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| <h4 class="subsection">30.3.1 Mount Information</h4> |
| |
| <p>For some programs it is desirable and necessary to access information |
| about whether a certain filesystem is mounted and, if it is, where, or |
| simply to get lists of all the available filesystems. The GNU libc |
| provides some functions to retrieve this information portably. |
| |
| <p>Traditionally Unix systems have a file named <samp><span class="file">/etc/fstab</span></samp> which |
| describes all possibly mounted filesystems. The <code>mount</code> program |
| uses this file to mount at startup time of the system all the |
| necessary filesystems. The information about all the filesystems |
| actually mounted is normally kept in a file named either |
| <samp><span class="file">/var/run/mtab</span></samp> or <samp><span class="file">/etc/mtab</span></samp>. Both files share the same |
| syntax and it is crucial that this syntax is followed all the time. |
| Therefore it is best to never directly write the files. The functions |
| described in this section can do this and they also provide the |
| functionality to convert the external textual representation to the |
| internal representation. |
| |
| <p>Note that the <samp><span class="file">fstab</span></samp> and <samp><span class="file">mtab</span></samp> files are maintained on a |
| system by <em>convention</em>. It is possible for the files not to exist |
| or not to be consistent with what is really mounted or available to |
| mount, if the system's administration policy allows it. But programs |
| that mount and unmount filesystems typically maintain and use these |
| files as described herein. |
| |
| <p><a name="index-g_t_005fPATH_005fFSTAB-3458"></a><a name="index-g_t_005fPATH_005fMNTTAB-3459"></a><a name="index-g_t_005fPATH_005fMOUNTED-3460"></a><a name="index-FSTAB-3461"></a><a name="index-MNTTAB-3462"></a><a name="index-MOUNTED-3463"></a>The filenames given above should never be used directly. The portable |
| way to handle these file is to use the macro <code>_PATH_FSTAB</code>, |
| defined in <samp><span class="file">fstab.h</span></samp>, or <code>_PATH_MNTTAB</code>, defined in |
| <samp><span class="file">mntent.h</span></samp> and <samp><span class="file">paths.h</span></samp>, for <samp><span class="file">fstab</span></samp>; and the macro |
| <code>_PATH_MOUNTED</code>, also defined in <samp><span class="file">mntent.h</span></samp> and |
| <samp><span class="file">paths.h</span></samp>, for <samp><span class="file">mtab</span></samp>. There are also two alternate macro |
| names <code>FSTAB</code>, <code>MNTTAB</code>, and <code>MOUNTED</code> defined but |
| these names are deprecated and kept only for backward compatibility. |
| The names <code>_PATH_MNTTAB</code> and <code>_PATH_MOUNTED</code> should always be used. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="fstab.html#fstab">fstab</a>: The <samp><span class="file">fstab</span></samp> file |
| <li><a accesskey="2" href="mtab.html#mtab">mtab</a>: The <samp><span class="file">mtab</span></samp> file |
| <li><a accesskey="3" href="Other-Mount-Information.html#Other-Mount-Information">Other Mount Information</a>: Other (non-libc) sources of mount information |
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