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GETPID(2) System Calls Manual GETPID(2)

getpid, getppid
get parent or calling process identification

#include <unistd.h>
pid_t
getpid(void);
pid_t
getppid(void);

getpid() returns the process ID of the calling process. Though the ID is guaranteed to be unique, it should NOT be used for constructing temporary file names; see mkstemp(3) instead.
getppid() returns the process ID of the parent of the calling process.

These functions are always successful, and no return value is reserved to indicate an error.

gethostid(3)

getpid() and getppid() conform to IEEE Std 1003.1-2008 (“POSIX.1”).
March 30, 2013 OpenBSD-5.8