getpid, getppid — get process identification
#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).
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).
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.
On Alpha, instead of a pair of getpid() and getppid() system calls, a single
getxpid() system call is
provided, which returns a pair of PID and parent PID. The
glibc getpid() and
getppid() wrapper functions
transparently deal with this. See syscall(2) for details
regarding register mapping.
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 5.11 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/.
|
Copyright 1993 Rickard E. Faith (faithcs.unc.edu) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |