Video Resolution For CentOS Guest

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Would someone please point me to some reasonably current instructions for getting greater than 1024×768 video resolution for a CentOS 6
guest on a CentOS 6 KVM/qemu host? When I search online I find stuff from 2009 and 2010 saying, “For details see …,” and linking to a URL
that no longer exists, or pages that say, “You need to switch from VNC
to Spice,” and giving a long list of out-of-date instructions for doing so. (With virt-manager it takes 2 clicks to do that. Of course it doesn’t help — still maxes out at 1024×768.)

I’ve found that I can just append “vga=0x380” to the kernel command line and see Plymouth come up with the full graphical boot screen in the correct 1440×900 resolution, but as soon as gdm starts up, the display scrambles. I find suggestions to generate an xorg.conf file, but no mention of what to put in it. I can run “Xorg -configure”, but the resulting file contains nothing about video modes, so it’s not apparent what needs to be added.

I find it particularly annoying that a Windows 7 guest can set any resolution I want up to 2560×1600, but a Linux guest can’t go higher than 1024×768.

3 thoughts on - Video Resolution For CentOS Guest

  • Thank you for the reassurance that it _should_ work. I finally got it going. The VM still always starts out in 1024×768 and I have to set the higher resolution every time I log in. For a while, that was working only the first time I set it, and on subsequent logins any attempt to change the resolution either locked up or caused the Xorg server to crash. All the RPMs verified OK and a forced fsck of the filesystems found nothing. I eventually just reinstalled the whole VM, and it’s working now.

    The whole thing was bringing back bad memories of an ancient version of Slackware and kernel version 0.99pl53.

  • In my experience, once I set the resolution, it keeps that resolution through reboots/logins. The initial login page sits at 1024×768, but once logged in, it takes the resolution I asked for.

  • It’s working that way for me now that I have installed kernel-ml-3.19.0
    from elrepo in the guest. With the 2.6.32 kernel that CentOS 6
    provides, the behavior could best be described as “confused.” I might get a login screen at 1024×768 but with the content rendered as though it were 1440×900 and the login dialog half off the edge of the screen. Or, I might be logged in and looking at a screen properly drawn at
    1024×768, but when I bring up the display preferences dialog it claims I
    am already at 1440×900 and refuses to change. And, occasionally when I
    would try to change the resolution the display would lock up and, one time, the whole X server crashed.

    All that goes away with the guest running 3.19.0 kernel, and that also makes sound work properly in the guest, so I’m happy now, at last.

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