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close - delete a descriptor
Standard C Library (libc, -lc)
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
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.
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
The close() system call will fail if:
[EBADF] The d argument is not an active descriptor.
[EINTR] An interrupt was received.
[ENOSPC] The underlying object did not fit, cached data was
[ECONNRESET] The underlying object was a stream socket that was
shut down by the peer before all pending data was
accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2),
The close() system call is expected to conform to ISO/IEC 9945-1:1990
The close() function appeared in Version 7 AT&T UNIX.