@arijitaich

Have you made any modifications to MySQL's configuration? Generally that specific error is caused by changes to the configuration, which are not valid, unless your MySQL directories were in fact removed somehow.

On Ubuntu, your MySQL data directory should be located at /var/lib/mysql. As long as that directory exists, then you should still have your data. If that directory has been removed, without backups, there's no way to restore it.

Quick Tip: Make sure you're regularly backing up your data/databases. If you don't have valid, working backups, there's no way to restore your data.

That said, what you can do is backup that directory -- do this first.

mkdir -p /usr/local/src/mysql

cp -R /var/lib/mysql/* /usr/local/src/mysql

The above creates a backup directory and then copies all files in the MySQL data directory to it, so if something should happen with what we do next, we have a backup copy of your data.

Now, we need to see what errors MySQL is throwing when you try to start MySQL, so go ahead and run:

service mysql restart

Then run this command to grab the last 30 lines from the error log:

tail -30 /var/log/mysql/error.log

Paste that output to a code block as a reply so it's formatted and we can see what's going on. I'd do this before we attempt to remove MySQL and then reinstall.