1, Linux graphical interface and command interface switching
Inside the virtual machine installed RedHat Linux system. To enter the graphical interface.
Switching from the graphical interface to the Linux command interface you can press Ctrl + Alt + Fn (n = 1,2,3,4,5,6), but the Ctrl + Alt has been occupied inside the virtual machine, the virtual machine that is switched cursor . So we need to press Ctrl + Shift + Alt + Fn (n = 1,2,3,4,5,6). (Horse of God? I installed the default startup is a graphical interface, and then press Ctrl + Alt + Fn (2,3,4,5,6) into the command line, press Ctrl + Alt + F1 back to the graphical interface)
Interface command to switch from Linux graphical interface you can press Alt + F7 (You can also type the command startx into the graphical interface).
If you want to enter the boot command interface, then you can modify the configuration file. Specific command is as follows (in the command interface, of course, must be root or have root privileges can modify the user name):
(1) vi / etc / inittab - with the vi editor to edit the / etc / inittab file
(2) Press i - to switch to INSERT mode, that is, to modify the mode
(3) found inside the file init: 5: initdefault line, into the 5 3 - 5 below and say what represent 3
(4) Press the Esc key - exit INSERT mode
(5) by: (colon) - lock the cursor to the last row
(6) wq (save and exit)
If you do not want to modify, then q! (Exit without saving)
Restart to enter the default command interface.
2, Linux run levels
Linux has 7 runlevels: init 
1: Single User
2: Multi-user state no network service
3: multi-user internet service status
4: The system does not use the reserved user
5: the graphical interface
Commonly run level 3 and 5, to modify the run level in the file / etc / inittab inside modify, change the default method, see 1 into the interface.
Here is set to 1 if the boot that will shut down, it will be set to 6 has been restarted.
3, modify the method to resolve a misconfigured
If you accidentally set it to run level 1 or 6 can not normally enter Linux, then we can solve the following methods. (Of course, it is not in the GRUB password)
(1) when the system is started several seconds Press "e" to enter the GRUB boot screen
(2) highlight the second line, enter "e" into the
(3) Enter "1" [single-user level], because the single-user level to start not read / etc / inittab file after entering
(4) Carriage Return GRUB interface
(5) Press "b" will enter the single mode
(6) In the single player mode which modify / etc / inittab file which can be in accordance with 1
Because Linux inside to change the password without entering the old password, so if you forget the password to be entered so single-mode changes.