I did not find a corresponding ticket, so I opened a new one. After installing Piwik without error messages I switched to the login page and got the following:
Warning: realpath() [function.realpath]: SAFE MODE Restriction in effect. The script whose uid is 577776 is not allowed to access /tmp owned by uid 0 in /SOME/FOLDERS/ARE/DISPLAYED/HERE/piwik/modules/Piwik.php on line 59 Backtrace --> <a href='/0'>#0</a> Piwik_ErrorHandler(2, realpath() [function.realpath]: SAFE MODE Restriction in effect. The script whose uid is 577776 is not allowed to access /tmp owned by uid 0, /SOME/FOLDERS/ARE/DISPLAYED/HERE/piwik/modules/Piwik.php, 59, Array ([path] => /tmp/templates_c,[mode] => 493,[denyAccess] => 1)) <a href='/1'>#1</a> realpath(/tmp) called at [/SOME/FOLDERS/ARE/DISPLAYED/HERE/piwik/modules/Piwik.php:59] <a href='/2'>#2</a> Piwik::mkdir(tmp/templates_c) called at [/SOME/FOLDERS/ARE/DISPLAYED/HERE/piwik/modules/Piwik.php:959] <a href='/3'>#3</a> Piwik::install() called at [/SOMEFOLDERS/ARE/DISPLAYED/HERE/piwik/modules/FrontController.php:323] <a href='/4'>#4</a> Piwik_FrontController->init() called at [/SOME/FOLDERS/ARE/DISPLAYED/HERE/piwik/index.php:51]
Any hints / ideas?
I can't reproduce the error yet. Can please post the values of the following php configuration parameters safe_mode, safe_mode_exec_dir, safe_mode_gid and safe_mode_include_dir? You can find the values, when you create an php-file with just "<?php phpinfo(); ?>" in it and open it in your browser.
Piwik is not compatible with SAFE_MODE.
If you want it to be, please send a patch :)