How to upgrade from Debian Linux 8 Jessie to Debian 9 Stretch using command line over ssh based session

To upgrade from Debian Linux 8 Jessie to Debian 9 Stretch using command line over an SSH-based session, follow these steps:

Log in to your Jessie system using SSH:
```
ssh user@hostname
```
Update the package index:
```
sudo apt-get update
```
Upgrade the system to the latest version of Jessie:
```
sudo apt-get upgrade
```
Make a backup of important data and configurations.
Edit the file /etc/apt/sources.list and replace all instances of jessie with stretch:
```
sudo nano /etc/apt/sources.list
```
Update the package index again:
```
sudo apt-get update
```
Run the upgrade command:
```
sudo apt-get dist-upgrade
```
The upgrade process will take some time and may require your intervention, such as confirming package removals or installations.
After the upgrade process is complete, you can reboot the system:
```
sudo reboot
```
Log in to your system and verify the version to confirm that you are now running Debian 9 Stretch.

lsb_release -a

It is recommended to take a backup of your important data and configurations before proceeding with the upgrade process.