| 1 | .\" Copyright (c) 1980 Regents of the University of California.
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| 2 | .\" All rights reserved. The Berkeley software License Agreement
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| 3 | .\" specifies the terms and conditions for redistribution.
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| 4 | .\"
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| 5 | .\" @(#)fork.2 6.4 (Berkeley) 5/22/86
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| 6 | .\"
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| 7 | .TH FORK 2 "May 22, 1986"
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| 8 | .UC
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| 9 | .SH NAME
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| 10 | fork \- create a new process
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| 11 | .SH SYNOPSIS
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| 12 | .nf
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| 13 | .ft B
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| 14 | #include <sys/types.h>
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| 15 | #include <unistd.h>
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| 16 |
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| 17 | pid_t fork(void)
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| 18 | .ft R
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| 19 | .fi
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| 20 | .SH DESCRIPTION
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| 21 | .de SP
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| 22 | .if t .sp 0.4
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| 23 | .if n .sp
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| 24 | ..
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| 25 | .B Fork
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| 26 | causes creation of a new process.
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| 27 | The new process (child process) is an exact copy of the
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| 28 | calling process except for the following:
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| 29 | .RS
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| 30 | .SP
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| 31 | The child process has a unique process ID.
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| 32 | .SP
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| 33 | The child process has a different parent process ID (i.e.,
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| 34 | the process ID of the parent process).
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| 35 | .SP
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| 36 | The child process has its own copy of the parent's descriptors.
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| 37 | These descriptors reference the same underlying objects, so that,
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| 38 | for instance, file pointers in file objects are shared between
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| 39 | the child and the parent, so that an
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| 40 | .BR lseek (2)
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| 41 | on a descriptor in the child process can affect a subsequent
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| 42 | .B read
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| 43 | or
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| 44 | .B write
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| 45 | by the parent.
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| 46 | This descriptor copying is also used by the shell to
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| 47 | establish standard input and output for newly created processes
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| 48 | as well as to set up pipes.
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| 49 | .SP
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| 50 | The child starts with no pending signals and an inactive alarm timer.
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| 51 | .RE
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| 52 | .SH "RETURN VALUE
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| 53 | Upon successful completion, \fBfork\fP returns a value
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| 54 | of 0 to the child process and returns the process ID of the child
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| 55 | process to the parent process. Otherwise, a value of \-1 is returned
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| 56 | to the parent process, no child process is created, and the global
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| 57 | variable \fBerrno\fP is set to indicate the error.
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| 58 | .SH ERRORS
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| 59 | .B Fork
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| 60 | will fail and no child process will be created if one or more of the
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| 61 | following are true:
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| 62 | .TP 15
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| 63 | [EAGAIN]
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| 64 | The system-imposed limit on the total
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| 65 | number of processes under execution would be exceeded.
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| 66 | This limit is configuration-dependent.
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| 67 | (The kernel variable NR_PROCS in <minix/config.h> (Minix), or
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| 68 | <minix/const.h> (Minix-vmd).)
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| 69 | .TP 15
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| 70 | [ENOMEM]
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| 71 | There is insufficient (virtual) memory for the new process.
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| 72 | .SH "SEE ALSO"
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| 73 | .BR execve (2),
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| 74 | .BR wait (2).
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