getpid man page

getpid, getppid ā€” get process identification


#include <sys/types.h>
#include <unistd.h>

pid_t getpid(void);
pid_t getppid(void);


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.

Conforming to

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.

See Also

clone(2), fork(2), kill(2), exec(3), mkstemp(3), tempnam(3), tmpfile(3), tmpnam(3), credentials(7), pid_namespaces(7)


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Referenced By

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).

2017-05-03 Linux Programmer's Manual