4.3BSD-UWisc/man/cat2/open.2
OPEN(2) UNIX Programmer's Manual OPEN(2)
NAME
open - open a file for reading or writing, or create a new
file
SYNOPSIS
#include <sys/file.h>
open(path, flags, mode)
char *path;
int flags, mode;
DESCRIPTION
_O_p_e_n opens the file _p_a_t_h for reading and/or writing, as
specified by the _f_l_a_g_s argument and returns a descriptor for
that file. The _f_l_a_g_s 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
_m_o_d_e as described in _c_h_m_o_d(2) and modified by the process'
umask value (see _u_m_a_s_k(2)).
_P_a_t_h is the address of a string of ASCII characters
representing a path name, terminated by a null character.
The flags specified are formed by _o_r'ing the following
values
O_RDONLY open for reading only
O_WRONLY open for writing only
O_RDWR open for reading and writing
O_NDELAY 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
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_NDELAY 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 (not
currently implemented).
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
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OPEN(2) UNIX Programmer's Manual OPEN(2)
of the file.
The new descriptor is set to remain open across _e_x_e_c_v_e sys-
tem calls; see _c_l_o_s_e(2).
The system imposes a limit on the number of file descriptors
open simultaneously by one process. _G_e_t_d_t_a_b_l_e_s_i_z_e(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 char-
acters, 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 argu-
ments specify it is to be opened for writ-
ting.
[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.
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OPEN(2) UNIX Programmer's Manual OPEN(2)
[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 direc-
tory entry or allocating the inode for
O_CREAT.
[ETXTBSY] The file is a pure procedure (shared text)
file that is being executed and the _o_p_e_n call
requests write access.
[EFAULT] _P_a_t_h 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)
Printed 12/27/86 May 14, 1986 3