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NAME | SYNOPSIS | DESCRIPTION | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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GETPID(2) Linux Programmer's Manual GETPID(2)
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 (PID) 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.
From a kernel perspective, the PID (which is shared by all of the
threads in a multithreaded process) is sometimes also known as the
thread group ID (TGID). This contrasts with the kernel thread ID
(TID), which is unique for each thread. For further details, see
gettid(2) and the discussion of the CLONE_THREAD flag in clone(2).
C library/kernel differences
From glibc version 2.3.4 up to and including version 2.24, the glibc
wrapper function for getpid() cached PIDs, with the goal of avoiding
additional system calls when a process calls getpid() repeatedly.
Normally this caching was invisible, but its correct operation relied
on support in the wrapper functions for fork(2), vfork(2), and
clone(2): if an application bypassed the glibc wrappers for these
system calls by using syscall(2), then a call to getpid() in the
child would return the wrong value (to be precise: it would return
the PID of the parent process). In addition, there were cases where
getpid() could return the wrong value even when invoking clone(2) via
the glibc wrapper function. (For a discussion of one such case, see
BUGS in clone(2).) Furthermore, the complexity of the caching code
had been the source of a few bugs within glibc over the years.
Because of the aforementioned problems, since glibc version 2.25, the
PID cache is removed: calls to getpid() always invoke the actual
system call, rather than returning a cached value.
clone(2), fork(2), gettid(2), kill(2), exec(3), mkstemp(3),
tempnam(3), tmpfile(3), tmpnam(3), credentials(7), pid_namespaces(7)
This page is part of release 4.15 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/.
Linux 2017-11-26 GETPID(2)
Pages that refer to this page: gawk(1), capget(2), clone(2), fcntl(2), gettid(2), sched_setaffinity(2), sched_setscheduler(2), syscalls(2), libcap(3), pmnotifyerr(3), raise(3), slapd.conf(5), slapd-config(5), credentials(7), fanotify(7), pid_namespaces(7), pthreads(7), signal-safety(7), slapd(8)
Copyright and license for this manual page
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