openmediavault is a Debian based distribution. It uses apt to install packages. All standard Debian packages are upgraded using the official Debian mirrors. openmediavault packages are upgraded using the http://packages.openmediavault.org repository.
The update manager displays all available packages for upgrade. You can select them if you want to do individual or mass upgrade. The server uses cron-apt to perform a daily apt-get update and fetch upgrade packages automatically. If you have notifications enabled you receive an email every time packages are ready for install.
If you want to update/upgrade in the console you can use
apt-get update then
This is wrapper script that basically executes:
$ apt-get update && apt-get upgrade
The full command is:
$ apt-get update && apt-get –yes –force-yes –fix-missing –auto-remove –allow-unauthenticated –show-upgraded –option DPkg::Options::=“–force-confold” dist-upgrade
This is a script included only in the last versions of openmediavault before moving to next major release version. For example: 0.5.60 to 1.x or 1.19 to 2.x. The command performs several tasks and modifications depending if the upgrade includes moving to a new base distribution. For example: Debian Squeeze to Wheezy or Wheezy to Jessie,
The plugins can installed either by repository selecting from the available list or uploading the deb package. If the plugin requires some extra software it will fetch all remaining packages from either Debian mirrors or another repo the plugin specifies.
You have to your availability all Debian software repository to install in your server
$ apt-get install <packagename>
$ apt-get remove <packagename>
Purge (remove package and configuration files):
$ apt-get purge <packagename>
The OS repositories are in this file
/etc/apt/sources.list. The default
openmediavault 2.0 (Wheezy):
deb http://ftp.us.debian.org/debian wheezy main contrib non-free deb http://ftp.debian.org/debian/ wheezy-updates main contrib non-free deb http://security.debian.org/ wheezy/updates main contrib non-free
openmediavault 3.0 (Jessie):
deb http://ftp.us.debian.org/debian jessie main contrib non-free deb http://ftp.debian.org/debian/ jessie-updates main contrib non-free deb http://security.debian.org/ jessie/updates main contrib non-free
openmediavault 4.0 (Stretch):
deb http://ftp.us.debian.org/debian stretch main contrib non-free deb http://ftp.debian.org/debian/ stretch-updates main contrib non-free deb http://security.debian.org/ stretch/updates main contrib non-free
The above repositories point directly to US servers. Since Debian Wheezy now is possible to use the redirector address, you only need to change the codename release. The redirector finds the closest mirror automatically. This is can be used as default for Debian Stretch:
deb http://deb.debian.org/debian/ stretch main contrib non-free deb http://deb.debian.org/debian/ stretch-updates main contrib non-free deb http://deb.debian.org/debian-security stretch/updates main contrib non-free
Debian provides the
/etc/apt/sources.d/ folder for adding external
repositories. If there is need to add a repository from a testing or unstable
Debian just to install recent software make sure the packages are properly pinned 
to avoid the system becoming unstable for adding core unsupported software my mistake.