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BSD 2.11 - man page for open (bsd section 2)

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OPEN(2) 										  OPEN(2)

NAME
       open - open a file for reading or writing, or create a new file

SYNOPSIS
       #include <fcntl.h>

       open(path, flags, mode)
       char *path;
       int flags, mode;

DESCRIPTION
       Open  opens  the  file path for reading and/or writing, as specified by the flags argument
       and returns a descriptor for that file.	The flags argument may indicate the file is to be
       created	if  it does not already exist (by specifying the O_CREAT flag), in which case the
       file is created with mode mode as described in chmod(2) and modified by the process' umask
       value (see umask(2)).

       Path  is  the address of a string of ASCII characters representing a path name, terminated
       by a null character.  The flags specified are formed by or'ing the following values

	       O_RDONLY open for reading only
	       O_WRONLY open for writing only
	       O_RDWR	open for reading and writing
	       O_NONBLOCK    do not block on open
	       O_APPEND append on each write
	       O_CREAT	create file if it does not exist
	       O_TRUNC	truncate size to 0
	       O_EXCL	error if create and file exists
	       O_NOCTTY do not acquire as controlling terminal
	       O_SHLOCK atomically obtain a shared lock
	       O_EXLOCK atomically obtain an exclusive lock

       Opening a file with O_APPEND set causes each write on the file to be appended to the  end.
       If  O_TRUNC  is	specified  and the file exists, the file is truncated to zero length.  If
       O_EXCL is set with O_CREAT, then if the file already exists, the open  returns  an  error.
       This  can  be used to implement a simple exclusive access locking mechanism.  If O_EXCL is
       set and the last component of the pathname is a symbolic link, the open will fail even  if
       the  symbolic link points to a non-existent name.  If the O_NONBLOCK flag is specified and
       the open call would result in the process being blocked for some reason (e.g. waiting  for
       carrier	on  a  dialup  line),  the  open returns immediately.  The first time the process
       attempts to perform i/o on the open file it will block.

       The flag O_NOCTTY indicates that even if the file is a terminal device,	the  call  should
       not  result  in	acquiring  the terminal device as the controlling terminal of the caller.
       This flag is not the default and is currently unimplemented (it will be Real Soon Now).

       When opening a file, a lock with flock(2) semantics can be obtained  by	setting  O_SHLOCK
       for  a  shared  lock, or O_EXLOCK for an exclusive lock.  If creating a file with O_CREAT,
       the request for the lock will never fail.

       Upon successful completion a non-negative integer termed a file	descriptor  is	returned.
       The file pointer used to mark the current position within the file is set to the beginning
       of the file.

       The new descriptor is set to remain open across execve system calls; see close(2).

       The system imposes a limit on the number of file descriptors open  simultaneously  by  one
       process.  Getdtablesize(2) returns the current system limit.

ERRORS
       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.

       [EINVAL]       The pathname contains a character with the high-order bit set.

       [ENAMETOOLONG] A  component  of a pathname exceeded 255 characters, or an entire path name
		      exceeded 1023 characters.

       [ENOENT]       O_CREAT is not set and the named file does not exist.

       [ENOENT]       A component of the path name that must exist does not exist.

       [EACCES]       Search permission is denied for a component of the path prefix.

       [EACCES]       The required permissions (for reading and/or writing) are  denied  for  the
		      named flag.

       [EACCES]       O_CREAT  is  specified, the file does not exist, and the directory in which
		      it is to be created does not permit writing.

       [ELOOP]	      Too many symbolic links were encountered in translating the pathname.

       [EISDIR]       The named file is a directory, and the arguments specify it is to be opened
		      for writting.

       [EROFS]	      The  named  file	resides on a read-only file system, and the file is to be
		      modified.

       [EMFILE]       The system limit for open file descriptors per  process  has  already  been
		      reached.

       [ENFILE]       The system file table is full.

       [ENXIO]	      The named file is a character special or block special file, and the device
		      associated with this special file does not exist.

       [ENOSPC]       O_CREAT is specified, the file does not exist, and the directory	in  which
		      the entry for the new file is being placed cannot be extended because there
		      is no space left on the file system containing the directory.

       [ENOSPC]       O_CREAT is specified, the file does not exist, and there are no free inodes
		      on the file system on which the file is being created.

       [EDQUOT]       O_CREAT  is  specified, the file does not exist, and the directory in which
		      the entry for the new fie is being placed cannot be  extended  because  the
		      user's quota of disk blocks on the file system containing the directory has
		      been exhausted.

       [EDQUOT]       O_CREAT is specified, the file does not exist,  and  the	user's	quota  of
		      inodes  on  the  file  system  on  which the file is being created has been
		      exhausted.

       [EIO]	      An I/O error occurred while making the directory entry  or  allocating  the
		      inode for O_CREAT.

       [ETXTBSY]      The  file is a pure procedure (shared text) file that is being executed and
		      the open call requests write access.

       [EFAULT]       Path points outside the process's allocated address space.

       [EEXIST]       O_CREAT and O_EXCL were specified and the file exists.

       [EOPNOTSUPP]   An attempt was made to open a socket (not currently implemented).

SEE ALSO
       chmod(2), close(2), dup(2), getdtablesize(2), lseek(2), read(2), write(2), umask(2)

4th Berkeley Distribution		   Nov 30, 1994 				  OPEN(2)
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