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CLOSE(2)                      System Calls Manual                     CLOSE(2)

NAME
     close - delete a descriptor

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     close(int d);

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 flock(2)).

     When a process exits, all associated 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 calls 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() 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 only if
     the execve() succeeds.  For this reason, the system call

           fcntl(d, F_SETFD, 1);

     is provided, which arranges that a descriptor "d" will be closed after a
     successful execve(); the system call

           fcntl(d, F_SETFD, 0);

     restores the default, which is to not close descriptor "d".

RETURN VALUES
     Upon successful completion, a value of 0 is returned.  Otherwise, a value
     of -1 is returned and errno is set to indicate the error.

     In either case, if d was an active descriptor, it is no longer active.
     That is, close() always closes the file descriptor, and, if it was the
     last reference to the underlying object, frees the associated resources
     -- even if some underlying I/O fails or it is interrupted by a signal.

     Callers must not retry failed close(), even on EINTR.  Retrying may
     inadvertently close a descriptor that was created by another thread
     concurrently after the first call to close() failed.

ERRORS
     close() will fail if:

     [EBADF]            d is not an active descriptor.

     [EINTR]            An interrupt was received.

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

STANDARDS
     The close() function conforms to IEEE Std 1003.1-1990 ("POSIX.1").

     The finality of close(), even on error, is not specified by POSIX, but
     most operating systems, including FreeBSD, OpenBSD, Linux, and Solaris,
     implement the same semantics.

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

NetBSD 11.99                   September 1, 2019                  NetBSD 11.99