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'''Runlevel ''' is a Unix/Linux term relating to the operating system's mode of operation. For example, if the operating system operates in text-based or graphical mode, reboot, shutdown, etc. {{Admon/important| Security Advice | We have seen that maintaining unneeded packages can be a security risk due to the unnecessary increase in the complexity of your system. Similarly, it is also unnecessarily hazardous, and even more so, to leave unneeded services running. In this investigation, we will learn how to control services, and turn off those that we think are not necessary.}}