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close(2) [linux man page]

CLOSE(2)						     Linux Programmer's Manual							  CLOSE(2)

NAME
close - close a file descriptor SYNOPSIS
#include <unistd.h> int close(int fd); DESCRIPTION
close() closes a file descriptor, so that it no longer refers to any file and may be reused. Any record locks (see fcntl(2)) held on the file it was associated with, and owned by the process, are removed (regardless of the file descriptor that was used to obtain the lock). If fd is the last file descriptor referring to the underlying open file description (see open(2)), the resources associated with the open file description are freed; if the descriptor was the last reference to a file which has been removed using unlink(2) the file is deleted. RETURN VALUE
close() returns zero on success. On error, -1 is returned, and errno is set appropriately. ERRORS
EBADF fd isn't a valid open file descriptor. EINTR The close() call was interrupted by a signal; see signal(7). EIO An I/O error occurred. CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001. NOTES
Not checking the return value of close() is a common but nevertheless serious programming error. It is quite possible that errors on a previous write(2) operation are first reported at the final close(). Not checking the return value when closing the file may lead to silent loss of data. This can especially be observed with NFS and with disk quota. A successful close does not guarantee that the data has been successfully saved to disk, as the kernel defers writes. It is not common for a file system to flush the buffers when the stream is closed. If you need to be sure that the data is physically stored use fsync(2). (It will depend on the disk hardware at this point.) It is probably unwise to close file descriptors while they may be in use by system calls in other threads in the same process. Since a file descriptor may be reused, there are some obscure race conditions that may cause unintended side effects. SEE ALSO
fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3) COLOPHON
This page is part of release 3.27 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 2007-12-28 CLOSE(2)

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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 /* See feature_test_macros(7) */ #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 3.27 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 2010-09-10 DUP(2)

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