.: One of the primary difficulties with teaching system administration as a formal university discipline, is that the industry and technology changes much faster than the typical textbook and coursework certification process. By the time a new textbook has spent years working through approvals and committees, the specific technology for which it is written may have changed significantly or is now obsolete.In addition, because of the practical nature of systems administration and the easy availability of open-source server software, many systems administrators enter the field self-taught.Generally, a prospective administrator will be required to have some experience with the computer system he or she is expected to manage. In some cases, candidates are expected to possess industry certifications such as the Microsoft MCSA, MCSE, Red Hat RHCE, Novell CNA, CNE, Cisco CCNA or CompTIA's A+ or Network+, Sun Certified SCNA, Linux Professional Institute among others.Sometimes, almost exclusively in smaller sites, the role of system administrator may be given to a skilled user in addition to or in replacement of his or her duties. For instance, it is not unusual for a mathematics or computing teacher to serve as the system administrator of a secondary school.