For some reason, I cannot edit the original post question and format it better; I get "403 – Forbidden! The page you were looking for could not be authorized." no matter what I try; so I'm going to try and post a better formatted version in this answer... Well, that seems to have worked - so could a forum administrator please replace the original question with this post? Thanks!

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EDIT: found the problem - even if I installed the addon as a user that I thought had full administrative permissions, I couldn't see the menu because, well, the user did not actually have permissions for that menu. Once I logged in as the default admin user, I could see the menu.

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I have a test instance of Odoo running on a Linux server, where it resides at:

    /home/odoo/odoo1_git/

Do note that:

• I'm trying to use Danish translation on it (so some things are translated, but not all)

• I'm using https://www.odoo.com/apps/modules/8.0/auth_from_http_remote_user/ so I can login directly from an Apache login (i.e. the default login of Odoo is not used), and I'm also using https://www.odoo.com/apps/modules/8.0/web_hide_db_manager_link/ (via https://github.com/OCA/web/tree/9.0/ and https://github.com/OCA/server-tools)

• I use the demo data
  

In any case, the install seems to work fine, and I get 9.0c as version of the installation when I look at the About menu:

At first, I thought I can only export the database if I install an addon/module - but that was apparently because I had hidden the DB manager link :) Still, I found http://stackoverflow.com/questions/27935745/backup-odoo-db-from-within-odoo - and so all I had to do was go to http://my-odoo-instance.example.com/web/database/manager, and I could export the database. So that is good too.

However, before I found that info, I tried to install "Database Auto-Backup" addon/module from https://www.odoo.com/apps/modules/8.0/auto_backup/ - and I couldn't succeed; so that is what this question is about. This is what I ended up doing to install it:

git clone https://github.com/Yenthe666/auto_backup.git auto_backup_git
cd auto_backup_git
git checkout 9.0
# Branch 9.0 set up to track remote branch 9.0 from origin.
# Switched to a new branch '9.0'
cd ..
sudo -H -u odoo cp -a auto_backup_git/auto_backup /home/odoo/odoo1_git/addons/

Then, I go to Apps/Update Apps List, get the Module Update screen:

... and click on Update; this seemingly completes, as now I can see the "Database Auto-Backup" app/module if I remove the "Apps" filter in the Apps view.

• Note: At this point, new entries are created in the `ir_module_module` and `ir_model_data` tables of the database, however, if I delete the folder `/home/odoo/odoo1_git/addons/auto_backup` and then run Update Apps List/Update again, the addon will still be shown in the Apps list - even if its folder is not present anymore! One must delete the entries from the `ir_module_module` and `ir_model_data` tables of the database to have the addon disappear from this list (see https://www.odoo.com/forum/help-1/question/how-to-uninstall-a-module-from-command-line-36076)

Ok, so at this point, I "Install" the module from the Apps list in the GUI, and all seems to complete; this is what I get for the module:

So, all is seemingly OK - however, at this point, if I click on Upgrade, Odoo seemingly starts doing something (as if updating), but then again shows the exact same state as on the image (i.e. "Upgrade" button is blue, version is 9.0.1.0). If here I click on Installed Features, I see:

... so I guess, I should see a new menu (Back-ups) under Settings/Technical. So, I enable "Developer Mode" from the About menu shown above, and then I try to check the Settings menu. However, there is no such menu shown under Settings/Technical - here is the entirety of the "Developer Mode" Settings menu I get:

Would anyone have an idea what am I doing wrong? Are there any logs where I could check why don't I get the menu for Auto-Backup that I expect?