close(2)

NAME

close − delete a descriptor

SYNTAX

close(d)
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, then it 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() associated naming information and queued data are discarded. On the last close of a file holding an advisory lock the lock is released. For further information, see flock(.).

A close of all of a process’s descriptors is automatic on exit, but since there is a limit on the number of active descriptors per process, close is necessary for programs which deal with many descriptors.

When a process forks all descriptors for the new child process reference the same objects as they did in the parent before the fork. For further information, see fork(.). If a new process is then to be run using execve(,), the process would normally inherit these descriptors. Most of the descriptors can be rearranged with dup2() 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 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.

RETURN VALUE

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.

DIAGNOSTICS

The close system call will fail if:

[EBADF]
D is not an active descriptor. If an error occurs on an asynchronous write over NFS, the error cannot be returned from the write system call. The error code will be returned on close or fsync.

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