28.7.2 Process Group Functions

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)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

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)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

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.

Function: pid_t getpgrp (void)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

The getpgrp function returns the process group ID of the calling process.

Function: int getpgid (pid_t pid)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

The getpgid function 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)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

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)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

This is the BSD Unix name for setpgid. Both functions do exactly the same thing.