The getpid() function returns the process ID of the calling process.

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

The getppid() function returns the parent process ID of the calling process.

The getpgid() function returns the process group ID of the process whose process ID is equal to pid, or the process group ID of the calling process, if pid is equal to 0.

Upon successful completion, these functions return the process group ID. Otherwise, getpgid() returns (pid_t)-1 and sets errno to indicate the error.

The getpgid() function will fail if:

EPERM

The process whose process ID is equal to pid is not in the same session as the calling process, and the implementation does not allow access to the process group ID of that process from the calling process.

ESRCH

There is no process with a process ID equal to pid.

The getpgid() function may fail if:

EINVAL

The value of the pid argument is invalid.

See attributes(5) for descriptions of the following attributes:

intro(2), exec(2), fork(2), getsid(2), setpgid(2), setpgrp(2), setsid (2), signal(3C), attributes(5)