Garbled Screen After RAM Scrub On Boot

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Dear All I am using CentOS 7 with Xen 4.6 on a Dell Poweredge T430
When the machine boots, after the ‘Scrubbing Free RAM’ message, I get a screen filled with little white squares until the login prompt, so I cannot see what is happening as the machine boots. Also there is nothing on the screen when I reboot.

My /etc/default/grub is

GRUB_DISTRIBUTOR=”$(sed ‘s, release .*$,,g’ /etc/system-release)”
GRUB_DEFAULT=saved GRUB_DISABLE_SUBMENU=true GRUB_CMDLINE_LINUX=”crashkernel=auto rhgb intremap=no_x2apic_optout”
GRUB_CMDLINE_XEN_DEFAULT=”dom0_mem312M,max:14336M dom0_max_vcpus=6 dom0_vcpus_pin”
GRUB_GFXMODE24×768
GRUB_GFXPAYLOAD_LINUX=keep GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT=”console=hvc0 earlyprintk=xen nomodeset”

I have tried setting (for a 1024×768 resolution) vgay2 in the GRUB_CMDLINE_LINUX and commenting out GRUB_GFXMODE and GRUB_GFXPAYLOAD_LINUX, but this makes no difference

What am I doing wrong?

Regards Francis

7 thoughts on - Garbled Screen After RAM Scrub On Boot

  • Yes I usually work headless, but I have been setting it up from new, so need to see what is going on. Regards Francis

    From: “Scot P. Floess”
    To: “Francis Greaves”
    Cc: “CentOS-virt”
    Sent: Monday, 22 February, 2016 17:02:12
    Subject: Re: [CentOS-virt] Garbled screen after RAM Scrub on boot

    When I was running Fedora 23 and using Xen (as the host OS), I saw something similar on my Dell Precision 470. I don’t recall seeing it now with CentOS 7, but I tend to boot that machine headless more than not…

    On Mon, 22 Feb 2016, Francis Greaves wrote:

    Scot P. Floess RHCT (Certificate Number 605010084735240)
    Chief Architect FlossWare http://sourceforge.net/projects/flossware http://flossware.sourceforge.net https://github.com/organizations/FlossWare

  • I get the same effect of screen blank on memory scrub.

    Just as a test try turning off the memory scrub in the xen boot options.

    I wonder if xen overwrites the video-ram memory as its cleaning up.

  • Francis,

    Thanks for reporting this. I’d suggest re-posting your question on xen-users — there are a lot more eyeballs watching that list than this one, and it’s easier to “escalate” the issue to the development list from there.

    My first instinct is wondering whether grub setting the graphics mode is part of the problem. Have you tried having grub just take the bios text mode that was given it, rather than changing it?

    (Obviously ideally Xen would work whatever the graphics mode is, but most developers are accessing test boxes over serial in a colo, so it’s not the kind of thing they’re prone to notice.)

    -George

  • _________________________________________^
    If you no not NEED a gfx boot at bare metal, remove the “rhgb” string, this switches grub from a “full graphic” mode to a “hires textmode”, AFAICS, this also influences all grub instances in the whole XEN
    infrastructure, so it could be a influence.

    [snip]

    – Yamaban.

  • I have tried that, but it makes no difference!
    I have removed all GFX settings, and vga= settings, and rhgb, still no good. All I would like is a 1024×768 screen which shows what is going on at boot. I know I can look in the logs, but it is useful to see. Everything is fine at the login prompt, but the resolution is low.

    —– Original Message —

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