/arp -n | grep
+ ping -c 1 ; /sbin/arp -n | grep

TIP: in case the remote logging agent is on a separate LAN subnet than
the sender, it is suggested to try specifying the default gateway's
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