Hi @Gokmen_ARSLAN,
The tar setting of /bin/tar looks OK to me, though of course /bin/tar needs to exist in your server and PHP has to be allowed to execute it. (Sometimes exec is disabled, and some PHP settings like open_basedir might prevent OJS from executing things there.)
Are the file permissions in plugins subdirectories (e.g. plugins/generic) sufficient to allow OJS to create files/directories there?
Regards,
Alec Smecher
Public Knowledge Project Team