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DUP3(3) Library Functions Manual DUP3(3) NAME dup3 -- duplicate an existing file descriptor LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <fcntl.h> #include <unistd.h> int dup3(int oldd, int newd, int flags); DESCRIPTION The dup3() function duplicates an existing object descriptor while al- lowing the value of the new descriptor to be specified. The close-on-exec flag on the new file descriptor is determined by the O_CLOEXEC bit in flags. The close-on-fork flag on the new file descriptor is determined by the O_CLOFORK bit in flags. If oldd != newd and flags == 0, the behavior is identical to dup2(oldd, newd). If oldd == newd, then dup3() fails, unlike dup2(2). RETURN VALUES The value -1 is returned if an error occurs. The external variable errno indicates the cause of the error. ERRORS The dup3() function fails if: [EBADF] The oldd argument is not a valid active descriptor or the newd argument is negative or exceeds the max- imum allowable descriptor number [EINVAL] The oldd argument is equal to the newd argument. [EINVAL] The flags argument has bits set other than O_CLOEXEC or O_CLOFORK. SEE ALSO accept(2), close(2), dup2(2), fcntl(2), getdtablesize(2), open(2), pipe(2), socket(2), socketpair(2) STANDARDS The dup3() function does not conform to any standard. HISTORY The dup3() function appeared in FreeBSD 10.0. The O_CLOFORK flag ap- peared in FreeBSD 15.0. FreeBSD 15.0 May 17, 2025 DUP3(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY
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