Transferred from: http://blog.chinaunix.net/uid-22746363-id-383989.html
Linux System has 7 runlevel (runlevel)
RunLevel 0: System down state, system default RunLevel cannot be set to 0, otherwise it will not start normally
RunLevel 1: Single User working status, root privilege, for system maintenance, remote login Forbidden
RunLevel 2: Multi-User State (no NFS)
RunLevel 3: Full multiuser State (with NFS), enter console command line mode after login
Run Level 4: System not used, reserved
Run level 5:x11 console, login to GUI mode
RunLevel 6: The system shuts down gracefully and restarts, the default runlevel cannot be set to 6, otherwise it will not start normally
the 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/etc/rc.d under the name of RCN.D.
Catalogue, corresponding to the 7 operating levels of the system
3. 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 service
For files beginning with S, the system will start the corresponding service
5. View run levels by: RunLevel
6. Go to other RunLevel by: Init N
7. Also init0 for shutdown, init 6 reboot system
Since the Linux system is now installed in the 5th level, that is, after the system started directly into the graphical interface, rather than in the character mode after logging in with StartX or xinit to start the graphical interface. It is recommended to set the default operating level of the system at level 3rd after the system installation is complete, and then manually enter it after the character terminal is logged in.
StartXcommand to start the graphical interface. You can modify it in the following ways:
Modify with a text editor/etc/inittabFile, put
Code:
Id:5:initdefault: This line, modified into
Code:
Id:3:initdefault: After the reboot is saved, the system will start to the character interface by default. The difference between the different run levels is that the system starts with a different service, such as running Level 3 does not start the X graphical interface service by default, and RunLevel 5 is started by default. There is no difference in nature, and it does not matter whether the function is strong or weak between different levels. Users are fully self-sufficient to define default services at different levels. At any run level, the user can use the init command to switch to another runlevel.
Because Ubuntu system does not have inittab files. Its configuration reference: http://blog.chinaunix.net/u2/82530/showart_2033617.html
I haven't tried it specifically.
Part of the article source: http://space.itpub.net/370491/viewspace-216954
7 operating levels for Linux systems
