open(2) open(2)
NAME
open - open for reading or writing
SYNOPSIS
#include <fcntl.h>
int open (path, oflag [ , mode ] )
char *path;
int oflag, 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
constructed by or-ing flags from the following list (only
one of the first three flags below may be used):
ORDONLY Open for reading only.
OWRONLY Open for writing only.
ORDWR Open for reading and writing.
ONDELAY This flag may affect subsequent reads and writes.
See read(2) and write(3).
When opening a FIFO with ORDONLY or OWRONLY set:
If ONDELAY 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 ONDELAY is 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 communication
line:
If ONDELAY is set:
The open will return without waiting for
carrier.
If ONDELAY is clear:
The open will block until carrier is present.
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open(2) open(2)
OAPPEND If set, the file pointer will be set to the end of
the file prior to each write.
OCREAT If the file exists, this flag has no effect.
Otherwise, 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, and the low-order 12 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).
OTRUNC If the file exists, its length is truncated to 0
and the mode and owner are unchanged.
OEXCL If OEXCL and OCREAT are set, open will fail if
the file exists.
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 set to remain open across exec
system calls. See fcntl(2).
The named file is opened unless one or more of the following
are true:
[ENOTDIR] A component of the path prefix is not a
directory.
[ENOENT] OCREAT is not set and the named file does
not exist.
[EACCES] A component of the path prefix denies search
permission.
[EACCES] oflag permission is denied for the named
file.
[EISDIR] The named file is a directory and oflag is
write or read/write.
[EROFS] The named file resides on a read-only file
system and oflag is write or read/write.
[EMFILE] Twenty (20) file descriptors are currently
open.
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open(2) open(2)
[ENXIO] The named file is a character special or
block special file, and the device associated
with this special 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.
Note: If you are running an NFS system and
you are accessing a shared binary remotely,
it is possible that you will not get this
errno.
[EFAULT] path points outside the allocated address
space of the process.
[EEXIST] OCREAT and OEXCL are set, and the named
file exists.
[ENXIO] ONDELAY is set, the named file is a FIFO,
OWRONLY is set, and no process has the file
open for reading.
[EINTR] A signal was caught during the open system
call.
[ENFILE] The system file table is full.
RETURN VALUE
Upon successful completion, the file descriptor is returned.
Otherwise, a value of -1 is returned and errno is set to
indicate the error.
SEE ALSO
chmod(2), close(2), creat(2), fcntl(2), lseek(2), read(2),
umask(2), write(2).
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