How do I back up files without a login to Ubuntu? Any utility I can use on flash drive? Or should I go to HDD and drag it from HDD?
How do I back up files without a login to Ubuntu?
First of all: I assume that your HDD is not encrypted (otherwise this story won't work)
Boot from your Ubuntu-MATE live USB stick.
(Your HDD will most likely be automatically mounted.)
You can now use gnome-disk-utility to make an ISO-file of any partition on your HDD.
Or you could use engrampa to tar.zip complete directorytrees
You could also use dd , tar , 7z, cpio or cp -a or any of the utilities mentioned here:
( If one of these is not available, you can install it on the live-ISO while running it. I just don't remember if these installs survive a reboot or not)
And then you also need a backupmedium,
i guess you will probably use an external HDD for that ?
Any utility I can use on flash drive?
Yes, AFAIK pretty much all of them would/could/should work from the live-ISO.
You might also take a look at https://clonezilla.org/ which is similar to 'Norton Ghost' or 'True Image' .
Or should I go to HDD and drag it from HDD?
Yes, that will also work perfectly.
Just don't forget to keep the file-permissions+owner+group and be sure to also drag the hidden-files along if you are backing up your complete system and/or home
(if you only want to copy some trivial data then these things don't matter)
If you want to try the commandline tools, the man command will tell you wat you need to know ( try man man or man tar and you'll see what I mean)
If you would describe in detail what you have and what you actually want to do with it, I might come up with a more specific and maybe even better answer