[lug] debugging workstation issue

[Davide Del Vento]

Got it, thanks.

On Fri, Apr 10, 2020 at 10:16 AM D. Stimits <stimits at comcast.net> wrote:

>
> On April 10, 2020 at 9:46 AM Davide Del Vento <davide.del.vento at gmail.com>
> wrote:
>
> Not sure I understand this suggestion.
>
> When/how could I get to the GRUB command line? At boot I certainly can,
> but the problem is way past that point, i.e. when running (or right before
> starting) the GUI.
> Or do you mean at the NEXT boot after the hang? How that would be
> different than looking at journalctl as Zan suggested?
>
> I always add GRUB delay so it is easy (I multi-boot and set up a 120
> second delay for myself), but in theory if you *hold down the shift key
> as GRUB loads* it will drop you into a GRUB command line. I think it is
> the "e" key which begins edit. From the GRUB editor you will need to find
> the kernel argument line, add a space and append " *
> systemd.unit=multi-user.target*". Tokens must not have spaces, and the
> delimiter between tokens is a space.
>
> *Whatever edit you make is only for that boot, so making a mistake isn't
> really a problem*. In a systemd type init (most newer distros) the GUI
> would be forced with " systemd.unit=graphical.target", and this is the
> indirect default so it wouldn't really change anything for you, but you'd
> be using " systemd.unit=multi-user.target" to avoid GUI. I'd also recommend
> removing the kernel command line " quiet" argument (I actually edit this
> out of my GRUB permanent config), and if you have a splash screen, e.g.,
> Fedora uses " splash", then you could remove the splash to see more debug
> information during boot (I also permanently remove the "splash" token, but
> editing GRUB command line through the editor is only a temp edit). All
> kinds of useful kernel command lines are available, e.g., you could force
> fsck with " fsck.mode=force". Or you could blacklist a kernel module to
> test (e.g., I blacklist Nouveau and use the NVIDIA driver instead).
> Temporarily disabling USB autosuspend is sometimes useful as well, e.g., "
> usbcore.autosuspend=-1".
>
> A list of some of the interesting command lines you can experiment with
> (each driver can have its own parameters, so this URL is just a main
> subset):
> https://www.kernel.org/doc/html/v4.14/admin-guide/kernel-parameters.html
> Tokens not understood are simply ignored.
>
> The trick is that you have to find the kernel command line...which is easy
> if you've seen it just once (just examine " cat /proc/cmdline" to get an
> idea). That line is very long sometimes and might wrap, but it has to be a
> single line...you don't use the "enter key" in the GRUB editor to continue
> as this would just split the line. I think it is CTRL-x to execute (there
> should be a cheat sheet at the bottom of the menu) once you are satisfied
> with your edit.
>
> This would be prior to a hang to see if the system is stable without the
> GUI. Or if GUI just doesn't work, you could get to command line without the
> GUI ever attempting to load. The "journalctl" is useful from here if the
> GUI is crashing or unstable.
>
> If you had booted normally, and then ran "sudo systemctl isolate
> multi-user.target", then this would switch to console mode for most systems
> in a way similar to the GRUB command line, but the GRUB command line never
> loads GUI code.
>
> Thanks for keeping up with ideas!
> Davide
>
> On Fri, Apr 10, 2020 at 9:32 AM D. Stimits < stimits at comcast.net> wrote:
>
> If you can get to the GRUB command line, then  you could tell it to just
> boot to non-graphical mode and perhaps it would work better. Even if this
> does not work better, then I would expect you'd be able to see more of the
> boot log. Depending on which flavor and release of Linux you use, the
> following appended to the kernel command line might do this for you:
> systemd.unit=multi-user.target
>
> Even if this doesn't work, then I'd expect it is at least some debug info.
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