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<a name="open"></a>
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<a name="open-1"></a>
<h4 class="unnumberedsubsubsec">open</h4>
<a name="index-open_002c-file_002di_002fo-system-call"></a>

<dl compact="compact">
<dt>Synopsis:</dt>
<dd><div class="smallexample">
<pre class="smallexample">int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);
</pre></div>

</dd>
<dt>Request:</dt>
<dd><p>&lsquo;<samp>Fopen,<var>pathptr</var>/<var>len</var>,<var>flags</var>,<var>mode</var></samp>&rsquo;
</p>
<p><var>flags</var> is the bitwise <code>OR</code> of the following values:
</p>
<dl compact="compact">
<dt><code>O_CREAT</code></dt>
<dd><p>If the file does not exist it will be created.  The host
rules apply as far as file ownership and time stamps
are concerned.
</p>
</dd>
<dt><code>O_EXCL</code></dt>
<dd><p>When used with <code>O_CREAT</code>, if the file already exists it is
an error and open() fails.
</p>
</dd>
<dt><code>O_TRUNC</code></dt>
<dd><p>If the file already exists and the open mode allows
writing (<code>O_RDWR</code> or <code>O_WRONLY</code> is given) it will be
truncated to zero length.
</p>
</dd>
<dt><code>O_APPEND</code></dt>
<dd><p>The file is opened in append mode.
</p>
</dd>
<dt><code>O_RDONLY</code></dt>
<dd><p>The file is opened for reading only.
</p>
</dd>
<dt><code>O_WRONLY</code></dt>
<dd><p>The file is opened for writing only.
</p>
</dd>
<dt><code>O_RDWR</code></dt>
<dd><p>The file is opened for reading and writing.
</p></dd>
</dl>

<p>Other bits are silently ignored.
</p>

<p><var>mode</var> is the bitwise <code>OR</code> of the following values:
</p>
<dl compact="compact">
<dt><code>S_IRUSR</code></dt>
<dd><p>User has read permission.
</p>
</dd>
<dt><code>S_IWUSR</code></dt>
<dd><p>User has write permission.
</p>
</dd>
<dt><code>S_IRGRP</code></dt>
<dd><p>Group has read permission.
</p>
</dd>
<dt><code>S_IWGRP</code></dt>
<dd><p>Group has write permission.
</p>
</dd>
<dt><code>S_IROTH</code></dt>
<dd><p>Others have read permission.
</p>
</dd>
<dt><code>S_IWOTH</code></dt>
<dd><p>Others have write permission.
</p></dd>
</dl>

<p>Other bits are silently ignored.
</p>

</dd>
<dt>Return value:</dt>
<dd><p><code>open</code> returns the new file descriptor or -1 if an error
occurred.
</p>
</dd>
<dt>Errors:</dt>
<dd>
<dl compact="compact">
<dt><code>EEXIST</code></dt>
<dd><p><var>pathname</var> already exists and <code>O_CREAT</code> and <code>O_EXCL</code> were used.
</p>
</dd>
<dt><code>EISDIR</code></dt>
<dd><p><var>pathname</var> refers to a directory.
</p>
</dd>
<dt><code>EACCES</code></dt>
<dd><p>The requested access is not allowed.
</p>
</dd>
<dt><code>ENAMETOOLONG</code></dt>
<dd><p><var>pathname</var> was too long.
</p>
</dd>
<dt><code>ENOENT</code></dt>
<dd><p>A directory component in <var>pathname</var> does not exist.
</p>
</dd>
<dt><code>ENODEV</code></dt>
<dd><p><var>pathname</var> refers to a device, pipe, named pipe or socket.
</p>
</dd>
<dt><code>EROFS</code></dt>
<dd><p><var>pathname</var> refers to a file on a read-only filesystem and
write access was requested.
</p>
</dd>
<dt><code>EFAULT</code></dt>
<dd><p><var>pathname</var> is an invalid pointer value.
</p>
</dd>
<dt><code>ENOSPC</code></dt>
<dd><p>No space on device to create the file.
</p>
</dd>
<dt><code>EMFILE</code></dt>
<dd><p>The process already has the maximum number of files open.
</p>
</dd>
<dt><code>ENFILE</code></dt>
<dd><p>The limit on the total number of files open on the system
has been reached.
</p>
</dd>
<dt><code>EINTR</code></dt>
<dd><p>The call was interrupted by the user.
</p></dd>
</dl>

</dd>
</dl>

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