This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
tcflow — suspend or restart the transmission or reception of data
int tcflow(int fildes, int action);
The tcflow() function shall suspend or restart transmission or reception of data on the object referred to by fildes, depending on the value of action. The fildes argument is an open file descriptor associated with a terminal.
- If action is TCOOFF, output shall be suspended.
- If action is TCOON, suspended output shall be restarted.
- If action is TCIOFF and fildes refers to a terminal device, the system shall transmit a STOP character, which is intended to cause the terminal device to stop transmitting data to the system. If fildes is associated with a pseudo-terminal, the STOP character need not be transmitted.
The default on the opening of a terminal file is that neither its input nor its output are suspended.
Attempts to use tcflow() from a process which is a member of a background process group on a fildes associated with its controlling terminal, shall cause the process group to be sent a SIGTTOU signal. If the calling thread is blocking SIGTTOU signals or the process is ignoring SIGTTOU signals, the process shall be allowed to perform the operation, and no signal is sent.
Upon successful completion, 0 shall be returned. Otherwise, −1 shall be returned and errno set to indicate the error.
The tcflow() function shall fail if:
- If action is TCION and fildes refers to a terminal device, the system shall transmit a START character, which is intended to cause the terminal device to start transmitting data to the system. If fildes is associated with a pseudo-terminal, the START character need not be transmitted.
- The fildes argument is not a valid file descriptor.
- The action argument is not a supported value.
- The process group of the writing process is orphaned, the calling thread is not blocking SIGTTOU, and the process is not ignoring SIGTTOU.
The following sections are informative.
The Base Definitions volume of POSIX.1‐2008, Chapter 11, General Terminal Interface, <termios.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
- The file associated with fildes is not a terminal.
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