GETPID(2) Linux Programmer's Manual GETPID(2)
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.
These functions are always successful.
POSIX.1-2001, 4.3BSD, SVr4.
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), cre-
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Linux 2008-09-23 GETPID(2)