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close(2) [centos man page]

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

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. When dealing with sockets, you have to be sure that there is no recv(2) still blocking on it on another thread, otherwise it might block forever, since no more messages will be send via the socket. Be sure to use shutdown(2) to shut down all parts the connection before clos- ing the socket. SEE ALSO
fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2007-12-28 CLOSE(2)

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CLOSE(2)							System Calls Manual							  CLOSE(2)

close - delete a descriptor SYNOPSIS
close(d) int d; DESCRIPTION
The close call deletes a descriptor from the per-process object reference table. If this is the last reference to the underlying object, then it will be deactivated. For example, on the last close of a file the current seek pointer associated with the file is lost; on the last close of a socket(2) associated naming information and queued data are discarded; on the last close of a file holding an advisory lock the lock is released (see further flock(2)). A close of all of a process's descriptors is automatic on exit, but since there is a limit on the number of active descriptors per process, close is necessary for programs that deal with many descriptors. When a process forks (see fork(2)), all descriptors for the new child process reference the same objects as they did in the parent before the fork. If a new process is then to be run using execve(2), the process would normally inherit these descriptors. Most of the descrip- tors can be rearranged with dup2(2) or deleted with close before the execve is attempted, but if some of these descriptors will still be needed if the execve fails, it is necessary to arrange for them to be closed if the execve succeeds. For this reason, the call ``fcntl(d, F_SETFD, 1)'' is provided, which arranges that a descriptor will be closed after a successful execve; the call ``fcntl(d, F_SETFD, 0)'' restores the default, which is to not close the descriptor. RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global integer variable errno is set to indicate the error. ERRORS
Close will fail if: [EBADF] D is not an active descriptor. SEE ALSO
accept(2), flock(2), open(2), pipe(2), socket(2), socketpair(2), execve(2), fcntl(2) 4th Berkeley Distribution May 22, 1986 CLOSE(2)
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