|
DataMuseum.dkPresents historical artifacts from the history of: ICL Comet 32 |
This is an automatic "excavation" of a thematic subset of
See our Wiki for more about ICL Comet 32 Excavated with: AutoArchaeologist - Free & Open Source Software. |
top - metrics - download
Length: 2423 (0x977)
Types: TextFile
Notes: UNIX file
Names: »pty.4«
└─⟦26887b7e0⟧ Bits:30009717 Comet 32 harddisk image
└─⟦28c352965⟧ »/a« UNIX Filesystem
└─⟦this⟧ »usr/man/man4/pty.4«
.ig @(#)pty.4 2.1 7/1/84 @(#)Copyright (C) 1983 by National Semiconductor Corp. .. .TH PTY 4 .SH NAME pty \- pseudo-terminal device .SH DESCRIPTION Ptys are controllers for terminals that exist only in software. For each pty device, there exists a corresponding software terminal (also known as the pty slave device). Software terminals act like real terminals, so that programs running on them act normally. However, instead of communicating with real users, their input and output go through the process which owns the corresponding pty. Ptys thus act similarly to pipes, but avoid the problems of pipes (for example, interrupt characters work on ptys.) .PP When a write is done to a pty, the data appears to have been ``typed'' into the corresponding software terminal, at which point the program running on that terminal can read the data as input. The normal terminal buffering mechanism is used, so that if too much is written to the pty too quickly, characters can be lost. This can be avoided by using the TIOCCHKINP ioctl, which returns whether or not any process is sleeping waiting for input on the terminal. Writing to the pty only when input is desired (or when an interrupt character has to be typed) will prevent most overflow problems. .PP When output is written to a software terminal, it is buffered using the normal terminal buffer mechanism. The data remains until a read is performed on the pty, at which time the data is returned. The read will return as much data as currently exists, and thus will sleep only if the terminal buffer is empty. The FIONREAD ioctl returns how much data is ready for reading on the pty, so that sleeps can be avoided. If the terminal buffer fills up, the program on the terminal will sleep so that no data is lost. .PP Ioctls performed on the pty are redirected to the corresponding software terminal. This allows the owner of the pty to read the settings of the terminal and act accordingly. .PP A pty is an exclusive-access device, so that it can be opened by only one user at a time. When the pty is closed, the processes on the corresponding terminal are sent a SIGHUP signal and the terminal buffers are flushed. Programs that use the software terminal when the corresponding pty is not in use will sleep until it is open. .PP .SH FILES /dev/ptyn The pty numbered n .br /dev/ttypn The corresponding software terminal numbered n .SH "SEE ALSO" tty(4)