close - close a file descriptor
int close(int fildes);
The close() function will deallocate the file descriptor
indicated by fildes. To deallocate means to make the file
descriptor available for return by subsequent calls to
open(2) or other functions that allocate file descriptors.
All outstanding record locks owned by the process on the
file associated with the file descriptor will be removed
(that is, unlocked).
If close() is interrupted by a signal that is to be caught,
it will return -1 with errno set to EINTR and the state of
fildes is unspecified.
When all file descriptors associated with a pipe or FIFO
special file are closed, any data remaining in the pipe or
FIFO will be discarded.
When all file descriptors associated with an open file
description have been closed the open file description will
If the link count of the file is 0, when all file descrip-
tors associated with the file are closed, the space occupied
by the file will be freed and the file will no longer be
If a STREAMS-based (see intro(2)) fildes is closed and the
calling process was previously registered to receive a SIG-
POLL signal (see signal(3C)) for events associated with that
STREAM (see I_SETSIG in streamio(7I)), the calling process
will be unregistered for events associated with the STREAM.
The last close() for a STREAM causes the STREAM associated
with fildes to be dismantled. If O_NONBLOCK and O_NDELAY are
not set and there have been no signals posted for the
STREAM, and if there is data on the module's write queue,
close() waits up to 15 seconds (for each module and driver)
for any output to drain before dismantling the STREAM. The
time delay can be changed via an I_SETCLTIME ioctl(2)
request (see streamio(7I)). If the O_NONBLOCK or O_NDELAY
flag is set, or if there are any pending signals, close()
does not wait for output to drain, and dismantles the STREAM
If fildes is associated with one end of a pipe, the last
close() causes a hangup to occur on the other end of the
pipe. In addition, if the other end of the pipe has been
named by fattach(3C), then the last close() forces the named
end to be detached by fdetach(3C). If the named end has no
open file descriptors associated with it and gets detached,
the STREAM associated with that end is also dismantled.
If fildes refers to the master side of a pseudo-terminal, a
SIGHUP signal is sent to the process group, if any, for
which the slave side of the pseudo-terminal is the control-
ling terminal. It is unspecified whether closing the master
side of the pseudo-terminal flushes all queued input and
If fildes refers to the slave side of a STREAMS-based
pseudo-terminal, a zero-length message may be sent to the
If fildes refers to a socket, close() causes the socket to
be destroyed. If the socket is connection-mode, and the
SOCK_LINGER option is set for the socket, and the socket has
untransmitted data, then close() will block for up to the
current linger interval until all data is transmitted.
Upon successful completion, 0 is returned. Otherwise, -1 is
returned and errno is set to indicate the error.
The close() function will fail if:
EBADF The fildes argument is not a valid file descriptor.
EINTR The close() function was interrupted by a signal.
The fildes argument is on a remote machine and the
link to that machine is no longer active.
There was no free space remaining on the device con-
taining the file.
The close() function may fail if:
EIO An I/O error occurred while reading from or writing to
the file system.
An application that used the stdio function fopen(3C) to
open a file should use the corresponding fclose(3C) function
rather than close().
When a UFS file system is mounted with logging enabled, file
system transactions that free blocks from files might not
actually add those freed blocks to the file system's free
list until some unspecified time in the future. This
behavior improves file system performance but does not con-
form to the POSIX, Single UNIX Specification, SPARC Confor-
mance Definition, System V Application Binary Interface,
System V Interface Definition, and X/Open Portability Guide
Standards, which require that freed space be available
immediately. To enable standards conformance regarding file
deletions or to address the problem of not being able to
grow files on a relatively full UFS file system even after
files have been deleted, disable UFS logging (see
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | Async-Signal-Safe |
mount_ufs(1M), intro(2), creat(2), dup(2), exec(2),
fcntl(2), ioctl(2), open(2) pipe(2), fattach(3C),
fclose(3C), fdetach(3C), fopen(3C), signal(3C), attri-
butes(5), signal(3HEAD), streamio(7I)
Man(1) output converted with