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CLOSE(2) NetBSD System Calls Manual CLOSE(2)
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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 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 han-
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 rear-
ranged 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''.
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate the error.
close() will fail if:
[EBADF] d is not an active descriptor.
[EINTR] An interrupt was received.
accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2),
The close() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').
The close() function appeared in Version 1 AT&T UNIX.
NetBSD 9.1 September 1, 2019 NetBSD 9.1