getpid man page
getpid, getppid — get process identification
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. This will be either the ID of the process that created this process using fork(), or, if that process has already terminated, the ID of the process to which this process has been reparented (either init(1) or a "subreaper" process defined via the prctl(2) PR_SET_CHILD_SUBREAPER operation).
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_namespaces(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 discussion 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), tmpfile(3), tmpnam(3), credentials(7), pid_namespaces(7)
This page is part of release 4.11 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
capget(2), clone(2), credentials(7), fanotify(7), fcntl(2), gawk(1), gettid(2), libcap(3), pid_namespaces(7), procenv(1), pthreads(7), raise(3), sched_setaffinity(2), sched_setscheduler(2), signal-safety(7), slapd(8), slapd.conf(5), slapd-config(5), syscalls(2).
The man page getppid(2) is an alias of getpid(2).