Here are descriptions of the functions for manipulating process groups.
Your program should include the header files sys/types.h and
unistd.h to use these functions.
— Function: pid_t setsid (void)
The setsid function creates a new session. The calling process
becomes the session leader, and is put in a new process group whose
process group ID is the same as the process ID of that process. There
are initially no other processes in the new process group, and no other
process groups in the new session.
This function also makes the calling process have no controlling terminal.
The setsid function returns the new process group ID of the
calling process if successful. A return value of -1 indicates an
error. The following errno error conditions are defined for this
function:
EPERM
The calling process is already a process group leader, or there is
already another process group around that has the same process group ID.
— Function: pid_t getsid (pid_t pid)
The getsid function returns the process group ID of the session
leader of the specified process. If a pid is 0, the
process group ID of the session leader of the current process is
returned.
In case of error -1 is returned and errno is set. The
following errno error conditions are defined for this function:
ESRCH
There is no process with the given process ID pid.
EPERM
The calling process and the process specified by pid are in
different sessions, and the implementation doesn't allow to access the
process group ID of the session leader of the process with ID pid
from the calling process.
The getpgrp function has two definitions: one derived from BSD
Unix, and one from the POSIX.1 standard. The feature test macros you
have selected (see Feature Test Macros) determine which definition
you get. Specifically, you get the BSD version if you define
_BSD_SOURCE; otherwise, you get the POSIX version if you define
_POSIX_SOURCE or _GNU_SOURCE. Programs written for old
BSD systems will not include unistd.h, which defines
getpgrp specially under _BSD_SOURCE. You must link such
programs with the -lbsd-compat option to get the BSD definition.
— POSIX.1 Function: pid_t getpgrp (void)
The POSIX.1 definition of getpgrp returns the process group ID of
the calling process.
— BSD Function: pid_t getpgrp (pid_t pid)
The BSD definition of getpgrp returns the process group ID of the
process pid. You can supply a value of 0 for the pid
argument to get information about the calling process.
— System V Function: int getpgid (pid_t pid)
getpgid is the same as the BSD function getpgrp. It
returns the process group ID of the process pid. You can supply a
value of 0 for the pid argument to get information about
the calling process.
In case of error -1 is returned and errno is set. The
following errno error conditions are defined for this function:
ESRCH
There is no process with the given process ID pid.
The calling process and the process specified by pid are in
different sessions, and the implementation doesn't allow to access the
process group ID of the process with ID pid from the calling
process.
— Function: int setpgid (pid_t pid, pid_t pgid)
The setpgid function puts the process pid into the process
group pgid. As a special case, either pid or pgid can
be zero to indicate the process ID of the calling process.
This function fails on a system that does not support job control.
See Job Control is Optional, for more information.
If the operation is successful, setpgid returns zero. Otherwise
it returns -1. The following errno error conditions are
defined for this function:
EACCES
The child process named by pid has executed an exec
function since it was forked.
EINVAL
The value of the pgid is not valid.
ENOSYS
The system doesn't support job control.
EPERM
The process indicated by the pid argument is a session leader,
or is not in the same session as the calling process, or the value of
the pgid argument doesn't match a process group ID in the same
session as the calling process.
ESRCH
The process indicated by the pid argument is not the calling
process or a child of the calling process.
— Function: int setpgrp (pid_t pid, pid_t pgid)
This is the BSD Unix name for setpgid. Both functions do exactly
the same thing.
Published under the terms of the GNU General Public License