TYPO3 Core

Are you using any accelerator or opcode cache?

No i dont use any opcode cache or accelerator

Apache Version Apache/2.4.6 (Linux/SUSE)
Apache API Version 20120211
Server Administrator [no address given]
Hostname:Port www.xxx.info:0
User/Group wwwrun(30)/8
Max Requests Per Child: 10000 - Keep Alive: on - Max Per Connection: 100
Timeouts Connection: 60 - Keep-Alive: 15
Virtual Server Yes
Server Root /srv/www
Loaded Modules core mod_access_compat mod_so http_core prefork mod_unixd mod_systemd mod_actions mod_alias mod_auth_basic mod_authn_file mod_authz_host mod_authz_groupfile mod_authz_user mod_autoindex mod_cgi mod_dir mod_env mod_expires mod_include mod_log_config mod_mime mod_negotiation mod_setenvif mod_ssl mod_userdir mod_php5 mod_reqtimeout mod_rewrite mod_authn_core mod_authz_core

Sorry I've no clue then what might be wrong. Maybe this is even a PHP issue.
Do you get other warnings too?

On the same system an installation with typo3-4.7.15 runs fine.
An update of a copy of this version to 6.2.2 was also OK (FE + BE were OK), but the problem with the install tool came up.
So i tried an installation without previous data.

See also http://forum.typo3.org/index.php/t/203554/ for another user with the same problem.

How could I debug the problem?

After an update of the running 4.7.15 version to 4.7.18 the same installtool problem comes up.
After resetting the symlink to 4.7.15 the installtool works normal.

But with 4.7.18 there are no entries in the error.log (even with full error_reporting)

The problem goes away after deinstallation of php-suhosin.
php-suhosin was in simulation-mode.

The installtool in 4.7.18 now (after deinstall of php-suhosin) is also OK