If you are using mysql db then you can use the following command by which you can easily make a back-up file for your database. The command are mention bellow :-
[root]# mysqldump -u [username] -p [password] [db_name] > [backfile.sql]
now you can easily replace the variable with in the bracket  by the required information. By this you will easily make your backup file. If you want to take backup of some specified file then you will use the following command.
[root]# mysqldump --add-drop-table -u [username] -p [password] [db_name] [tablename1] [tablename2] > [backfile.sql]