1 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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25 .TH GETPID 2 2017-05-03 "Linux" "Linux Programmer's Manual"
27 getpid, getppid \- get process identification
29 .B #include <sys/types.h>
31 .B #include <unistd.h>
33 .B pid_t getpid(void);
35 .B pid_t getppid(void);
38 returns the process ID of the calling process.
39 (This is often used by
40 routines that generate unique temporary filenames.)
43 returns the process ID of the parent of the calling process.
44 This will be either the ID of the process that created this process using
46 or, if that process has already terminated,
47 the ID of the process to which this process has been reparented (either
49 or a "subreaper" process defined via the
51 .BR PR_SET_CHILD_SUBREAPER
54 These functions are always successful.
56 POSIX.1-2001, POSIX.1-2008, 4.3BSD, SVr4.
58 If the caller's parent is in a different PID namespace (see
59 .BR pid_namespaces (7)),
63 .SS C library/kernel differences
64 Since glibc version 2.3.4,
65 the glibc wrapper function for
68 so as to avoid additional system calls when a process calls
71 Normally this caching is invisible,
72 but its correct operation relies on support in the wrapper functions for
77 if an application bypasses the glibc wrappers for these system calls by using
81 in the child will return the wrong value
82 (to be precise: it will return the PID of the parent process).
83 .\" The following program demonstrates this "feature":
85 .\" #define _GNU_SOURCE
86 .\" #include <sys/syscall.h>
87 .\" #include <sys/wait.h>
88 .\" #include <stdio.h>
89 .\" #include <stdlib.h>
90 .\" #include <unistd.h>
93 .\" main(int argc, char *argv[])
95 .\" /* The following statement fills the getpid() cache */
97 .\" printf("parent PID = %ld\n", (long) getpid());
99 .\" if (syscall(SYS_fork) == 0) {
100 .\" if (getpid() != syscall(SYS_getpid))
101 .\" printf("child getpid() mismatch: getpid()=%ld; "
102 .\" "syscall(SYS_getpid)=%ld\n",
103 .\" (long) getpid(), (long) syscall(SYS_getpid));
104 .\" exit(EXIT_SUCCESS);
110 for discussion of a case where
112 may return the wrong value even when invoking
114 via the glibc wrapper function.
125 .BR pid_namespaces (7)