It looks like a permissions issue on the mattermost log file. Steps to make it work
Gitlab on a clean machine
sudo vi /etc/gitlab/gitlab.rb- setup and uncomment
mattermost_external_url - Notice: I didn't need to add the following for a clean install
mattermost['db2_backup_created'] = true
mattermost['db2_team_name'] = 'TEAMNAME'sudo gitlab-ctl reconfigure- notice all the files in
/var/log/gitlab/mattermost/are the root owner sudo chown -R mattermost:mattermost /var/log/gitlab/mattermost/- comment out
mattermost_external_url sudo gitlab-ctl reconfigure- uncomment out
mattermost_external_url sudo gitlab-ctl reconfigure
Service should be running now.
You can verify mattermost is installed correctly with
sudo -u mattermost -i bash
cd /opt/gitlab/embedded/service/mattermost
/opt/gitlab/embedded/bin/mattermost -config='/var/opt/gitlab/mattermost/config.json' -version