setsid(2)
NAME
setsid - create session and set process group ID
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
pid_t setsid(void);
DESCRIPTION
The setsid() function creates a new session, if the calling
process is not a process group leader. Upon return the cal-
ling process will be the session leader of this new session,
will be the process group leader of a new process group, and
will have no controlling terminal. The process group ID of
the calling process will be set equal to the process
ID of the calling process. The calling process will be the
only process in the new process group and the only process
in the new session.
RETURN VALUES
Upon successful completion, setsid() returns the value of
the process group ID of the calling process. Otherwise it
returns (pid_t)-1 and sets errno to indicate the error.
ERRORS
The setsid() function 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.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | Async-Signal-Safe |
|_____________________________|_____________________________|
SEE ALSO
getsid(2), setpgid(2), setpgrp(2), attributes(5)
WARNINGS
A call to setsid() by a process that is a process group
leader will fail. A process can become a process group
leader by being the last member of a pipeline started by a
job control shell. Thus, a process that expects to be part
of a pipeline, and that calls setsid(), should always first
fork; the parent should exit and the child should call set-
sid(). This will ensure that the calling process will work
reliably when started by both job control shells and non-job
control shells.
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