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32 .\" @(#)dup.2 8.1 (Berkeley) 6/4/93
33 .\" $FreeBSD: src/lib/libc/sys/dup.2,v 1.9.2.6 2001/12/14 18:34:00 ru Exp $
34 .\" $DragonFly: src/lib/libc/sys/dup.2,v 1.2 2003/06/17 04:26:47 dillon Exp $
42 .Nd duplicate an existing file descriptor
50 .Fn dup2 "int oldd" "int newd"
53 duplicates an existing object descriptor and returns its value to
60 is a small non-negative integer index in
61 the per-process descriptor table. The value must be less
62 than the size of the table, which is returned by
64 The new descriptor returned by the call
65 is the lowest numbered descriptor
66 currently not in use by the process.
68 The object referenced by the descriptor does not distinguish
78 are duplicate references to an open
84 calls all move a single pointer into the file,
85 and append mode, non-blocking I/O and asynchronous I/O options
86 are shared between the references.
87 If a separate pointer into the file is desired, a different
88 object reference to the file must be obtained by issuing an
92 The close-on-exec flag on the new file descriptor is unset.
96 the value of the new descriptor
98 is specified. If this descriptor is already in use and
102 the descriptor is first deallocated as if a
107 is not a valid descriptor, then
116 is a valid descriptor, then
118 is successful, and does nothing.
120 The value -1 is returned if an error occurs in either call.
121 The external variable
123 indicates the cause of the error.
134 is not a valid active descriptor
136 Too many descriptors are active.
142 .Xr getdtablesize 2 ,
152 function calls are expected to conform to
159 function call appeared in