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About the TTY Subsystem

A series of four processes--init(1M), getty(1M) or uugetty(1M), login(1), and either sh(1), csh(1), or ksh(1)--connect a user to the IRIX system. init is invoked as the last step in the boot procedure and is responsible for spawning general processes. It spawns a process for each serial line that a user may log in on, as defined by instructions in the file /etc/inittab. The getty or uugetty commands in /etc/inittab require a <line> argument, which is the name of a special file in the /dev directory. For a description of other arguments that may be used with getty and uugetty, see the getty(1M) and uugetty(1M) reference pages.

A user attempting to make a connection generates a signal that is routed by the hardware to the getty process (derived from "get a tty") for one of the TTY line files in /dev. getty responds by sending an entry from the file /etc/gettydefs down the line. The gettydefs entry used depends on the <speed> argument used with the getty command. (In the Synopsis of the getty(1M) reference page, the argument name is <speed>, but it is really a pointer to the <label> field of a gettydefs entry.) If no <speed> argument is provided, getty uses the first entry in gettydefs. Among the fields in the gettydefs entry is the login prompt (described in "Checking Line Settings Using IRIX Shell Commands").

On receiving the login prompt, the user enters a login name. getty starts login, using the login name as an argument. login issues the prompt for a password, evaluates the user's response, and, if the password is acceptable, calls in the user's shell as listed in the /etc/passwd entry for the login name. If no shell is named, /bin/sh is furnished by default.

/bin/sh executes /etc/profile and then executes the user's .profile, if it exists. /bin/csh executes /etc/cshrc, .cshrc, and .login. The .profile, .cshrc, or .login file often contains stty commands that reset terminal options that differ from the defaults. The connection between the user and the IRIX system has now been made.

Terms

The following terms are used to describe serial devices and the TTY system:

TTY

The near-classic abbreviation for teletypewriter. The term covers the whole area of access between the IRIX system and peripheral serial devices, including the system console. It shows up in commands such as getty and stty, in the names of device special files such as /dev/ttyd1, and in the names of files such as /etc/gettydefs, which is used by getty.

TTY line

The cable connecting the computer to the serial device.

port

The connector on the computer where the TTY line attaches.

line settings

A set of characteristics for data transmission over the line.

baud rate

The speed at which data is transmitted over the line. A part of the line settings.

mode

The characteristics of the terminal interface and a part of the line settings. The TTY line and the terminal must be working in the same mode before communication can take place. Described in termio(7).

hunt sequence

A series of line settings such as different baud rates. During the login sequence, a user looking for a compatible connection to the computer can go from one setting to the next by sending a BREAK signal. Also referred to as a rotary.

terminal options


Settings that define the way a given terminal operates. Described in termio(7).

Terms

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