close

CLOSE(2)                     BSD System Calls Manual                    CLOSE(2)

NAME
     close — delete a descriptor

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.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,
     the object 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)).  However, the semantics of System V and
     IEEE Std 1003.1-1988 (“POSIX.1”) dictate that all fcntl(2) advisory record
     locks associated with a file for a given process are removed when any file
     descriptor for that file is closed by that process.

     When a process exits, all associated file descriptors are freed, but since
     there is a limit on active descriptors per processes, the close() system
     call is useful when a large quantity of file descriptors are being handled.

     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 descriptors can be
     rearranged with dup2(2) or deleted with close() before the execve(2) 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)”
     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 VALUES
     The close() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     The close() system call will fail if:

     [EBADF]            The fd argument is not an active descriptor.

     [EINTR]            An interrupt was received.

     [ENOSPC]           The underlying object did not fit, cached data was lost.

     [ECONNRESET]       The underlying object was a stream socket that was shut
                        down by the peer before all pending data was delivered.

     In case of any error except EBADF, the supplied file descriptor is
     deallocated and therefore is no longer valid.

SEE ALSO
     accept(2), closefrom(2), execve(2), fcntl(2), flock(2), open(2), pipe(2),
     socket(2), socketpair(2)

STANDARDS
     The close() system call is expected to conform to ISO/IEC 9945-1:1990
     (“POSIX.1”).

HISTORY
     The close() function appeared in Version 1 AT&T UNIX.

BSD                             December 1, 2017                             BSD