<!-- Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009, 2013 The President and Fellows of Harvard College. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. --> <html> <head> <title>fork</title> <body bgcolor=#ffffff> <h2 align=center>fork</h2> <h4 align=center>OS/161 Reference Manual</h4> <h3>Name</h3> <p> fork - copy the current process </p> <h3>Library</h3> <p> Standard C Library (libc, -lc) </p> <h3>Synopsis</h3> <p> <tt>#include <unistd.h></tt><br> <br> <tt>pid_t</tt><br> <tt>fork(void);</tt> </p> <h3>Description</h3> <p> <tt>fork</tt> duplicates the currently running process. The two copies are identical, except that one (the "new" one, or "child"), has a new, unique process id, and in the other (the "parent") the process id is unchanged. </p> <p> The process id must be greater than 0. </p> <p> The two processes do not share memory or open file tables; this state is copied into the new process, and subsequent modification in one process does not affect the other. </p> <p> However, the file handle objects the file tables point to are shared, so, for instance, calls to lseek in one process can affect the other. </p> <h3>Return Values</h3> <p> On success, <tt>fork</tt> returns twice, once in the parent process and once in the child process. In the child process, 0 is returned. In the parent process, the process id of the new child process is returned. </p> <p> On error, no new process is created. <tt>fork,</tt> only returns once, returning -1, and <A HREF=errno.html>errno</A> is set according to the error encountered. </p> <h3>Errors</h3> <p> The following error codes should be returned under the conditions given. Other error codes may be returned for other errors not mentioned here. <table width=90%> <tr><td width=5% rowspan=3> </td> <td width=10% valign=top>EMPROC</td> <td>The current user already has too many processes.</td></tr> <tr><td valign=top>ENPROC</td> <td>There are already too many processes on the system.</td></tr> <tr><td valign=top>ENOMEM</td> <td>Sufficient virtual memory for the new process was not available.</td></tr> </table> </p> </body> </html>