getpid, getppid — 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.


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)


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  Copyright 1993 Rickard E. Faith (

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