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some important courses like CCNA , MCSA , MCSE , ITIL , some basics for Linux OS thats will be enough for starting and always keep your self on contact with the new technology and improve your knowledge on cloud and virtualization
Simply you have to know your core experience then follow the trending technology that's help you in your career
To become System admin ,you should study ccna and mcsa courses as a start , then you need to learn linux OS and its commands and scripts. you must also know the databases like sql and pl sql . ITIL foundatinon.
