Is it possible to create a snapshot of your entire disk so you can restore EVERYTHING if something goes wrong?
I tried Timeshift on external USB Drive, but when I reopen Timeshift it doesn’t see the backups made…
Is there a solution to create a full system backup on USB storage?
Clonezilla or Rescuezilla to name two.
Isn’t there a solution without turning off the PC and starting a clonezilla live?
gnome-disk-utility can do that.
dd can as well, but be very, very careful with this one.
See man dd and read up on this one.
partclone may also be an option.
To create a reliable snapshot of your system disk you need to do a cold clone.
While it is technically possible to create a hot clone is not recommended.
Timeshift is not intended for backing up the entire disk only the OS.
Does it also save downloaded packages and all system configurations?
It creates a copy of the running system using rsync - that includes system wide configuration but never user configuration - as those resides in $HOME
If you mean something similar to ‘Time Machine’ on macOS, the short answer is no.
The software already mentioned share a common theme: they all rely on imaging your chosen drive (or partition); effectively cloning it. None of them are truly a backup solution, in the traditional sense.
That said, cloning a drive is an effective way to ‘backup everything’, and yes, booting with a dvd/usb is the safest way to restore the data.
CloneZilla is ideal for this.
Using gnome-disk-utility may allow easier restoration from the image; but I’ve never tried it, so don’t quote me. My opinion is that its just as easy to create a ‘tarball’ (or a zip archive) rather than the disk-utility method. Cheers.