OPEN(2-SVR4) RISC/os Reference Manual OPEN(2-SVR4)
NAME
open - open for reading or writing
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int open (const char *path, int oflag, ... /* modet mode
*/);
DESCRIPTION
path points to a path name naming a file. open opens a file
descriptor for the named file and sets the file status flags
according to the value of oflag. oflag values are con-
structed by OR-ing Flags from the following list (only one
of the first three flags below may be used):
O_RDONLY Open for reading only.
O_WRONLY Open for writing only.
O_RDWR Open for reading and writing.
O_NDELAY or O_NONBLOCK These flags may affect subse-
quent reads and writes [see read(2) and
write(2)]. If both O_NDELAY and O_NONBLOCK
are set, O_NONBLOCK will take precedence.
When opening a FIFO with O_RDONLY or O_WRONLY
set:
If O_NDELAY or O_NONBLOCK is set: An open
for reading-only will return without
delay; an open for writing-only will
return an error if no process currently
has the file open for reading.
If O_NDELAY and O_NONBLOCK are clear: An
open for reading-only will block until a
process opens the file for writing; an
open for writing-only will block until a
process opens the file for reading.
When opening a file associated with a terminal
line:
If O_NDELAY or O_NONBLOCK is set: The
open will return without waiting for the
device to be ready or available; subse-
quent behavior of the device is device
specific.
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If O_NDELAY and O_NONBLOCK are clear: The
open will block until the device is ready
or available.
O_APPEND If set, the file pointer will be set to the
end of the file prior to each write.
O_SYNC When opening a regular file, this flag affects
subsequent writes. If set, each write(2) will
wait for both the file data and file status to
be physically updated.
O_NOCTTY If set and the file is a terminal, the termi-
nal will not be allocated as the calling
process's controlling terminal.
O_CREAT If the file exists, this flag has no effect,
except as noted under O_EXCL below. Other-
wise, the file is created and the owner ID of
the file is set to the effective user ID of
the process, the group ID of the file is set
to the effective group ID of the process, or
if the S_ISGID bit is set in the directory in
which the file is being created, the file's
group ID is set to the group ID of its parent
directory. If the group ID of the new file
does not match the effective group ID or one
of the supplementary groups IDs, the S_ISGID
bit is cleared. The access permission bits of
the file mode are set to the value of mode,
modified as follows [see creat(2)]:
All bits set in the file mode creation
mask of the process are cleared [see
umask(2)].
The save text image after execution bit of
the mode is cleared [see chmod(2)].
O_TRUNC If the file exists, its length is truncated to
0 and the mode and owner are unchanged.
O_TRUNC has no effect on FIFO special files or
directories.
O_EXCL If O_EXCL and O_CREAT are set, open will fail
if the file exists. The check for the
existence of the file and the creation of the
file if it does not exist is atomic with
respect to other processes executing open nam-
ing the same filename in the same directory
with O_EXCL and O_CREAT set.
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OPEN(2-SVR4) RISC/os Reference Manual OPEN(2-SVR4)
When opening a STREAMS file, oflag may be constructed from
O_NDELAY or O_NONBLOCK OR-ed with either O_RDONLY, O_WRONLY,
or O_RDWR. Other flag values are not applicable to STREAMS
devices and have no effect on them. The values of O_NDELAY
and O_NONBLOCK affect the operation of STREAMS drivers and
certain system calls [see read(2), getmsg(2), putmsg(2), and
write(2)]. For drivers, the implementation of O_NDELAY and
O_NONBLOCK is device specific. Each STREAMS device driver
may treat these options differently.
When open is invoked to open a named stream, and the connld
module [see connld(7)] has been pushed on the pipe, open
blocks until the server process has issued an I_RECVFD ioctl
[see streamio(7)] to receive the file descriptor.
If path is a symbolic link and O_CREAT and O_EXCL are set,
the link is not followed.
The file pointer used to mark the current position within
the file is set to the beginning of the file.
The new file descriptor is the lowest numbered file descrip-
tor available and is set to remain open across exec system
calls [see fcntl(2)].
Certain flag values can be set following open as described
in fcntl(2).
If O_CREAT is set and the file did not previously exist,
upon successful completion open marks for update the
st_atime, st_ctime and st_mtime fields of the file and the
st_ctime and st_mtime fields of the parent directory.
If O_TRUNC is set and the file did previously exist, upon
successful completion open marks for update the st_ctime and
st_mtime fields of the file.
The named file is opened unless one or more of the following
are true:
EACCES The file does not exist and write per-
mission is denied by the parent direc-
tory of the file to be created.
EACCES O_TRUNC is specified and write permis-
sion is denied
EACCES A component of the path prefix denies
search permission.
EACCES oflag permission is denied for an exist-
ing file.
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EAGAIN The file exists, mandatory file/record
locking is set, there are outstanding
record locks on the file [see chmod(2)]
and O_TRUNC is specified.
EEXIST O_CREAT and O_EXCL are set, and the
named file exists.
EFAULT path points outside the allocated
address space of the process.
EINTR A signal was caught during the open sys-
tem call.
EIO A hangup or error occurred during the
open of the STREAMS-based device.
EISDIR The named file is a directory and oflag
is write or read/write.
ELOOP Too many symbolic links were encountered
in translating path.
EMFILE The process has too many open files [see
getrlimit(2)].
EMULTIHOP Components of path require hopping to
multiple remote machines and the file
system does not allow it.
ENAMETOOLONG The length of the path argument exceeds
{PATH_MAX}, or the length of a path com-
ponent exceeds {NAME_MAX} while
{_POSIX_NO_TRUNC} is in effect.
ENFILE The system file table is full.
ENOENT O_CREAT is not set and the named file
does not exist.
ENOENT O_CREAT is set and a component of the
path prefix does not exist or is the
null pathname.
ENOLINK path points to a remote machine, and the
link to that machine is no longer
active.
ENOMEM The system is unable to allocate a send
descriptor.
ENOSPC O_CREAT and O_EXCL are set, and the file
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system is out of inodes.
ENOSPC O_CREAT is set and the directory that
would contain the file cannot be
extended.
ENOSR Unable to allocate a stream.
ENOTDIR A component of the path prefix is not a
directory.
ENXIO The named file is a character special or
block special file, and the device asso-
ciated with this special file does not
exist.
ENXIO O_NDELAY or O_NONBLOCK is set, the named
file is a FIFO, O_WRONLY is set, and no
process has the file open for reading.
ENXIO A STREAMS module or driver open routine
failed.
EROFS The named file resides on a read-only
file system and either O_WRONLY, O_RDWR,
O_CREAT, or O_TRUNC is set in oflag (if
the file does not exist).
ETXTBSY The file is a pure procedure (shared
text) file that is being executed and
oflag is write or read/write.
SEE ALSO
intro(2), chmod(2), close(2), creat(2), dup(2), exec(2),
fcntl(2), getrlimit(2), lseek(2), read(2), getmsg(2),
putmsg(2), stat(2), umask(2), write(2), stat(5).
DIAGNOSTICS
Upon successful completion, the file descriptor is returned.
Otherwise, a value of -1 is returned and errno is set to
indicate the error.
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