@ysageev posted a new topic, subject "Mint 20: Cannot upgrade 5.0 to 5.1". It read:

   I know Mint/Ubuntu is not officially supported, but...
    
    I had no trouble installing pihole on Mint 18 and upgrading to 5.0 on Mint 18. Then I upgraded to Mint 20. pihole 5.0 works fine but when I try to upgrade to 5.1 I get the OS_UNSUPPORTED error and setting the environment variable doesn't help. Attached is my debug log (upload/token didn't work).
    
    pihole-debug-log.txt (69.8 KB)
    
    I'm running the OS on a VM in ESXi 6.7
    
    **What I have changed since installing Pi-hole:**
    
      1. The upgrade to 5.0 overwrote the static IP and port assigned to lighttpd, which I restored by editing lighttpd.conf.

Then @yubiuser (Yubiuser) said

    Mint is not an officially supported OS. Since v5.1 this is pointed out to the user more directly.  
    Try
    [code] 
        export PIHOLE_SKIP_OS_CHECK=true pihole -up
        
    [/code]

So @ysageev replied

    I mentioned "setting the environment variable doesn't help". I should have been more explicit. The result of doing so has no effect -- it still tells me that OS not supported.
    
    image829×903 150 KB

Then @yubiuser (Yubiuser) said

    Someone was successful using
    [code] 
        sudo export PIHOLE_SKIP_OS_CHECK=true pihole -up
        
    [/code]
    
    I cannot update to Pihole 5.1 on OSMC Community Help
    
    > Hi I am using OSMC 2020.06-1 and I cannot perform the upgrade of Pihole. When I do: pihole -up I get: [✗] Unsupported OS detected Redirecting... This check can be skipped by setting the environment variable PIHOLE_SKIP_OS_CHECK to true e.g: export PIHOLE_SKIP_OS_CHECK=true By setting this variable to true you acknowledge there may be issues with Pi-hole during or after the install If that is the case, you can feel free to ask the community on Discourse with the Community Help catego…

After which, @ysageev added

    Thank you! It worked!
    
    Note: It's not  
    `sudo export PIHOLE_SKIP_OS_CHECK=true pihole -up`
    
    but
    
    `sudo PIHOLE_SKIP_OS_CHECK=true pihole -up`


{'source': 'discourse', 'url': 'https://discourse.pi-hole.net/t/mint-20-cannot-upgrade-5-0-to-5-1/35661', 'title': 'Mint 20: Cannot upgrade 5.0 to 5.1', 'views': 1094, 'has_accepted_answer': True, 'word_count': 229, 'like_count': 1, 'reply_count': 1, 'participant_count': 2, 'posts': 5, 'tags': '', 'author': '@ysageev', 'participants': '@ysageev, @yubiuser (Yubiuser)', 'image_url': [None], 'created_at': '2020-07-16T13:57:22.757Z', 'last_posted_at': '2020-07-16T15:51:55.154Z'}