Re: SysRq over usb serial adapters

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On Tue, Oct 1, 2013 at 1:51 PM, Warren Young <warren@xxxxxxxxxxx> wrote:
> On 9/30/2013 21:34, Barry Brimer wrote:
>>> I'm using 115200, 8N1, VT102.  I can echo m > /proc/sysctl-trigger,
>>> and dmesg shows that the sysrq was received when initiated via the
>>> procfs interface.  But not over serial, and that's what I need.
>>
>> I could be wrong .. but you may need to edit your grub config to convince
>> your system that the serial terminal is a/the console ..
>
> That's only part of it.  The topic has a whole HOWTO dedicated to it:
>
>      http://www.tldp.org/HOWTO/Remote-Serial-Console-HOWTO/

I'm familiar with that howto, and have set up serial console many
times.  The only thing new here is the usb serial adapter.

I am not particularly interested in having serial access during the
early stages of booting, which is what you configure in grub.  I want
it to come up post-boot, preferably after insertion of a specific USB
serial dongle.  And I cannot break (if you pardon the pun) sysrq (or
any other) capability at the physical ps2/vga console.

To be clear, serial console WORKS currently for me with usb serial
adapters.  What DOESN'T work is SysRq via that serial console.

My understanding is that the 'console=' kernel argument controls
pre-init serial console, so that you can see the output of various
kernel modules as they load.  Once an agetty starts, it takes over the
serial console functionality from the kernel.

Because I'm only interested in adding this serial console post-boot, I
don't think I need to configure console=.  I'd like to know why this
is wrong if it is.

-- 
Billy Crook • Network and Security Administrator • RiskAnalytics, LLC
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