No Grub Menu
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  1. #1
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    No Grub Menu

    This morning I upgraded my desktop machine from F29 to F30 and all went well, until the reboot at the end, which leaves me at a black screen with grub>. After reading around the forum I suspect it may have to do with the new bootloader spec. The problem is I can't get a terminal up from the grub> prompt. None of the Fn keys or anything else I tried pushing brings up a terminal.
    help?
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  2. #2
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    Re: No Grub Menu

    The problem is I can't get a terminal up from the grub> prompt. None of the Fn keys or anything else I tried pushing brings up a terminal.
    If you are talking about a Linux bash terminal then there is a simple explanation. Linux of course has not booted up yet which is why you are at the grub prompt.

    You will need to use a live USB to get into your desktop, chroot into it properly, and then generate a new config. I am still using F29 so I haven't had to do that yet.

    You will likely have to run the transformation script manually. Then check if it worked by looking for entries in /boot/loader/entries.

    Code:
    $ type grub2-switch-to-blscfg
    grub2-switch-to-blscfg is /usr/sbin/grub2-switch-to-blscfg
    
    NAME
           grub-switch-to-blscfg  Switch to using BLS config files.
    
    SYNOPSIS
           grub-switch-to-blscfg [--grub-directory=DIR] [--config-file=FILE] [--grub-defaults=FILE]
    
    DESCRIPTION
           grub-switch-to-blscfg reconfigures grub-mkconfig to use BLS-style config files, and then regenerates the GRUB configuration.

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    Re: No Grub Menu

    I installed the live image on a thumb drive, but when I boot it goes through the process then when I'd expect to see a gui, it reboots and ends up at grub>. Tried it several times. I can boot the live image on my laptop though, and / and /home on the laptop are already mounted and accessible in the live version. Anyway, hopefully I can figure out why the live version keeps rebooting just when it's almost booted on my desktop.
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    Re: No Grub Menu

    Still working on this. It would have been nice if Fedora would have issued a warning like, 'Oh BTW if you upgrade to F30 your OS will be totally borked and you will have to spend lots of time and effort trying to recover it.'
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    Re: No Grub Menu

    Since I couldn't get in with live on a usb stick I tried it with a live DVD, and it still reboots before the gui shows. I tried a clean install, but the install DVD does the same thing the live ones do; reboots before the installer shows. So I have no way in, and can't even do a clean install.

    Not being able to boot any bootable media suggests a problem with the bios but 3 years ago when the machine was new I did a clean install of Fedora with no problems, and I've changed nothing in the bios. I'm not expecting an answer to this problem, but thought I'd at least put it out there.
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    Re: No Grub Menu

    I think when I upgraded to F30 the last F29 kernel should still be there, and I know that kernel number. Does anyone know what I need type at the grub> prompt to try and get that kernel to boot?
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  7. #7
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    Re: No Grub Menu

    A google search found:
    https://www.linux.com/tutorials/how-...-grub-2-linux/
    Look under "Booting From grub>
    "

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    Re: No Grub Menu

    VernDog, thanks for the link It's a start. I Googled but I missed that one. According to the instructions this should get it to boot, 5.2.9-200 being the F30 kernel installed during the update:

    Code:
    grub> set root=(hd0,1)
    grub> linux /boot/vmlinuz-5.2.9-200-generic root=/dev/sda1
    grub> initrd /boot/initrd.img-5.2.9-200-generic
    grub> boot
    But grub> is telling me that kernel and the previous F29 kernel don't exist, even though 'ls' shows that they do. I have an idea that I will try today.
    I know things. It's what I do.

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    Re: No Grub Menu

    OK this morning I tried again. I can make grub> display the contents of the /boot/ folder and it shows the F30 kernel and two F29 kernels, but when I try them it says it can't find them. I can also display the contents of /boot/grub2/ and it shows grub.cfg but if I try to display it, again it says it can't find it. And all the while the files are displayed on the top half of the screen. *bangs head on wall*

    There is a difference though; in the example doing 'ls' on (hd0,1) shows all of his folders on /. On mine it shows only the /boot folder. I checked my laptop and hd0,1 is /boot and hdo,2 is /, but grub> 'ls' (hdo,2) returns 'Partition hdo,2: No known filesystem detected. I tried making hd0,2 root and running the commands again, but got the same 'No known filesystem detected'. So, grub can't detect the root file system, maybe because it's on a logical volume? Or, my entire root file system has vanished.
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  10. #10
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    Re: No Grub Menu

    OK this morning I tried again. I can make grub> display the contents of the /boot/ folder and it shows the F30 kernel and two F29 kernels, but when I try them it says it can't find them.
    grub> linux /boot/vmlinuz-5.2.9-200-generic root=/dev/sda1
    grub> initrd /boot/initrd.img-5.2.9-200-generic
    This doesn't look like a Fedora kernel. There should be a fc30 and an arch extension such as .x86_64 . Also your / may be on LVM and it wouldn't be sda1 which is your /boot partition. What is in the guide does not apply to you.

    Code:
    $ uname -r
    5.2.7-100.fc29.x86_64
    I can also display the contents of /boot/grub2/ and it shows grub.cfg but if I try to display it, again it says it can't find it
    How are you trying to display it ? What commands are you using ? Are you using the full path of grub.cfg ?

    If the config file looks fine then you can use the configfile command with the grub root and prefix set.

    And all the while the files are displayed on the top half of the screen. *bangs head on wall*
    You need to set the grub pager. Enter set pager=1 at the grub> prompt. This was in the guide.

    There is a difference though; in the example doing 'ls' on (hd0,1) shows all of his folders on /. On mine it shows only the /boot folder.
    This means that you have a separate /boot partition and your / could be on LVM. You have a more complex installation than what is in the guide.

    I checked my laptop and hd0,1 is /boot and hdo,2 is /, but grub> 'ls' (hdo,2) returns 'Partition hdo,2: No known filesystem detected. I tried making hd0,2 root and running the commands again, but got the same 'No known filesystem detected'. So, grub can't detect the root file system, maybe because it's on a logical volume?
    This is likely the explanation. You need to insert the grub lvm module to be able to read a logical volume. Then try reading hd0,2 again.

    grub> insmod lvm

    I tried making hd0,2 root and running the commands again
    The grub root and the linux root are in general different as in the case of a separate /boot partition. hd0,1 is your grub root (your ext4 /boot partition) and hd0,2 is your linux root partition on LVM. Whoever wrote this "guide" was incompetent.

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    Re: No Grub Menu

    Amiga, thanks for the feedback.

    Yes I did start with set pager=1, and I think the '-generic' at the end of the kernel number is supposed to cover any suffix, but I did also try the full kernel names of the F30 and both F29 kernels with the same result; 'can't find blah blah... I tried the grub> insmod lvm, and it still says 'No known filesystem detected.'

    Besides grub.cfg there is a grub.cfg.rpmnew in /grub2/. If there was a way I'd try to rename grub.cfg to grub.cfg.old and rename grub.cfg.rpmnew to grub.cfg, just to see what happens.
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  12. #12
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    Re: No Grub Menu

    I tried the grub> insmod lvm, and it still says 'No known filesystem detected.'
    I now realize that I left out some important information. The hd0,2 partition is an LVM Physical Volume that contains Logical Volumes inside of it. Well technically the PV is part of a Volume Group that contains logical volumes. So hd0,2 itself does not contain any known filesystem such as ext4. It contains LVM physical extents. It is the logical volumes inside this PV that do contain filesystems such as ext4 with the / partition of your installation.

    After you enter grub> insmod lvm you need to run ls again to list all of the partitions grub sees. It should now see several LVM logical partitions such as (lvm/vg_name-lv_name). The lvm partition for your root will contain an ext4 or xfs filesystem. Also you have to load the module for whatever filesystem you are using such as insmod ext2 for ext2/3/4 or insmod xfs for xfs.

    I think the '-generic' at the end of the kernel number is supposed to cover any suffix
    Where did you read this ?
    Last edited by amiga; 2nd September 2019 at 05:05 AM.

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    Re: No Grub Menu

    I think the '-generic' at the end of the kernel number is supposed to cover any suffix
    Where did you read this ?
    I didn't read it I assumed it. Wondering why it was used instead of the entire kernel name I assumed it was being used like a wildcard in a search.

    insmod lvm and insmod ext2 lets 'ls' add to my list of drives (lvm/home), (lvm/fedora-swap) and (lvm fedora-root), and 'ls (lvm/fedora-root)' shows my root folders. That's progress.

    Starting with 'grub> set root=(lvm/fedora-root)' seems to work as it goes back to grub> without giving me an error. But, 'grub> linux /boot/vmlinuz-5.2.9-200-generic root=/dev/sda2' returns 'not found' whether I use the '-generic' or spell out the entire kernel name.

    Not sure why it can't find the kernels when I can see that they exist. Is it possible I need to tell it where the /boot folder is, like: grub> set boot (hdo1)' ?
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  14. #14
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    Re: No Grub Menu

    Starting with 'grub> set root=(lvm/fedora-root)' seems to work as it goes back to grub> without giving me an error. But, 'grub> linux /boot/vmlinuz-5.2.9-200-generic root=/dev/sda2' returns 'not found' whether I use the '-generic' or spell out the entire kernel name.
    This is quite wrong. I already explained this. (lvm/fedora-root) is your Linux root. (hd0,1) is your grub root as this is your ext4 /boot partition. Since you have a separate /boot partition they are different.

    Also since you are using lvm your Linux root would be root=/dev/mapper/fedora-root

    Code:
    grub> set root=(hd0,1)
    grub> linux /vmlinuz-5.2.9-200-fc30.x86_64 root=/dev/mapper/fedora-root ro rd.lvm.lv=fedora/root
    grub> initrd /initramfs-5.2.9-200-fc30.x86_64.img
    grub> boot
    Note: Since you have a separate /boot partition you don't need the path /boot/ above as (hd0,1) has these files in its top directory. This is why it couldn't find them before as the /boot directory does not exist in a separate /boot partition.

    Not sure why it can't find the kernels when I can see that they exist. Is it possible I need to tell it where the /boot folder is, like: grub> set boot (hdo1)' ?
    You just have to set the grub root to the /boot partition. Grub doesn't care about the Linux root. It only cares about where the boot files are located.
    Last edited by amiga; 2nd September 2019 at 07:33 PM.

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    Re: No Grub Menu

    Also since you are using lvm your Linux root would be root=/dev/mapper/fedora-root
    When I display my drives, (hd0), (hdo,1) etc, the Linux root displays as ((lvm/fedora-root)

    After looking at grub.cfg on my laptop I have already tried:

    grub> set root=(lvm/fedora-root)
    grub> linux /vmlinuz-5.2.9-200-fc30.x86_64 root=/dev/mapper/fedora-root ro rd.lvm.lv=fedora/root

    After reading your last post I changed the first 2 lines to:

    grub> set root=(hd0.1)
    grub> linux /vmlinuz-5.2.9-200-fc30.x86_64 root=/dev/mapper/fedora-root ro rd.lvm.lv=fedora/root

    Either way it tells me the kernel is 'not found'.
    I know things. It's what I do.

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