NAME    [Toc]    [Back]

     fork - create a new process

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #include <unistd.h>

     pid_t
     fork(void);

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     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.  This limit is configurationdependent.


     [EAGAIN]  The limit RLIMIT_NPROC on the total number of processes under
               execution by this user id would be exceeded.

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

SEE ALSO    [Toc]    [Back]

     execve(2), setrlimit(2), wait(2)

STANDARDS    [Toc]    [Back]

     The fork() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').

HISTORY    [Toc]    [Back]

     A fork() system call appeared in Version 6 AT&T UNIX.

BSD                              June 4, 1993                              BSD