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Thread: Can UEFI system manually load a Legacy O/S

  1. #1
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    Ubuntu 18.04 Bionic Beaver

    Can UEFI system manually load a Legacy O/S

    Folks,

    I know how to manually boot from a GRUB menu, I have a number of custom entries in /etc/grub.d/40_custom so have an idea as to what is needed to load an O/S but far from an expert

    I have an older external drive that to date I have switched to legacy BIOS to use but looking at the GRUB entries they look the same or similar to a manual boot from UEFI

    I did try a manual boot of the legacy system but got some message telling me the kernel was too old (Apologies, didn't note it properly) whereas it boots fine if I switch to legacy.

    Geoff

  2. #2
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    Re: Can UEFI system manually load a Legacy O/S

    It could be that the message is simply warning that the version had reached end of its support life.

    If we are dual booting on a UEFI system then we should take note of this advice

    Having a PC with UEFI firmware does not mean that you need to install Ubuntu in UEFI mode. What is important is below:


    • if the other systems (Windows Vista/7/8, GNU/Linux...) of your computer are installed in UEFI mode, then you must install Ubuntu in UEFI mode too.
    • if the other systems (Windows, GNU/Linux...) of your computer are installed in Legacy (not-UEFI) mode, then you must install Ubuntu in Legacy mode too. Eg if your computer is old (<2010), is 32bits, or was sold with a pre-installed Windows XP.

    • if Ubuntu is the only operating system on your computer, then it does not matter whether you install Ubuntu in UEFI mode or not.
    https://help.ubuntu.com/community/UEFI

    So, you may have go through a complicated ritual each time you want to boot into one or the other of the installed OS.

    Regards.
    It is a machine. It is more stupid than we are. It will not stop us from doing stupid things.
    Ubuntu user #33,200. Linux user #530,530


  3. #3
    Join Date
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    Ubuntu 18.04 Bionic Beaver

    Re: Can UEFI system manually load a Legacy O/S

    Quote Originally Posted by grahammechanical View Post
    It could be that the message is simply warning that the version had reached end of its support life.

    If we are dual booting on a UEFI system then we should take note of this advice



    https://help.ubuntu.com/community/UEFI

    So, you may have go through a complicated ritual each time you want to boot into one or the other of the installed OS.

    Regards.
    Strange, the manual entries for both seem identical so having difficulty understanding the logic behind each. Got an external drive with msdos partition table and six Linux O/Ss (Extended partition with logical drives) and boots fine using UEFI but older disk with 2 Ubuntu systems installed using Legacy BIOS won't.

    Seldom have a need to use the old drive installed under Legacy BIOS so mere curiosity as to why same manual commands on UEFI and Legacy don't work.

    Ah well, with the thousands or millions of instructions involved it is a wonder anything works

    Geoff

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