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

NAME
     fork - create a new process

SYNOPSIS
     #include <unistd.h>

     pid_t
     fork(void);

DESCRIPTION
     Fork() 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).

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
     indicate the error.

ERRORS
     Fork() will fail and no child process will be created if:

     [EAGAIN]  The system-imposed limit on the total number of processes under
               execution would be exceeded.  The limit is given by the
               sysctl(3) MIB variable KERN_MAXPROC.  (The limit is actually
               one 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 parameter RLIMIT_NPROC would be
               exceeded (see getrlimit(2)).

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

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

HISTORY
     A fork(2) function call appeared in Version 6 AT&T UNIX.

BSD 4                            June 4, 1993                            BSD 4

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

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