open, create, close – open a file for reading or writing, create file
int open(char *file, int omode)
int create(char *file, int omode, ulong perm)
int close(int fd)
for I/O and returns an associated file descriptor.
is one of
asking for permission to read, write, read and write, or execute, respectively.
In addition, there are three values that can be ORed with the
says to truncate the file
to zero length before opening it;
says to close the file when an
system call is made;
says to remove the file when it is closed (by everyone who has a copy of the file descriptor).
fails if the file does not exist or the user does not have
permission to open it for the requested purpose
for a description of permissions).
The user must have write permission on the
bit is set.
(unlike the implicit
is actually identical to
creates a new
or prepares to rewrite an existing
opens it according to
(as described for
and returns an associated file descriptor.
If the file is new,
the owner is set to the userid of the creating process group;
the group to that of the containing directory;
the permissions to
ANDed with the permissions of the containing directory.
If the file already exists,
it is truncated to 0 length,
and the permissions, owner, and group remain unchanged.
The created file is a directory if the
bit is set in
an exclusive-use file if the
bit is set, and an append-only file if the
bit is set.
Exclusive-use files may be open for I/O by only one client at a time,
but the file descriptor may become invalid if no I/O is done
for an extended period; see
fails if the path up to the last element of
cannot be evaluated, if the user doesn’t have write permission
in the final directory, if the file already exists and
does not permit the access defined by
or if there are no free file descriptors.
In the last case, the file may be created even when
an error is returned.
If the file is new and the directory in which it is created is
a union directory (see
then the constituent directory where the file is created
depends on the structure of the union: see
may succeed even if the file exists, a special mechanism is necessary
for those applications that require an atomic create operation.
bit is set in the
the call succeeds only if the file does not already exist;
closes the file associated with a file descriptor.
Provided the file descriptor is a valid open descriptor,
is guaranteed to close it; there will be no error.
Files are closed automatically upon termination of a process;
allows the file descriptor to be reused.
These functions set