CLOSE(2)CLOSE(2)NAMEclose - delete a descriptor
SYNOPSIS
#include <libc.h> int close(int fd);
DESCRIPTION
The close system 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 lseek(2) pointer associated with the file is lost;
on the last close of a socket(2) its associated naming information and
queued data are discarded; on the last close of a file holding any
locks the locks are released (see further flock(2) and fcntl(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, the process
would normally inherit these descriptors. Most of the descriptors can
be rearranged with dup2 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,
FD_CLOEXEC)'' (POSIX) or ``fcntl(d, F_SETFD, 1)'' (BSD) 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.
You should always check the return value of close when closing a file
that might be on a remote file system, such as NFS or AFS. The reason
is this: remote file systems often cache writes on the client side and
return a successful error code to the process calling write(2).
However, an error may occur when the cached file data is finally
written. For example, the server could be out of disk space. close
forces all cached writes to be completed to the server. If the call to
close fails, then the file has not been written out successfully, and
you should give the user the option of saving the file to a different
place.
When all file descriptors associated with a pipe or FIFO special file
have been closed, any data remaining in the pipe or FIFO is discarded.
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
The close function will fail if:
[EBADF] fd is not an active descriptor.
[EINTR] The close function was interrupted by a signal.
SEE ALSOaccept(2), flock(2), open(2), pipe(2), socket(2), socketpair(2),
execve(2), fcntl(2), creat(2), dup(2), fork(2), unlink(2)
August 1, 1992 CLOSE(2)
