DUP(2) System Calls DUP(2)

dup - duplicate an open file descriptor

#include <unistd.h>
int dup(int fildes);

The dup() function returns a new file descriptor having the following in common with the original open file descriptor fildes:

same open file (or pipe)
same file pointer (that is, both file descriptors share one file pointer)
same access mode (read, write or read/write).

The new file descriptor is set to remain open across exec functions (see fcntl(2)).

The file descriptor returned is the lowest one available.

The dup(fildes) function call is equivalent to:

fcntl(fildes, F_DUPFD, 0)

Upon successful completion, a non-negative integer representing the file descriptor is returned. Otherwise, −1 is returned and errno is set to indicate the error.

The dup() function will fail if:


The fildes argument is not a valid open file descriptor.


A signal was caught during the execution of the dup() function.


The process has too many open files (see getrlimit(2)).


The fildes argument is on a remote machine and the link to that machine is no longer active.

See attributes(7) for descriptions of the following attributes:

Interface Stability Standard
MT-Level Async-Signal-Safe

close(2), creat(2), exec(2), fcntl(2), getrlimit(2), open(2), pipe(2), dup2(3C), lockf(3C), attributes(7), standards(7)

December 28, 1996 OmniOS