[MAN] setsid

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SETSID

Section: User Commands (1)
Updated: July 2014
Index Return to Main Contents

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NAME

setsid - run a program in a new session  

SYNOPSIS

setsid [options] program [arguments]  

DESCRIPTION

setsid runs a program in a new session. The command calls fork(2) if already a process group leader. Otherwise, it executes a program in the current process.  

OPTIONS

-c, --ctty

Set the controlling terminal to the current one.

-w, --wait

Wait for the execution of the program to end, and return the exit value of this program as the return value of setsid.

-V, --version

Display version information and exit.

-h, --help

Display help text and exit.

 

SEE ALSO

setsid(2)  

AUTHOR

Rick Sladkey <jrs@world.std.com>  

AVAILABILITY

The setsid command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.

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Index

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

SEE ALSO

AUTHOR

AVAILABILITY

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SETSID

Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
Index Return to Main Contents

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NAME

setsid - creates a session and sets the process group ID  

SYNOPSIS

#include <sys/types.h>
#include <unistd.h>

pid_t setsid(void);
 

DESCRIPTION

setsid() creates a new session if the calling process is not a process group leader. The calling process is the leader of the new session (i.e., its session ID is made the same as its process ID). The calling process also becomes the process group leader of a new process group in the session (i.e., its process group ID is made the same as its process ID).

The calling process will be the only process in the new process group and in the new session.

Initially, the new session has no controlling terminal. For details of how a session acquires a controlling terminal, see credentials(7).  

RETURN VALUE

On success, the (new) session ID of the calling process is returned. On error, (pid_t) -1 is returned, and errno is set to indicate the error.  

ERRORS

EPERM

The process group ID of any process equals the PID of the calling process. Thus, in particular, setsid() fails if the calling process is already a process group leader.

 

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4.  

NOTES

A child created via fork(2) inherits its parent's session ID. The session ID is preserved across an execve(2).

A process group leader is a process whose process group ID equals its PID. Disallowing a process group leader from calling setsid() prevents the possibility that a process group leader places itself in a new session while other processes in the process group remain in the original session; such a scenario would break the strict two-level hierarchy of sessions and process groups. In order to be sure that setsid() will succeed, call fork(2) and have the parent _exit(2), while the child (which by definition can't be a process group leader) calls setsid().

If a session has a controlling terminal, and the CLOCAL flag for that terminal is not set, and a terminal hangup occurs, then the session leader is sent a SIGHUP signal.

If a process that is a session leader terminates, then a SIGHUP signal is sent to each process in the foreground process group of the controlling terminal.  

SEE ALSO

setsid(1), getsid(2), setpgid(2), setpgrp(2), tcgetsid(3), credentials(7), sched(7)  

COLOPHON

This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

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Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

CONFORMING TO

NOTES

SEE ALSO

COLOPHON

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