delete a descriptor
Standard C Library (libc, -lc)
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
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
However, the semantics of System V and IEEE Std 1003.1-1988
(“POSIX.1”) dictate that all
advisory record locks associated with a file for a given process are removed
when any file descriptor for that file is closed by that
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
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
the process would normally inherit these descriptors. Most of the
descriptors can be rearranged with
or deleted with
close() before the
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 “
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.
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.
close() system call will fail if:
- The fd argument is not an active descriptor.
- An interrupt was received.
- The underlying object did not fit, cached data was lost.
- 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
supplied file descriptor is deallocated and therefore is no longer
close() system call is expected to conform to
IEEE Std 1003.1-1990 (“POSIX.1”).
close() function appeared in
Version 1 AT&T UNIX.