tcgetpgrp

Synopsis

#include <unistd.h>

pid_t tcgetpgrp(int fildes);

Status

Partially implemented

Conformance

IEEE Std 1003.1-2017

Description

tcgetpgrp() - get the foreground process group ID

The tcgetpgrp() function shall return the value of the process group ID of the foreground process group associated with the terminal.

If there is no foreground process group, tcgetpgrp() shall return a value greater than 1 that does not match the process group ID of any existing process group.

The tcgetpgrp() function is allowed from a process that is a member of a background process group; however, the information may be subsequently changed by a process that is a member of a foreground process group.

Return value

The functions can never return. Upon successful completion, tcgetpgrp() shall return the value of the process group ID of the foreground process associated with the terminal. Otherwise, -1 shall be returned and errno set to indicate the error.

Errors

The tcgetpgrp() function shall fail if:

• EBADF - The fildes argument is not a valid file descriptor.

• EINVAL - The file associated with fildes is not a terminal, and the server handling it reports unsupported requests with EINVAL (see POSIX deviations).

• ENOTTY - The calling process does not have a controlling terminal, or the file is not the controlling terminal.

POSIX deviations

If the file associated with fildes is not a terminal, the error reported by tcgetpgrp() depends on the server handling the file. The function is implemented on top of ioctl(), and the kernel forwards every request to the server without checking the type of the file. Servers that do not handle terminal requests report them either with ENOTTY (for example files in jffs2) or with EINVAL (for example pipes and files in dummyfs).