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CLOSE(2) | System Calls Manual | CLOSE(2) |
NAME¶
close
—
delete a descriptor
LIBRARY¶
Standard C Library (libc, -lc)SYNOPSIS¶
#include
<unistd.h>
int
close
(int
fd);
DESCRIPTION¶
Theclose
() 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 further flock(2)).
However, the semantics of System V and IEEE Std
1003.1-1988 (“POSIX.1”) dictate that all
fcntl(2) advisory record locks associated with a
file for a given process are removed when any
file descriptor for that file is closed by that process.
When a process exits, all associated file 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 forks (see 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(2) 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, FD_CLOEXEC)
” 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 VALUES¶
Theclose
() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate
the error.
ERRORS¶
Theclose
() system call will fail if:
- [
EBADF
] - The fd argument is not an active descriptor.
- [
EINTR
] - An interrupt was received.
- [
ENOSPC
] - The underlying object did not fit, cached data was lost.
- [
ECONNRESET
] - The underlying object was a stream socket that was shut down by the peer before all pending data was delivered.
EBADF
, the
supplied file descriptor is deallocated and therefore is no longer valid.
SEE ALSO¶
accept(2), closefrom(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)STANDARDS¶
Theclose
() system call is expected to
conform to IEEE Std 1003.1-1990
(“POSIX.1”).
HISTORY¶
Theclose
() function appeared in
Version 7 AT&T UNIX.September 11, 2013 | Debian |