Category Archives: Linux

Talk about unix and linux stuff.

TTY – TeleTYpewriter on Linux

I came accross a tutorial talking about TTY command in linux. Basically its pertaining to terminals in the container. Lets drill down the terminology first.

– Terminal is just a term use pointing to a dumb machine connected to the main computer. Consist of a display and a keyboard.

– Console is use to describe a TERMINAL physically connected to the computer. Let say like a personal computer connected with a keyboard and monitor. Or like xbox console and ps4.

– TTY and PTY . TTY is technology that handles input and output to a display and the program it executes.It is a virtual console refer above to communicate with the host. Most terminal in linux is PTY pseudo-tty. Meaning a fake or technology that acts similar to tty.  Ssh terminal is type of PTY.

Using command tty, shows device name you are currently on. tty0 usually refers to your current terminal.

What are virtual terminals and when to use it?
“A Virtual Terminal is a full-screen terminal which doesn't run inside an X window (unlike the terminal window on your graphical desktop). Virtual terminals are found on all GNU/Linux systems, even on systems which don't have a desktop environment or graphical system installed.

Virtual terminals can be accessed on an Ubuntu system by pressing Ctrl+Alt+F1 till F6. To come back to the graphical session, press Ctrl+Alt+F7.“

So all in all my understanding is when you SSH to a server, you are using a pseudo-tty to the server giving you a virtual terminal to manage the machine. This also gives you a interactive shell. When you spawn a connection to sshd, it mounts a /dev/pts/* dynamically. Making it look like a real terminal is connected or physical device. And you can use this to refer to your connection, by using tty command on your terminal. Pseudo because you are emulating tty functionality, instead of actually connected to the server physically.

In the olden days terminal are real physical device connected to the pc. Linux didnt have a GUI before. To manage it, you remote to it and creates a “virtual terminal” or “virtual console”  like a real physical device terminal.

The tty 1-6 ctrl + alt + f1-6 are basically the same as a virtual console or terminal. The f7+ keys shortcut is when you have a gui terminal on the server. Gui terminal refers to let say, your ubuntu is your server. It can open a terminal in its window as you do. Then pressing keys above f(1-6) opens tty terminal without the gui as if you are back in a gui-less server and use your keyboard and monitor to manage it. Take note pressing these keys only works when you are physically logged-in on the console. But your terminal is still virtual, see below.

Additional info, when you are executing a command to connect to your server using ssh -t or -T flag remotely.

-t means to provide an interactive terminal or TTY terminal to execute commands.

-T to disable any interactivity.

Upon saying this. When you open a terminal connection via ssh. You most likely want tty/interactivity, that can execute commands etc. tty is just the technology that creates this connection between your remote pc keyboard to a server. A linux box by itself is a console. Connect a keyboard and a monitor to it and will generate a virtual console or terminal to administer it.

Taken from red-hat website

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/installation_guide/sn-guimode-virtual-consoles-ppc

“A virtual console is a shell prompt in a non-graphical environment, accessed from the physical machine, not remotely. Multiple virtual consoles can be accessed simultaneously.”

CentOS Administration

List of administration tasks on a CentOS machine with VirtualMin/WebMin installed