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[NET] netconsole: Add some useful tips to documentation 

Based upon initial work by Keiichi Kii <k-keiichi@bx.jp.nec.com>.

Add some useful general-purpose tips.  Also suggest solution for the frequent
problem of console loglevel set too low numerically (i.e.  for high priority
messages only) on the sender.

Signed-off-by: Satyam Sharma <satyam@infradead.org>
Acked-by: Keiichi Kii <k-keiichi@bx.jp.nec.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Satyam Sharma 2007-08-10 15:31:19 -07:00 committed by David S. Miller
parent 0cc120bea1
commit 8d4ef88b5d
1 changed files with 25 additions and 0 deletions
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25
Documentation/networking/netconsole.txt
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@ -44,11 +44,36 @@ 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.
TIP: some LAN switches may be configured to suppress ethernet broadcasts
so it is advised to explicitly specify the remote agents' MAC addresses
from the config parameters passed to netconsole.
TIP: to find out the MAC address of, say, 10.0.0.2, you may try using:
ping -c 1 10.0.0.2 ; /sbin/arp -n | grep 10.0.0.2
TIP: in case the remote logging agent is on a separate LAN subnet than
the sender, it is suggested to try specifying the MAC address of the
default gateway (you may use /sbin/route -n to find it out) as the
remote MAC address instead.
NOTE: the network device (eth1 in the above case) can run any kind
of other network traffic, netconsole is not intrusive. Netconsole
might cause slight delays in other traffic if the volume of kernel
messages is high, but should have no other impact.
NOTE: if you find that the remote logging agent is not receiving or
printing all messages from the sender, it is likely that you have set
the "console_loglevel" parameter (on the sender) to only send high
priority messages to the console. You can change this at runtime using:
dmesg -n 8
or by specifying "debug" on the kernel command line at boot, to send
all kernel messages to the console. A specific value for this parameter
can also be set using the "loglevel" kernel boot option. See the
dmesg(8) man page and Documentation/kernel-parameters.txt for details.
Netconsole was designed to be as instantaneous as possible, to
enable the logging of even the most critical kernel bugs. It works
from IRQ contexts as well, and does not enable interrupts while