There are 7 runtime run levels under LinuxRun Level 0 system shutdown state, the system default RunLevel cannot be set to 0, otherwise it will not start normallyRun Level 1 single user working status, root privilege, for system maintenance, remote login ForbiddenRun Level 2 multi-user state (no NFS)Run Level 3 full multiuser state (with NFS), enter console command line mode after loginRun Level 4 system not used, reservedRun Level 5 X11 console, enter GUI mode after loginRun level 6 system shuts down gracefully and restarts, default RunLevel cannot be set to 6, otherwise it will not start normallythe operating level principle:1. There are many server scripts under directory/ETC/RC.D/INIT.D, commonly referred to as services (service)2. There are 7 directories named RCN.D under/ETC/RC.D, corresponding to the 7 RunLevel of the system3. RCN.D directories are symbolic link files that point to a service script file under the INIT.D directory, with a naming convention of k+nn+ service name or s+nn+ service name, where NN is a two-digit number. 4. The system will enter the corresponding RCN.D directory according to the specified RunLevel, and retrieve the linked files under the directory in the order of file name .for files starting with K, the system terminates the corresponding servicefor files beginning with S, the system will start the corresponding service5. View run levels by: RunLevel6. Go to other RunLevel by: Init N7. Also init0 for shutdown, init 6 reboot systemmodifying numbers in a diagram
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There are 7 runtime run levels under Linux
