There are a lot of services that load when Ubuntu boots up. Many of
these may not be useful for every user. Not allowing these services to start not only leaves more resources free but also is a very good security measure. These services can be turned off by using the Services Administration Tool located in System --> Administration --> Services. Refer to Figure 7. Before turning off services, it is best to know what each service does. For example, I do not use any Bluetooth devices, so I can safely turn off this service from loading during boot up and can manually start this service when required.

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A much more flexible, but tedious, way to do the same is to look at
the start up links in /etc/re2. d and /etcireS. d folders and turn them off. Thus, the Bluetooth service can be turned off by issumg this command in a terminal:

The start up link is located in /etclre2.d as '825bluetooth', where '8' means that it is meant to start and '25' would indicate its priority level. Priority level 1 would mean that the service would start first. This information is irrelevant to the update-reo d command.