I've got problems with updating Joomla! on my chrooted host. Update package was properly downloaded to temporary folder but instead of extracting into root of my server, it landed into administrator/components/com_joomlaupdate. This problem was reported before: #7383 and #7866. The latter report is especially valuable.

After closer examination, I found out that JPATH_ROOT is the most probable culprit. It is set independently in two places: includes/defines.php and administrator/includes/defines.php. The code in the first of these, simply “exploded” JPATH_BASE (which in fact is simply __DIR__) only to “reassemble” it back again to the same form as before. Unless I omitted something important, this didn't change a thing, so I removed this code and assigned JPATH_BASE to JPATH_ROOT directly.

When it comes to second file (administrator/includes/defines.php), it worked fine as long as there was more than one directory from root (/). As soon as administrator directory is placed directly in / (JPATH_BASE is /administrator), the code in defines.php sets JPATH_ROOT to an empty string instead of /. This is most probably what causes the update to be extracted into the wrong place.

The cause of this is this part:

$parts = explode(DIRECTORY_SEPARATOR, JPATH_BASE);
array_pop($parts);
define('JPATH_ROOT', implode(DIRECTORY_SEPARATOR, $parts));

When JPATH_BASE value is /administrator, explode() splits it into array of 2 elements '' (empty string) and administrator. array_pop() removes administrator part of the array (I guess, to establish “real” root of all Joomla! files) leaving array with only one element. However, when array has only one element, implode() returns only this element alone, without even adding separator. This leads to an empty string, which, further down the road, leads to acting in given script working directory instead of actual JPATH_ROOT.

Quick fix for this problem appears to be using dirname() function, instead of explode()→array_pop()→implode() chain, since it all seems to be about stripping administrator from JPATH_BASE in the first place.

Please review my pull request. Not being able to update Jommla! on chrooted host is really PITA :}.