explain_dup2_or_die(3) Library Functions Manual explain_dup2_or_die(3)NAME
explain_dup2_or_die - duplicate a file descriptor and report errors
SYNOPSIS
#include <libexplain/dup2.h>
void explain_dup2_or_die(int oldfd, int newfd);
DESCRIPTION
The explain_dup2_or_die function is used to call the dup2(2) system call. On failure an explanation will be printed to stderr, obtained
from explain_dup2(3), and then the process terminates by calling exit(EXIT_FAILURE).
This function is intended to be used in a fashion similar to the following example:
explain_dup2_or_die(oldfd, newfd);
oldfd The oldfd, exactly as to be passed to the dup2(2) system call.
newfd The newfd, exactly as to be passed to the dup2(2) system call.
Returns:
This function only returns on success. On failure, prints an explanation and exits.
SEE ALSO dup2(2) duplicate a file descriptor
explain_dup2(3)
explain dup2(2) errors
exit(2) terminate the calling process
COPYRIGHT
libexplain version 0.52
Copyright (C) 2008 Peter Miller
explain_dup2_or_die(3)
Check Out this Related Man Page
DUP(2) Linux Programmer's Manual DUP(2)NAME
dup, dup2, dup3 - duplicate a file descriptor
SYNOPSIS
#include <unistd.h>
int dup(int oldfd);
int dup2(int oldfd, int newfd);
#define _GNU_SOURCE
#include <unistd.h>
int dup3(int oldfd, int newfd, int flags);
DESCRIPTION
These system calls create a copy of the file descriptor oldfd.
dup() uses the lowest-numbered unused descriptor for the new descriptor.
dup2() makes newfd be the copy of oldfd, closing newfd first if necessary, but note the following:
* If oldfd is not a valid file descriptor, then the call fails, and newfd is not closed.
* If oldfd is a valid file descriptor, and newfd has the same value as oldfd, then dup2() does nothing, and returns newfd.
After a successful return from one of these system calls, the old and new file descriptors may be used interchangeably. They refer to the
same open file description (see open(2)) and thus share file offset and file status flags; for example, if the file offset is modified by
using lseek(2) on one of the descriptors, the offset is also changed for the other.
The two descriptors do not share file descriptor flags (the close-on-exec flag). The close-on-exec flag (FD_CLOEXEC; see fcntl(2)) for the
duplicate descriptor is off.
dup3() is the same as dup2(), except that:
* The caller can force the close-on-exec flag to be set for the new file descriptor by specifying O_CLOEXEC in flags. See the description
of the same flag in open(2) for reasons why this may be useful.
* If oldfd equals newfd, then dup3() fails with the error EINVAL.
RETURN VALUE
On success, these system calls return the new descriptor. On error, -1 is returned, and errno is set appropriately.
ERRORS
EBADF oldfd isn't an open file descriptor, or newfd is out of the allowed range for file descriptors.
EBUSY (Linux only) This may be returned by dup2() or dup3() during a race condition with open(2) and dup().
EINTR The dup2() or dup3() call was interrupted by a signal; see signal(7).
EINVAL (dup3()) flags contain an invalid value. Or, oldfd was equal to newfd.
EMFILE The process already has the maximum number of file descriptors open and tried to open a new one.
VERSIONS
dup3() was added to Linux in version 2.6.27; glibc support is available starting with version 2.9.
CONFORMING TO
dup(), dup2(): SVr4, 4.3BSD, POSIX.1-2001.
dup3() is Linux-specific.
NOTES
The error returned by dup2() is different from that returned by fcntl(..., F_DUPFD, ...) when newfd is out of range. On some systems
dup2() also sometimes returns EINVAL like F_DUPFD.
If newfd was open, any errors that would have been reported at close(2) time are lost. A careful programmer will not use dup2() or dup3()
without closing newfd first.
SEE ALSO close(2), fcntl(2), open(2)COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2008-10-09 DUP(2)