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PTY(4) BSD Kernel Interfaces Manual PTY(4) NAME pty -- pseudo terminal driver SYNOPSIS device pty DESCRIPTION The pty driver provides support for a device-pair termed a pseudo terminal. A pseudo terminal is a pair of character devices, a master de- vice and a slave device. The slave device provides to a process an in- terface identical to that described in tty(4). However, whereas all other devices which provide the interface described in tty(4) have a hardware device of some sort behind them, the slave device has, instead, another process manipulating it through the master half of the pseudo terminal. That is, anything written on the master device is given to the slave device as input and anything written on the slave device is pre- sented as input on the master device. The following ioctl(2) calls apply only to pseudo terminals: TIOCSTOP Stops output to a terminal (e.g. like typing `^S'). Takes no parameter. TIOCSTART Restarts output (stopped by TIOCSTOP or by typing `^S'). Takes no parameter. TIOCPKT Enable/disable packet mode. Packet mode is enabled by speci- fying (by reference) a nonzero parameter and disabled by specifying (by reference) a zero parameter. When applied to the master side of a pseudo terminal, each subsequent read(2) from the terminal will return data written on the slave part of the pseudo terminal preceded by a zero byte (symbolically defined as TIOCPKT_DATA), or a single byte reflecting control status information. In the latter case, the byte is an in- clusive-or of zero or more of the bits: TIOCPKT_FLUSHREAD whenever the read queue for the terminal is flushed. TIOCPKT_FLUSHWRITE whenever the write queue for the terminal is flushed. TIOCPKT_STOP whenever output to the terminal is stopped a la `^S'. TIOCPKT_START whenever output to the terminal is restarted. TIOCPKT_DOSTOP whenever t_stopc is `^S' and t_startc is `^Q'. TIOCPKT_NOSTOP whenever the start and stop characters are not `^S/^Q'. While this mode is in use, the presence of control status in- formation to be read from the master side may be detected by a select(2) for exceptional conditions. This mode is used by rlogin(1) and rlogind(8) to implement a remote-echoed, locally `^S/^Q' flow-controlled remote login with proper back-flushing of output; it can be used by other similar programs. TIOCUCNTL Enable/disable a mode that allows a small number of simple user ioctl(2) commands to be passed through the pseudo-termi- nal, using a protocol similar to that of TIOCPKT. The TIOCUCNTL and TIOCPKT modes are mutually exclusive. This mode is enabled from the master side of a pseudo terminal by specifying (by reference) a nonzero parameter and disabled by specifying (by reference) a zero parameter. Each subsequent read(2) from the master side will return data written on the slave part of the pseudo terminal preceded by a zero byte, or a single byte reflecting a user control operation on the slave side. A user control command consists of a special ioctl(2) operation with no data; the command is given as UIOCCMD(n), where n is a number in the range 1-255. The op- eration value n will be received as a single byte on the next read(2) from the master side. The ioctl(2) UIOCCMD(0) is a no-op that may be used to probe for the existence of this fa- cility. As with TIOCPKT mode, command operations may be de- tected with a select(2) for exceptional conditions. FILES /dev/pty[p-sP-S][0-9a-v] master pseudo terminals /dev/tty[p-sP-S][0-9a-v] slave pseudo terminals DIAGNOSTICS None. SEE ALSO tty(4) HISTORY The pty driver appeared in 4.2BSD. BSD November 30, 1993 BSD
NAME | SYNOPSIS | DESCRIPTION | FILES | DIAGNOSTICS | SEE ALSO | HISTORY
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