we have released gitlab 6.4.3. Could you please test if it installs correctly now?.
Before do it, please run this command:
If it is not installing well, could you please copy&paste the output of:
grep "gitlab_ci" /etc/passwd
grep "gitlab_ci" /etc/group
It should be useful too, if you could run the installer with "--debugtrace filename.txt" and you could send it to support [at] bitrock [dot] com. The subject of the mail must be the link to this case.