Install Gitlab on Debian 7

Install Gitlab

sudo apt-get install curl
curl -sS https://packages.gitlab.com/install/repositories/gitlab/gitlab-ce/script.deb.sh | sudo bash
sudo apt-get install gitlab-ce
sudo gitlab-ctl reconfigure

Open file /etc/gitlab/gitlab.rb
sudo nano /etc/gitlab/gitlab.rb

Change lines

external_url 'http://yougitdomain.com'

gitlab_rails['gitlab_email_from'] = 'notification@yourdomain.com'
gitlab_rails['gitlab_email_display_name'] = 'Notification'
gitlab_rails['gitlab_email_reply_to'] = 'notification@yourdomain.com'

gitlab_rails['smtp_enable'] = true
gitlab_rails['smtp_address'] = "smtp.gmail.com"
gitlab_rails['smtp_port'] = 587
gitlab_rails['smtp_user_name'] = "yourgmail@gmail.com"
gitlab_rails['smtp_password'] = "yourpassword"
gitlab_rails['smtp_domain'] = "smtp.gmail.com"
gitlab_rails['smtp_authentication'] = "login"
gitlab_rails['smtp_enable_starttls_auto'] = true
gitlab_rails['smtp_tls'] = false
gitlab_rails['smtp_openssl_verify_mode'] = 'peer'
gitlab_rails['smtp_ca_path'] = "/etc/ssl/certs"
gitlab_rails['smtp_ca_file'] = "/etc/ssl/certs/ca-certificates.crt"

nginx['listen_port'] = 5555 #replace by your port

Reconfig Gitlab
sudo gitlab-ctl reconfigure

Gitlab will run on port 5555 (as above config)

Troubleshoot: when restart OS, maybe Gitlab cannot start, you will install systemd to auto boot Gitlab

sudo apt-get install systemd