getpid() returns the process ID of the calling process. (This is often
used by routines that generate unique temporary filenames.)
getppid() returns the process ID of the parent of the calling process.
These functions are always successful.
POSIX.1-2001, POSIX.1-2008, 4.3BSD, SVr4.
If the caller's parent is in a different PID namespace (see pid_names-
paces(7)), getppid() returns 0.
C library/kernel differences
Since glibc version 2.3.4, the glibc wrapper function for getpid()
caches PIDs, so as to avoid additional system calls when a process
calls getpid() repeatedly. Normally this caching is invisible, but its
correct operation relies on support in the wrapper functions for
fork(2), vfork(2), and clone(2): if an application bypasses the glibc
wrappers for these system calls by using syscall(2), then a call to
getpid() in the child will return the wrong value (to be precise: it
will return the PID of the parent process). See also clone(2) for dis-
cussion of a case where getpid() may return the wrong value even when
invoking clone(2) via the glibc wrapper function.
clone(2), fork(2), kill(2), exec(3), mkstemp(3), tempnam(3), tmp-
file(3), tmpnam(3), credentials(7), pid_namespaces(7)
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Linux 2015-07-23 GETPID(2)
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