freebsd man page for setsid

SETSID(2)						      BSD System Calls Manual							 SETSID(2)

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), tcgetpgrp(3), tcsetpgrp(3)

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

BSD
								   June 4, 1993 							       BSD