| CLOSE(2) | System Calls Manual | CLOSE(2) | 
close —
#include <unistd.h>
int
  
  close(int
    d);
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”.
close() will fail if:
close() function conforms to IEEE
  Std 1003.1-1990 (“POSIX.1”).
close() function appeared in
  Version 1 AT&T UNIX.
| September 1, 2019 | NetBSD 9.4 |