/etc/securetty file

/etc/The Securetty file allows you to specify which TTY device the "root" user can log on from. The login program (usually/bin/login) need to read "/etc/securetty "file. Its format: Listed TTY devices are allowed to log in, commented out or not in this file is not allowed root login.
The user cannot log on as the root user from a device that does not exist with the file and can only log in as a normal user, and is converted to the root user with the SU command. If the file is an empty file, then the root user cannot log on to the system from any device, can only log on as a normal user, is converted to root using the SU command, and if the file does not exist, the root user can log in from anywhere, which will cause security problems. So the file is necessarily present in the system.
#Note: Renaming this price or commenting out the file does not affect the SSH application, because SSH Telnet uses pts instead of TTY, and this file modification prevents Telnet from logging on through root. Terminal is a type of character device, he has multiple types, usually using a TTY for short-range terminal equipment. TTY generally refers to the terminal, the topmost terminal, which is a terminal that communicates directly with Linux. PTS is a pseudo-terminal, in general, the Windows-based Linux open terminal are pts, but this window-type terminal (that is, the terminal containing the graphical interface we operate) is generally a TTY. The console appears to refer to the current console (or monitor), such as when you ctrl+alt+x, and then echo "1111">/dev/The console,1111 will be displayed on your monitor. VC is Virtual Console, can also be understood as a dummy monitor, when you ctrl+alt+x, it will switch to VCX, in/dev/there is no direct corresponding device file, but if you try echo "1111">/dev/VSC1, you can see it on monitor, but switch to the corresponding VC. VT refers to virtual terminal, a virtual terminal, which is typically a dummy console



TTY control terminal includes (1) TTY login from Virtual Console (2) PTS Open Shell window in X is shown as pts
1.tty has RS232, rs422, vcon three kinds of equipment, usually mainly use the RS232 excuse the serial port do heartbeat or link serial device.
2.pst each remote connection will produce a PST device.
3.console when the system is installed, you can select the serial terminal or connect the video card directly. 

/etc/securetty file