sudo docker exec -it sql1 /opt/mssql-tools/bin/sqlcmd -S localhost -U SA -P '<YourStrong!Passw0rd>' -Q 'BACKUP DATABASE  [demodb] TO DISK = "/var/opt/mssql/data/demodb_LogBackup.bak" WITH STATS = 10'

sudo docker cp "sql1:/var/opt/mssql/data/demodb_LogBackup.bak" "C:\temp\DATABASESQLSERVER1.bak" 

sudo docker cp  "C:\temp\DATABASESQLSERVER1.bak" "sql2:/var/opt/mssql/data/demodb_LogBackup.bak"

sudo docker exec -it sql2 /opt/mssql-tools/bin/sqlcmd -S localhost -U SA -P '<YourNewStrong!Passw0rd>' -Q 'RESTORE DATABASE  [yourdbname] FROM DISK = "/var/opt/mssql/data/demodb_LogBackup.bak"'