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<title>accessx()--Determine File Accessibility for a Class of Users</title>
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<h2>accessx()--Determine File Accessibility for a Class of Users</h2>
<div class="box" style="width: 70%;">
<br>
&nbsp;&nbsp;Syntax<br>
<pre>
#include &lt;unistd.h&gt;
int accessx(const char <em>*path</em>, int <em>amode</em>, int <em>who</em>);
</pre>
&nbsp;&nbsp;Service Program Name: QP0LLIB1<br>
<!-- iddvc RMBR -->
<br>
&nbsp;&nbsp;Default Public Authority: *USE<br>
<!-- iddvc RMBR -->
<br>
&nbsp;&nbsp;Threadsafe: Conditional; see <a href="#USAGE_NOTES">Usage Notes</a>.<br>
<!-- iddvc RMBR -->
<br>
</div>
<p>The <strong>accessx()</strong> function determines whether a file can be
accessed by a specified class of users in a particular manner.
The caller must have authority to all components in the path name
prefix. Adopted authority is not used.</p>
<br>
<h3>Parameters</h3>
<dl>
<dt><strong><em>path</em></strong></dt>
<dd>(Input) A pointer to the null-terminated path name for the file to be
checked for accessibility.
<p>This parameter is assumed to be represented in the CCSID (coded character
set identifier) currently in effect for the job. If the CCSID of the job is
65535, this parameter is assumed to be represented in the default CCSID of the
job.</p>
<p><samp>const char</samp> *<em>path</em> is the name of the file whose
accessibility you want to determine. If the named file is a symbolic link,
<strong>accessx()</strong> resolves the symbolic link.</p>
<p>See <a href="accessxu.htm">QlgAccessx</a>-- Determine File Accessibility for
Class of Users (using NLS-enabled path name) for a description and an example
of supplying the <em>path</em> in any CCSID.</p>
<br>
</dd>
<dt><strong><em>amode</em></strong></dt>
<dd>(Input) A bitwise representation of the access permissions to be checked.
<p>The following symbols, which are defined in the
&lt;<strong>unistd.h</strong>&gt; header file, can be used in <em>
amode</em>:</p>
<dl compact>
<dt><em><samp>F_OK</samp></em></dt>
<dd>(<em>x'00'</em>) Tests whether the file exists</dd>
<dt><em><samp>R_OK</samp></em></dt>
<dd>(<em>x'04'</em>) Tests whether the file can be accessed for reading</dd>
<dt><em><samp>W_OK</samp></em></dt>
<dd>(<em>x'02'</em>) Tests whether the file can be accessed for writing</dd>
<dt><em><samp>X_OK</samp></em></dt>
<dd>(<em>x'01'</em>) Tests whether the file can be accessed for execution</dd>
</dl>
<p>You can take the bitwise inclusive OR of any or all of the last three
symbols to test several access modes at once. If you are using F_OK to test for
the existence of the file, you cannot use OR with any of the other symbols. If
any other bits are set in <em>amode</em>, <strong>accessx()</strong> returns
the [EINVAL] error.</p>
<br>
</dd>
<dt><strong><em>who</em></strong></dt>
<dd>(Input) The class of users whose authority is to be checked.
<p>The following symbols, which are defined in the
&lt;<strong>unistd.h</strong>&gt; header file, can be used in <em>who</em>:</p>
<dl compact>
<dt><em><samp>ACC_SELF</samp></em></dt>
<dd>(<em>x'00'</em>) Determines if specified access is permitted for the
current thread. The effective user and group IDs are used.
<p><strong>Note:</strong> If the real and effective user ID are the same and
the real and effective group ID are the same, the request is treated as
ACC_INVOKER. See the Usage Notes for more details.</p>
</dd>
<dt><em><samp>ACC_INVOKER</samp></em></dt>
<dd>(<em>x'01'</em>) Determines if specified access is permitted for the
current thread. The real user and group IDs are used.
<p><strong>Note:</strong> The expression <strong>access</strong>(<em>path,
amode</em>) is equivalent to <strong>accessx</strong>(<em>path, amode,</em>
<strong>ACC_INVOKER</strong>)</p>
</dd>
<dt><em><samp>ACC_OTHERS</samp></em></dt>
<dd>(<em>x'08'</em>) Determines if specified access is permitted for any user
other than the object owner. Only one of <em>R_OK</em>, <em>W_OK</em>, and <em>
X_OK</em> is permitted when <em>who</em> is <em>ACC_OTHERS</em>. Privileged
users (users with *ALLOBJ special authority) are not considered in this
check.<br>
<br>
</dd>
<dt><em><samp>ACC_ALL</samp></em></dt>
<dd>(<em>x'20'</em>) Determines if specified access is permitted for all users.
Only one of <em>R_OK</em>, <em>W_OK</em>, and <em>X_OK</em> is permitted when
<strong>who</strong> is <em>ACC_ALL</em>. Privileged users (users with *ALLOBJ
special authority) are not considered in this check.</dd>
</dl>
</dd>
</dl>
<br>
<h3>Authorities</h3>
<br>
<p><strong><a name="TBLAACCESSX">Authorization Required to Path Prefix for
accessx()</a></strong><br>
</p>
<table border cellpadding="5" width="80%">
<!-- cols="60 20 20" -->
<tr>
<th align="left" valign="bottom">Object Referred to</th>
<th align="left" valign="bottom">Authority Required</th>
<th align="left" valign="bottom">errno</th>
</tr>
<tr>
<td align="left" valign="top" width="90%">Each directory in the path name
preceding the object to be tested</td>
<td align="left" valign="top" width="5%">*X</td>
<td align="left" valign="top" width="5%">EACCES</td>
</tr>
</table>
<p>The following authorities are required if the <strong>who</strong> parameter
is <em>ACC_SELF</em> or <em>ACC_INVOKER</em>. If <em>ACC_SELF</em> is
specified, the effective UID and GID of the caller are used. If <em>
ACC_INVOKER</em> is used, the real UID and GID of the caller are used.</p>
<p><strong><a name="TBLAACCESSX2">Authorization Required to Object for
accessx()</a></strong><br>
</p>
<table border cellpadding="5" width="80%">
<!-- cols="60 20 20" -->
<tr>
<th align="left" valign="bottom">Object Referred to</th>
<th align="left" valign="bottom">Authority Required</th>
<th align="left" valign="bottom">errno</th>
</tr>
<tr>
<td align="left" valign="top" width="90%">Object when R_OK is specified</td>
<td align="left" valign="top" width="5%">*R</td>
<td align="left" valign="top" width="5%">EACCES</td>
</tr>
<tr>
<td align="left" valign="top">Object when W_OK is specified</td>
<td align="left" valign="top">*W</td>
<td align="left" valign="top">EACCES</td>
</tr>
<tr>
<td align="left" valign="top">Object when X_OK is specified</td>
<td align="left" valign="top">*X</td>
<td align="left" valign="top">EACCES</td>
</tr>
<tr>
<td align="left" valign="top">Object when R_OK | W_OK is specified</td>
<td align="left" valign="top">*RW</td>
<td align="left" valign="top">EACCES</td>
</tr>
<tr>
<td align="left" valign="top">Object when R_OK | X_OK is specified</td>
<td align="left" valign="top">*RX</td>
<td align="left" valign="top">EACCES</td>
</tr>
<tr>
<td align="left" valign="top">Object when W_OK | X_OK is specified</td>
<td align="left" valign="top">*WX</td>
<td align="left" valign="top">EACCES</td>
</tr>
<tr>
<td align="left" valign="top">Object when R_OK | W_OK | X_OK is specified</td>
<td align="left" valign="top">*RWX</td>
<td align="left" valign="top">EACCES</td>
</tr>
<tr>
<td align="left" valign="top">Object when F_OK is specified</td>
<td align="left" valign="top">None</td>
<td align="left" valign="top">None</td>
</tr>
</table>
<p>If the thread has *ALLOBJ special authority, <strong>accessx()</strong> with
<em>ACC_SELF</em> or <em>ACC_INVOKER</em> will indicate success for R_OK, W_OK,
or X_OK even if none of the permission bits are set.</p>
<br>
<h3>Return Value</h3>
<dl compact>
<dt><em>0</em></dt>
<dd><strong>accessx()</strong> was successful.</dd>
<dt><em>-1</em></dt>
<dd><strong>accessx()</strong> was not successful (or the specified access is
not permitted for the class of users being checked). The <em>errno</em> global
variable is set to indicate the error.</dd>
</dl>
<br>
<h3>Error Conditions</h3>
<p>If <strong>access()</strong> is not successful, <em>errno</em> usually
indicates one of the following errors. Under some conditions, <em>errno</em>
could indicate an error other than those listed here.</p>
<table cellpadding="5">
<!-- cols="25 75" -->
<tr>
<th align="left" valign="bottom">Error condition</th>
<th align="left" valign="bottom">Additional information</th>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EACCES">EACCES</a>]</em></td>
<td align="left" valign="top">
<p>The class of users specified by the <em>who</em> parameter does not have the
permission indicated by the <em>amode</em> parameter.</p>
<p>If you are accessing a remote file through the Network File System, update
operations to file permissions at the server are not reflected at the client
until updates to data that is stored locally by the Network File System take
place. (Several options on the Add Mounted File System (ADDMFS) command
determine the time between refresh operations of local data.) Access to a
remote file may also fail due to different mappings of user IDs (UID) or group
IDs (GID) on the local and remote systems.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EAGAIN">EAGAIN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EBADFID">EBADFID</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EBADNAME">EBADNAME</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EBUSY">EBUSY</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONVERT">ECONVERT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EDAMAGE">EDAMAGE</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EFAULT">EFAULT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EFILECVT">EFILECVT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EINVAL">EINVAL</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EIO">EIO</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EINTR">EINTR</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ELOOP">ELOOP</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENAMETOOLONG">ENAMETOOLONG</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOENT">ENOENT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOSPC">ENOSPC</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTAVAIL">ENOTAVAIL</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTDIR">ENOTDIR</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTSAFE">ENOTSAFE</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTSUP">ENOTSUP</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EROOBJ">EROOBJ</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ESTALE">ESTALE</a>]</em></td>
<td align="left" valign="top">
<p>If you are accessing a remote file through the Network File System, the file
may have been deleted at the server.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ETXTBSY">ETXTBSY</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EUNKNOWN">EUNKNOWN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
</table>
<p>If interaction with a file server is required to access the object, <em>
errno</em> could indicate one of the following errors:</p>
<table cellpadding="5">
<!-- cols="25 75" -->
<tr>
<th align="left" valign="bottom">Error condition</th>
<th align="left" valign="bottom">Additional information</th>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EADDRNOTAVAIL">EADDRNOTAVAIL</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONNABORTED">ECONNABORTED</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONNREFUSED">ECONNREFUSED</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONNRESET">ECONNRESET</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EHOSTDOWN">EHOSTDOWN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EHOSTUNREACH">EHOSTUNREACH</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENETDOWN">ENETDOWN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENETRESET">ENETRESET</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENETUNREACH">ENETUNREACH</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ESTALE">ESTALE</a>]</em></td>
<td align="left" valign="top">
<p>If you are accessing a remote file through the Network File System, the file
may have been deleted at the server.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ETIMEDOUT">ETIMEDOUT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EUNATCH">EUNATCH</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
</table>
<br>
<br>
<h3>Error Messages</h3>
<p>The following messages may be sent from this function:</p>
<table width="100%" cellpadding="5">
<tr>
<th align="left" valign="top">Message ID</th>
<th align="left" valign="top">Error Message Text</th>
</tr>
<tr>
<td width="15%" valign="top">CPE3418 E</td>
<td width="85%" valign="top">Possible APAR condition or hardware failure.</td>
</tr>
<tr>
<td valign="top">CPFA0D4 E</td>
<td valign="top">File system error occurred. Error number &amp;1.</td>
</tr>
<tr>
<td valign="top">CPF3CF2 E</td>
<td valign="top">Error(s) occurred during running of &amp;1 API.</td>
</tr>
<tr>
<td valign="top">CPF9872 E</td>
<td valign="top">Program or service program &amp;1 in library &amp;2 ended.
Reason code &amp;3.</td>
</tr>
</table>
<br>
<br>
<h3><a name="usage_notes">Usage Notes</a></h3>
<ol type="1">
<li>This function will fail with error code [ENOTSAFE] when both of the
following conditions occur:
<ul>
<li>Where multiple threads exist in the job.<br>
</li>
<li>The object this function is operating on resides in a file system that is
not threadsafe. Only the following file systems are threadsafe for this
function:
<ul>
<li>"Root" (/)</li>
<li>QOpenSys</li>
<li>User-defined</li>
<li>QNTC</li>
<li>QSYS.LIB</li>
<li>Independent ASP QSYS.LIB</li>
<li>QOPT</li>
<li>Network File System</li>
<li>QFileSvr.400</li>
</ul>
</li>
</ul>
<br>
</li>
<li>ACC_SELF Mapped to ACC_INVOKER
<p>Some physical file systems do not support <em>ACC_SELF</em> for the <em>
who</em> parameter. Therefore, <strong>accessx()</strong> will change the <em>
who</em> parameter from <em>ACC_SELF</em> to <em>ACC_INVOKER</em> if the
caller's real and effective user ID are equal, and the caller's real and
effective group ID are equal.</p>
<br>
</li>
<li>Network File System Differences
<p>The Network File System will only support the value <em>ACC_INVOKER</em> for
the <em>who</em> parameter. If <strong>accessx()</strong> is called on a file
in a mounted Network File System directory with a value for <em>who</em> other
than <em>ACC_INVOKER</em>, the call will return -1 and errno ENOTSUP. <strong>
Note:</strong> If the value for <em>who</em> has been mapped from <em>
ACC_SELF</em> to <em>ACC_INVOKER</em> as previously described, then ENOTSUP
will not be returned.</p>
<p>Local access to remote files through the Network File System may produce
unexpected results due to conditions at the server. Once a file is open,
subsequent requests to perform operations on the file can fail because file
attributes are checked at the server on each request. If permissions on the
file are made more restrictive at the server or the file is unlinked or made
unavailable by the server for another client, your operation on an open file
descriptor will fail when the local Network File System receives these updates.
The local Network File System also impacts operations that retrieve file
attributes. Recent changes at the server may not be available at your client
yet, and old values may be returned from operations. (Several options on the
Add Mounted File System (ADDMFS) command determine the time between refresh
operations of local data.)</p>
<br>
</li>
<li>QNTC File System Differences
<p>The QNTC File System will only support the value <em>ACC_INVOKER</em> for
the <em>who</em> parameter. If <strong>accessx()</strong> is called on a file
in the QNTC File System with a value for <em>who</em> other than <em>
ACC_INVOKER</em>, the call will return -1 and errno ENOTSUP. <strong>
Note:</strong> If the value for <em>who</em> has been mapped from <em>
ACC_SELF</em> to <em>ACC_INVOKER</em> as previously described, then ENOTSUP
will not be returned.</p>
<br>
</li>
<li>QOPT File System Differences
<p>If the object exists on a volume formatted in Universal Disk Format (UDF),
the authorization that is checked for the object and preceding directories in
the path name follows the rules described in <a href="#TBLAACCESSX2">the
previous table</a>, Authorization Required to Object for <strong>
accessx()</strong>. If the object exists on a volume formatted in some other
media format, no authorization checks are made on the object or preceding
directories. The volume authorization list is checked for the requested
authority regardless of the volume media format.</p>
<br>
</li>
<li>QFileSvr.400 File System Differences<br>
<br>
<p>The QFileSvr.400 File System will only support the value <em>
ACC_INVOKER</em> for the <em>who</em> parameter. If <strong>accessx()</strong>
is called on a file in the QFileSvr.400 File System with a value for <em>
who</em> other than <em>ACC_INVOKER</em>, the call will return -1 and errno
ENOTSUP. <strong>Note:</strong> If the value for <em>who</em> has been mapped
from <em>ACC_SELF</em> to <em>ACC_INVOKER</em> as previously described, then
ENOTSUP will not be returned.</p>
<br>
</li>
<li>QNetWare File System Differences<br>
<br>
<p>The QNetWare File System will only support the value <em>ACC_INVOKER</em>
for the <em>who</em> parameter. If <strong>accessx()</strong> is called on a
file in the QNetWare File System with a value for <em>who</em> other than <em>
ACC_INVOKER</em>, the call will return -1 and errno ENOTSUP. <strong>
Note:</strong> If the value for <em>who</em> has been mapped from <em>
ACC_SELF</em> to <em>ACC_INVOKER</em> as previously described, then ENOTSUP
will not be returned.</p>
</li>
</ol>
<br>
<h3>Related Information</h3>
<ul>
<li>The &lt;<strong>unistd.h</strong>&gt; file (see <a href="unix13.htm">Header
Files for UNIX-Type Functions</a>)
</li>
<li>The &lt;<strong>limits.h</strong>&gt; file (see <a href="unix13.htm">Header
Files for UNIX-Type Functions</a>)
</li>
<li><a href="chmod.htm">chmod()</a>--Change File Authorizations
</li>
<li><a href="open.htm">open()</a>--Open File
</li>
<li><a href="access.htm">access()</a>--Determine File Accessibility
</li>
<li><a href="faccessx.htm">faccessx()</a>--Determine File Accessibility for a
Class of Users
</li>
<li><a href="accessxu.htm">QlgAccessx()</a>--Determine File Accessibility for a
Class of Users (using NLS-enabled path name)
</li>
<li><a href="accessu.htm">QlgAccess()</a>--Determine File Accessibility (using
NLS-enabled path name)
</li>
<li><a href="stat.htm">stat()</a>--Get File Information
</li>
</ul>
<br>
<h3>Example</h3>
<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
for information pertaining to code examples.</p>
<p>The following example determines how a file is accessed:</p>
<pre>
#include &lt;stdio.h&gt;
#include &lt;unistd.h&gt;
main() {
char path[]="/myfile";
if (accessx(path, R_OK, ACC_OTHERS) == 0)
printf("Someone besides the owner has read access to '%s'\n", path);
if (accessx(path, W_OK, ACC_OTHERS) == 0)
printf("Someone besides the owner has write access to '%s'\n", path);
if (accessx(path, X_OK, ACC_OTHERS) == 0)
printf("Someone besides the owner has search access to '%s'\n", path);
}
</pre>
<p><strong>Output:</strong></p>
<p>In this example <strong>accessx()</strong> was called on '/myfile'. The
following would be the output if someone other than the owner has *R authority,
someone besides the owner has *W authority, and noone other than the owner has
*X authority.</p>
<br>
<pre>
Someone besides the owner has read access to '/'
Someone besides the owner has write access to '/'
</pre>
<br>
<br>
<hr>
API introduced: V5R2
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