2

Some basic info of my machine:


# uname -a
Linux iZ2zeirtviyt9b8s96ery2Z 6.8.0-40-generic #40-Ubuntu SMP PREEMPT_DYNAMIC Fri Jul  5 10:34:03 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux

# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:16:3e:3d:fb:0d brd ff:ff:ff:ff:ff:ff
    altname enp0s5
    altname ens5
    inet 172.25.37.57/18 metric 100 brd 172.25.63.255 scope global dynamic eth0
       valid_lft 1887925919sec preferred_lft 1887925919sec
    inet6 fe80::216:3eff:fe3d:fb0d/64 scope link 
       valid_lft forever preferred_lft forever

In session 1, I run modprobe netconsole netconsole=@/,@127.0.0.1/ , and the dmesg show:

[4235827.031716] netpoll: netconsole: local port 6665
[4235827.031724] netpoll: netconsole: local IPv4 address 0.0.0.0
[4235827.031726] netpoll: netconsole: interface 'eth0'
[4235827.031727] netpoll: netconsole: remote port 6666
[4235827.031729] netpoll: netconsole: remote IPv4 address 127.0.0.1
[4235827.031730] netpoll: netconsole: remote ethernet address ff:ff:ff:ff:ff:ff
[4235827.031734] netpoll: netconsole: local IP 172.25.37.57
[4235827.031794] printk: legacy console [netcon0] enabled
[4235827.031797] netconsole: network logging started

In session 2, I run

# nc -u -l -v 127.0.0.1 6666
Bound on localhost 6666

So I think the setup is done.

Then I send some logs to dmesg:

# dmesg -n 8 && echo "NETCONSOLE SUCCESS" | sudo tee /dev/kmsg
NETCONSOLE SUCCESS

# dmesg | tail
[4235827.031729] netpoll: netconsole: remote IPv4 address 127.0.0.1
[4235827.031730] netpoll: netconsole: remote ethernet address ff:ff:ff:ff:ff:ff
[4235827.031734] netpoll: netconsole: local IP 172.25.37.57
[4235827.031794] printk: legacy console [netcon0] enabled
[4235827.031797] netconsole: network logging started
[4235853.405638] NETCONSOLE SUCCESS
[4235864.247827] NETCONSOLE SUCCESS
[4235901.736691] NETCONSOLE SUCCESS
[4235902.538482] NETCONSOLE SUCCESS

But in session 2, I cannot see any received log. I expect I could see received log in Session 2. Could anyone help me how to further debug this?

Note: Why use one machine? I just want to learn how netconsole work for demo.

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1 Answer 1

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You're running netconsole on a single machine and directing messages to 127.0.0.1, but netconsole doesn’t transmit logs over the loopback interface (lo), even when targeting localhost.

Assign a proper IP address to your device if not already done, and try using that IP instead.

Also check if your firewall, if active is blocking traffic to the port. You can also use socat or tcpdump to test whether the traffic is getting through/reaching its destination.

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  • Do you mean netconsole cannot send logs over lo? Should I use the real IP address of my machine? Commented Jun 9 at 9:16
  • Yes use the real ip Commented Jun 9 at 9:18
  • Is this your real ip: 172.25.37.57 ? Than use this... Commented Jun 9 at 9:18
  • You can add more than one ip if you like to the same interface. Commented Jun 9 at 9:20
  • And does it work now? Commented Jun 10 at 9:56

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