Install GitLab Community Edition

The official tutorial is hear : https://about.gitlab.com/installation/#debian?version=ce
CE or EE : https://about.gitlab.com/installation/ce-or-ee/?distro=debian

Install Community Edition on Debian Linux.

Prepare: Install and configure the necessary dependencies

sudo apt-get install -y curl openssh-server ca-certificates
sudo apt-get install -y postfix

Install GitLab

(Replace gitlab.example.com by your git domain name or add gitlab.example.com to hosts)

curl -sS https://packages.gitlab.com/install/repositories/gitlab/gitlab-ce/script.deb.sh | sudo bash
sudo EXTERNAL_URL="http://gitlab.example.com" apt-get install gitlab-ce

Visit and Use the default account's username root to login.

Documentation : https://docs.gitlab.com/omnibus/README.html#installation-and-configuration-using-omnibus-package

GitLab configuration

Edit configuration file : 
/etc/gitlab/gitlab.rb

Note : GitLab was unable to detect a valid hostname for your instance. Please configure a URL for your GitLab instance by setting `external_url`

Reload configuration:
sudo gitlab-ctl reconfigure