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Old 12-14-2007, 08:12 PM   #1
fanoliv
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Boot messages to serial port


Hi, I am trying to boot an Ubuntu 7.10 Live CD, but my system is hanging somewhere along the way. I was wondering if there is a way to print the boot messages to the serial port, instead of to the monitor? This way I can see where it stops and maybe what happened just before that. Because when it hangs, the screen just goes blank. Thank you.
 
Old 12-15-2007, 06:36 AM   #2
blackhole54
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Disclaimer: I have not tried this, and sadly, I do not have a new enough system with a serial port that I can try this (wish I did!). For background and explanation, my source on this is Serial Linux Console HOWTO. Look down toward the bottom of the article to the section Optional: Configure serial port as THE system console. Also, I verified entering kernel parameters on an edgy live CD, but it will probably work the same way on gutsy.

Boot the CD, and when presented with the boot choices, instead of selecting one, hit the ESCAPE (Esc) key. When asked, confirm that you wish to enter the "text mode interface."

Then at the boot prompt enter (type what is in bold):

Code:
boot:  live console=ttyS1,38400
I just copied that boot parameter from the HOWTO linked above. Adjust the serial port (ttyS1; ttys0 = comm 1) and baud rate (38400) as needed.

Please let me know if this works!

Last edited by blackhole54; 12-15-2007 at 06:39 AM.
 
Old 12-17-2007, 02:00 PM   #3
fanoliv
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Thank you for your help. This seems to almost work. I put in "console=ttyS0,115200", as the parameter. I see some garbage coming out to the terminal. So at least something's being redirected to the serial port. I think I'll have to play around with other parameters like parity, etc. to get it to print out something readable.
 
Old 12-18-2007, 09:33 PM   #4
fanoliv
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I finally got it to print out readable characters instead of garbage. Just had to change my TeraTerm setting from 8 bit of data to 7 bit. Thanks a lot for the tip. This will be very useful for me.
 
Old 12-18-2007, 10:00 PM   #5
blackhole54
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I'm glad you got it working.

For future reference (and for anybody else that stumbles onto this thread), it appears you can also control some of that from the boot parameter. The file Documentation/kernel-parameters.txt in the kernel source code tarball is perhaps a bit too succinct when it describes the parameter thusly:

Quote:
console= [KNL] output console + comm spec (speed, control, parity)
I am guessing the full thing might look something like:

Code:
console=ttyS0,115200,8,n
for 115200 baud, 8 bit, no parity, for example. If I don't have it quite right, then Google is your friend!

Last edited by blackhole54; 12-19-2007 at 01:59 AM. Reason: ttys0 -> ttyS0; on -> onto
 
Old 12-19-2007, 12:59 AM   #6
JZL240I-U
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Thanks to both of you for coming back and rounding off the subject .
 
Old 12-19-2007, 12:15 PM   #7
archtoad6
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Very nice, all.
A fine example of how LQ works at its best.
 
Old 03-10-2008, 09:04 PM   #8
phantomfive
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console=ttyS0,115200,8,n

Not quite right, it should be

console=ttyS0,115200n8
 
  


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