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dup - dups of open files


bind #d /fd







The dup device serves a one-level directory containing files whose names are decimal numbers. Each such file also has an associated control file. A file of name n corresponds to open file descriptor n in the current process.

A sys-open(2) of file n results in a file descriptor identical to what would be returned from a system call sys->dup(n, -1). Note that the result is no longer a file in the dup device.

The stat operation returns information about the device file, not the open file it points to. A stat of #d/n will contain n for the name, 0 for the length, and 400, 200, or 600 (octal) for the mode, depending on whether the dup target is open for reading, writing, or both.

A file of name nctl may be read to discover the properties of the associated file descriptor, in format identical to that of the fd file in prog(3).





DUP(3) Rev:  Tue Mar 31 02:42:38 GMT 2015