man(1) Manual page archive

     FORK(2)                                                   FORK(2)

          fork, rfork - manipulate process resources

          #include <u.h>
          #include <libc.h>

          int fork(void)

          int rfork(int flags)

          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
          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).


          intro(2), proc(3),

          These functions set errstr.