Manual browser: close(2)

CLOSE(2) System Calls Manual CLOSE(2)


closedelete a descriptor


Standard C Library (libc, -lc)


#include <unistd.h>

close(int d);


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 handled.

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 rearranged 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:
d is not an active descriptor.
An interrupt was received.


The close() function conforms to IEEE Std 1003.1-1990 (“POSIX.1”).
April 19, 1994 NetBSD 7.0