NAME
setsid - create session and set process group ID
SYNOPSIS
#include <unistd.h>
pid_t setsid(void);
DESCRIPTION
The setsid() function shall create a new session, if the calling
process is not a process group leader. Upon return the calling process
shall be the session leader of this new session, shall be the process
group leader of a new process group, and shall have no controlling
terminal. The process group ID of the calling process shall be set
equal to the process ID of the calling process. The calling process
shall be the only process in the new process group and the only process
in the new session.
RETURN VALUE
Upon successful completion, setsid() shall return the value of the new
process group ID of the calling process. Otherwise, it shall return
(pid_t)-1 and set errno to indicate the error.
ERRORS
The setsid() function shall 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.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
The setsid() function is similar to the setpgrp() function of System V.
System V, without job control, groups processes into process groups and
creates new process groups via setpgrp(); only one process group may be
part of a login session.
Job control allows multiple process groups within a login session. In
order to limit job control actions so that they can only affect
processes in the same login session, this volume of
IEEE Std 1003.1-2001 adds the concept of a session that is created via
setsid(). The setsid() function also creates the initial process group
contained in the session. Additional process groups can be created via
the setpgid() function. A System V process group would correspond to a
POSIX System Interfaces session containing a single POSIX process
group. Note that this function requires that the calling process not be
a process group leader. The usual way to ensure this is true is to
create a new process with fork() and have it call setsid(). The fork()
function guarantees that the process ID of the new process does not
match any existing process group ID.
FUTURE DIRECTIONS
None.
SEE ALSO
getsid() , setpgid() , setpgrp() , the Base Definitions volume of
IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .