so i love mate but since i have download it i have been unable to boot from usb live iso. i get a warning saying it a security violation to boot from usb/ little help
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You've not provided any release details which are the starting point.
If your system is fully-upgraded/patched for the boothole vulnerability for example; Ubuntu-MATE 18.04.5 & earlier media won't boot on it as it's signed with a now expired key. That is the reason 18.04.6 media was created, however flavors like Ubuntu-MATE had already past the three years support for 18.04 so no 18.04.6 flavor media was produced; upgraded media was produced for Ubuntu-MATE 20.04 however.
ie. the starting point is your actual release details, otherwise we'll be guessing possible causes such as boothole I'm using as an example. The fix for that issue is used patched media [or don't use Secure-uEFI].
Did you verify the ISO? and write to media? (using the method appropriate for your unstated release; can't provide a single link for that as that varies).
Running 21.10 "Impish Indri and iso verify
I had some problems installing Impirish Indri on one of my computers. First I used dd to to create the bootalbe flashdrive, it failed, prompting me to grub rescue due to error in the filesystem. gnome-disk-utility also failed, resulting in the same error. I inspected the usb and found that it was lacking a number of files that I typically spot when installing any distro. I have finally achieved success using UNetbootin.
The image Ubuntu Mate 20.04.4. LTS does not work for raspbberry 4 booting from a usb drive. I get a blank screen and nothing more. The other version is ok.