---
name: "setsid"
section: "2"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/setsid/2"
---

# setsid(2)

create session and set process group ID

## NAME

**setsid** – create session and set process group ID

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*pid\_t*\

**setsid**(*void*);

## DESCRIPTION

The **setsid**() system call creates a new session. The calling process is the session leader of the new session, is the process group leader of a new process group and has no controlling terminal. The calling process is the only process in either the session or the process group.

## RETURN VALUES

Upon successful completion, the **setsid**() system call returns the value of the process group ID of the new process group, which is the same as the process ID of the calling process. If an error occurs, **setsid**() returns -1 and the global variable *errno* is set to indicate the error.

## ERRORS

The **setsid**() system call will fail if:

- \[EPERM\]

  The calling process is already a process group leader, or the process group ID of a process other than the calling process matches the process ID of the calling process.

## SEE ALSO

[setpgid(2)](/setpgid/2.md), [tcgetpgrp(3)](/tcgetpgrp/3.md), [tcsetpgrp(3)](/tcsetpgrp/3.md)

## STANDARDS

The **setsid**() system call is expected to be compliant with the ISO/IEC 9945-1:1990 (“POSIX.1”) specification.