open(2) open(2)
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 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 or ONONBLOCK
These flags may affect subsequent reads and writes [see
read(2) and write(2)]. If both ONDELAY and ONONBLOCK
are set, ONONBLOCK will take precedence.
When opening a FIFO with ORDONLY or OWRONLY set:
If ONDELAY or ONONBLOCK 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 and ONONBLOCK 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 ONDELAY or ONONBLOCK is set: The open will
return without waiting for the device to be ready
or available; subsequent behavior of the device is
device specific.
If ONDELAY and ONONBLOCK are clear: The open
will block until the device is ready or available.
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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.
OSYNC 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.
ONOCTTY If set and the file is a terminal, the terminal will
not be allocated as the calling process's controlling
terminal.
OCREAT If the file exists, this flag has no effect, except as
noted under OEXCL below. Otherwise, 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 SISGID 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 SISGID
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)].
OTRUNC If the file exists, its length is truncated to 0 and
the mode and owner are unchanged. OTRUNC has no
effect on FIFO special files or directories.
OEXCL If OEXCL and OCREAT 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
naming the same filename in the same directory with
OEXCL and OCREAT set.
When opening a STREAMS file, oflag may be constructed from ONDELAY
or ONONBLOCK OR-ed with either ORDONLY, OWRONLY , or ORDWR.
Other flag values are not applicable to STREAMS devices and have no
effect on them. The values of ONDELAY and ONONBLOCK 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 ONDELAY and ONONBLOCK is device specific. Each STREAMS device
driver may treat these options differently.
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open(2) open(2)
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 IRECVFD ioctl [see streamio(7)] to
receive the file descriptor.
If path is a symbolic link and OCREAT and OEXCL 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 descriptor
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 OCREAT is set and the file did not previously exist, upon
successful completion open marks for update the statime, stctime
and stmtime fields of the file and the stctime and stmtime fields
of the parent directory.
If OTRUNC is set and the file did previously exist, upon successful
completion open marks for update the stctime and stmtime 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 permission is
denied by the parent directory of the file to be
created.
EACCES OTRUNC is specified and write permission is
denied
EACCES A component of the path prefix denies search
permission.
EACCES oflag permission is denied for an existing file.
EAGAIN The file exists, mandatory file/record locking is
set, and there are outstanding record locks on
the file [see chmod(2)].
EEXIST OCREAT and OEXCL are set, and the named file
exists.
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open(2) open(2)
EFAULT path points outside the allocated address space
of the process.
EINTR A signal was caught during the open system 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
{PATHMAX}, or the length of a path component
exceeds {NAMEMAX} while {POSIXNOTRUNC} is in
effect.
ENFILE The system file table is full.
ENOENT OCREAT is not set and the named file does not
exist.
ENOENT OCREAT 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 OCREAT and OEXCL are set, and the file system
is out of inodes.
ENOSPC OCREAT 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.
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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.
ENXIO ONDELAY or ONONBLOCK is set, the named file is
a FIFO, OWRONLY 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 OWRONLY, ORDWR, OCREAT, or OTRUNC
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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