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close — close a file descriptor


#include <unistd.h>

int close(int fd);


close() closes a file descriptor, so that it no longer refers to any file and may be reused. Any record locks (see fcntl(2)) held on the file it was associated with, and owned by the process, are removed (regardless of the file descriptor that was used to obtain the lock).

If fd is the last file descriptor referring to the underlying open file description (see open(2)), the resources associated with the open file description are freed; if the file descriptor was the last reference to a file which has been removed using unlink(2), the file is deleted.

Return Value

close() returns zero on success. On error, -1 is returned, and errno is set appropriately.


fd isn't a valid open file descriptor.
The close() call was interrupted by a signal; see signal(7).
An I/O error occurred.

Conforming to

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.


Not checking the return value of close() is a common but nevertheless serious programming error. It is quite possible that errors on a previous write(2) operation are first reported at the final close(). Not checking the return value when closing the file may lead to silent loss of data. This can especially be observed with NFS and with disk quota. Note that the return value should be used only for diagnostics. In particular close() should not be retried after an EINTR since this may cause a reused file descriptor from another thread to be closed.

A successful close does not guarantee that the data has been successfully saved to disk, as the kernel uses the buffer cache to defer writes. Typically, filesystems do not flush buffers when a file is closed. If you need to be sure that the data is physically stored on the underlying disk, use fsync(2). (It will depend on the disk hardware at this point.)

The close-on-exec file descriptor flag can be used to ensure that a file descriptor is automatically closed upon a successful execve(2); see fcntl(2) for details.

It is probably unwise to close file descriptors while they may be in use by system calls in other threads in the same process. Since a file descriptor may be reused, there are some obscure race conditions that may cause unintended side effects.

When dealing with sockets, you have to be sure that there is no recv(2) still blocking on it on another thread, otherwise it might block forever, since no more messages will be send via the socket. Be sure to use shutdown(2) to shut down all parts the connection before closing the socket.

See Also

fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3)


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Referenced By

archive_read(3), archive_write(3), bpf(2), closedir(3), closefrom(3), cpuset(7), drm(7), dup(2), epoll(7), epoll_create(2), eventfd(2), explain(1), explain(3), explain_close(3), explain_close_or_die(3), explain_lca2010(1), fanotify(7), fclose(3), fcloseall(3), filter_create_fd(3), flock(2), fts(3), funopen(3), getdtablesize(3), inotify(7), mkfifo(3), mount.fuse(8), mq_overview(7), nbdkit-plugin(3), ncl_cgm(3), nfs(5), open(2), perfmonctl(2), pidfile(3), pipe(7), __pmConnectLogger(3), posix_spawn(3), read(2), rmt(1), shm_open(3), shm_overview(7), signalfd(2), socat(1), socket(2), socket(7), spu_create(2), spufs(7), spu_run(2), star(1), stdio(3), stress-ng(1), syscalls(2), systemd.socket(5), tar_open(3), timerfd_create(2), write(2), zip_fdopen(3).

2016-10-08 Linux Linux Programmer's Manual