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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 $
41 .Nd duplicate an existing file descriptor
49 .Fn dup2 "int oldd" "int newd"
52 duplicates an existing object descriptor and returns its value to
59 is a small non-negative integer index in
60 the per-process descriptor table. The value must be less
61 than the size of the table, which is returned by
63 The new descriptor returned by the call
64 is the lowest numbered descriptor
65 currently not in use by the process.
67 The object referenced by the descriptor does not distinguish
77 are duplicate references to an open
83 calls all move a single pointer into the file,
84 and append mode, non-blocking I/O and asynchronous I/O options
85 are shared between the references.
86 If a separate pointer into the file is desired, a different
87 object reference to the file must be obtained by issuing an
91 The close-on-exec flag on the new file descriptor is unset.
95 the value of the new descriptor
97 is specified. If this descriptor is already in use and
101 the descriptor is first deallocated as if a
106 is not a valid descriptor, then
115 is a valid descriptor, then
117 is successful, and does nothing.
119 The value -1 is returned if an error occurs in either call.
120 The external variable
122 indicates the cause of the error.
133 is not a valid active descriptor
135 Too many descriptors are active.
141 .Xr getdtablesize 2 ,
151 function calls are expected to conform to
158 function call appeared in