SQL Oracle export error
The syntax should be exp username/password@instance , please also check if the listener is running ps -ef|grep tns and if it has the service listed lsnrctl services (the error "ORA-12154: TNS:could not resolve the connect identifier specified" points out that there is a problem related to that). You can also use the new tool expdp which in my opinion is more easy to use. Ex: expdp sys/password schema=userID dumpfile=userID.dmp directory=data_pump_dir logfile=userID_dmp.log  . You can see where the data_pump_dir points to from sqlplus select * from dba_directories and even create your own directory CREATE DIRECTORY dmpdir AS '/opt/oracle'; and use it in the directory clause. But if you want to use exp, check the listener and also the syntax of your command.