I have had serious problems with Download and especially with Format in ./flash_tool on my Debian Testing machine.
I received many errors and googling them leads to no results or to the misleading results.
The solution was:
- use Java 8 instead of the newer one (download/extract from Oracle, export PATH=...../java8/bin:$PATH, check the version: java -version)
If errors will not disapear with J8, then try older kernel.
My problems were on current 4.17 version, so do something like:
apt install linux-image-4.9.0-7-amd64 linux-headers-4.9.0-7-amd64 ; update-grub
and maybe boot with Shift. I don't know exactly, I have used the 2-nd machine with 4.9.0-5.
PS: MT6589 is supported in Flash Tool 5.1724 and older.