Unable to locate gitlab backup file

I installed gitlab server from omnibus package 7.12 on a ubantu 14.04. while running sudo gitlab-rake gitlab:backup:create command, I receive a successfull creating message, but i was unable to locate this file. Initially i tried this command with default installation(i have 3 repositories) and then i modified the gitlab.rb file at /opt/gitlab/embedded/service/gitlab-rails/docker/data/assets . i added the backup location parameters into this file and reconfigured the gitlab. the output path set at this rb file is /opt/gitlab/backups. the backups folder is created manually .

Any help would be appreciated. Iam quite beginner at Linux commands.

I have the very same question.
I run gitlab in a container. Just created a backup using

docker exec -t gitlab-rake gitlab:backup:create

but do not know where the reported tar file is acessible now.