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  • serial terminal options for GRUB2 (RHEL 9 kvm guest image)

    Posted on

    In the KVM guest image,

    grub.cfg
    is very small and references some variables immediately before calling
    blscfg
    :

    [root@ipa6 ~]# cat /boot/grub2/grub.cfg 
    
    set timeout=0
    
    # load the grubenv file
    load_env
    
    # selection of the next boot entry via variables 'next_entry' and
    # `saved_entry` present in the 'grubenv' file. Both variables are
    # set by grub tools, like grub2-reboot, grub2-set-default
    
    if [ "${next_entry}" ] ; then
       set default="${next_entry}"
       set next_entry=
       save_env next_entry
       set boot_once=true
    else
       set default="${saved_entry}"
    fi
    
    search --no-floppy --set=root --fs-uuid 5e75a2b9-1367-4cc8-bb38-4d6abc3964b8
    set boot=${root}
    function load_video {
      insmod all_video
    }
    ${serial}${terminal_input}${terminal_output}
    blscfg
    

    I guess these are taken from

    /boot/grub2/grubenv
    and are manipulated by
    grub2-editenv
    . I've tried the following:

    grub2-editenv /boot/grub2/grubenv set serial='serial --unit=0 --speed=115200' terminal_input='terminal_input serial' terminal_output='terminal_output serial'
    
    grub2-editenv /boot/grub2/grubenv set serial=$'serial --unit=0 --speed=115200\n' terminal_input=$'terminal_input serial\n' terminal_output=$'terminal_output serial\n'
    
    grub2-editenv /boot/grub2/grubenv set serial='serial --unit=0 --speed=115200;' terminal_input='terminal_input serial;' terminal_output='terminal_output serial;'
    

    but neither seem to do anything: while watching the serial port during boot, I can see the output from the BIOS, followed by nothing for a few seconds while presumably GRUB is displaying a menu somewhere, followed by the kernel output.

    Does anyone know the proper way to enable serial output from GRUB2 with the kvm guest image?

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