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CLOSE(2) System Calls Manual CLOSE(2)

closedelete a descriptor

#include <unistd.h>

close(int d);

The () call deletes a descriptor d 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 pointer associated with the file is lost; on the last close of a socket(2), associated naming information and queued data are discarded; and on the last close of a file holding an advisory lock, the lock is released (see 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 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 process, the () 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 image is to then 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 () before the execve(2) is attempted, but since some of these descriptors may still be needed should the execve(2) fail, it is necessary to arrange for them to be closed when the execve(2) succeeds. For this reason, the call (d, F_SETFD, FD_CLOEXEC) is provided, which arranges that a descriptor will be closed after a successful execve(2); the call fcntl(d, F_SETFD, 0) restores the default, which is to not close the descriptor.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

close() will fail if:

d is not an active descriptor.
An interrupt was received.
An I/O error occurred while writing to the file system.

accept(2), closefrom(2), dup2(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)

close() conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

The close() system call first appeared in Version 1 AT&T UNIX.

December 10, 2014 OpenBSD-6.6