First, let's start the next level (Runlevel):
Refers to a Unix or Unix-like operating systems under different operating modes, operation is usually divided into seven levels:
Run Level 0: system shutdown, the system can not be set by default to run level 0, or can not start properly
run level 1: single-user work status, root permission for system maintenance, prohibits remote login, no network connection, the daemon is not running , does not allow non-root user login.
run level 2: multi-user state, no network connection, do not run daemons
run level 3: full multi-user state (there are NFS), after landing into the console command line mode, the normal login status
run level 4: the system does not use, retention, user-defined
run level 5: X11 console after you log in GUI mode graphics is common with a graphical interface model
run level 6: a normal system shutdown and restart, the default operating level 6 can not be set, or can not start properly
(Also: if forget the root password can be reset by a single-user mode power hotkey, provided to come into contact with the host)
Runlevel target has been used instead of the new Linux systemd, as multi-user.target equivalent to init 3, graphical.target equivalent to init 5, but still compatible SystemD run level (Runlevel).
The current release has adopted the vast majority of systemd instead of UNIX System V.
To set the boot into the non-graphical interface from the command line, the default is to boot into run level 5 is changed to boot into run level 3,
Proceed as follows:
1. Switch to the root user: su -root password again
Note: There may be situations where:
The root cause of the failure is wrong password or no password (such as this konjac ..) for the root, it would first set the root password: sudo passwd root
2. Modify the grub file: vim / etc / default / grub
3. Update grub: update-grub
4. Set the boot into the command line: systemctl set-default multi-user.target
5. Restart Ubuntu: reboot
Then see into the command line mode, succeeded ~~
Thank the authors of these blog:
https://www.cnblogs.com/weiyiming007/p/9913449.html
https://blog.csdn.net/ctthuangcheng/article/details/51219848