DUP(3)DUP(3)NAMEdup - 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 con‐
trol file. A file of name n corresponds to open file descriptor n in
the current process.
An open(2) of file n results in a file descriptor identical to what
would be returned from a system call 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 0400, 0200, or 0600 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 asso‐
ciated file descriptor, in format identical to that of the fd file in