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In U-Boot, we implemented the networked console via the standard
"devices" mechanism, which means that you can switch between the
serial and network input/output devices by adjusting the 'stdin' and
'stdout' environment variables. To switch to the networked console,
set either of these variables to "nc". Input and output can be
switched independently.
We use an environment variable 'ncip' to set the IP address and the
port of the destination. The format is <ip_addr>:<port>. If <port> is
omitted, the value of 6666 is used. If the env var doesn't exist, the
broadcast address and port 6666 are used. If it is set to an IP
address of 0 (or then no messages are sent to the network.
For example, if your server IP is, you could use:
=> setenv nc 'setenv stdout nc;setenv stdin nc'
=> setenv ncip
=> saveenv
=> run nc
On the host side, please use this script to access the console:
tools/netconsole <ip> [port]
The script uses netcat to talk to the board over UDP. It requires you to
specify the target IP address (or host name, assuming DNS is working). The
script can be interrupted by pressing ^T (CTRL-T).
Be aware that in some distributives (Fedora Core 5 at least)
usage of nc has been changed and -l and -p options are considered
as mutually exclusive. If nc complains about options provided,
you can just remove the -p option from the script.
It turns out that 'netcat' cannot be used to listen to broadcast
packets. We developed our own tool 'ncb' (see tools directory) that
listens to broadcast packets on a given port and dumps them to the
standard output. use it as follows:
#! /bin/bash
[ $# = 1 ] || { echo "Usage: $0 target_ip" >&2 ; exit 1 ; }
stty icanon echo intr ^T
./ncb &
nc -u ${TARGET_IP} 6666
stty icanon echo intr ^C
kill 0
Again, this script takes exactly one argument, which is interpreted
as the target IP address (or host name, assuming DNS is working). The
script can be interrupted by pressing ^T (CTRL-T).
The 'ncb' tool can be found in the tools directory; it will be built
when compiling for a board which has CONFIG_NETCONSOLE defined.
For Linux, the network-based console needs special configuration.
Minimally, the host IP address needs to be specified. This can be
done either via the kernel command line, or by passing parameters
while loading the netconsole.o module (when used in a loadable module
configuration). Please refer to Documentation/networking/logging.txt
file for the original Ingo Molnar's documentation on how to pass
parameters to the loadable module.
The format of the kernel command line parameter (for the static
configuration) is as follows:
src-port source for UDP packets
(defaults to 6665)
src-ip source IP to use
(defaults to the interface's address)
dev network interface
(defaults to eth0)
tgt-port port for logging agent
(defaults to 6666)
tgt-ip IP address for logging agent
(this is the required parameter)
tgt-macaddr ethernet MAC address for logging agent
(defaults to broadcast)
Please note that for the Linux networked console to work, the
ethernet interface has to be up by the time the netconsole driver is
initialized. This means that in case of static kernel configuration,
the respective Ethernet interface has to be brought up using the "IP
Autoconfiguration" kernel feature, which is usually done by defaults
in the ELDK-NFS-based environment.
To browse the Linux network console output, use the 'netcat' tool invoked
as follows:
nc -u -l -p 6666
Note that unlike the U-Boot implementation the Linux netconsole is
unidirectional, i. e. you have console output only in Linux.