Terminal

• Text-Terminal-HOWTO v1.41 February 2008, v1.28, January 2002
• Linux Console - Virtual Terminal & Terminal Windows

Controlling Terminal

• /dev/tty
• A terminal may belong to a process as its controlling-terminal, which is a terminal uniquely associated with one session. Each process of a session with a controlling-terminal has the same controlling-terminal assigned to it. Each session may have at most one controlling-terminal associated with it and vice versa. A terminal may be assigned to at most one session as the controlling-terminal.
• /dev/tty stands for the controlling terminal (if any) for the current process
• To find out which tty's are attached to which processes use the "ps -a" command at the shell prompt (command line). Type "tty" at the shell prompt to see what it is.

• The controlling-terminal and process-groups

Serial Console/Serial Port Terminal

• Linux Serial Console HOWTO
• Remote Serial Console HOWTO

• /dev/ttySn
• /dev/ttsn
  • starting with kernel 2.4

Console

• PC monitor is usually called the console and has several device special files associated with it: tty0, tty1, tty2; the console for a PC Linux system is normally the computer monitor in text mode. It emulates a terminal of type "Linux".
• On modern small computers the console is usually the computer's attached monitor and keyboard; On many older computers the console is an RS-232 link to a terminal such as a DEC VT100(Serial Console.)

• Logical system console
  • /dev/console is used to send messages to the console.
  • /dev/syscon for some System V
• Physical system console
  • /dev/systty points to the device which is used by the attached monitor and keyboard, often /dev/tty0

• 1.3. Alternative meanings of "console"

Virtual Terminal(VT)/Virtual Console(VC)

• /dev/ttyn
• /dev/tty0 is just an alias for the current virtual terminal and it's where messages from the system are sent. Thus messages from the system will be seen on the console (monitor) regardless of which virtual terminal it is displaying.

• There are often six virtual terminals available and you press Ctrl+Alt+Fx to go to a virtual terminal.

Pseudo Terminal

• Applications
  • terminal emulator(xterm)
    • The X Terminal HOWTO
    • terminal emulator process is associated with the master device
    • the shell is associated with the slave
    • Any terminal operations performed by the shell in a terminal emulator session are received and handled by the terminal emulator process itself.
    • The terminal emulator process receives input from the keyboard and mouse using windowing events, and is thus able to transmit these characters to the shell, giving the shell the appearance of the terminal emulator being an underlying hardware object.
  • remote login handlers(ssh and telnet servers)
    • remote login handlers serve as the master for a corresponding shell

• BSD
  • /dev/pty[p-za-e][0-9a-f] for masters
  • /dev/tty[p-za-e][0-9a-f] for slaves

• Unix98
  • /dev/ptmx for masters
  • /dev/pts/x for slaves

getty

• getty
  • open and initialize the tty line, read a login name, and invoke login
  • After you type in your user name, getty takes it and calls the login program telling it your user name. The getty process is replaced by the login process. The login process asks for your password, checks it and starts whatever process is specified in your password file. This process is often the bash shell. If so, bash starts and replaces the login process.

• for directly connected terminals
  • agetty (sometimes just called getty)
  • getty
    • part of the getty_ps package

• for modems
  • mgetty
    • the best one for modems; works for terminals too but inferior
  • uugetty
    • for modems only; part of the getty_ps package

• Simple gettys to use if you don't use a real text-terminal(not suitable for serial lines)
  • mingetty(mingetty is a minimal getty for use on virtual consoles)
  • fbgetty(fbgetty is a getty for use on virtual consoles with framebuffer support like mingetty)

terminfo(formerly termcap) database

• has an entry (or file) for each model or type (such as vt100) of terminal and tells what the terminal can do, what codes to send for various actions, and what codes to send to the terminal to initialize it.
• One way in which terminfo gives the its information to an application program is via the "ncurses" functions that a programmer may put into a C program. For example, if a program wants to move the cursor to row 3, col 6 it simply calls: move(3,6). The move() function (part of ncurses) knows how to do this for your terminal (it has read terminfo).

environment variables

• TERM
  • must always be set to the type of the terminal you are using (such as vt100)

• TERMINFO
  • contains the path to the terminfo database

Line Discipline

• struct tty_ldisc

• N_TTY
  • //path to kernel souce/drivers/char/n_tty.c

• Terminal Emulation
  • make the PC computer behave like a text terminal
  • a real terminal to emulate another brand/model of terminal