dup2 - duplicate a file descriptor
int dup2(int oldfd, int newfd);
dup2 creates a copy of the file descriptor oldfd.
After successful return of dup2(2), the old and new descriptors may be used interchangeably. They share locks, file position pointers and flags; for example, if the file position is modified by using lseek(2) on one of the descriptors, the position is also changed for the other.
The two descriptors do not share the close-on-exec flag, however.
dup2(2) makes newfd be the copy of oldfd, closing newfd first if necessary.
dup2 returns the new descriptor, or -1 if an error occurred (in which case, errno is set appropriately).
- oldfd isn't an open file descriptor, or newfd is out of the allowed range for file descriptors.
- The process already has the maximum number of file descriptors open and tried to open a new one.
The error returned by dup2(2) is different to that returned by fcntl(..., F_DUPFD, ...) (fcntl(2)) when newfd is out of range. On some systems dup2(2) also sometimes returns EINVAL like F_DUPFD.
SVr4, SVID, POSIX, X/OPEN, BSD 4.3. SVr4 documents additional EINTR and ENOLINK error conditions. POSIX.1 adds EINTR.
fcntl(2), open(2), close(2)