dmesg output to tty

joeuser123 · 02-25-2009, 04:45 PM

I have what I believe is a simple question...

I would like to add a line to the inittab that will create a terminal console, lets say tty11, and I would like that console to display the output from dmesg. (this tty will have no other purpose in life but to output dmesg)

this would allow me to press alt+f11 at any time to view anything that might have changed/updated both during the boot process and after.

thanks

Agrouf · 02-26-2009, 10:15 AM

bash -c "dmesg >/dev/tty11"

Agrouf · 02-26-2009, 10:19 AM

but dmesg is not streaming kernel messages...
better:

bash -c "cat /proc/kmsg >/dev/tty11"

joeuser123 · 02-26-2009, 10:24 AM

Thank you Agrouf, so I just need to add:

bash -c "cat /proc/kmsg >/dev/tty11"

to the bottom of my inittab?

Agrouf · 02-26-2009, 12:04 PM

In inittab, you add a line like (in you are running standard sysV init):
c7:2345:respawn:bash -c "cat /proc/kmsg >/dev/tty11"
or you can add it anywhere in your boot process (like in /etc/rc.d or anywhere your distro execute the code)

frieza · 02-26-2009, 12:24 PM

try adding the following to the kernel arguments in /boot/grub/menu.lst

console=tty11

joeuser123 · 02-26-2009, 04:09 PM

I have tried placing the:

c7:2345:respawn:bash -c "cat /proc/kmsg >/dev/tty11"

line in the inittab and I get messages on tty1 saying that c7 will be halted for 5 min.
when I switch over to tty11 I see no output

also tried:

c7:2345:respawn:bash -c "dmesg -c >/dev/tty11"

while I was able to see the information I expected to see on tty11 but I was unable to scroll up or down, and I was still recieving the c7 will be halted for 5min messages on tty1

I like the output generated by dmesg, it is helpful when different events trigger... such as inserting a usb device ...it is also helpful to be able to see what is going on during the boot process, so I can learn how things are being loaded.

I must be missing something...

as for the console=tty11 setting, I do not have the /boot/grub/menu.lst file.

frieza · 02-26-2009, 04:22 PM

/boot/grub/grub.conf ?

frieza · 02-26-2009, 04:33 PM

another thought would be to create a shell script
such as

Code:

#!/bin/bash
x=0
while ((x==0))
do
dmesg | tail
for ((z=1;z<=1000000;z++)) do y=3;done
done

log in to any existing tty that you don't plan to use
and run the script
the above example runs dmesg, waits, dumps dmesg again etc.. until you kill the program with ctl-c
or a more fancy example

Code:

#!/bin/bash
x=0
while ((x==0))
do
dmesg | tail --lines=(number of lines to dump) > /dev/tty11
for ((z=1;z<=1000000;z++)) do y=3;done
done

which would dump the last (number of lines) from dmesg to /dev/tty11
and could be run at any terminal by sh myscript.sh&

Agrouf · 02-27-2009, 12:25 AM

does it work if you just type bash -c "cat /proc/kmsg >/dev/tty11" on the terminal as root?
expected result: the command should hang and you should see kernel messages on /des/tty11 (only new messages, not old ones). At first if will not print anything but if you insert a module it should be printed there.