---
name: "tcsetsid"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/tcsetsid"
---

# tcsetsid(3)

set session ID associated with a controlling terminal

## NAME

**tcsetsid** – set session ID associated with a controlling terminal

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<termios.h\>**

*int*\

**tcsetsid**(*int fd*, *pid\_t pid*);

## DESCRIPTION

The **tcsetsid**() function sets associates a session identified by *pid* with a controlling terminal specified by *fd*.

This implementation only allows the controlling terminal to be changed by the session leader itself. This implies that *pid* always has to be equal to the process ID.

It is unsupported to associate with a terminal that already has an associated session. Conversely, it is also unsupported to associate to a terminal when the session is already associated with a different terminal.

## ERRORS

If an error occurs, **tcsetsid**() returns -1 and the global variable *errno* is set to indicate the error, as follows:

- \[EBADF\]

  The *fd* argument is not a valid file descriptor.

- \[ENOTTY\]

  The file descriptor represented by *fd* is not a terminal.

- \[EINVAL\]

  The *pid* argument is not equal to the session ID of the calling process.

- \[EPERM\]

  The calling process is not a session leader.

- \[EPERM\]

  The session already has an associated terminal or the terminal already has an associated session.

## SEE ALSO

[getsid(2)](/getsid/2.md), [setsid(2)](/setsid/2.md), [tcgetpgrp(3)](/tcgetpgrp/3.md), [tcgetsid(3)](/tcgetsid/3.md)

## HISTORY

A **tcsetsid**() function first appeared in QNX. It does not comply to any standard.