[syslinux] garbage on serial console after pxelinux.0 is loaded

Scheie, Peter M Petre.Scheie at gd-ms.com
Mon Mar 5 09:56:40 PST 2018

We have some x86_64 systems that have DisplayPort and USB ports for a monitor & keyboard and when I use these to PXE boot, everything works fine.  However, these systems will eventually become headless and in the production process access to the console will be via serial port.  Using the serial port mostly works in that once we get to the PXE boot: prompt we can type in the name of the desired stanza from default and the kernel and initramfs specified will be loaded & executed.  But when the system initially reaches that boot: prompt, something starts spitting small strings of garbage, say 20-40 characters, in random places on the screen, about once per second or every other second.  The strings contain bits of text that were previously displayed, e.g., I can make out part of Peter Anvin's name sometimes in the garbage, suggesting it has something to do with the screen refresh.  Entering the name of the desired stanza works at this point, although it looks like what is being typed is getting messed up (even if that is just an illusion).  But the production folks won't put up with this, and they shouldn't have to, so I have to fix it.

I don't think it's a baud rate mismatch between the terminal software (minicom) and the system board because all the text about choosing network boot, broadcasting for a DHCP server, etc. looks just fine (and we see the same behavior using putty on Windows for the terminal program).  The problem doesn't appear until the pxelinux.0 module is loaded.  I vaguely recall seeing a similar problem with pxelinux five or six years ago, but I could be imagining that.  Any ideas as to what is going on?

BTW, has syslinux gotten so stable that the latest release is really from Oct. 2014?  That's amazing!


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