Manpage of GETPID
GETPIDSection: Linux Programmer's Manual (2)
NAMEgetpid, getppid - get process identification
DESCRIPTIONgetpid() 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. 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_SUBREAPERoperation).
ERRORSThese functions are always successful.
CONFORMING TOPOSIX.1-2001, POSIX.1-2008, 4.3BSD, SVr4.
NOTESIf the caller's parent is in a different PID namespace (see pid_namespaces(7)), getppid() returns 0.
C library/kernel differencesFrom 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.
SEE ALSOclone(2), fork(2), kill(2), exec(3), mkstemp(3), tempnam(3), tmpfile(3), tmpnam(3), credentials(7), pid_namespaces(7)
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