NAME

dup − duplicate an open file descriptor

SYNOPSIS

#include <unistd.h>

int dup(int fildes);

DESCRIPTION

fildes is a file descriptor obtained from a creat, open, dup, fcntl, pipe, or ioctl system call.  dup returns a new file descriptor having the following in common with the original:

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 system calls [see fcntl(2)]. 

The file descriptor returned is the lowest one available. 

dup will fail if one or more of the following are true:

EBADF fildes is not a valid open file descriptor. 

EINTR A signal was caught during the dup system call. 

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

ENOLINK fildes is on a remote machine and the link to that machine is no longer active. 

SEE ALSO

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

DIAGNOSTICS

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