The jPC's primary storage is divided into the following partitions. To understand this partition layout and its purpose, please become familiar with the overlay file system and the Filesystem Hierarchy Standard.
<html> <table class=“inline table”>
<thead>
<tr>
<th>Partition Label</th>
<th>Capacity</th>
<th style="width: 80px">Mutability</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>boot</strong></td>
<td>256MB</td>
<td>read-only</td>
<td>Contains kernel and bootloader configuration to boot the operating system.<br/><br/>
Changes to this partition should not be necessary except under exceptional circumstances.
</td>
</tr>
<tr>
<td><strong>lower</strong></td>
<td>5GB</td>
<td>read-only</td>
<td>Contains lower layer of the root overlay file system.<br/><br/>
Changes to this partition should not be necessary except under exceptional circumstances.
</td>
</tr>
<tr>
<td><strong>upper</strong></td>
<td>1GB</td>
<td>read-write*</td>
<td>Contains the upper layer of the root overlay file system.<br/><br/>
Any changes made to the operating system's will be stored here and merged with the lower layer.<br/><br/>
* After making changes, this partition can also be made read-only by deleting the file <code>/var/lib/jpc/mount-read-write</code> and rebooting. To make the partition read-write again, create the <code>/var/lib/jpc/mount-read-write</code> again and reboot.
</td>
</tr>
<tr>
<td><strong>data</strong></td>
<td>Remaining capacity</td>
<td>read-write</td>
<td>Contains files that are updated often, but need to be retained between boots.<br/><br/>
By default <code>/var</code> and <code>/media</code> are bind mounted to this partition so they remain read-write even when the upper and lower partitions are read-only. Additional bind mounts can be created by editing <code>/etc/fstab</code>.<br/><br/>
Transactional databases, log files, and files too large for <code>/tmp</code> can be stored on this partition.
</td>
</tr>
</tbody>
</table> </html>
If COMFILE Technology releases an update to the operating system, existing devices can be updated by restoring only the boot and lower partitions, thus preserving any developer or user changes stored on the upper and data partitions.
With the upper and lower partitions read-only, their file systems can withstand abrupt loss of power without corruption, avoiding the need to shut down the system.