Visit Our UNIX and Linux User Community

Linux and UNIX Man Pages

Test Your Knowledge in Computers #932
Difficulty: Easy
Most first-generation personal computers did not keep track of dates and times.
True or False?
Linux & Unix Commands - Search Man Pages

dup(2) [osx man page]

DUP(2)							      BSD System Calls Manual							    DUP(2)

NAME
dup, dup2 -- duplicate an existing file descriptor SYNOPSIS
#include <unistd.h> int dup(int fildes); int dup2(int fildes, int fildes2); DESCRIPTION
Dup() duplicates an existing object descriptor and returns its value to the calling process (fildes2 = dup(fildes)). The argument fildes is a small non-negative integer index in the per-process descriptor table. The value must be less than the size of the table, which is returned by getdtablesize(2). The new descriptor returned by the call is the lowest numbered descriptor currently not in use by the process. The object referenced by the descriptor does not distinguish between fildes and fildes2 in any way. Thus if fildes2 and fildes are duplicate references to an open file, read(2), write(2) and lseek(2) calls all move a single pointer into the file, and append mode, non-blocking I/O and asynchronous I/O options are shared between the references. If a separate pointer into the file is desired, a different object reference to the file must be obtained by issuing an additional open(2) call. The close-on-exec flag on the new file descriptor is unset. In dup2(), the value of the new descriptor fildes2 is specified. If fildes and fildes2 are equal, then dup2() just returns fildes2; no other changes are made to the existing descriptor. Otherwise, if descriptor fildes2 is already in use, it is first deallocated as if a close(2) call had been done first. RETURN VALUES
Upon successful completion, the new file descriptor is returned. Otherwise, a value of -1 is returned and the global integer variable errno is set to indicate the error. ERRORS
The dup() and dup2() system calls will fail if: [EBADF] fildes is not an active, valid file descriptor. [EINTR] Execution is interrupted by a signal. [EMFILE] Too many file descriptors are active. The dup2() system call will fail if: [EBADF] fildes2 is negative or greater than the maximum allowable number (see getdtablesize(2)). SEE ALSO
accept(2), close(2), fcntl(2), getdtablesize(2), open(2), pipe(2), socket(2), socketpair(2) STANDARDS
Dup() and dup2() are expected to conform to IEEE Std 1003.1-1988 (``POSIX.1''). 4th Berkeley Distribution December 1, 2010 4th Berkeley Distribution

Check Out this Related Man Page

dup2(3C)						   Standard C Library Functions 						  dup2(3C)

NAME
dup2 - duplicate an open file descriptor SYNOPSIS
#include <unistd.h> int dup2(int fildes, int fildes2); DESCRIPTION
The dup2() function causes the file descriptor fildes2 to refer to the same file as fildes. The fildes argument is a file descriptor refer- ring to an open file, and fildes2 is a non-negative integer less than the current value for the maximum number of open file descriptors allowed the calling process. See getrlimit(2). If fildes2 already refers to an open file, not fildes, it is closed first. If fildes2 refers to fildes, or if fildes is not a valid open file descriptor, fildes2 will not be closed first. The dup2() function is equivalent to fcntl(fildes, F_DUP2FD, fildes2). RETURN VALUES
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. ERRORS
The dup2() function will fail if: EBADF The fildes argument is not a valid open file descriptor. EBADF The files2 argument is negative or is not less than the current resource limit returned by getrlimit(RLIMIT_NOFILE, ...). EINTR A signal was caught during the dup2() call. EMFILE The process has too many open files. See fcntl(2). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ SEE ALSO
close(2), creat(2), exec(2), fcntl(2), getrlimit(2), open(2), pipe(2), lockf(3C), attributes(5), standards(5) SunOS 5.10 19 Dec 2003 dup2(3C)

Featured Tech Videos