netconsole is a kernel module that sends all kernel log messages (i.e. dmesg) over the network to another computer, without involving user space (e.g. syslogd). Name "netconsole" is a misnomer because it's not really a "console", more like a remote logging service.
It can be used either built-in or as a module. Built-in netconsole initializes immediately after NIC cards and will bring up the specified interface as soon as possible. The module is mainly used for capturing kernel panic output from a headless machine, or in other situations where the user space is no more functional.
Documentation is available in the Linux kernel tree under Documentation/networking/netconsole.txt
Netconsole and other modules' Kernel parameters can be passed from a bootloader to kernel at its startup via kernel command line by modifying the bootloader environment, which is type and version specific. Example for Uboot, where 1st IP is Dockstar ArchLinux device's netconsole Out IP and Port, and 2nd IP is your PC's netconsole In IP and Port:
fw_setenv usb_custom_params 'loglevel=7 firstname.lastname@example.org/eth0,email@example.com/00:13:32:20:r9:a5'
Logging is done by your ArchLinux set logger like syslog-ng, so available loglevels (output details) are defined in that logger docs, and may differ for each log type. One can also pass netconsole string parameters at kernel runtime (no config file required), then start netconsole on a remote PC and restart it on the PC or device you are logging:
# set log level for kernel messages dmesg -n 8 firstname.lastname@example.org/eth0,email@example.com/00:43:24:96:d7:v5
Netconsole can be loaded as one of kernel modules after boot manually or at boot depending on your module config.
# set log level for kernel messages dmesg -n 8 modprobe configfs modprobe netconsole mount none -t configfs /sys/kernel/config # 'netconsole' dir is auto created if the module is loaded mkdir /sys/kernel/config/netconsole/target1 cd /sys/kernel/config/netconsole/target1 # set local IP address echo 192.168.0.111 > local_ip # set destination IP address echo 192.168.0.17 > remote_ip # find destination MAC address arping `cat remote_ip` -f |grep -o ..:..:..:..:..:.. > remote_mac echo 1 > enabled
netconsole should now be configured. To verify, run 'dmesg |tail' and you should see "netconsole: network logging started". Check available log levels by running 'dmesg -h'.
nc -u -l 6666
nc -u -l -p 6666