[sagher]

first things first..
"debian 9 release is " testing/unstable" Sid"
NOT TRUE!!!!!!

release code name / alias can be - jessie, stretch, buster, sid etc. these are fixed.

release class can be - oldstable, stable, testing, unstable. these indicate code names...true. but they keep changing with time. Right now,
Deb 8 jessie is oldstable
Deb 9 stretch is stable
Deb 10 buster is testing
beyond Deb 12 lies unstable or sid.

@rudra Check this out ..

root@xxxxxxxxx:~# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description: Debian GNU/Linux buster/sid
Release: testing
Codename: buster

root@xxxxxxxxxx:~# cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux buster/sid"
NAME="Debian GNU/Linux"
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

it's my machine information.

i generate source.list from there
https://debgen.simplylinux.ch/

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I think it's enough to mess-up with this thing. kindly suggest me a good stable ubuntu 64bit version for my vps-9. what you say about ubuntu 18.04 lts ?