CLOSE(2) System Calls Manual CLOSE(2)

closedelete a descriptor

#include <unistd.h>

close(int fildes);

The () 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 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)).

When a process exits, all associated file descriptors are freed, but since there is a limit on active descriptors per processes, 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 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 () 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 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.

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.

The close() system call will fail if:

fildes is not a valid, active file descriptor.
Its execution was interrupted by a signal.
A previously-uncommitted write(2) encountered an input/output error.

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

close() conforms to IEEE Std 1003.1-1988 (“POSIX.1”).

April 19, 1994 BSD 4