OPEN(2) OPEN(2)
NAME
open, creat, close - open a file for reading or writing,
create file
SYNOPSIS
int open(file, rwmode)
char *file;
int creat(file, mode)
char *file;
int close(fildes)
DESCRIPTION
Open opens the file, for reading if rwmode is 0, for writing
if rwmode is 1, or for both if rwmode is 2, and returns an
associated file descriptor. File is a null-terminated
string representing a path name. The file pointer is set to
0.
Creat creates a new file or prepares to rewrite an existing
file, opens it for writing, and returns an associated file
descriptor. If the file is new, the owner is set to the
effective userid of the creating process; the group to that
of the containing directory; the mode to mode as modified by
the mode mask of the creating process; see umask(2). Mode
need not allow writing. If the file already exists, it is
truncated to 0 length; the mode, owner, and group remain
unchanged, and must permit writing.
A program may reserve a filename for exclusive use by call-
ing creat with a mode that forbids writing. If the file
does not exist, creat will succeed; further attempts to
creat the same file will be denied. More sophisticated (but
less portable) concurrent access control may be obtained by
setting the S_ICCTYP field in the mode; see stat(2).
Close closes the file associated with a file descriptor.
Files are closed upon termination of a process, but since
there is a limit on the number of open files per process,
close is necessary for programs which deal with many files.
It is possible to arrange for files to be closed by exec(2);
see FIOCLEX in ioctl(2).
SEE ALSO
dup(2), pipe(2), read(2), exec(2), ioctl(2), stat(2),
unlink(2)
DIAGNOSTICS
open, creat: EACCES, EBUSY, ECONC, EFAULT, EINTR, EIO,
OPEN(2) OPEN(2)
EISDIR, ELOOP, EMFILE, ENFILE, ENOENT, ENOTDIR, EROFS,
ETXTBSY
creat: ENOSPC
close: EBADF
BUGS
It should be possible to call open without waiting for car-
rier on communication lines.
The group of a newly-created file should (once again) be the
effective groupid of the creating process.
The trick of creating a file with an unwritable mode fails
for the super-user.