In fully utf8 unicode MySQL the collation connection makes trouble

[voter viparmenia]

I am trying to configure mysql compiled originally with latin1, now as fully utf8. I set in [mysqld] section in my.cnf

collation_server=utf8_unicode_ci
character_set_server=utf8

But when I am using also
collation_connection=utf8_unicode_ci

Starting service MySQL fails with

"warning: /var/lib/mysql/mysql.sock didn't appear within 30 seconds"

Any idea what else I need to define to push connections into unicode, too?