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BSD 2.11 - man page for pty (bsd section 4)

PTY(4)					       Kernel Interfaces Manual 				       PTY(4)

NAME
pty - pseudo terminal driver
SYNOPSIS
/sys/conf/SYSTEM: NPTY ptys # pseudo-terminals, in groups of 8
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 device and a slave device. The slave device provides processes an interface iden- tical 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 presented as input on the master device. In configuring, ptys specifies the number of pseudo terminal pairs are configured. The following ioctl 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 specifying (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 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 inclusive-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 information to be read from the master side may be detected by a select for exceptional conditions. This mode is used by rlogin(1C) and rlogind(8C) to implement a remote-echoed, locally ^S/^Q flow-con- trolled 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 commands to be passed through the pseudo-terminal, 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 subse- quent read from the master side will return data written on the slave part of the pseudo terminal pre- ceded 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 operation with no data; the command is given as UIOCCMD(n), where n is a number in the range 1-255. The operation value n will be received as a single byte on the next read from the master side. The ioctl UIOCCMD(0) is a no-op that may be used to probe for the existence of this facility. As with TIOCPKT mode, command operations may be detected with a select for exceptional conditions. TIOCREMOTE A mode for the master half of a pseudo terminal, independent of TIOCPKT. This mode causes input to the pseudo terminal to be flow controlled and not input edited (regardless of the terminal mode). Each write to the control terminal produces a record boundary for the process reading the terminal. In nor- mal usage, a write of data is like the data typed as a line on the terminal; a write of 0 bytes is like typing an end-of-file character. TIOCREMOTE can be used when doing remote line editing in a window manager, or whenever flow controlled input is required.
FILES
/dev/pty[p-r][0-9a-f] master pseudo terminals /dev/tty[p-r][0-9a-f] slave pseudo terminals
DIAGNOSTICS
None. 4.2 Berkeley Distribution May 19, 1986 PTY(4)


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