FORK(2) FORK(2) NAME fork, rfork - manipulate process resources SYNOPSIS #include <u.h> #include <libc.h> int fork(void) int rfork(int flags) DESCRIPTION Forking is the only way new processes are created. The flags argument to rfork selects which resources of the invoking process (parent) are shared by the new process (child) or initialized to their default values. The resources include the file name space, the open file descriptor table (which, when shared, permits processes to open and close files for other processes), the set of envi- ronment variables (see env(3)), the note group (the set of processes that receive notes written to a member's notepg file; see proc(3)), and open files. Flags is the logical OR of some subset of RFPROC If set a new process is created; otherwise changes affect the current process. RFNOWAIT If set, the child process will be dissociated from the parent. Upon exit the child will leave no Waitmsg (see wait(2)) for the parent to collect. RFNAMEG If set, the new process inherits a copy of the parent's name space; otherwise the new process shares the parent's name space. The tag space for rendezvous(2) is considered part of the name space. Is mutually exclusive with RFCNAMEG. RFCNAMEG If set, the new process starts with a clean name space. A new name space must be built from a mount of an open file descriptor. Is mutually exclusive with RFNAMEG. RFENVG If set, the environment variables are copied; oth- erwise the two processes share environment vari- ables. Is mutually exclusive with RFCENVG. RFCENVG If set, the new process starts with an empty envi- ronment. Is mutually exclusive with RFENVG. RFNOTEG Each process is a member of a group of processes that all receive notes when a note is written to any of their notepg files (see proc(3)). The group of a new process is by default the same as its parent, but if RFNOTEG is set (regardless of RFPROC), the process becomes the first in a new group, isolated from previous processes. FORK(2) FORK(2) RFFDG If set, the invoker's file descriptor table (see intro(2)) is copied; otherwise the two processes share a single table. RFCFDG If set, the new process starts with a clean file descriptor table. Is mutually exclusive with RFFDG. RFMEM If set, the kernel will mark segments of type data and bss as shared. The child will then inherit all the shared segments the parent process owns. Other segment types will be unaffected. Subsequent forks by the parent will then propagate the shared data and bss between children. The stack segment is always split. May be set only with RFPROC. File descriptors in a shared file descriptor table are kept open until either they are explicitly closed or all pro- cesses sharing the table exit. If RFPROC is set, the value returned in the parent process is the process id of the child process; the value returned in the child is zero. Without RFPROC, the return value is zero. Process ids range from 1 to the maximum integer (int) value. Rfork will sleep, if necessary, until required pro- cess resources are available. Fork is just a call of rfork(RFFDG|RFPROC). SOURCE /sys/src/libc/9syscall /sys/src/libc/9sys/fork.c SEE ALSO intro(2), proc(3), DIAGNOSTICS These functions set errstr.