close.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)close.2	8.1	9/11/90
.TH close 2
.SH Name
close \- delete a descriptor
.SH Syntax
.B close(\fIfd\fP)
.br
.B "int \fIfd\fP;"
.SH Description
.NXR "close system call"
.NXA "close system call" "open system call"
.NXA "file descriptor" "process reference table"
.NXR "file descriptor" "deleting"
The
.PN close
call deletes a descriptor from the per-process object
reference table.
If the descriptor is the last reference to the underlying object, then
the object is deactivated.  For example, on the last close
of a file, the current 
.PN seek
pointer associated with the file is lost.
On the last close of a socket,
.PN close
discards 
associated naming information and queued data. 
On the last close of a file holding an advisory lock, the lock is released. 
For further information, see
.MS flock 2 .
.PP
A process's descriptors are automatically closed when a process exits, 
but because each process can have a limited number of active
descriptors,
.PN close
is necessary for programs that deal with many descriptors.
.PP
When a process forks, all descriptors for the new child process
reference the same objects as they did in the parent process before the fork.
For further information, see 
.MS fork 2 .
If a new process is then to be run using 
.PN execve ,
the process would normally inherit these descriptors.  Most
of the descriptors can be rearranged with the
.PN dup2 
system call or deleted with
.PN close
before 
.PN execve
is called. However, if any descriptors are
needed if the 
.PN execve
fails, they must be closed if the execve succeeds.
For this reason, the call, fcntl(d, F_SETFD, 1), is provided. This call
arranges that a descriptor is closed after a successful
.PN execve
call.
The call, fcntl(d, F_SETFD, 0), restores the default,
which is to not close the descriptor.
.PP
When 
.PN close
is used on a descriptor that refers to a
remote file over NFS, and that file has been modified by
using 
.MS write 2 , 
then any cached 
.PN write
data is flushed
before 
.PN close
returns. If an asynchronous
write error has occurred previously with this remote file, or
occurred as part of the flush operation described above,
then 
.PN close 
returns \-1 and errno will be set to the
error code. The return code from 
.MS close 2 
should be inspected
by any program that can 
.PN write
over NFS.
.SH Return Values
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned, and the global integer variable,
.I errno,
is set to indicate the error.  
.SH Diagnostics
The
.PN close
system call fails under the following conditions:
.TP 15
[EBADF]
\fID\fP is not an active descriptor.  
.TP 15
[EINTR]
The
.PN close
function was interrupted by a signal.
.PP
If an error occurs on an
asynchronous write over NFS, the error cannot always 
be returned from a
.PN write
system call.  The error code is returned on
.PN close
or
.PN fsync . 
The following are NFS-only error messages:
.TP 15
[EACCESS]
The requested address is protected, and the current user
has inadequate permission to access it.
.TP 15
[ENOSPC]
There is no free space remaining on the file system containing
the file.
.TP 15
[EDQUOT]
The user's quota of disk blocks on the file system containing
the file has been exhausted.
.TP 15
[EIO]
An I/O error occurred while reading from or writing to the file
system.
.TP 15
[EROFS]
The file is on a read-only file system.
.TP 15
[ESTALE]
The
.I fd
argument is invalid because the file referred
to by that file handle no longer exists or has been revoked.
.TP
[ETIMEDOUT]
A write operation failed
because the server
did not properly respond after a period
of time that is dependent on the
.MS mount 8nfs
options.
.SH See Also
accept(2), execve(2), fcntl(2), flock(2), fsync(2),
open(2), pipe(2), socket(2), socketpair(2), write(2)