Ubuntu 12.04 install xdebug

I´m trying to get xdebug running on an Ubuntu 12.04 webserver with php 5.3

I fired

apt-get install php5-xdebug

after that I´ve edited my php.ini to enable it

zend_extension="/usr/lib/php5/20090626/xdebug.so"
xdebug.default_enable = 0
xdebug.overload_var_dump = 0

but after that I´getting following 500 errror: Fatal error: Module 'xdebug' already loaded
So I disabled it again in php.ini. Unfortunately I cannot find an .ini file where it was enabled nor do I get any profiler output which should looking at phpino() be written to /tmp

What is needed here to use xdebug correctly?

phpinfo():

Directive   Local Value Master Value
xdebug.auto_trace   Off Off
xdebug.collect_assignments  Off Off
xdebug.collect_includes On  On
xdebug.collect_params   0   0
xdebug.collect_return   Off Off
xdebug.collect_vars Off Off
xdebug.default_enable   Off Off
xdebug.dump.COOKIE  no value    no value
xdebug.dump.ENV no value    no value
xdebug.dump.FILES   no value    no value
xdebug.dump.GET no value    no value
xdebug.dump.POST    no value    no value
xdebug.dump.REQUEST no value    no value
xdebug.dump.SERVER  no value    no value
xdebug.dump.SESSION no value    no value
xdebug.dump_globals On  On
xdebug.dump_once    On  On
xdebug.dump_undefined   Off Off
xdebug.extended_info    On  On
xdebug.file_link_format no value    no value
xdebug.idekey   no value    no value
xdebug.manual_url   http://www.php.net  http://www.php.net
xdebug.max_nesting_level    100 100
xdebug.overload_var_dump    Off Off
xdebug.profiler_aggregate   Off Off
xdebug.profiler_append  Off Off
xdebug.profiler_enable  Off Off
xdebug.profiler_enable_trigger  Off Off
xdebug.profiler_output_dir  /tmp    /tmp
xdebug.profiler_output_name cachegrind.out.%p   cachegrind.out.%p
xdebug.remote_autostart Off Off
xdebug.remote_connect_back  Off Off
xdebug.remote_cookie_expire_time    3600    3600
xdebug.remote_enable    Off Off
xdebug.remote_handler   dbgp    dbgp
xdebug.remote_host  localhost   localhost
xdebug.remote_log   no value    no value
xdebug.remote_mode  req req
xdebug.remote_port  9000    9000
xdebug.scream   Off Off
xdebug.show_exception_trace Off Off
xdebug.show_local_vars  Off Off
xdebug.show_mem_delta   Off Off
xdebug.trace_format 0   0
xdebug.trace_options    0   0
xdebug.trace_output_dir /tmp    /tmp
xdebug.trace_output_name    trace.%c    trace.%c
xdebug.var_display_max_children 128 128
xdebug.var_display_max_data 512 512
xdebug.var_display_max_depth    3   3