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Test Your Knowledge in Computers #493
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When a program executes, each command executes one after the other, top-to-bottom. This is known as inconsequential control flow.
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ttys(5) [bsd man page]

TTYS(5) 							File Formats Manual							   TTYS(5)

NAME
ttys - terminal initialization data DESCRIPTION
The ttys file contains information that is used by various routines to initialize and control the use of terminal special files. This information is read with the getttyent(3) library routines. There is one line in the ttys file per special file. Fields are separated by tabs and/or spaces. Some fields may contain more than one word and should be enclosed in double quotes. Blank lines and comments can appear anywhere in the file; comments are delimited by `#' and new line. Unspecified fields default to null. The first field is the termi- nal's entry in the device directory, /dev. The second field of the file is the command to execute for the line, typically getty(8), which performs such tasks as baud-rate recognition, reading the login name, and calling login(1). It can be, however, any desired command, for example the start up for a window system terminal emulator or some other daemon process, and can contain multiple words if quoted. The third field is the type of terminal normally connected to that tty line, as found in the termcap(5) data base file. The remaining fields set flags in the ty_status entry (see getttyent(3)) or specify a window system process that init(8) will maintain for the terminal line. As flag values, the strings `on' and `off' specify whether init should execute the command given in the second field, while `secure' in addition to `on' allows root to login on this line. These flag fields should not be quoted. The string `window=' is followed by a quoted command string which init will execute before starting getty. If the line ends in a comment, the comment is included in the ty_comment field of the ttyent structure. Some examples: console "/usr/libexec/getty std.1200" vt100 on secure ttyd0 "/usr/libexec/getty d1200" dialup on # 555-1234 ttyh0 "/usr/libexec/getty std.9600" hp2621-nl on # 254MC ttyh1 "/usr/libexec/getty std.9600" plugboard on # John's office ttyp0 none network ttyp1 none network off ttyv0 "/usr/new/xterm -L :0" vs100 on window="/usr/new/Xvs100 0" The first example permits root login on the console at 1200 baud, the second allows dialup at 1200 baud without root login, the third and fourth allow login at 9600 baud with terminal types of "hp2621-nl" and "plugboard" respectively, the fifth and sixth line are examples of network pseudo ttys, which should not have getty enabled on them, and the last example shows a terminal emulator and window system startup entry. FILES
/etc/ttys SEE ALSO
login(1), getttyent(3), gettytab(5), init(8), getty(8) 7th Edition November 16, 1996 TTYS(5)

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GETTY(8)						      System Manager's Manual							  GETTY(8)

NAME
getty - set typewriter mode SYNOPSIS
/etc/getty [ char ] DESCRIPTION
Getty is invoked by init(8) immediately after a typewriter is opened following a dial-up. It reads the user's login name and calls login(1) with the name as argument. While reading the name getty attempts to adapt the system to the speed and type of terminal being used. Init calls getty with a single character argument taken from the ttys(5) file entry for the terminal line. This argument determines a sequence of line speeds through which getty cycles, and also the `login:' greeting message, which can contain character sequences to put various kinds of terminals in useful states. The user's name is terminated by a new-line or carriage-return character. In the second case CRMOD mode is set (see ioctl(2)). The name is scanned to see if it contains any lower-case alphabetic characters; if not, and if the name is nonempty, the system is told to map any future upper-case characters into the corresponding lower-case characters. If the terminal's `break' key is depressed, getty cycles to the next speed appropriate to the type of line and prints the greeting message again. Finally, login is called with the user's name as argument. The following arguments from the ttys file are understood. 0 Cycles through 300-1200-150-110 baud. Useful as a default for dialup lines accessed by a variety of terminals. - Intended for an on-line Teletype model 33, for example an operator's console. 1 Optimized for a 150-baud Teletype model 37. 2 Intended for an on-line 9600-baud terminal, for example the Textronix 4104. 3 Starts at 1200 baud, cycles to 300 and back. Useful with 212 datasets where most terminals run at 1200 speed. 5 Same as `3' but starts at 300. 4 Useful for on-line console DECwriter (LA36). SEE ALSO
init(8), login(1), ioctl(2), ttys(5) GETTY(8)

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