CLOSE(2) | System Calls Manual | CLOSE(2) |
close
—
#include <unistd.h>
int
close
(int
d);
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”.
close
() will fail if:
close
() function conforms to IEEE
Std 1003.1-1990 (“POSIX.1”).
close
() function appeared in
Version 1 AT&T UNIX.
September 1, 2019 | NetBSD 9.0 |