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FORK(2)                   FreeBSD System Calls Manual                  FORK(2)

NAME
     fork -- create a new process

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     pid_t
     fork(void);

DESCRIPTION
     The fork() system call causes creation of a new process.  The new process
     (child process) is an exact copy of the calling process (parent process)
     except for the following:

           +o   The child process has a unique process ID.

           +o   The child process has a different parent process ID (i.e., the
               process ID of the parent process).

           +o   The child process has its own copy of the parent's descriptors.
               These descriptors reference the same underlying objects, so
               that, for instance, file pointers in file objects are shared
               between the child and the parent, so that an lseek(2) on a
               descriptor in the child process can affect a subsequent read(2)
               or write(2) by the parent.  This descriptor copying is also
               used by the shell to establish standard input and output for
               newly created processes as well as to set up pipes.

           +o   The child process' resource utilizations are set to 0; see
               setrlimit(2).

           +o   All interval timers are cleared; see setitimer(2).

RETURN VALUES
     Upon successful completion, fork() returns a value of 0 to the child
     process and returns the process ID of the child process to the parent
     process.  Otherwise, a value of -1 is returned to the parent process, no
     child process is created, and the global variable errno is set to indi-
     cate the error.

ERRORS
     The fork() system call will fail and no child process will be created if:

     [EAGAIN]           The system-imposed limit on the total number of pro-
                        cesses under execution would be exceeded.  The limit
                        is given by the sysctl(3) MIB variable KERN_MAXPROC.
                        (The limit is actually ten less than this except for
                        the super user).

     [EAGAIN]           The user is not the super user, and the system-imposed
                        limit on the total number of processes under execution
                        by a single user would be exceeded.  The limit is
                        given by the sysctl(3) MIB variable
                        KERN_MAXPROCPERUID.

     [EAGAIN]           The user is not the super user, and the soft resource
                        limit corresponding to the resource argument
                        RLIMIT_NPROC would be exceeded (see getrlimit(2)).

     [ENOMEM]           There is insufficient swap space for the new process.

SEE ALSO
     execve(2), rfork(2), setitimer(2), setrlimit(2), vfork(2), wait(2)

HISTORY
     The fork() function appeared in Version 6 AT&T UNIX.

FreeBSD 6.2                      June 4, 1993                      FreeBSD 6.2

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY

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