Hi @Gnana Balaji Kanagaraj ,
You can follow Dan's step to change sa password.
Change the SA Password
1. Stop the mssql-server service:
sudo systemctl stop mssql-server
2. Change the SA password:
sudo /opt/mssql/bin/mssql-conf set-sa-password
3. Start the mssql-server service:
sudo systemctl start mssql-server
About another question, it is not possible to connect to SQLCMD with the root user in Linux. There are only two types of authentication for SQL Server: Windows authentication and SQL authentication.
Best regards,
Seeya
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