CLOSE(2)

NAME
close - delete a descriptor

LIBRARY
libc

SYNOPSIS
#include <unistd.h>
int
close(int d);

DESCRIPTION
The close() 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 p1003.1-88 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() function call is useful when a large quantity of file descriptors are being handled.

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, 1)” 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.

IMPLEMENTATION NOTES

In the non-threaded library close() is implemented as the close syscall.

In the threaded library, the close syscall is assembled to _thread_sys_close() and close() is implemented as a function which locks d for read and write, then calls _thread_sys_close(). Before returning, close() unlocks d.

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

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 call is expected to conform to p1003.1-90.

HISTORY
A close() function call appeared in AT&T UNIX.